2015年9月21日

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Key Takeaways:

Eliminate background noises before you hit record. Turn off fans, AC, or heaters, and set your phone to airplane mode.
Listeners notice sound quality. Background noise and room echo is distracting and degrades the listening experience.
If you have a noisy room or a room with a lot of echo and you can’t treat it, record with a dynamic mic instead of a condenser and grab blankets or couch cushions and make a blanket tent or pillow fort.
Some materials (sound panels) are more sound absorbent than others. Look up Noise Reduction Coefficients (NRC) numbers before buying materials to help absorb sound
It’s possible to improve sound quality a little bit with post production, but it’s better to fix the problems before recording.

How Do I Get Rid of the Hollow Sound or Room Echo In My Podcast Recording?

I’ve noticed that a lot of people struggle with room echo and background noises, so I wanted to do this episode to help you start taking steps towards inproving the quality of your recordings.

Sound Proofing and Sound Treatment

Sound Proofing is the process of sealing your room so that outside noises don’t get recorded by your microphone. This is normally done by installing special sound-absorbing fiberglass or mineral wool in the walls, floor or ceilings.

You may not have much control over how sound proof your room is, but there are some things you can do to control the sounds being created in your space.

Eliminate as much excess noise as you can:

If you have loud AC or heating, turn it off while you record.
Turn off notifications on your computer and phone.
Set your phone to airplane mode.
If you have pets, put them in a kennel or in a room far away from where you’re recording.
Put up a sign to let people know you’re recording.
Throw a thick blanket by the bottom of the door, or cover your windows to help reduce noise coming in.

Remember: Eliminate background noises before you hit record. Turn off fans, AC, or heaters, and set your phone to airplane mode.

Sound Treatment is reducing the echos and sound reflections in a room by adding things like sound-absorbing foam panels, bass traps, and sound diffusors.

The Different Kinds of Echo

Standing waves happen in rectangular rooms when a sound wave bounces off one wall, then back and forth between the two walls until the energy dissipates. This is most common in low-end frequencies, but can happen in high frequencies as well. Too much energy in the low-mid range (200-500hz) can cause a track to sound muddy or boomy.

Remember: Listeners notice sound quality. Background noise and room echo is distracting and degrades the listening experience.

Flutter echo is a ringing sound caused by sound bouncing off of parallel walls. You’ll hear this in the high-end of the frequency range.

Choosing the Right Room to Record In

We don’t always have a choice about the room we record in. When I started recording the seanwes podcast back in late 2013, I was recording in my “office” (which is just my dining room with a standing desk).

It was a small room with only a little furniture in it, so there was quite a bit of flutter echo in my recordings. I tried to compensate for this by bringing in some big couch cushions. I ended up moving to a spare bedroom and building some sound absorbing panels to help with the reflections. (They did help.)

The ideal room will be a room with quite a bit of soft stuff in it. Furniture like chairs, couches and bookshelves can all help absorb and diffuse sound waves.

“Pretty much every room has its own sound, when you walk in the room, there is an enormous amount of factors that control what that room sounds like. The size of the room, the materials that make up the floor, the walls, any furniture in the room, all these things affect the sound of that particular room.” – Joe Gilder, Home Studio Corner

The Kind of Mic You Use Matters

I've found that most dynamic microphones are less sensitive to background noise and reflections than condenser microphones.

Condenser microphones are more sensitive, more detailed, but they pick up EVERYTHING. So if you have a perfectly treated room with good acoustics, a condenser mic will give you great sound. If you are in a room that hasn’t been treated and soundproofed, you’ll run into problems.

If you have a noisy room or a room with a lot of echo and you can’t treat it, record with a dynamic mic instead of a condenser. Here's the gear I recommend if you're interested.

When I first started recording podcasts, I was using a Shure PG42. It’s a decent condenser USB mic, but I was recording in my dining room, so there was a lot of echo. If I had known then what I know now, I would have sold the PG42 and switched to a dynamic mic.

Mic Technique for Podcasters

Mic technique is another big part of how much room sound you’ll hear in your recordings. The further away from the mic you are, the more room sound you’ll hear. You should try to stay between 3 and 6 inches away from your mic while recording.

How to Treat Room Echo

I learned something new while doing research for this episode. It’s something called NRC: Noise Reduction Coefficient.

The NRC is a single-number (0 to 1) index determined in a lab test and used for rating how absorptive a material is.

So a 0 is not sound absorbant at all (a surface that is complete reflective when it comes to sound waves), and 1 means the surgace absorbs all sound (no sound reflection at all).

