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Hey Ben.
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Hey Matt.
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It has been a while, hasn't it?
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Been a bit.
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I mean, not for our listener, obviously. Our listener, it's just been a month. But for us, things... life has overtaken us. A lot of things are going on. We are, in fact, on different continents right now.
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And I'm looking at my sound levels, in fact, and I'm wondering how awful this is going to sound. So I'm going to just tweak something. But, yeah, I apologize in advance to the poor editor who has to edit this because I am recording...
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on my laptop from my wife's childhood home in her bedroom where she grew up in Birmingham in the UK, which is not where I was planning on being around this time.
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Mm-hmm.
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But nevertheless, adult things happen and you end up in a different landmass. So that's me.
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Right.
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So apologies for the sound. And I still haven't actually changed it. Let me just do that now. OK. Now I'm going to start clipping and... let's see what that does. That looks... that looks better. No, maybe I am clipping now. I got excited. All right.
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This, my... this, dear listener, is going to be a heavily not edited at all podcast because Ben and I just need to record something so that you've got something to listen to.
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Yeah.
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Yeah. I met a number of people claiming to be our single listener at a conference recently, which was lovely. So shout out to the many single listeners that we had there. That was good to hear. It's always nice to get feedback. I mean, like, it's a funny thing that we do, right? We just chat, talk to each other. Apparently people listen to this, which is on them, in fairness. They don't have to. We're not making them.
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Okay.
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Yeah. Yeah.
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It's amazing. I don't understand it.
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So here we are. Yeah, we have no idea, as is normal, as is usual. But I've been doing some cool things that I would have just talked to you about because normally we would do this down the pub.
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Right.
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Yeah.
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But again, due to 4,000 miles between us, this is...
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Yeah. I haven't actually heard about any of this stuff, so it's not going to be... Yeah, I'm genuinely interested because I have not talked to you in a long time.
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the first time. So you know that I...
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Due to the aforementioned time dilation created by you going across the Atlantic Ocean that is stretched out.
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Is that what it is?
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Yes.
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That... it does make me wonder, because it does feel like we're in like the 1950s here in the UK, because they haven't got air conditioning and it is very, very, very hot.
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Uh-huh.
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Right. Right. That's...
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Someone should tell them about this new technology.
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Yeah.
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Oh, and they will not let me back in the country. Yeah. So one of the things that I got really excited about, well, you know, I love emulators. That's my thing. When I'm not forcing compilers to do things they shouldn't do, I am...
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emulating my childhood. And the thing that has really annoyed me all the time is that monitors are too crisp.
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Yep.
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Yep.
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I mean, we've talked about this before in a podcast, but like, you know, my very first computer, the first computer I programmed on was plugged into a portable color television, you know, full CRT bulbous screen,
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Yeah.
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Yeah. Right.
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Right.
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like analog push buttons, like when radio buttons were actual, the buttons you had on radios with a physical mechanism, you press one and the others pop out, you know, right.
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Right, right, right. Yeah.
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And then behind that was a tiny little thing you would tune to get it to the right channel. And then your, so your computer that you plugged in had to pretend to be a TV station, right?
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Right.
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It would generate radio frequency of PAL or NTSC at some frequency. You tune it into channel 36 in the UK or channel...
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Yeah, it was like three or four, I think. Yeah, three or four, something like that.
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Yeah. In the US, right.
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Right.
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And the TV didn't know that it wasn't actually plugged into an aerial listening to something off the...
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Right.
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But what that meant was, you know, not only was the CRT... not a perfect device. It's a very, very analog device that involves phosphors and things that... don't instantly light up and instantly fade away, which is part of their charm. But the picture quality was rubbish because you had to squirt color information down a single line. And it wasn't even like you could use a digital encoding, because this stuff had to work on like 1950s
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analog components when color TV was invented.
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Right.
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It's like the worst of all worlds. But it's really, really nostalgic to see the terrible picture quality that came from it.
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Right.
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And people would use this, right? There were tricks you could do to make colors look more blended and in some cases to achieve extra effects on a real TV that you won't get on an emulator.
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Anyway, this was annoying me.
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Mm-hmm.
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So I thought, right, sod it. I'm going to learn how this stuff works and I'm going to make my emulator faithfully reproduce all of the things, warts and all. And so I did one pass of this and it's a... it's kind of a fudge. It's like, yeah, we need to blur it a little bit. We need to do some of these effects. But it was like, no, this is not a first principles simulation of what's going on. So I thought I'm going to go deep rather than start by like just synthesizing the picture quality and that kind of stuff. Why don't I learn how to do it? How do I learn to be a TV person?
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I want to take a real BBC Micro or Sega Master System. I'm going to plug it into my computer. I'm going to use a software defined radio, which lets me decode radio frequency signals into essentially a stream of ones and zeros that I can read fast. And then I'm going to software decode that thing back into a color picture.
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And that's going to teach me everything I know about how the heck this works. And then I'm going to look at each bit of the code and kind of go, which things are available... What parts of that could I have done using analog electronics back in the day? Which things are like DSP tricks that you would only have had in high-end televisions and stuff like that? And now I can actually pluggably make a TV and say, I want a 1990s era
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type display, or I want... no, I want the actual 1984 Thorn TV that I had in my bedroom, which I have a photograph of, and I found... and I've got the manuals for, and I'm going to try and find an actual real one so I can do some real sampling. But you know, that's... it's been a journey, my friend. What do you want to know?
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Wow.
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Wow. Well, so, okay. So just to clarify exactly what you're saying here is you didn't have enough emulator in your emulator. So you added another layer of emulation on top of your emulator.
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So you have two layers of emulation.
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In fairness, I haven't put this into the emulator yet. There's a version in the emulator, but this is purely learning about the decoding. What I hadn't registered really is there's kind of two parts to the whole thing.
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Yeah.
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One is the RGB that is actually being generated by the computer, right? There is obviously RGB at some point.
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Mm-hmm.
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With the exception of NESes, which is a whole other story, and we don't have time for that, but like there is RGB, and then it goes through encoding.
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Yeah.
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And then the BBC Micro's output encoding circuitry would differ from the ZX Spectrum's one, from the Sega Master System.
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I'm sure all of the systems would come up with their own compromises about what's cheap to do or appropriate to do, to generate the signal. Then they would go through RF modulation, which adds a whole other thing in.
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They may or may not mix in the audio, because the audio is in there as well. And then they would send it off to the TV, right? So there's stage one is how does the output stage generate the RF signal that's coming out. And then stage two is which type of TV have you plugged it into?
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Is it a modern one? Is it a cheap and nasty color TV? Is it one of those ones where, you know, effectively over time, the heat of your... this is what I had with my friend Richard, we would go around his house.
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And after a lot of programming, the screen would start getting worse and worse and start shimmering. And we realized that, oh, you'd have to retune the TV as everything had gotten hot. And so all these analog components had gone out of lock effectively.
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And there was no... so it's...
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Yeah.
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Honestly, it's an amazing thing. And yeah, there's just so many layers. I've learned so much about how SDRs work, about how fast you have to sample stuff. Essentially, it's like an ADC.
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So it's like a sampler, an audio sampler, right?
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Right. Yeah, yeah, yeah.
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But not running at 44 kilohertz or 64 kilohertz. It's running at 32 megahertz.
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So it's 32 million samples a second, which is not totally unreasonable. It's fine. But the RF that we're looking at is a signal that varies and wiggles around a frequency that's like 400 megahertz or 300, 200 megahertz or something like that. So there's a kind of an analog trick for bringing down the signal from that really high domain down to a lower domain that you could then sample.
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Right.
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And how musical are you, Ben?
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You know, not particularly. And it's also possible that our listener is also not. So, you know, over-explaining is probably a good thing here.
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Right, that's fair. But right, so have you ever, you know when something is slightly out of tune, if you heard two notes that were slightly out of tune, they were both trying to be the same pitch.
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And so like, an A is 440 hertz, right? And now... yeah, I can't tell it's an A, right?
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Okay, yeah.
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I haven't got perfect pitch. But if it's... and then I also... someone played a 441 hertz sound,
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Right.
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I wouldn't be able to hear the difference. But if you played the two together, there's that horrible wobbling, whoa, whoa, whoa, whoa kind of thing that happens when they grate against each other.
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Yeah. Yeah.
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It's a crunchy, horrible thing when something is nearly in tune, but it isn't in tune, right?
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Mm-hmm. Mm-hmm.
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That, the frequency of the whoa, whoa, whoa of the two, beating and grating against each other, is the difference of the two frequencies.
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So 440 and 441 would give you a once a second wobbling sound.
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Okay, yeah, that makes sense.
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Right, right.
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So the trick, and anyone who knows about this for real, who's like done electronic engineering or whatever, is like screaming at their speakers right now, this is not a trick.
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Mm-hmm. I know.
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This is like just how it's done. But like the trick to me is, what you do is you play the two frequencies... when you want to tune to, say, 200 megahertz, you generate a local 200 megahertz signal using just your own oscillator.
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Okay.
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And you play that again at the same time. You multiply them. You mix them together. You multiply them in this instance. But like, go with me in this, my music analogy, right? And the result is, yes, you hear both of those tunes, but they're so high-pitched and high-frequency that they're then beyond what you can sample with your sampler. But the difference between them, the wobbling around, is much lower frequency. It's the difference of their frequencies.
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Okay.
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And so now you get a signal that is around about plus or minus, you know, however wide the various frequencies might be. And so by playing a 200 megahertz tone and multiplying that with whatever noise is happening off the radio,
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Okay.
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I can then sample that at, say, 32 megasamples a second. And what I've got is essentially a plus or minus, sort of, Nyquist limit is half of that, 16 megahertz around the 200 megahertz window.
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So I can get from minus, because it's the same, you can't tell if it's one hertz above or one hertz below.
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Okay.
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They both beat at once a second. So you get both the signals that are from like 200 to 216 and down to 184, whatever that... Right.
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Okay.
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But, and that's the band.
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And this is all to like bring these frequencies down into a range where you can sample them at the rate that you're able to sample them with the hardware that you have?
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Exactly. Without getting all those sort of like pointless noise of like lower frequency things that you don't care about.
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Okay.
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And then there's some other tricks that you have to do because, you know, again, you can't discriminate between something that's one hertz higher from what's only one hertz lower. And there's a trick. Maybe we want... if we talk about every trick here, we're going to be here for three hours.
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So I'm...
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And then the thing that's melting my brain here is that it's like, you know, you talk about this with audio and I can kind of like think about it, but it's like, this is television, right?
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Correct. Yes.
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So it's like, you know, it's not just audio. In fact, it's not even primarily audio. It's the signal that you're using to, you know, bend this, you know, electron ray, whatever the heck it is.
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Electron beam that's flashing back and forth.
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That's... yeah.
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Exactly.
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Right.
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And again, and it all had to be done in analog.
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Right.
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So you know this first stage I just described, you could imagine some kind of magical thing that oscillates. You get it tuning. When you're tuning the television, what you're really doing is tuning that oscillator to a frequency... that there's more...
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There's a middle stage. There's an intermediate frequency and stuff like that. But like for the purposes of this conversation, you're tuning an oscillator. And then the difference between the oscillator you tuned and the signal that's just got, of course, every TV station mixed into it will...
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will give you, will center it around the thing that you care about. And then if you filter the stuff that's higher and lower frequency, now you've just got your TV tune. But yeah, now you've got like another layer of encoding. So think about it as encoding. Now you've probably talked about, and I'm going to say a word that you're going to say a different way to me. And I don't know if it's a me thing or a UK thing, US thing. So the not-RF signal that you would plug in, the yellow lead on your old consoles where you didn't have the audio in, you would have like three leads, you'd have left and right audio, which would be red and white.
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Yeah.
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Yeah.
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And then the yellow lead, which would be the video.
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Yeah.
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Well, that will be what kind of video?
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Oh, I don't know. RF video. I mean, but yeah, I always think of it as like, you've got component and comPOSite and... okay.
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COMposite is the word I was looking for there. Yes. So yes, I would say COMposite.
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Yeah. Oh, okay.
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I don't know if it's just a thing that I say. So, you know, our listener can have a think. But yes, so effectively there are like several layers of encoding.
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Yeah.
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The first thing is we're going to make something RF so we could transmit it over the... what, the waves, the airwaves, right? The composite is too low frequency and everyone would pick the same one.
