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What Is Audio Compression and Why Should I Care?

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vocal compression“Compression” is one of those many audio terms that you hear a lot but maybe don’t truly understand. You wouldn’t be alone. There are lots of ways to get confused.
First of all, “audio compression” is different from “data compression,” which refers to making a large file smaller (like turning wav audio file into an mp3) to optimize it for use on the internet. We’re NOT talking about that. Audio compression is something very specific.

Okay, so what the heck IS audio compression?

The most basic way to explain it is this: Compression “turns down” only the loudest parts of an audio file so that the overall volume is more even. If you then turn up the overall volume, the quite parts are more audible and the loudest parts are not as loud. Things are much more even and consistent.
So in a way it is sort of like a trash-compactor for sound.  Why use compression?  Have you ever been in a car, and a song started, and you could barely hear it?  So you turn the volume up only to have your eardrums shredded when the loud parts of the song come in.  You may have found yourself turning the volume up and down several times during a song to compensate for the extremes in quietness and loudness.
What you were doing while turning it up and down was manually compressing the audio!  You were compressing the audio by turning the loudest parts down and the quietest parts up.

So a “compressor” automates that

Wouldn’t it be easier if you could just push a button on your car stereo and have that happen automatically?  Well you probably can!  The factory radio/CD player in my last car had a button that simply has a “C” on it.  I had no idea what it meant until I looked it up in the manual.  Guess what the “C” stands for?  Yup, “compression.”  Check your manuals; there might be something similar on your car’s audio controls.

Using compression for audio recording

So what about the folks recording or producing audio, or those who want to learn?  How can you use compression?  Well, for one thing, you can check out these other articles I’ve written: – Improve Or Ruin Your Audio With an Effect Called Compression, Vocal Compression Using Reaper’s ReaComp Effect Plugin. and Using An Audio Compressor For Voice Over Jobs.
Every audio recording program out there has built-in compressor tools.  That’s how common and important it is in audio production.
The first thing you’ll probably want to do when recording music is apply compression to individual tracks, such as the vocal track or guitar track, etc.
Lead vocals pretty much always need some compression.  Pop music tends to put a lot of compression on a lead vocal.  That’s because it’s the most important thing in the song and in order to keep it loud enough to be heard through the music as it gets louder, but not overpower the music during the softer bits, a compressor is used to automatically even out the levels of the vocal track.
One warning here though…if you overdo the compression on a vocal track, it tends to make the singer sound like they are lisping, and some other odd things.

Compression for the entire mix

Another useful way to use compression is to boost the average volume of an entire song (or whatever kind of audio you’re listening to).  This is because the loudest an audio file can be without distorting (you know that nasty buzzing sound you hear when you turn the TV on too loud for your speakers?), the very loudest part of that audio file must not exceed a certain volume level (0dB if you care :-P).
Many audio programs simply won’t allow you to turn audio up if the loudest bit of it will exceed that “distortion” ceiling.  So if the audio is not loud enough, but you can’t increase the volume because there are just one or two places where it got really loud, and those are “bumping” up against that ceiling, you could just reduce the volume of ONLY those two places, leaving the rest of the audio alone.  At that point, the loudest parts are much lower, and you can turn the whole thing up much louder before any of it bumps up against that ceiling again.
That last technique is often used when editing an entire song in order to make it seem much louder.  Louder can often be interpreted as “better” by some people.  But be careful here too.  The more you compress a final mix, the less dynamic range the song has, which basically means it won’t get softer and louder as much.  That can suck the life right out some audio.
So now you know what compression is.  Cool, huh?  If you want to experiment with recording and producing audio, there are lots of tutorials out there on the web.  Of course I think you’ll like the ones you can check out free here.  But I may be biased.  Either way, go forth and make the world safe for better audio, or both!

Using An Audio Compressor For Voice Over Jobs

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Compression is one of the most misunderstood effects in audio recording. And though it is a very useful tool, you can easily harm your recordings with it if you’re not careful. So you really should know what an audio compressor is, and what it does.

What Does Compression Mean?

In audio recording, “compression” means – evening out the volume of your audio. But as simple as that sounds, it doesn’t clearly describe what is really going on. Let’s break it down.

Most sounds, especially the human voice, are loud sometimes, quiet sometimes, and just sort of “medium volume” most of the time. It’s totally natural for the loudness of a human voice to fluctuate a lot. It’s a huge part of how we communicate.
In fact, it would be downright unnatural is if there were no changes in volume. That’s how we tend to think robots sound. Heck, nowadays, what with Alexa and Siri, etc. even bots are made to sound more human by – among other things – varying the pitch and amplitude of the voice.