Here are the noise reduction coefficients numbers for some common materials:

Brick, unpainted .00 – .05
Carpet, indoor-outdoor .15 – .20
Cork, wall tiles (1″ thick) .30 – .70
Drapery, light weight (10oz.) .05 – .15
Fiberglass, 3-1/2″ batt .90 – .95
Fiberglass, 1″ Semi-rigid .50 – .75
Marble .00
Plywood .10 – .15
Moving Blankets 0.3 – 0.5

Some materials are more sound absorbant than others. Look up Noise Reduction Coefficients (NRC) numbers before buying materials to help absorb sound.

Sound Treatment Solutions for Podcasters

If you’re interested in buying sound treatment materials, here’s what you need to know.

1. Egg Crate Foam. Almost worthless for low end frequencies, but decent for absorbing frequencies in the mid and high mid ranges. Pretty ugly, so I’d suggest buying acoustic foam instead.

2. Portable Sound Shields. The idea here is to have a shield wrap around the back of your microphone to stop your voice from reflecting off the wall in front of you and bouncing around. These work well (from what I hear) and start at around $50.

3. Furniture. Bookshelves, desks and couches/chairs can all help with sound absorbtion/diffusion, depending on the material they’re made out of.

4. Blankets. Most blankets are only going to absorb the high end frequencies, and only if they’re thick. A good thick duvet will be your best bet.

5. Carpet. Having carpet in your room will help a little. Thicker is better, but don’t expect too much.

6. Bass Traps. Bass traps are usually wood frames with a lot of sound-absorbing mineral wool or fiberglass, usually at least 3 inches thick for absorbing extra low end frequencies. Very commonly places in the corners of a room.

7. Sound Diffusors. Sound diffusers are designed to scatter or disperse sound by using irregular hard surfaces to break up and scatter the sound waves. So imagine a table top covered with pieces of two by fours cut to various heights, that’s what most sound diffusion panels look like. You can buy these online or build them yourself.

8. Acoustic Foam. Most acoustic foam doesn’t do anything to stop low frequencies, but it will absorb the higher frequencies. If you hear a lot of flutter echo in your room, you can invest money in some acoustic foam panels to help treat it.

DIY Sound Absorption and Diffusion Products for Podcasters

You can build a lot of these absorption and diffusion products yourself. Check out:

Build your own acoustic foam shield
Build your own sound absorption panels (I used this site to build 6 of my own)
Build your own bass traps

Fixing Room Echo and Noise in Post Production

You can use EQ to remove or reduce certain frequencies, 400hz for example. Listen to your recording and try to identify the frequcies where the room echo is most noticable, and then cut a couple db. Be careful not to remove too much; that will make your voice sound unnatural.

There are various de-reverb and noise removal plugins available for audio editing apps like Logic Pro X and GarageBand, and Audacity has a noise removal feature built-in.

My favorite method so far for cleaning up room echo has been an EQ plugin to remove some of the low-mid range (between 300 and 1200 hz).

My favorite for removing background noise is a tie between Logic Pro X's legacy Speach Enhancer plugin (it has a nice denoise feature), or Izotope's RX plugins, which are often on sale for $29 (there's a plugin included in that pack called Dialog Denoiser that also works great for removing background and line noise).

One other great option is the Auphonic website, which will clean and enhance up to 2 hours of audio per month (you'll pay for more time after that). The only downside is that it'll take a little longer because you'll have to upload the audio to a website for processing instead doing it on your computer.

It’s possible to improve sound quality a little bit with post production, but it’s better to fix the problems before recording.

Finally, if you’re having problems with buzzing or other electronic noise in your recordings that you can't identify the source for, you may have a problem with your power supply.

Buy a Furman power conditioner ($60), plug your computer and audio gear into that, and see if that solves the issue. If it doesn’t, you may have faulty recording equipment or cables.

Q&A:

Kelsey asked: Can you discuss room noise related to living near an airport and frequent thunderstorms?

Sound proofing is going to be your best bet here, but it’s going to be challenging because you’ll have to do some major construction to sound proof a room. Some people build a “floating room”, which is a room frame inside a room to make it more sound proof. You can read more about that here.

Other than that, I would suggest learning more using post-production to fix or remove background noises. There are lots of software solutions for cleaning up audio files (see the several I listed above).

Terence Tang asked: Without A/C or fans on, it gets hot in the room. For podcasting, it’s fine because you can’t see the person sweating, but what about with video? I don’t want to be drenched in sweat on camera. Any suggestions?

First; are you sure your viewers don’t want to see your drenched in sweat?

Seriously though, you can buy a quiet fan to help push some air, or just run the AC at full blast until right before you hit record. If you’re recording with a shotgun mic, place the fan directly behind the mic to reduce the amount of fan noise the mic will hear.

For podcasters wondering the same thing: The supercardioid microphone I'm currently (Shure Beta 87A) using doesn't pick up fan noise, but you should always make a test recording to hear how your recording sounds. If you can leave a quiet fan running without having it be terribly noticable, go for it.

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