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So obviously every channel has its own. But in there are two things, right? One is the composite video, which is itself composed of more things, which we'll get to.
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Mm-hmm.
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And then there's essentially like an FM radio signal that is the audio that is just on the edge of the video signal, either side of it, the way that it works out. And I'm a bit vague on this bit because I haven't got to that yet.
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But you can imagine, yeah, given the amount of spectrum that you're allowed to use, the bandwidth of radio range, you would kind of fiddle it around and say, okay, the FM lives in this part of it.
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Mm-hmm.
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And then the middle part is all this. And the much wider part, for what it's worth, is the TV signal, which is itself composed of several things, right? Red, green, blue, synchronization pulses, like this is the top of the screen. This is a new line, right? Now in our... you and me, these are packets. These are like binary encoding and you go like, how about the start frame, you know, whatever. But like, this is... it can't be the case, because we're talking analog era electronics.
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And so first of all, the first trick is that it's amplitude modulated onto the carrier. So there is the carrier, you know, the 200 megahertz that I mentioned before, is just a wiggling 200 megahertz signal.
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Yeah. Yeah.
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And we just turn the volume of that up and down like old AM radio, right?
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Yeah. Right.
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Forget frequency modulation. We're not modulating the frequency. But by flapping the amplitude up and down fast enough, we are actually using frequencies around it.
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Right.
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If you were to put it through a spectrum analyzer, you see that you get this bandwidth just because of the way it...
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OK, so just to reiterate some of this back to make sure I understand what's going on here. You've got, because it's television, you have this limited frequency in which you're allowed to use for your signal, right?
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Yeah.
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Yeah.
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Correct.
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You're going to slice off some of that for the audio. You're going to slice off some of that for, you know, both channels of the audio. You're going to slice off some of that for the video. And then within that frequency, you're actually encoding the signal in the amplitude of the waves in that frequency.
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Correct, by modulating the up and down of that.
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Have I got that right?
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Yeah, yeah.
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Yeah. OK.
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And so the way that it's done is that a black picture is the brightest. So it's inverted, right? So a totally black screen would be just the normal
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OK.
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full amplitude... the RF signal.
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Yeah.
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Right.
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And this is also true, incidentally... Yeah, no, sorry, I'm confusing myself here. Right, forget... Go ahead.
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Is that true for the audio, too? This seems counterintuitive.
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I don't... I don't think so. The audio is separate from this. At this point, we've left the audio behind. It's been filtered off.
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OK.
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It goes into audio circuitry, and I haven't looked at that too much.
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But yeah, we've got this amplitude modulated thing where we want to extract from that essentially a single continuous analog signal from this wiggling thing.
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Okay.
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Okay. Okay.
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And the way that we do that is we treat the... Actually, I'm not sure what the circuitry does at this point, but we're looking for the amplitude. So let's just ignore the fact that it's wiggling anymore and just say it's the amplitude of this.
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We've got a thing that comes out. And now the amplitude is inverted such that the darkest picture is bright, the loudest, and the brightest picture would be almost no signal.
178
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It never goes completely zero, because then you don't have anything to lock onto.
179
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Yeah. Yeah.
180
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But it's there. So we've got a range now. We've got a range of, say, voltages. And... It's unimportant that it's inverted, other than like the very dark signal is always there. So even if the picture's black, you can tune into the stupid thing and actually know that you've picked up a black picture, right? So from now on... quickly, early on, you invert it the other way around. So it looks sane to humans where, you know, bright is high and dark is low. Let's go with that, right?
181
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Yeah.
182
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You with me so far? Because, yeah... the first thing is we invert it.
183
00:18:42.520 --> 00:18:46.820
Yeah. Is this why television static is mostly white?
184
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It is... we'll get to that actually. That's good, hold that thought, my friend, because this is the cool bit, right?
185
00:18:51.880 --> 00:18:52.880
Okay. All right. All right.
186
00:18:52.880 --> 00:19:05.420
So yes, we've got this, let's just say goes between zero and one volt, right? Where white is... one volt is bright white and zero would be black, except what we're gonna do is we're gonna say, no, no, no. We need a way of signaling the synchronization pulses.
187
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We need to say, this is the beginning of the screen. And we need to say, this is the beginning of a line, because what's happening behind the scenes is that there is... we want to synchronize the electromagnets in the TV with this picture so that they start at the top of the screen, they slowly go down and more quickly, they flip from left to right.
188
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Mm-hmm. Mm-hmm.
189
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And we wanna make sure that everything's synchronized. Otherwise the picture rolls or it's diagonally skewed because the rows aren't aligned, right?
190
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Yeah.
191
00:19:32.040 --> 00:19:42.860
But we need a way of saying, this is a big... this is like, we sort of out of band. And so the out of band is lower than black. It's like we go... we say, right, black is actually gonna be 0.3 volts.
192
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And anything below 0.3 volts is like blacker than black, and it's actually a signal. It's like, a thing is happening. It's our sort of out-of-band signal, because we know also that while we're between lines and while we're pulling the beam from the bottom to the top, we actually don't want to paint anything to the screen. Otherwise, you'd start seeing splurge as the light... as the beam retraces its steps, right? And you get pictures being overwritten with crap. So we want it to be low and we might as well just say, well, when it goes really low, that's a signal to you.
193
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Okay.
194
00:20:17.900 --> 00:20:19.640
Good so far?
195
00:20:19.640 --> 00:20:27.800
So you said blacker than black, like the amplitude... as the amplitude decreases, that is our range of signal, right?
196
00:20:27.800 --> 00:20:33.790
Yes. So we've got effectively between like 0.3 and one volt is the normal black to white.
197
00:20:33.790 --> 00:20:35.040
Okay.
198
00:20:35.040 --> 00:20:39.200
And then below, we're already talking... yeah, sorry, I've already inverted it so that it makes sane.
199
00:20:39.200 --> 00:20:39.860
So you've... we've already talked about it being flipped at this point. Got it.
200
00:20:39.860 --> 00:20:40.890
Yeah, yeah, yeah, yeah.
201
00:20:40.890 --> 00:20:40.990
Yeah, yeah, yeah, yeah.
202
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I'm sorry about that, yeah.
203
00:20:41.160 --> 00:20:42.800
No, that makes sense. I'm back with you again.
204
00:20:42.800 --> 00:21:07.720
Okay, yeah, I did do a bait-and-switch, changed my sort of... there, because it's just easier to think of it the right way up, right, the way you would want to see it, right, the way that it actually gets transmitted when you're using a composite cable. Because effectively by the time we have taken it away from being this amplitude modulated signal to just a signal between zero and one volts and turned it the right way up so that it makes sense, where now that's what you would get out of your composite cable.
205
00:21:07.720 --> 00:21:08.610
Right, yes. Right, right.
206
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Yeah.
207
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Yeah.
208
00:21:09.280 --> 00:21:09.880
OK, got it.
209
00:21:09.880 --> 00:21:20.060
Right. So no audio, no weird wiggling, just pure something you could put into an oscilloscope directly and go, oh, I can see what that's doing, as opposed to just a mass of wiggly lines.
210
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Right.
211
00:21:20.560 --> 00:21:21.110
Yeah. Yeah.
212
00:21:21.110 --> 00:21:22.210
Right. And I forget...
213
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Right.
214
00:21:22.480 --> 00:21:27.100
So TVs used to be black and white. You probably remember this.
215
00:21:27.100 --> 00:21:30.500
I don't know. Actually, that's not true. I did actually own a black and white TV.
216
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You're younger than me. I never... I think we had one black and white TV, but it was in my nan's house.
217
00:21:35.540 --> 00:21:37.620
Yeah. We had a cheap one that was black and white. That was like an extra one.
218
00:21:37.620 --> 00:21:50.540
But yeah, so the trick is that whatever we do to get color into our signal had to be, back in the 40s and 50s, whenever it was color was, had to be backwards compatible in the worst possible way.
219
00:21:50.540 --> 00:21:50.540
Yeah.
220
00:21:50.540 --> 00:21:50.540
Mm-hmm.
221
00:21:50.540 --> 00:21:59.360
Like they couldn't squeeze three copies. They couldn't go, oh, this is now red and this is now green and this is blue, because your black and white TV would be like, well, it's just... I only show what red is, or something like that.
222
00:21:59.360 --> 00:21:59.550
Right, right.
223
00:21:59.550 --> 00:21:59.740
Yeah, yeah.
224
00:21:59.740 --> 00:22:18.270
So there was a trick here. Yeah. Oh, but I missed over the... Going below 0.3 volts is a signal to either pull the signal up to the top of the screen if it's a long period of time, or if it's a short burst below 0.3 volts, it pulls it back to the left.
225
00:22:18.270 --> 00:22:18.500
Mm-hmm.
226
00:22:18.500 --> 00:22:27.770
So there are like two independent circuits that are always running inside the TV, one of which is just a square, both of which are sawtoothed.
227
00:22:27.770 --> 00:22:29.660
Yeah.
228
00:22:29.660 --> 00:22:31.330
Sawtooths, excuse me, sawtooths.
229
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Mm-hmm.
230
00:22:31.650 --> 00:22:31.960
Yeah.
231
00:22:31.960 --> 00:22:46.730
And they're set to be, you know, just slightly longer than a frame and just slightly longer than a line, so that they will naturally just kind of go zero to left to right, left to right continuously, and top to bottom slower, but continuously.
232
00:22:46.730 --> 00:22:47.440
Mm-hmm. Mm-hmm.
233
00:22:47.440 --> 00:22:59.760
But the pulse going that low for a while is a signal to say, doesn't matter where you think you are, start dragging yourself to the top of the screen if you're the top to bottom, or left of the screen.
234
00:22:59.760 --> 00:23:07.180
So that also gives you a certain amount of slop, where... not AI slop for a change, slop where if, for example, your TV's
235
00:23:07.180 --> 00:23:07.180
Yeah.
236
00:23:07.180 --> 00:23:32.230
crystal oscillators, or they weren't even crystals, but the little oscillators that were doing these sawtooths, was slightly out of spec, then, you know, you just keep rewiring, pulling them back onto the right sort of thing. And if there was no signal at all, then they would sort of free run. And that's when you would see the picture rolling, for example. If there was enough to see where the picture was, but you didn't... the TV couldn't pick up that synchronization pulse anymore, then it would just free run.
237
00:23:32.230 --> 00:23:32.270
Yeah.
238
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Yeah.
239
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And so the whole picture would spin over and over again. And I realize I'm gesturing wildly with my hands, which doesn't help our listener at all.
240
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Yeah. Yeah.
241
00:23:41.360 --> 00:23:56.180
So without getting into too many of the specifics, both of those things cause the TV to reset the top bit and the left to right bit. The interesting thing for me for the first time about this was like realizing that that sawtooth from top to bottom is always running.
242
00:23:56.180 --> 00:24:06.760
You know, you and I think that the beam scans from left to right, then it goes down a bit and comes back again sort of diagonally, and then it scans the next row left to right.
243
00:24:06.760 --> 00:24:11.600
But it doesn't. It's doing... it's always a slightly diagonal line from left to right.
244
00:24:11.600 --> 00:24:11.880
Yeah.
245
00:24:11.880 --> 00:24:16.680
And then it's a much less diagonal angle from right to left, because it's much quicker going back than it is going across.
246
00:24:16.680 --> 00:24:17.060
Mm-hmm.
247
00:24:17.060 --> 00:24:23.970
And so you'd think that the whole picture would be slightly wonky because it's... and it is.
248
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Yeah.
249
00:24:24.160 --> 00:24:30.000
And so they just adjust the damn magnets to turn them by half a degree backwards so that it's all the right way around again.
250
00:24:30.000 --> 00:24:31.350
It's just, you know, beautiful.
251
00:24:31.350 --> 00:24:31.540
Oh...
252
00:24:31.540 --> 00:24:35.040
And I had to model that because I'm like, why is everything slightly off?
253
00:24:35.040 --> 00:24:35.540
Right.
254
00:24:35.540 --> 00:24:36.180
Oh, yeah. Yeah.
255
00:24:36.180 --> 00:24:54.780
Okay, so that's the retrace. So we were talking about black and white. So you could imagine now it's really, really easy. We have these two electromagnets that are being dragged... dragging the electron beam up and down, left and right. They're synchronized with the signal. And then the rest of it is just the brightness.
256
00:24:54.780 --> 00:25:07.980
And that's just how many electrons we squirt at the screen in the direction the beam is currently pointing. And there you go. You've got a black and white telly. You are done. Hooray, high fives all round.
257
00:25:07.980 --> 00:25:16.550
But now we want color. And so, you know, as a computer programmer, we would say, oh, V2, you know, or you sort of come up with something.
258
00:25:16.550 --> 00:25:16.740
Right.
259
00:25:16.740 --> 00:25:29.980
Well, we've got the red, the green, and blue, and three channels. And then somehow, oh, there's also a black and white version. But no, they had to come up with a really clever way of getting color into the signal.
260
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So the trick, and this is the great thing, the trick is take... we take the color information and we break it down into three components.
261
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Rather than red, green and blue, we pick brightness, which we already have, because that's what the black and white signal was. And then we have two chrominance signals.
262
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Mm-hmm.
263
00:25:52.660 --> 00:26:02.410
And you know if you've ever pulled up a color picker in any of your art packages, you've probably seen the ones where you've got HSV and you know you've got brightness and then two different other sliders.
264
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Mm-hmm.
265
00:26:02.550 --> 00:26:02.700
Mm-hmm.
266
00:26:02.700 --> 00:26:15.780
And you can pick any color with three things. That's the beauty of like any space is that if it's a 3D space, you can have any coordinate system and you can get to all the points of the coordinate system as long as you've got three of them.
267
00:26:15.780 --> 00:26:28.580
And that's what it is. So like we have essentially a brightness, which is overall how bright something is. We have how saturated a color is, between totally that color or white,
268
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white, however white the brightness would let us go. And then we have a kind of color wheel for the third axis, which says, well, which color, if we're not white, which color are we tending towards?
269
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And you could imagine you're just, you know, just a genuine, honest kind of color wheel and like, well, it's a direction on there. And so now we've got three signals again. So that's cool. And one of them is one we're already transmitting.
270
00:26:51.520 --> 00:26:59.980
So can we hide the other two signals somewhere that a black and white telly that hasn't even... doesn't even know the color exists
271
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Right.
272
00:27:01.060 --> 00:27:08.350
doesn't see them, without using more bandwidth, because we can't add... you know, we've got all these TV channels packed into the RF spectrum.
273
00:27:08.350 --> 00:27:08.720
Yeah.
274
00:27:08.720 --> 00:27:29.060
And although we're talking... I'm talking about the composite part now, the width of that signal has to somehow be squished into the radio spectrum. So what we do is we observe that if we wiggle the brightness really fast and not that much, maybe the black and white TV won't notice it.
275
00:27:29.060 --> 00:27:29.480
Mm-hmm.
276
00:27:29.480 --> 00:27:45.150
Because it's a crap old piece of analog electronics, it's old anyway, a higher frequency wiggle in the brightness would probably go unnoticed, or at worst just makes the white areas look a little stippled in places where it's just varying quite quickly.
277
00:27:45.150 --> 00:27:45.780
Mm-hmm.
278
00:27:45.780 --> 00:27:57.060
Okay, but now we've got a wiggle. What do we do with this wiggle? Well, this wiggle, we can somehow encode two pieces of information with that wiggle.
279
00:27:57.060 --> 00:28:02.080
The amplitude of that wiggle could be one of the other dimensions.
280
00:28:02.080 --> 00:28:04.560
Oh, OK. Yeah, and the frequency is the other one?
281
00:28:04.560 --> 00:28:08.480
So now we've got one of them, but how do we get the third one?
282
00:28:08.480 --> 00:28:10.700
Yeah. Is it the frequency of the wiggle?
283
00:28:10.700 --> 00:28:12.500
What else... what's that, sorry?
284
00:28:12.500 --> 00:28:14.740
Is it the frequency of the wiggle?
285
00:28:14.740 --> 00:28:25.950
It's not the frequency... that would make sense at some level. And I think SECAM, the French thing, used something akin to that. But that would be too easy.
286
00:28:25.950 --> 00:28:26.520
OK.
287
00:28:26.520 --> 00:28:40.760
Also, there are limitations on what frequencies we can use for a variety of reasons, to do with the fact it has to not be a frequency that's going to interfere with this signaling itself, because all these other components are going.
288
00:28:40.760 --> 00:28:50.360
And also the RF... sorry, the audio is in there as well. So there was some careful picking of these numbers so they all don't divide into each other and you end up with like stripes or things like that.
289
00:28:50.360 --> 00:28:50.540
Okay.
290
00:28:50.540 --> 00:29:02.320
Because there are artifacts, which is partly why we're talking about this, because it... those are artifacts I'm trying to capture in the emulator. So the other thing that we can fiddle around that isn't the frequency is the phase.
291
00:29:02.320 --> 00:29:04.240
Oh, okay. Yeah.
292
00:29:04.240 --> 00:29:10.890
So you can slide that back and forth and have the peak at this point in time or push it back a little bit, and now we've got another dimension.
293
00:29:10.890 --> 00:29:11.240
Right.
294
00:29:11.240 --> 00:29:25.740
And so the phase, as you'll recall, can be measured as between 0 and 360 degrees, if you want to think about it, right, as a sine wave. You can like slide the sine wave back and forth. And that maps nicely into our 360 degree color wheel that we had.
295
00:29:25.740 --> 00:29:29.610
So that's how we pick the color. The color is just the phase of that wiggle.
296
00:29:29.610 --> 00:29:29.840
Okay.
297
00:29:29.840 --> 00:29:45.350
And then how saturated it is, is how wiggly... the brightness of that wiggle. So heavily saturated colors on a black and white television do have a grainy texture over the top of them now, because you can see the wiggle in it if you look hard.
298
00:29:45.350 --> 00:29:46.060
Mm-hmm.
299
00:29:46.060 --> 00:30:01.830
So that's cool. We have smuggled two pieces of extra information into our channel. Black and white TV people don't really notice it. But we've now got a new problem, which is that analog electronics is not very good at measuring things like phase differences.
300
00:30:01.830 --> 00:30:10.940
Because how accurate do you have to be with your signal to know if it's in or out of phase? And in and out of phase with what?
301
00:30:10.940 --> 00:30:11.900
Right.
302
00:30:11.900 --> 00:30:15.560
Maybe you need a PTP timestamp synchronization and now everyone's on the same page.
303
00:30:15.560 --> 00:30:15.560
Maybe.
304
00:30:15.560 --> 00:30:23.400
You're down to the... No, no, we haven't got any of that. It's got to work with crap electronics in a 1960s box.
305
00:30:23.400 --> 00:30:24.120
Yeah.
306
00:30:24.120 --> 00:30:25.840
Can I... can I take a guess?
307
00:30:25.840 --> 00:30:28.370
So we need... Yeah, please. This would be great, because I've been just jabbering.
308
00:30:28.370 --> 00:30:28.820
Can I... can I guess?
309
00:30:28.820 --> 00:30:30.620
So tell me, what do you think?
310
00:30:30.620 --> 00:30:36.960
So there's two checkpoints that you have. One is the screen reset and one is the line reset.
311
00:30:36.960 --> 00:30:38.000
Yes, go on.
312
00:30:38.000 --> 00:30:43.040
So it could be either of those, or maybe even both.
313
00:30:43.040 --> 00:30:49.700
You are bang on the money, my friend. And it almost makes me think you're cheating and Googling, but I can see your hands, so I know you aren't. Yeah.
314
00:30:49.700 --> 00:30:51.840
I am not. I am not.
315
00:30:51.840 --> 00:31:01.330
So at the beginning of each line, after we've had the little dip below the 0.3 volts that says, hey, this is the beginning of the line.
316
00:31:01.330 --> 00:31:01.740
Mm-hmm.
317
00:31:01.740 --> 00:31:10.030
And so we know that the electron beam has been dragged back and is currently now way off the left-hand side of the screen.
318
00:31:10.030 --> 00:31:10.480
Mm-hmm.
319
00:31:10.480 --> 00:31:16.730
We then come up to like a black level, because we're in the sort of border on the left-hand side.
320
00:31:16.730 --> 00:31:17.020
Right.
321
00:31:17.020 --> 00:31:20.990
And just before then, and there's something like... there's the front porch and the back porch.
322
00:31:20.990 --> 00:31:21.160
Right.
323
00:31:21.160 --> 00:31:25.400
There's some stupid names for these things, which is, you know, stupid, hilariously funny.
324
00:31:25.400 --> 00:31:25.660
Interesting. Yeah.
325
00:31:25.660 --> 00:31:37.100
We just do a quick burst of that color signal, just a little of it, that's short enough that, again, it's not going to be visible. It's off the side of the screen.
326
00:31:37.100 --> 00:31:45.540
But anything that's looking for it will see it and go, ah, two things. One, this is a color TV signal. It's not a black and white TV signal.
327
00:31:45.540 --> 00:31:45.620
Right.
328
00:31:45.620 --> 00:31:54.580
It's a color TV signal, because I've seen the color burst. Two, synchronize my very short-lived one-line's worth signal
329
00:31:54.580 --> 00:31:55.140
Right.
330
00:31:55.140 --> 00:32:16.360
local oscillator of this color frequency, so that I've now got a reference that I can compare everything else to, and I can compare it to see if it's in or out of phase and by how much. And so that is the trick of getting color. Now decoding that is a pain, but you mentioned something about the black, you know, static.
331
00:32:16.360 --> 00:32:18.470
So do you think you can answer your own question now?
332
00:32:18.470 --> 00:32:18.620
Yeah.
333
00:32:18.620 --> 00:32:20.620
Why is it black and white?
334
00:32:20.620 --> 00:32:27.980
Well, because it's not going to have that burst right at the right time to tell it that it's a color TV.
335
00:32:27.980 --> 00:32:34.370
Bingo. Bingo. So the color TV set will... will assume it's a black and white picture, because it can't synchronize to it and it can't find the color burst.
336
00:32:34.370 --> 00:32:34.630
Yeah.
337
00:32:34.630 --> 00:32:34.880
Yeah.
338
00:32:34.880 --> 00:32:42.880
And so it will suppress all of its own color decoding circuitry. And so the noise only comes out in black and white. Congratulations, sir.
339
00:32:42.880 --> 00:32:43.520
Wow.
340
00:32:43.520 --> 00:32:45.000
You've won today's podcast.
341
00:32:45.000 --> 00:32:50.330
Well, I just want to thank everyone involved, you know, my friends, my family here to support me.
342
00:32:50.330 --> 00:32:50.420
Yeah.
343
00:32:50.420 --> 00:32:57.160
And I'm just really proud of this accomplishment today. So thank you. Thank you all. Really appreciate it.
344
00:32:57.160 --> 00:33:18.890
But so I guess, you know, and so emulating and simulating this has been an absolute blast, and learning all of the various things that they do to the TVs that do that, like, period appropriate. And I learned, for example, that there are delay lines for something we'll hopefully talk about in a second, which required a piece of glass that's exactly the right size so that like essentially it puts...
345
00:33:18.890 --> 00:33:19.180
Wow.
346
00:33:19.180 --> 00:33:31.700
There's like a piezoelectric crystal on both sides of this bit of glass, and it knows it takes 64 microseconds for the vibrations to make it through to the other side. And that's how you get a delay line, an analog delay line, for 64 micros.
347
00:33:31.700 --> 00:33:32.700
You're like, what?
348
00:33:32.700 --> 00:33:33.140
Wow.
349
00:33:33.140 --> 00:33:46.840
There are other things that use specially shaped piezo crystals that then can filter out frequencies. It's just so clever. But while we're here, and as we've just been talking about the color burst in particular,
350
00:33:46.840 --> 00:33:48.720
This sounds like an amazing project. Yeah. Yeah.
351
00:33:48.720 --> 00:33:56.380
What is the name of the European, or most of the European, TV standard?
352
00:33:56.380 --> 00:33:57.840
PAL.
353
00:33:57.840 --> 00:33:59.760
Do you know what PAL stands for?
354
00:33:59.760 --> 00:34:02.840
Oh, I do not.
355
00:34:02.840 --> 00:34:21.400
It stands for phase alternating lines. And I think that probably tells you something about what happens on each line. And maybe about the color part, because this is where NTSC, which is something like the North American Television Standards Committee or something like that, which was developed first, incidentally.
356
00:34:21.400 --> 00:34:21.710
Phase alternating lines.
357
00:34:21.710 --> 00:34:22.020
Yeah, yeah. Uh-huh.
358
00:34:22.020 --> 00:34:33.440
So NTSC predates PAL by about a decade or so. And so PAL learned from NTSC and went, we like everything about this, but... there's this one thing, and they fixed something.
359
00:34:33.440 --> 00:34:33.540
Yeah.
360
00:34:33.540 --> 00:34:36.500
And one thing, so phase alternating lines.
361
00:34:36.500 --> 00:34:36.900
Uh-huh.
362
00:34:36.900 --> 00:34:49.260
So if we're using phase to control color, the hue, right, then my guess here is that we shift the phase every other line.
363
00:34:49.260 --> 00:34:49.860
Okay.
364
00:34:49.860 --> 00:34:57.520
I'm trying to think of why that helps, though. I don't know why that helps.
365
00:34:57.520 --> 00:35:02.120
Exactly. Yeah. Well, let's talk briefly, because I've looked... we're at 35 minutes, gosh.
366
00:35:02.120 --> 00:35:02.500
Why does that help?
367
00:35:02.500 --> 00:35:02.600
Right.
368
00:35:02.600 --> 00:35:17.820
Let's talk briefly about one of the problems that NTSC had. And actually, this would be interesting, because I didn't grow up with an NTSC set. I grew up cursing them in the 90s, because we had to like try and make our graphics look good on NTSC TVs for like games.
369
00:35:17.820 --> 00:35:32.830
But they wouldn't have suffered from the problem I'm about to describe. So... The problem with the phase being the color information is that tiny, tiny errors start moving you around on that color wheel, right?
370
00:35:32.830 --> 00:35:32.920
Mm-hmm. Mm-hmm.
371
00:35:32.920 --> 00:35:45.800
If you're just out by one degree, you're moving around this color wheel. And so you had a... you may have had an extra control on your early analog TVs that I would not have had.
372
00:35:45.800 --> 00:35:54.860
I had color, brightness, contrast. Those were the three things. Do you remember another one? I'm really... you're younger than me, so you probably don't.
373
00:35:54.860 --> 00:35:56.980
You know, I don't remember.
374
00:35:56.980 --> 00:35:57.370
It's been a while.
375
00:35:57.370 --> 00:35:57.800
It's been a bit.
376
00:35:57.800 --> 00:36:05.440
So my understanding is that earlier American sets would have a tint as well.
377
00:36:05.440 --> 00:36:08.460
Oh, yeah. Yes. 100%. Mm-hmm.
378
00:36:08.460 --> 00:36:38.420
And so you would fiddle with the tint, because people's skin color would look like orangey or greeny or whatever sometimes, because... now you probably know where I'm going with this... because of small errors in the phase. Those errors commonly come from the signal being reflected off a building near you. And if you take two signals that are identical and add them together with just a tiny delay in one of them, it's similar to shifting the phase of everything.
379
00:36:38.420 --> 00:36:39.060
Oh, yeah.
380
00:36:39.060 --> 00:36:43.260
And I'm going to wave my hands a lot here, because I've read the math a few times and it hasn't really gone in.
381
00:36:43.260 --> 00:36:43.560
OK.
382
00:36:43.560 --> 00:37:00.240
But there's sort of an unfortunate thing, either if the TV is just not good at locking onto that signal and the parts aren't great, or if there's a systematic error because everything's being slightly delayed and you're getting a mirror copy coming in, then the colors would morph, and it would depend on where the TV set is.
383
00:37:00.240 --> 00:37:00.500
Right.
384
00:37:00.500 --> 00:37:16.640
And it depends on like how warm things are. And you... so fiddle around with this tint. So this is the thing the Germans who came up with PAL was like, how can we fix this? And they made the observation, which to this day lives on in things like JPEG.
385
00:37:16.640 --> 00:37:22.400
So, and that is, humans care about the brightness far more than they care about the color.
386
00:37:22.400 --> 00:37:22.400
Okay.
387
00:37:22.400 --> 00:37:22.400
Right. So, you know, in, say, a JPEG, we store the... the brightness information at a higher resolution than we store the color information, because then you tend not to notice.
388
00:37:22.400 --> 00:37:22.400
Okay. Yeah.
389
00:37:22.400 --> 00:37:22.400
Yeah. Yeah.
390
00:37:22.400 --> 00:37:38.960
This trick comes from this area.
391
00:37:38.960 --> 00:37:39.040
Right.
392
00:37:39.040 --> 00:38:11.200
So they said, well, what if it didn't really matter if we were storing color on every line, unique color in every line? And so it's not... it's not actually that they changed it. But what they said was like, if we flip the phase every other line and we delay the previous line's color and add it to the current line's color, we cancel out any phase error between the two of them, because they've been affected by 180 degrees different in each direction.
393
00:38:11.200 --> 00:38:23.400
And every time I say that out loud, I go, there seems like there's something wrong with that. But I sit down, I do the maths, and the phase error cancels out. But at the loss of like the fact that you are mixing together two lines' worth of color information to kind of get one blurrier line of color information.
394
00:38:23.400 --> 00:38:23.400
Of course it was the Germans.
395
00:38:23.400 --> 00:38:53.700
So that is the... and again, probably without a picture or even, again, without me being very confident about it, but that phase alternation and knowing that the TV is going to do obviously the reverse, any error, any fixed error that you've added in cancels out, because when you reverse it the second time, you're adding minus... if you're bouncing off a building, it's adding three degrees of error.
396
00:38:53.700 --> 00:38:54.200
Yeah.
397
00:38:54.200 --> 00:39:00.530
You add in three degrees of error on the first line. You subtract three degrees of error on the second line. You assume that the other part is the same.
398
00:39:00.530 --> 00:39:00.780
Yeah.
399
00:39:00.780 --> 00:39:05.690
And so those two cancel out. You divide by two and you get just the right phase out of it.
400
00:39:05.690 --> 00:39:05.840
Yeah.
401
00:39:05.840 --> 00:39:06.460
Okay.
402
00:39:06.460 --> 00:39:16.310
And so PAL, phase alternating lines, and NTSC, which was "never twice the same color" for that reason.
403
00:39:16.310 --> 00:39:16.540
PAL.
404
00:39:16.540 --> 00:39:19.570
That was the bad acronym for it.
405
00:39:19.570 --> 00:39:20.080
That's funny.
406
00:39:20.080 --> 00:39:47.940
So, yeah, this has been... an odyssey of discovery, as I said. I can now just about real time in software decode... without using GPU trickery, I can decode this all in software, and I can point at each bit of the code and I can say, yeah, I know what that bit's doing. And whatever... things I didn't cover, because we're already 40 minutes here, is that having done this decode, I now do a physically based electron beam simulation where I actually use a lot of
407
00:39:47.940 --> 00:39:47.940
Wow.
408
00:39:47.940 --> 00:39:54.120
virtual magnets to drag a virtual stream of electrons onto virtual phosphor, which then bloom.
409
00:39:54.120 --> 00:39:54.760
Oh, wow. Wow.
410
00:39:54.760 --> 00:40:11.160
And as the overvolting of like a too-strong, too-white signal happens, the pixels bloom. The current starts going high in the electron guns and you get more, wider spew of like electrons that hit more area of the screen.
411
00:40:11.160 --> 00:40:27.940
What else? Then you can... I can simulate the fact that like they often... the flyback, which is this hilariously named but complicated thing that builds up enough charge to have this really high voltage that's needed, you can deplete it by having too much white for too long.
412
00:40:27.940 --> 00:40:38.470
And then essentially the picture starts sagging after that, which is, you know, on... again, on cheap sets where there wasn't much capacitance, or, you know, you would put a pretty big white thing.
413
00:40:38.470 --> 00:40:38.920
Wow.
414
00:40:38.920 --> 00:40:43.300
And but I remember having one, my dad nicked a monitor from work. And it had this problem where if you had like a bright white title bar of like a game, everything else underneath it was kinked, because that bright white area had kind of gone and dragged all the power out of it.
415
00:40:43.300 --> 00:41:10.690
And it's like, had to recharge it up to be able to like pull the electron beam properly. It's just amazing. It's so fun. And you have been a fantastic foil listening to me. I think I needed this more than I knew, actually. I did say to people at ACCU, I said, this is therapy for us... well, for me.
416
00:41:10.690 --> 00:41:10.860
I will...
417
00:41:10.860 --> 00:41:16.940
I cannot... I cannot wait to see this working in person. I just... I really am looking forward to this.
418
00:41:16.940 --> 00:41:32.440
So the fun thing is is that I've left my desktop computer plugged in with the SDR in Chicago, 4,000 miles from where I'm sitting here, and I've left my Sega... foolishly left my Sega Master System plugged into it and turned on, with a Wonder Boy 3 cartridge in it.
419
00:41:32.440 --> 00:41:54.200
And I'm still able... I could just about stream the picture live that's being decoded, everything could just about keep up, and I could just about transmit fast enough, like some crap MJPEG stuff, to get to me here. And I've got the satisfaction of watching the little character play the attract mode in full color with, you know, all of... warts and all. It's been a journey. It's been fun. But yeah.
420
00:41:54.200 --> 00:41:57.920
Did it... did that survive the power outage up in Evanston a couple of weeks ago? Okay.
421
00:41:57.920 --> 00:42:06.000
No, no, I had to ask the dog sitter who was in the house to go, can you just go and press this button?
422
00:42:06.000 --> 00:42:06.120
Oh, my God.
423
00:42:06.120 --> 00:42:16.540
I had to send a pic... Luckily, I had a picture from one of the many times I was doing the Advent of Compiler Optimization for like the thumbnails. I said, the computer is here, like a big drawn-on arrow, press this button.
424
00:42:16.540 --> 00:42:16.540
Okay.
425
00:42:16.540 --> 00:42:20.020
And yeah, they were able to turn it back on for me.
426
00:42:20.020 --> 00:42:20.180
My god.
427
00:42:20.180 --> 00:42:31.790
And yeah, I didn't get them to go in the basement and turn the NAS on, which has also died, but... my son has now done that. But yeah, hilarious stuff, man.
428
00:42:31.790 --> 00:42:32.940
All right. Excellent.
429
00:42:32.940 --> 00:42:45.820
Thank you for listening, my friend. This has been fun for me. I don't know what else to do now other than go on... I'm spent. I've been talking at the screen for this time.
430
00:42:45.820 --> 00:42:50.250
But yeah, good... good shout on working out where the puzzles were.
431
00:42:50.250 --> 00:42:50.560
This is... this is an amazing project.
432
00:42:50.560 --> 00:42:52.540
That was... that was impressive thinking on your feet.
433
00:42:52.540 --> 00:42:58.860
I mean, you know, whatever. We're all just nerds here. That's how that works.
434
00:42:58.860 --> 00:43:11.790
So I'm probably going to edit this and put it out like in a couple of days' time, which I think will probably be the first time ever that we've had a Two's Complement go out within the time that we recorded it, which then unfortunately means we have none left in the bank.
435
00:43:11.790 --> 00:43:12.000
Oh, yeah. Within a few... Right.
436
00:43:12.000 --> 00:43:18.880
So dear listener, you will... the next one in August will be another seat-of-the-pants job. But...
437
00:43:18.880 --> 00:43:22.140
Hopefully it's released on time, but no promises at this point.
438
00:43:22.140 --> 00:43:23.350
Correct.
439
00:43:23.350 --> 00:43:24.920
Right. Yeah.
440
00:43:24.920 --> 00:43:26.750
Correct. Events may overtake us at this stage.
441
00:43:26.750 --> 00:43:27.140
Yeah.
442
00:43:27.140 --> 00:43:28.220
Yeah, that's true.
443
00:43:28.220 --> 00:43:29.060
Yeah. All right.
444
00:43:29.060 --> 00:43:29.700
Well, until then.
445
00:43:29.700 --> 00:43:33.900
Until then, yeah, have yourself a great time.
446
00:43:33.900 --> 00:43:35.060
Okay. Cool. See you later.
447
00:43:35.060 --> 00:43:37.060
Bye.
1
00:00:18.920 --> 00:00:20.280
Hey Ben.
2
00:00:20.280 --> 00:00:21.440
Hey Matt.
3
00:00:21.440 --> 00:00:24.000
It has been a while, hasn't it?
4
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Been a bit.
5
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I mean, not for our listener, obviously. Our listener, it's just been a month. But for us, things... life has overtaken us. A lot of things are going on. We are, in fact, on different continents right now.
6
00:00:36.820 --> 00:00:49.160
And I'm looking at my sound levels, in fact, and I'm wondering how awful this is going to sound. So I'm going to just tweak something. But, yeah, I apologize in advance to the poor editor who has to edit this because I am recording...
7
00:00:49.160 --> 00:01:03.700
on my laptop from my wife's childhood home in her bedroom where she grew up in Birmingham in the UK, which is not where I was planning on being around this time.
8
00:01:03.700 --> 00:01:03.820
Mm-hmm.
9
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But nevertheless, adult things happen and you end up in a different landmass. So that's me.
10
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Right.
11
00:01:09.740 --> 00:01:23.540
So apologies for the sound. And I still haven't actually changed it. Let me just do that now. OK. Now I'm going to start clipping and... let's see what that does. That looks... that looks better. No, maybe I am clipping now. I got excited. All right.
12
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This, my... this, dear listener, is going to be a heavily not edited at all podcast because Ben and I just need to record something so that you've got something to listen to.
13
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Yeah.
14
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Yeah. I met a number of people claiming to be our single listener at a conference recently, which was lovely. So shout out to the many single listeners that we had there. That was good to hear. It's always nice to get feedback. I mean, like, it's a funny thing that we do, right? We just chat, talk to each other. Apparently people listen to this, which is on them, in fairness. They don't have to. We're not making them.
15
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Okay.
16
00:02:02.830 --> 00:02:03.060
Yeah. Yeah.
17
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It's amazing. I don't understand it.
18
00:02:05.560 --> 00:02:17.950
So here we are. Yeah, we have no idea, as is normal, as is usual. But I've been doing some cool things that I would have just talked to you about because normally we would do this down the pub.
19
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Right.
20
00:02:18.050 --> 00:02:18.160
Yeah.
21
00:02:18.160 --> 00:02:19.820
But again, due to 4,000 miles between us, this is...
22
00:02:19.820 --> 00:02:27.520
Yeah. I haven't actually heard about any of this stuff, so it's not going to be... Yeah, I'm genuinely interested because I have not talked to you in a long time.
23
00:02:27.520 --> 00:02:28.160
the first time. So you know that I...
24
00:02:28.160 --> 00:02:33.700
Due to the aforementioned time dilation created by you going across the Atlantic Ocean that is stretched out.
25
00:02:33.700 --> 00:02:34.480
Is that what it is?
26
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Yes.
27
00:02:35.720 --> 00:02:43.700
That... it does make me wonder, because it does feel like we're in like the 1950s here in the UK, because they haven't got air conditioning and it is very, very, very hot.
28
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Uh-huh.
29
00:02:43.980 --> 00:02:45.100
Right. Right. That's...
30
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Someone should tell them about this new technology.
31
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Yeah.
32
00:02:47.700 --> 00:03:00.160
Oh, and they will not let me back in the country. Yeah. So one of the things that I got really excited about, well, you know, I love emulators. That's my thing. When I'm not forcing compilers to do things they shouldn't do, I am...
33
00:03:00.160 --> 00:03:08.930
emulating my childhood. And the thing that has really annoyed me all the time is that monitors are too crisp.
34
00:03:08.930 --> 00:03:09.710
Yep.
35
00:03:09.710 --> 00:03:10.500
Yep.
36
00:03:10.500 --> 00:03:23.800
I mean, we've talked about this before in a podcast, but like, you know, my very first computer, the first computer I programmed on was plugged into a portable color television, you know, full CRT bulbous screen,
37
00:03:23.800 --> 00:03:24.110
Yeah.
38
00:03:24.110 --> 00:03:24.740
Yeah. Right.
39
00:03:24.740 --> 00:03:25.340
Right.
40
00:03:25.340 --> 00:03:35.580
like analog push buttons, like when radio buttons were actual, the buttons you had on radios with a physical mechanism, you press one and the others pop out, you know, right.
41
00:03:35.580 --> 00:03:36.120
Right, right, right. Yeah.
42
00:03:36.120 --> 00:03:46.780
And then behind that was a tiny little thing you would tune to get it to the right channel. And then your, so your computer that you plugged in had to pretend to be a TV station, right?
43
00:03:46.780 --> 00:03:47.620
Right.
44
00:03:47.620 --> 00:03:58.090
It would generate radio frequency of PAL or NTSC at some frequency. You tune it into channel 36 in the UK or channel...
45
00:03:58.090 --> 00:04:01.840
Yeah, it was like three or four, I think. Yeah, three or four, something like that.
46
00:04:01.840 --> 00:04:02.180
Yeah. In the US, right.
47
00:04:02.180 --> 00:04:02.860
Right.
48
00:04:02.860 --> 00:04:06.960
And the TV didn't know that it wasn't actually plugged into an aerial listening to something off the...
49
00:04:06.960 --> 00:04:07.980
Right.
50
00:04:07.980 --> 00:04:38.690
But what that meant was, you know, not only was the CRT... not a perfect device. It's a very, very analog device that involves phosphors and things that... don't instantly light up and instantly fade away, which is part of their charm. But the picture quality was rubbish because you had to squirt color information down a single line. And it wasn't even like you could use a digital encoding, because this stuff had to work on like 1950s
51
00:04:38.690 --> 00:04:41.520
analog components when color TV was invented.
52
00:04:41.520 --> 00:04:41.920
Right.
53
00:04:41.920 --> 00:04:50.810
It's like the worst of all worlds. But it's really, really nostalgic to see the terrible picture quality that came from it.
54
00:04:50.810 --> 00:04:58.480
Right.
55
00:04:58.480 --> 00:05:04.960
And people would use this, right? There were tricks you could do to make colors look more blended and in some cases to achieve extra effects on a real TV that you won't get on an emulator.
56
00:05:04.960 --> 00:05:05.970
Anyway, this was annoying me.
57
00:05:05.970 --> 00:05:07.160
Mm-hmm.
58
00:05:07.160 --> 00:05:42.300
So I thought, right, sod it. I'm going to learn how this stuff works and I'm going to make my emulator faithfully reproduce all of the things, warts and all. And so I did one pass of this and it's a... it's kind of a fudge. It's like, yeah, we need to blur it a little bit. We need to do some of these effects. But it was like, no, this is not a first principles simulation of what's going on. So I thought I'm going to go deep rather than start by like just synthesizing the picture quality and that kind of stuff. Why don't I learn how to do it? How do I learn to be a TV person?
59
00:05:42.300 --> 00:06:06.980
I want to take a real BBC Micro or Sega Master System. I'm going to plug it into my computer. I'm going to use a software defined radio, which lets me decode radio frequency signals into essentially a stream of ones and zeros that I can read fast. And then I'm going to software decode that thing back into a color picture.
60
00:06:06.980 --> 00:06:34.320
And that's going to teach me everything I know about how the heck this works. And then I'm going to look at each bit of the code and kind of go, which things are available... What parts of that could I have done using analog electronics back in the day? Which things are like DSP tricks that you would only have had in high-end televisions and stuff like that? And now I can actually pluggably make a TV and say, I want a 1990s era
61
00:06:34.320 --> 00:06:51.330
type display, or I want... no, I want the actual 1984 Thorn TV that I had in my bedroom, which I have a photograph of, and I found... and I've got the manuals for, and I'm going to try and find an actual real one so I can do some real sampling. But you know, that's... it's been a journey, my friend. What do you want to know?
62
00:06:51.330 --> 00:06:51.740
Wow.
63
00:06:51.740 --> 00:07:02.310
Wow. Well, so, okay. So just to clarify exactly what you're saying here is you didn't have enough emulator in your emulator. So you added another layer of emulation on top of your emulator.
64
00:07:02.310 --> 00:07:04.820
So you have two layers of emulation.
65
00:07:04.820 --> 00:07:14.950
In fairness, I haven't put this into the emulator yet. There's a version in the emulator, but this is purely learning about the decoding. What I hadn't registered really is there's kind of two parts to the whole thing.
66
00:07:14.950 --> 00:07:15.300
Yeah.
67
00:07:15.300 --> 00:07:25.160
One is the RGB that is actually being generated by the computer, right? There is obviously RGB at some point.
68
00:07:25.160 --> 00:07:25.740
Mm-hmm.
69
00:07:25.740 --> 00:07:31.760
With the exception of NESes, which is a whole other story, and we don't have time for that, but like there is RGB, and then it goes through encoding.
70
00:07:31.760 --> 00:07:31.760
Yeah.
71
00:07:31.760 --> 00:07:40.520
And then the BBC Micro's output encoding circuitry would differ from the ZX Spectrum's one, from the Sega Master System.
72
00:07:40.520 --> 00:07:52.300
I'm sure all of the systems would come up with their own compromises about what's cheap to do or appropriate to do, to generate the signal. Then they would go through RF modulation, which adds a whole other thing in.
73
00:07:52.300 --> 00:08:06.960
They may or may not mix in the audio, because the audio is in there as well. And then they would send it off to the TV, right? So there's stage one is how does the output stage generate the RF signal that's coming out. And then stage two is which type of TV have you plugged it into?
74
00:08:06.960 --> 00:08:18.560
Is it a modern one? Is it a cheap and nasty color TV? Is it one of those ones where, you know, effectively over time, the heat of your... this is what I had with my friend Richard, we would go around his house.
75
00:08:18.560 --> 00:08:30.260
And after a lot of programming, the screen would start getting worse and worse and start shimmering. And we realized that, oh, you'd have to retune the TV as everything had gotten hot. And so all these analog components had gone out of lock effectively.
76
00:08:30.260 --> 00:08:33.210
And there was no... so it's...
77
00:08:33.210 --> 00:08:34.080
Yeah.
78
00:08:34.080 --> 00:08:46.100
Honestly, it's an amazing thing. And yeah, there's just so many layers. I've learned so much about how SDRs work, about how fast you have to sample stuff. Essentially, it's like an ADC.
79
00:08:46.100 --> 00:08:49.280
So it's like a sampler, an audio sampler, right?
80
00:08:49.280 --> 00:08:50.180
Right. Yeah, yeah, yeah.
81
00:08:50.180 --> 00:08:55.740
But not running at 44 kilohertz or 64 kilohertz. It's running at 32 megahertz.
82
00:08:55.740 --> 00:09:24.320
So it's 32 million samples a second, which is not totally unreasonable. It's fine. But the RF that we're looking at is a signal that varies and wiggles around a frequency that's like 400 megahertz or 300, 200 megahertz or something like that. So there's a kind of an analog trick for bringing down the signal from that really high domain down to a lower domain that you could then sample.
83
00:09:24.320 --> 00:09:24.420
Right.
84
00:09:24.420 --> 00:09:25.140
And how musical are you, Ben?
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You know, not particularly. And it's also possible that our listener is also not. So, you know, over-explaining is probably a good thing here.
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Right, that's fair. But right, so have you ever, you know when something is slightly out of tune, if you heard two notes that were slightly out of tune, they were both trying to be the same pitch.
87
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And so like, an A is 440 hertz, right? And now... yeah, I can't tell it's an A, right?
88
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Okay, yeah.
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I haven't got perfect pitch. But if it's... and then I also... someone played a 441 hertz sound,
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Right.
91
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I wouldn't be able to hear the difference. But if you played the two together, there's that horrible wobbling, whoa, whoa, whoa, whoa kind of thing that happens when they grate against each other.
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Yeah. Yeah.
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It's a crunchy, horrible thing when something is nearly in tune, but it isn't in tune, right?
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Mm-hmm. Mm-hmm.
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That, the frequency of the whoa, whoa, whoa of the two, beating and grating against each other, is the difference of the two frequencies.
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So 440 and 441 would give you a once a second wobbling sound.
97
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Okay, yeah, that makes sense.
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Right, right.
99
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So the trick, and anyone who knows about this for real, who's like done electronic engineering or whatever, is like screaming at their speakers right now, this is not a trick.
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Mm-hmm. I know.
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This is like just how it's done. But like the trick to me is, what you do is you play the two frequencies... when you want to tune to, say, 200 megahertz, you generate a local 200 megahertz signal using just your own oscillator.
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Okay.
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And you play that again at the same time. You multiply them. You mix them together. You multiply them in this instance. But like, go with me in this, my music analogy, right? And the result is, yes, you hear both of those tunes, but they're so high-pitched and high-frequency that they're then beyond what you can sample with your sampler. But the difference between them, the wobbling around, is much lower frequency. It's the difference of their frequencies.
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Okay.
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And so now you get a signal that is around about plus or minus, you know, however wide the various frequencies might be. And so by playing a 200 megahertz tone and multiplying that with whatever noise is happening off the radio,
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Okay.
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I can then sample that at, say, 32 megasamples a second. And what I've got is essentially a plus or minus, sort of, Nyquist limit is half of that, 16 megahertz around the 200 megahertz window.
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So I can get from minus, because it's the same, you can't tell if it's one hertz above or one hertz below.
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Okay.
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They both beat at once a second. So you get both the signals that are from like 200 to 216 and down to 184, whatever that... Right.
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Okay.
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But, and that's the band.
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And this is all to like bring these frequencies down into a range where you can sample them at the rate that you're able to sample them with the hardware that you have?
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Exactly. Without getting all those sort of like pointless noise of like lower frequency things that you don't care about.
115
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Okay.
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And then there's some other tricks that you have to do because, you know, again, you can't discriminate between something that's one hertz higher from what's only one hertz lower. And there's a trick. Maybe we want... if we talk about every trick here, we're going to be here for three hours.
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So I'm...
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And then the thing that's melting my brain here is that it's like, you know, you talk about this with audio and I can kind of like think about it, but it's like, this is television, right?
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Correct. Yes.
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So it's like, you know, it's not just audio. In fact, it's not even primarily audio. It's the signal that you're using to, you know, bend this, you know, electron ray, whatever the heck it is.
121
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Electron beam that's flashing back and forth.
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That's... yeah.
123
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Exactly.
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Right.
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And again, and it all had to be done in analog.
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Right.
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So you know this first stage I just described, you could imagine some kind of magical thing that oscillates. You get it tuning. When you're tuning the television, what you're really doing is tuning that oscillator to a frequency... that there's more...
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There's a middle stage. There's an intermediate frequency and stuff like that. But like for the purposes of this conversation, you're tuning an oscillator. And then the difference between the oscillator you tuned and the signal that's just got, of course, every TV station mixed into it will...
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will give you, will center it around the thing that you care about. And then if you filter the stuff that's higher and lower frequency, now you've just got your TV tune. But yeah, now you've got like another layer of encoding. So think about it as encoding. Now you've probably talked about, and I'm going to say a word that you're going to say a different way to me. And I don't know if it's a me thing or a UK thing, US thing. So the not-RF signal that you would plug in, the yellow lead on your old consoles where you didn't have the audio in, you would have like three leads, you'd have left and right audio, which would be red and white.
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Yeah.
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Yeah.
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And then the yellow lead, which would be the video.
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Yeah.
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Well, that will be what kind of video?
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Oh, I don't know. RF video. I mean, but yeah, I always think of it as like, you've got component and comPOSite and... okay.
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COMposite is the word I was looking for there. Yes. So yes, I would say COMposite.
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Yeah. Oh, okay.
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I don't know if it's just a thing that I say. So, you know, our listener can have a think. But yes, so effectively there are like several layers of encoding.
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Yeah.
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The first thing is we're going to make something RF so we could transmit it over the... what, the waves, the airwaves, right? The composite is too low frequency and everyone would pick the same one.
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So obviously every channel has its own. But in there are two things, right? One is the composite video, which is itself composed of more things, which we'll get to.
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Mm-hmm.
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And then there's essentially like an FM radio signal that is the audio that is just on the edge of the video signal, either side of it, the way that it works out. And I'm a bit vague on this bit because I haven't got to that yet.
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But you can imagine, yeah, given the amount of spectrum that you're allowed to use, the bandwidth of radio range, you would kind of fiddle it around and say, okay, the FM lives in this part of it.
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Mm-hmm.
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And then the middle part is all this. And the much wider part, for what it's worth, is the TV signal, which is itself composed of several things, right? Red, green, blue, synchronization pulses, like this is the top of the screen. This is a new line, right? Now in our... you and me, these are packets. These are like binary encoding and you go like, how about the start frame, you know, whatever. But like, this is... it can't be the case, because we're talking analog era electronics.
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And so first of all, the first trick is that it's amplitude modulated onto the carrier. So there is the carrier, you know, the 200 megahertz that I mentioned before, is just a wiggling 200 megahertz signal.
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Yeah. Yeah.
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And we just turn the volume of that up and down like old AM radio, right?
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Yeah. Right.
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Forget frequency modulation. We're not modulating the frequency. But by flapping the amplitude up and down fast enough, we are actually using frequencies around it.
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Right.
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If you were to put it through a spectrum analyzer, you see that you get this bandwidth just because of the way it...
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OK, so just to reiterate some of this back to make sure I understand what's going on here. You've got, because it's television, you have this limited frequency in which you're allowed to use for your signal, right?
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Yeah.
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Yeah.
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Correct.
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You're going to slice off some of that for the audio. You're going to slice off some of that for, you know, both channels of the audio. You're going to slice off some of that for the video. And then within that frequency, you're actually encoding the signal in the amplitude of the waves in that frequency.
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Correct, by modulating the up and down of that.
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Have I got that right?
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Yeah, yeah.
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Yeah. OK.
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And so the way that it's done is that a black picture is the brightest. So it's inverted, right? So a totally black screen would be just the normal
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OK.
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full amplitude... the RF signal.
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Yeah.
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Right.
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And this is also true, incidentally... Yeah, no, sorry, I'm confusing myself here. Right, forget... Go ahead.
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Is that true for the audio, too? This seems counterintuitive.
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I don't... I don't think so. The audio is separate from this. At this point, we've left the audio behind. It's been filtered off.
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OK.
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It goes into audio circuitry, and I haven't looked at that too much.
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But yeah, we've got this amplitude modulated thing where we want to extract from that essentially a single continuous analog signal from this wiggling thing.
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Okay.
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Okay. Okay.
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And the way that we do that is we treat the... Actually, I'm not sure what the circuitry does at this point, but we're looking for the amplitude. So let's just ignore the fact that it's wiggling anymore and just say it's the amplitude of this.
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We've got a thing that comes out. And now the amplitude is inverted such that the darkest picture is bright, the loudest, and the brightest picture would be almost no signal.
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It never goes completely zero, because then you don't have anything to lock onto.
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Yeah. Yeah.
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But it's there. So we've got a range now. We've got a range of, say, voltages. And... It's unimportant that it's inverted, other than like the very dark signal is always there. So even if the picture's black, you can tune into the stupid thing and actually know that you've picked up a black picture, right? So from now on... quickly, early on, you invert it the other way around. So it looks sane to humans where, you know, bright is high and dark is low. Let's go with that, right?
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Yeah.
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You with me so far? Because, yeah... the first thing is we invert it.
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Yeah. Is this why television static is mostly white?
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It is... we'll get to that actually. That's good, hold that thought, my friend, because this is the cool bit, right?
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Okay. All right. All right.
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So yes, we've got this, let's just say goes between zero and one volt, right? Where white is... one volt is bright white and zero would be black, except what we're gonna do is we're gonna say, no, no, no. We need a way of signaling the synchronization pulses.
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We need to say, this is the beginning of the screen. And we need to say, this is the beginning of a line, because what's happening behind the scenes is that there is... we want to synchronize the electromagnets in the TV with this picture so that they start at the top of the screen, they slowly go down and more quickly, they flip from left to right.
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Mm-hmm. Mm-hmm.
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And we wanna make sure that everything's synchronized. Otherwise the picture rolls or it's diagonally skewed because the rows aren't aligned, right?
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Yeah.
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But we need a way of saying, this is a big... this is like, we sort of out of band. And so the out of band is lower than black. It's like we go... we say, right, black is actually gonna be 0.3 volts.
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And anything below 0.3 volts is like blacker than black, and it's actually a signal. It's like, a thing is happening. It's our sort of out-of-band signal, because we know also that while we're between lines and while we're pulling the beam from the bottom to the top, we actually don't want to paint anything to the screen. Otherwise, you'd start seeing splurge as the light... as the beam retraces its steps, right? And you get pictures being overwritten with crap. So we want it to be low and we might as well just say, well, when it goes really low, that's a signal to you.
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Okay.
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Good so far?
195
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So you said blacker than black, like the amplitude... as the amplitude decreases, that is our range of signal, right?
196
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Yes. So we've got effectively between like 0.3 and one volt is the normal black to white.
197
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Okay.
198
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And then below, we're already talking... yeah, sorry, I've already inverted it so that it makes sane.
199
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So you've... we've already talked about it being flipped at this point. Got it.
200
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Yeah, yeah, yeah, yeah.
201
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Yeah, yeah, yeah, yeah.
202
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I'm sorry about that, yeah.
203
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No, that makes sense. I'm back with you again.
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Okay, yeah, I did do a bait-and-switch, changed my sort of... there, because it's just easier to think of it the right way up, right, the way you would want to see it, right, the way that it actually gets transmitted when you're using a composite cable. Because effectively by the time we have taken it away from being this amplitude modulated signal to just a signal between zero and one volts and turned it the right way up so that it makes sense, where now that's what you would get out of your composite cable.
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Right, yes. Right, right.
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Yeah.
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Yeah.
208
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OK, got it.
209
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Right. So no audio, no weird wiggling, just pure something you could put into an oscilloscope directly and go, oh, I can see what that's doing, as opposed to just a mass of wiggly lines.
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Right.
211
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Yeah. Yeah.
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Right. And I forget...
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Right.
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So TVs used to be black and white. You probably remember this.
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I don't know. Actually, that's not true. I did actually own a black and white TV.
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You're younger than me. I never... I think we had one black and white TV, but it was in my nan's house.
217
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Yeah. We had a cheap one that was black and white. That was like an extra one.
218
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But yeah, so the trick is that whatever we do to get color into our signal had to be, back in the 40s and 50s, whenever it was color was, had to be backwards compatible in the worst possible way.
219
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Yeah.
220
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Mm-hmm.
221
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Like they couldn't squeeze three copies. They couldn't go, oh, this is now red and this is now green and this is blue, because your black and white TV would be like, well, it's just... I only show what red is, or something like that.
222
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Right, right.
223
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Yeah, yeah.
224
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So there was a trick here. Yeah. Oh, but I missed over the... Going below 0.3 volts is a signal to either pull the signal up to the top of the screen if it's a long period of time, or if it's a short burst below 0.3 volts, it pulls it back to the left.
225
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Mm-hmm.
226
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So there are like two independent circuits that are always running inside the TV, one of which is just a square, both of which are sawtoothed.
227
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Yeah.
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Sawtooths, excuse me, sawtooths.
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Mm-hmm.
230
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Yeah.
231
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And they're set to be, you know, just slightly longer than a frame and just slightly longer than a line, so that they will naturally just kind of go zero to left to right, left to right continuously, and top to bottom slower, but continuously.
232
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Mm-hmm. Mm-hmm.
233
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But the pulse going that low for a while is a signal to say, doesn't matter where you think you are, start dragging yourself to the top of the screen if you're the top to bottom, or left of the screen.
234
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So that also gives you a certain amount of slop, where... not AI slop for a change, slop where if, for example, your TV's
235
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Yeah.
236
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crystal oscillators, or they weren't even crystals, but the little oscillators that were doing these sawtooths, was slightly out of spec, then, you know, you just keep rewiring, pulling them back onto the right sort of thing. And if there was no signal at all, then they would sort of free run. And that's when you would see the picture rolling, for example. If there was enough to see where the picture was, but you didn't... the TV couldn't pick up that synchronization pulse anymore, then it would just free run.
237
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Yeah.
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Yeah.
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And so the whole picture would spin over and over again. And I realize I'm gesturing wildly with my hands, which doesn't help our listener at all.
240
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Yeah. Yeah.
241
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So without getting into too many of the specifics, both of those things cause the TV to reset the top bit and the left to right bit. The interesting thing for me for the first time about this was like realizing that that sawtooth from top to bottom is always running.
242
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You know, you and I think that the beam scans from left to right, then it goes down a bit and comes back again sort of diagonally, and then it scans the next row left to right.
243
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But it doesn't. It's doing... it's always a slightly diagonal line from left to right.
244
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Yeah.
245
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And then it's a much less diagonal angle from right to left, because it's much quicker going back than it is going across.
246
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Mm-hmm.
247
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And so you'd think that the whole picture would be slightly wonky because it's... and it is.
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Yeah.
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And so they just adjust the damn magnets to turn them by half a degree backwards so that it's all the right way around again.
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It's just, you know, beautiful.
251
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Oh...
252
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And I had to model that because I'm like, why is everything slightly off?
253
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Right.
254
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Oh, yeah. Yeah.
255
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Okay, so that's the retrace. So we were talking about black and white. So you could imagine now it's really, really easy. We have these two electromagnets that are being dragged... dragging the electron beam up and down, left and right. They're synchronized with the signal. And then the rest of it is just the brightness.
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And that's just how many electrons we squirt at the screen in the direction the beam is currently pointing. And there you go. You've got a black and white telly. You are done. Hooray, high fives all round.
257
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But now we want color. And so, you know, as a computer programmer, we would say, oh, V2, you know, or you sort of come up with something.
258
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Right.
259
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Well, we've got the red, the green, and blue, and three channels. And then somehow, oh, there's also a black and white version. But no, they had to come up with a really clever way of getting color into the signal.
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So the trick, and this is the great thing, the trick is take... we take the color information and we break it down into three components.
261
00:25:41.940 --> 00:25:51.930
Rather than red, green and blue, we pick brightness, which we already have, because that's what the black and white signal was. And then we have two chrominance signals.
262
00:25:51.930 --> 00:25:52.660
Mm-hmm.
263
00:25:52.660 --> 00:26:02.410
And you know if you've ever pulled up a color picker in any of your art packages, you've probably seen the ones where you've got HSV and you know you've got brightness and then two different other sliders.
264
00:26:02.410 --> 00:26:02.550
Mm-hmm.
265
00:26:02.550 --> 00:26:02.700
Mm-hmm.
266
00:26:02.700 --> 00:26:15.780
And you can pick any color with three things. That's the beauty of like any space is that if it's a 3D space, you can have any coordinate system and you can get to all the points of the coordinate system as long as you've got three of them.
267
00:26:15.780 --> 00:26:28.580
And that's what it is. So like we have essentially a brightness, which is overall how bright something is. We have how saturated a color is, between totally that color or white,
268
00:26:28.580 --> 00:26:40.280
white, however white the brightness would let us go. And then we have a kind of color wheel for the third axis, which says, well, which color, if we're not white, which color are we tending towards?
269
00:26:40.280 --> 00:26:51.520
And you could imagine you're just, you know, just a genuine, honest kind of color wheel and like, well, it's a direction on there. And so now we've got three signals again. So that's cool. And one of them is one we're already transmitting.
270
00:26:51.520 --> 00:26:59.980
So can we hide the other two signals somewhere that a black and white telly that hasn't even... doesn't even know the color exists
271
00:26:59.980 --> 00:27:01.060
Right.
272
00:27:01.060 --> 00:27:08.350
doesn't see them, without using more bandwidth, because we can't add... you know, we've got all these TV channels packed into the RF spectrum.
273
00:27:08.350 --> 00:27:08.720
Yeah.
274
00:27:08.720 --> 00:27:29.060
And although we're talking... I'm talking about the composite part now, the width of that signal has to somehow be squished into the radio spectrum. So what we do is we observe that if we wiggle the brightness really fast and not that much, maybe the black and white TV won't notice it.
275
00:27:29.060 --> 00:27:29.480
Mm-hmm.
276
00:27:29.480 --> 00:27:45.150
Because it's a crap old piece of analog electronics, it's old anyway, a higher frequency wiggle in the brightness would probably go unnoticed, or at worst just makes the white areas look a little stippled in places where it's just varying quite quickly.
277
00:27:45.150 --> 00:27:45.780
Mm-hmm.
278
00:27:45.780 --> 00:27:57.060
Okay, but now we've got a wiggle. What do we do with this wiggle? Well, this wiggle, we can somehow encode two pieces of information with that wiggle.
279
00:27:57.060 --> 00:28:02.080
The amplitude of that wiggle could be one of the other dimensions.
280
00:28:02.080 --> 00:28:04.560
Oh, OK. Yeah, and the frequency is the other one?
281
00:28:04.560 --> 00:28:08.480
So now we've got one of them, but how do we get the third one?
282
00:28:08.480 --> 00:28:10.700
Yeah. Is it the frequency of the wiggle?
283
00:28:10.700 --> 00:28:12.500
What else... what's that, sorry?
284
00:28:12.500 --> 00:28:14.740
Is it the frequency of the wiggle?
285
00:28:14.740 --> 00:28:25.950
It's not the frequency... that would make sense at some level. And I think SECAM, the French thing, used something akin to that. But that would be too easy.
286
00:28:25.950 --> 00:28:26.520
OK.
287
00:28:26.520 --> 00:28:40.760
Also, there are limitations on what frequencies we can use for a variety of reasons, to do with the fact it has to not be a frequency that's going to interfere with this signaling itself, because all these other components are going.
288
00:28:40.760 --> 00:28:50.360
And also the RF... sorry, the audio is in there as well. So there was some careful picking of these numbers so they all don't divide into each other and you end up with like stripes or things like that.
289
00:28:50.360 --> 00:28:50.540
Okay.
290
00:28:50.540 --> 00:29:02.320
Because there are artifacts, which is partly why we're talking about this, because it... those are artifacts I'm trying to capture in the emulator. So the other thing that we can fiddle around that isn't the frequency is the phase.
291
00:29:02.320 --> 00:29:04.240
Oh, okay. Yeah.
292
00:29:04.240 --> 00:29:10.890
So you can slide that back and forth and have the peak at this point in time or push it back a little bit, and now we've got another dimension.
293
00:29:10.890 --> 00:29:11.240
Right.
294
00:29:11.240 --> 00:29:25.740
And so the phase, as you'll recall, can be measured as between 0 and 360 degrees, if you want to think about it, right, as a sine wave. You can like slide the sine wave back and forth. And that maps nicely into our 360 degree color wheel that we had.
295
00:29:25.740 --> 00:29:29.610
So that's how we pick the color. The color is just the phase of that wiggle.
296
00:29:29.610 --> 00:29:29.840
Okay.
297
00:29:29.840 --> 00:29:45.350
And then how saturated it is, is how wiggly... the brightness of that wiggle. So heavily saturated colors on a black and white television do have a grainy texture over the top of them now, because you can see the wiggle in it if you look hard.
298
00:29:45.350 --> 00:29:46.060
Mm-hmm.
299
00:29:46.060 --> 00:30:01.830
So that's cool. We have smuggled two pieces of extra information into our channel. Black and white TV people don't really notice it. But we've now got a new problem, which is that analog electronics is not very good at measuring things like phase differences.
300
00:30:01.830 --> 00:30:10.940
Because how accurate do you have to be with your signal to know if it's in or out of phase? And in and out of phase with what?
301
00:30:10.940 --> 00:30:11.900
Right.
302
00:30:11.900 --> 00:30:15.560
Maybe you need a PTP timestamp synchronization and now everyone's on the same page.
303
00:30:15.560 --> 00:30:15.560
Maybe.
304
00:30:15.560 --> 00:30:23.400
You're down to the... No, no, we haven't got any of that. It's got to work with crap electronics in a 1960s box.
305
00:30:23.400 --> 00:30:24.120
Yeah.
306
00:30:24.120 --> 00:30:25.840
Can I... can I take a guess?
307
00:30:25.840 --> 00:30:28.370
So we need... Yeah, please. This would be great, because I've been just jabbering.
308
00:30:28.370 --> 00:30:28.820
Can I... can I guess?
309
00:30:28.820 --> 00:30:30.620
So tell me, what do you think?
310
00:30:30.620 --> 00:30:36.960
So there's two checkpoints that you have. One is the screen reset and one is the line reset.
311
00:30:36.960 --> 00:30:38.000
Yes, go on.
312
00:30:38.000 --> 00:30:43.040
So it could be either of those, or maybe even both.
313
00:30:43.040 --> 00:30:49.700
You are bang on the money, my friend. And it almost makes me think you're cheating and Googling, but I can see your hands, so I know you aren't. Yeah.
314
00:30:49.700 --> 00:30:51.840
I am not. I am not.
315
00:30:51.840 --> 00:31:01.330
So at the beginning of each line, after we've had the little dip below the 0.3 volts that says, hey, this is the beginning of the line.
316
00:31:01.330 --> 00:31:01.740
Mm-hmm.
317
00:31:01.740 --> 00:31:10.030
And so we know that the electron beam has been dragged back and is currently now way off the left-hand side of the screen.
318
00:31:10.030 --> 00:31:10.480
Mm-hmm.
319
00:31:10.480 --> 00:31:16.730
We then come up to like a black level, because we're in the sort of border on the left-hand side.
320
00:31:16.730 --> 00:31:17.020
Right.
321
00:31:17.020 --> 00:31:20.990
And just before then, and there's something like... there's the front porch and the back porch.
322
00:31:20.990 --> 00:31:21.160
Right.
323
00:31:21.160 --> 00:31:25.400
There's some stupid names for these things, which is, you know, stupid, hilariously funny.
324
00:31:25.400 --> 00:31:25.660
Interesting. Yeah.
325
00:31:25.660 --> 00:31:37.100
We just do a quick burst of that color signal, just a little of it, that's short enough that, again, it's not going to be visible. It's off the side of the screen.
326
00:31:37.100 --> 00:31:45.540
But anything that's looking for it will see it and go, ah, two things. One, this is a color TV signal. It's not a black and white TV signal.
327
00:31:45.540 --> 00:31:45.620
Right.
328
00:31:45.620 --> 00:31:54.580
It's a color TV signal, because I've seen the color burst. Two, synchronize my very short-lived one-line's worth signal
329
00:31:54.580 --> 00:31:55.140
Right.
330
00:31:55.140 --> 00:32:16.360
local oscillator of this color frequency, so that I've now got a reference that I can compare everything else to, and I can compare it to see if it's in or out of phase and by how much. And so that is the trick of getting color. Now decoding that is a pain, but you mentioned something about the black, you know, static.
331
00:32:16.360 --> 00:32:18.470
So do you think you can answer your own question now?
332
00:32:18.470 --> 00:32:18.620
Yeah.
333
00:32:18.620 --> 00:32:20.620
Why is it black and white?
334
00:32:20.620 --> 00:32:27.980
Well, because it's not going to have that burst right at the right time to tell it that it's a color TV.
335
00:32:27.980 --> 00:32:34.370
Bingo. Bingo. So the color TV set will... will assume it's a black and white picture, because it can't synchronize to it and it can't find the color burst.
336
00:32:34.370 --> 00:32:34.630
Yeah.
337
00:32:34.630 --> 00:32:34.880
Yeah.
338
00:32:34.880 --> 00:32:42.880
And so it will suppress all of its own color decoding circuitry. And so the noise only comes out in black and white. Congratulations, sir.
339
00:32:42.880 --> 00:32:43.520
Wow.
340
00:32:43.520 --> 00:32:45.000
You've won today's podcast.
341
00:32:45.000 --> 00:32:50.330
Well, I just want to thank everyone involved, you know, my friends, my family here to support me.
342
00:32:50.330 --> 00:32:50.420
Yeah.
343
00:32:50.420 --> 00:32:57.160
And I'm just really proud of this accomplishment today. So thank you. Thank you all. Really appreciate it.
344
00:32:57.160 --> 00:33:18.890
But so I guess, you know, and so emulating and simulating this has been an absolute blast, and learning all of the various things that they do to the TVs that do that, like, period appropriate. And I learned, for example, that there are delay lines for something we'll hopefully talk about in a second, which required a piece of glass that's exactly the right size so that like essentially it puts...
345
00:33:18.890 --> 00:33:19.180
Wow.
346
00:33:19.180 --> 00:33:31.700
There's like a piezoelectric crystal on both sides of this bit of glass, and it knows it takes 64 microseconds for the vibrations to make it through to the other side. And that's how you get a delay line, an analog delay line, for 64 micros.
347
00:33:31.700 --> 00:33:32.700
You're like, what?
348
00:33:32.700 --> 00:33:33.140
Wow.
349
00:33:33.140 --> 00:33:46.840
There are other things that use specially shaped piezo crystals that then can filter out frequencies. It's just so clever. But while we're here, and as we've just been talking about the color burst in particular,
350
00:33:46.840 --> 00:33:48.720
This sounds like an amazing project. Yeah. Yeah.
351
00:33:48.720 --> 00:33:56.380
What is the name of the European, or most of the European, TV standard?
352
00:33:56.380 --> 00:33:57.840
PAL.
353
00:33:57.840 --> 00:33:59.760
Do you know what PAL stands for?
354
00:33:59.760 --> 00:34:02.840
Oh, I do not.
355
00:34:02.840 --> 00:34:21.400
It stands for phase alternating lines. And I think that probably tells you something about what happens on each line. And maybe about the color part, because this is where NTSC, which is something like the North American Television Standards Committee or something like that, which was developed first, incidentally.
356
00:34:21.400 --> 00:34:21.710
Phase alternating lines.
357
00:34:21.710 --> 00:34:22.020
Yeah, yeah. Uh-huh.
358
00:34:22.020 --> 00:34:33.440
So NTSC predates PAL by about a decade or so. And so PAL learned from NTSC and went, we like everything about this, but... there's this one thing, and they fixed something.
359
00:34:33.440 --> 00:34:33.540
Yeah.
360
00:34:33.540 --> 00:34:36.500
And one thing, so phase alternating lines.
361
00:34:36.500 --> 00:34:36.900
Uh-huh.
362
00:34:36.900 --> 00:34:49.260
So if we're using phase to control color, the hue, right, then my guess here is that we shift the phase every other line.
363
00:34:49.260 --> 00:34:49.860
Okay.
364
00:34:49.860 --> 00:34:57.520
I'm trying to think of why that helps, though. I don't know why that helps.
365
00:34:57.520 --> 00:35:02.120
Exactly. Yeah. Well, let's talk briefly, because I've looked... we're at 35 minutes, gosh.
366
00:35:02.120 --> 00:35:02.500
Why does that help?
367
00:35:02.500 --> 00:35:02.600
Right.
368
00:35:02.600 --> 00:35:17.820
Let's talk briefly about one of the problems that NTSC had. And actually, this would be interesting, because I didn't grow up with an NTSC set. I grew up cursing them in the 90s, because we had to like try and make our graphics look good on NTSC TVs for like games.
369
00:35:17.820 --> 00:35:32.830
But they wouldn't have suffered from the problem I'm about to describe. So... The problem with the phase being the color information is that tiny, tiny errors start moving you around on that color wheel, right?
370
00:35:32.830 --> 00:35:32.920
Mm-hmm. Mm-hmm.
371
00:35:32.920 --> 00:35:45.800
If you're just out by one degree, you're moving around this color wheel. And so you had a... you may have had an extra control on your early analog TVs that I would not have had.
372
00:35:45.800 --> 00:35:54.860
I had color, brightness, contrast. Those were the three things. Do you remember another one? I'm really... you're younger than me, so you probably don't.
373
00:35:54.860 --> 00:35:56.980
You know, I don't remember.
374
00:35:56.980 --> 00:35:57.370
It's been a while.
375
00:35:57.370 --> 00:35:57.800
It's been a bit.
376
00:35:57.800 --> 00:36:05.440
So my understanding is that earlier American sets would have a tint as well.
377
00:36:05.440 --> 00:36:08.460
Oh, yeah. Yes. 100%. Mm-hmm.
378
00:36:08.460 --> 00:36:38.420
And so you would fiddle with the tint, because people's skin color would look like orangey or greeny or whatever sometimes, because... now you probably know where I'm going with this... because of small errors in the phase. Those errors commonly come from the signal being reflected off a building near you. And if you take two signals that are identical and add them together with just a tiny delay in one of them, it's similar to shifting the phase of everything.
379
00:36:38.420 --> 00:36:39.060
Oh, yeah.
380
00:36:39.060 --> 00:36:43.260
And I'm going to wave my hands a lot here, because I've read the math a few times and it hasn't really gone in.
381
00:36:43.260 --> 00:36:43.560
OK.
382
00:36:43.560 --> 00:37:00.240
But there's sort of an unfortunate thing, either if the TV is just not good at locking onto that signal and the parts aren't great, or if there's a systematic error because everything's being slightly delayed and you're getting a mirror copy coming in, then the colors would morph, and it would depend on where the TV set is.
383
00:37:00.240 --> 00:37:00.500
Right.
384
00:37:00.500 --> 00:37:16.640
And it depends on like how warm things are. And you... so fiddle around with this tint. So this is the thing the Germans who came up with PAL was like, how can we fix this? And they made the observation, which to this day lives on in things like JPEG.
385
00:37:16.640 --> 00:37:22.400
So, and that is, humans care about the brightness far more than they care about the color.
386
00:37:22.400 --> 00:37:22.400
Okay.
387
00:37:22.400 --> 00:37:22.400
Right. So, you know, in, say, a JPEG, we store the... the brightness information at a higher resolution than we store the color information, because then you tend not to notice.
388
00:37:22.400 --> 00:37:22.400
Okay. Yeah.
389
00:37:22.400 --> 00:37:22.400
Yeah. Yeah.
390
00:37:22.400 --> 00:37:38.960
This trick comes from this area.
391
00:37:38.960 --> 00:37:39.040
Right.
392
00:37:39.040 --> 00:38:11.200
So they said, well, what if it didn't really matter if we were storing color on every line, unique color in every line? And so it's not... it's not actually that they changed it. But what they said was like, if we flip the phase every other line and we delay the previous line's color and add it to the current line's color, we cancel out any phase error between the two of them, because they've been affected by 180 degrees different in each direction.
393
00:38:11.200 --> 00:38:23.400
And every time I say that out loud, I go, there seems like there's something wrong with that. But I sit down, I do the maths, and the phase error cancels out. But at the loss of like the fact that you are mixing together two lines' worth of color information to kind of get one blurrier line of color information.
394
00:38:23.400 --> 00:38:23.400
Of course it was the Germans.
395
00:38:23.400 --> 00:38:53.700
So that is the... and again, probably without a picture or even, again, without me being very confident about it, but that phase alternation and knowing that the TV is going to do obviously the reverse, any error, any fixed error that you've added in cancels out, because when you reverse it the second time, you're adding minus... if you're bouncing off a building, it's adding three degrees of error.
396
00:38:53.700 --> 00:38:54.200
Yeah.
397
00:38:54.200 --> 00:39:00.530
You add in three degrees of error on the first line. You subtract three degrees of error on the second line. You assume that the other part is the same.
398
00:39:00.530 --> 00:39:00.780
Yeah.
399
00:39:00.780 --> 00:39:05.690
And so those two cancel out. You divide by two and you get just the right phase out of it.
400
00:39:05.690 --> 00:39:05.840
Yeah.
401
00:39:05.840 --> 00:39:06.460
Okay.
402
00:39:06.460 --> 00:39:16.310
And so PAL, phase alternating lines, and NTSC, which was "never twice the same color" for that reason.
403
00:39:16.310 --> 00:39:16.540
PAL.
404
00:39:16.540 --> 00:39:19.570
That was the bad acronym for it.
405
00:39:19.570 --> 00:39:20.080
That's funny.
406
00:39:20.080 --> 00:39:47.940
So, yeah, this has been... an odyssey of discovery, as I said. I can now just about real time in software decode... without using GPU trickery, I can decode this all in software, and I can point at each bit of the code and I can say, yeah, I know what that bit's doing. And whatever... things I didn't cover, because we're already 40 minutes here, is that having done this decode, I now do a physically based electron beam simulation where I actually use a lot of
407
00:39:47.940 --> 00:39:47.940
Wow.
408
00:39:47.940 --> 00:39:54.120
virtual magnets to drag a virtual stream of electrons onto virtual phosphor, which then bloom.
409
00:39:54.120 --> 00:39:54.760
Oh, wow. Wow.
410
00:39:54.760 --> 00:40:11.160
And as the overvolting of like a too-strong, too-white signal happens, the pixels bloom. The current starts going high in the electron guns and you get more, wider spew of like electrons that hit more area of the screen.
411
00:40:11.160 --> 00:40:27.940
What else? Then you can... I can simulate the fact that like they often... the flyback, which is this hilariously named but complicated thing that builds up enough charge to have this really high voltage that's needed, you can deplete it by having too much white for too long.
412
00:40:27.940 --> 00:40:38.470
And then essentially the picture starts sagging after that, which is, you know, on... again, on cheap sets where there wasn't much capacitance, or, you know, you would put a pretty big white thing.
413
00:40:38.470 --> 00:40:38.920
Wow.
414
00:40:38.920 --> 00:40:43.300
And but I remember having one, my dad nicked a monitor from work. And it had this problem where if you had like a bright white title bar of like a game, everything else underneath it was kinked, because that bright white area had kind of gone and dragged all the power out of it.
415
00:40:43.300 --> 00:41:10.690
And it's like, had to recharge it up to be able to like pull the electron beam properly. It's just amazing. It's so fun. And you have been a fantastic foil listening to me. I think I needed this more than I knew, actually. I did say to people at ACCU, I said, this is therapy for us... well, for me.
416
00:41:10.690 --> 00:41:10.860
I will...
417
00:41:10.860 --> 00:41:16.940
I cannot... I cannot wait to see this working in person. I just... I really am looking forward to this.
418
00:41:16.940 --> 00:41:32.440
So the fun thing is is that I've left my desktop computer plugged in with the SDR in Chicago, 4,000 miles from where I'm sitting here, and I've left my Sega... foolishly left my Sega Master System plugged into it and turned on, with a Wonder Boy 3 cartridge in it.
419
00:41:32.440 --> 00:41:54.200
And I'm still able... I could just about stream the picture live that's being decoded, everything could just about keep up, and I could just about transmit fast enough, like some crap MJPEG stuff, to get to me here. And I've got the satisfaction of watching the little character play the attract mode in full color with, you know, all of... warts and all. It's been a journey. It's been fun. But yeah.
420
00:41:54.200 --> 00:41:57.920
Did it... did that survive the power outage up in Evanston a couple of weeks ago? Okay.
421
00:41:57.920 --> 00:42:06.000
No, no, I had to ask the dog sitter who was in the house to go, can you just go and press this button?
422
00:42:06.000 --> 00:42:06.120
Oh, my God.
423
00:42:06.120 --> 00:42:16.540
I had to send a pic... Luckily, I had a picture from one of the many times I was doing the Advent of Compiler Optimization for like the thumbnails. I said, the computer is here, like a big drawn-on arrow, press this button.
424
00:42:16.540 --> 00:42:16.540
Okay.
425
00:42:16.540 --> 00:42:20.020
And yeah, they were able to turn it back on for me.
426
00:42:20.020 --> 00:42:20.180
My god.
427
00:42:20.180 --> 00:42:31.790
And yeah, I didn't get them to go in the basement and turn the NAS on, which has also died, but... my son has now done that. But yeah, hilarious stuff, man.
428
00:42:31.790 --> 00:42:32.940
All right. Excellent.
429
00:42:32.940 --> 00:42:45.820
Thank you for listening, my friend. This has been fun for me. I don't know what else to do now other than go on... I'm spent. I've been talking at the screen for this time.
430
00:42:45.820 --> 00:42:50.250
But yeah, good... good shout on working out where the puzzles were.
431
00:42:50.250 --> 00:42:50.560
This is... this is an amazing project.
432
00:42:50.560 --> 00:42:52.540
That was... that was impressive thinking on your feet.
433
00:42:52.540 --> 00:42:58.860
I mean, you know, whatever. We're all just nerds here. That's how that works.
434
00:42:58.860 --> 00:43:11.790
So I'm probably going to edit this and put it out like in a couple of days' time, which I think will probably be the first time ever that we've had a Two's Complement go out within the time that we recorded it, which then unfortunately means we have none left in the bank.
435
00:43:11.790 --> 00:43:12.000
Oh, yeah. Within a few... Right.
436
00:43:12.000 --> 00:43:18.880
So dear listener, you will... the next one in August will be another seat-of-the-pants job. But...
437
00:43:18.880 --> 00:43:22.140
Hopefully it's released on time, but no promises at this point.
438
00:43:22.140 --> 00:43:23.350
Correct.
439
00:43:23.350 --> 00:43:24.920
Right. Yeah.
440
00:43:24.920 --> 00:43:26.750
Correct. Events may overtake us at this stage.
441
00:43:26.750 --> 00:43:27.140
Yeah.
442
00:43:27.140 --> 00:43:28.220
Yeah, that's true.
443
00:43:28.220 --> 00:43:29.060
Yeah. All right.
444
00:43:29.060 --> 00:43:29.700
Well, until then.
445
00:43:29.700 --> 00:43:33.900
Until then, yeah, have yourself a great time.
446
00:43:33.900 --> 00:43:35.060
Okay. Cool. See you later.
447
00:43:35.060 --> 00:43:37.060
Bye.