What Does Compression Do?

Take a look at this picture of a short vocal recording.

Notice that the first part is a sort of medium volume. Then the volume goes way down in the area marked “quiet part.” Then later, the volume gets really loud where it says “Loud part.” Here is what the above sounds like:

There are a couple of different problems here. First, whoever is listening will likely reach for a volume knob during the quiet parts to turn it up. But when the loud parts come, the listener will be reaching for the knob again to turn it down. We don’t want that.

So how do we fix it?

At first, we might be tempted to turn everything up so the quiet parts can be heard better. But we can’t do that because those loud parts have already spiked to the volume limit. You simply cannot turn the entire file up at this point. Any attempt to do it will cause those loud parts to distort terribly.
Well, what if we could turn ONLY the loud part down? That would allow us to turn EVERYTHING up, including the quiet parts. THAT is what an audio compressor would do.
However, what if I’m happy with the volume of everything that isn’t “quiet” or “loud”? I might not want EVERYTHING turned up. I might want to JUST turn up the quiet part and JUST turn down the loud part, leaving everything else alone.
While you COULD do this with a compressor effect. I like to to simply do it manually by selecting JUST the loud part and turning it down. Then select JUST the quiet part and turn it up.
Here is what the audio would look like if you did just that:

The volume of the audio has been evened out by quite a bit. I compressed this audio, though I did not use “a compressor.” The two benefits of having done this are:

  1. The listener probably will not need to reach for any volume knobs, and
  2. I can increase the volume of the entire file now without anything distorting. If you want to maximize the overall volume, you turn up the entire audio waveform until the loudest bits reach the upper limit (0 dB). That’s known as “normalizing” audio. See my article Audio Normalization: What Is It And Should I Care?

Here is what my (manually) compressed audio sounds like:

Note that even though the volume of the previously quiet and loud parts have been changed, the intensity of the vocal remains. You can still tell the quiet part is intending to be soft and whispery, while the loud part is intended to be shouted. That is another benefit of compression – you make the audio easier to hear and understand without necessarily damaging the dynamics of the speech.
Though it isn’t technically part of this article on audio compressors, I would typically “normalize” my audio at this point in a voice over job. That gives it a good chance of being well understood immediately without the listener having to turn their volume up. Here is what the compressed audio now sounds like after I normalized it (the whole thing is basically just louder):

You Said You An Audio Compressor Could Harm My Audio?

Yes, I did say that. A compressor has many settings that can be confusing, such as threshold, attack time, release time, etc. You can find out what those mean in my post and video here: Vocal Compression Using Reaper’s ReaComp Effect Plugin.
A compressor makes it convenient to automatically and quickly affect an entire audio file. But lots of things happen in the background that you should be aware of. For instance, if you compress all your audio and then automatically turn everything up afterwards (using “makeup gain”), you may easily bring up the volume of any little bit of noise that might have been inaudible before. So though the volume may be more even and louder overall, it might be noisier as well. Not good.
Also, compressor algorithms can cause certain “artifacts” in the audio if settings are too extreme. “S” sounds can become more pronounced, or muted, making it sound like you’re lisping. Another common issue is “pumping.” This is when the compressor is trying to quickly respond to the sudden starts and stops of vocal phrases, and makes it sound like the audio is almost rhythmically breathing or “pumping.”
More commonly, you can easily suck the life right out of your voice. If the volume is TOO steady with not enough variation, not only does it lose the ability to create nuanced communication, but it can get fatiguing to the listener. This might be OK for a 30-second hard-sell ad. But for an audio book, your listener will actively want to STOP listening after awhile. Again – no bueno.
Just for kicks, I put the above recording through an audio compressor plugin with some of the settings a bit too high. Here is what that sounds like:

You can hear some of that pumping I mentioned. The worst part is that the breaths are unnaturally loud and just weird sounding, like I’m gasping for breath. And there are noisy bits and other weirdness coming through. Ultimately, this does not sound natural. And honestly, I think it sounds pretty bad.
So hopefully, you now know what audio compression is, what it does, and how it could possibly harm your audio if you aren’t careful.
Should you use it in your voice over jobs? Well ask yourself a question first. Do you need it? Is there a chance the listener might want to adjust their volume a few times to hear soft parts or turn down loud parts. If so, you should use it. But if not, DO NOT use it. This logic should apply to any effect when recording voice overs. NEVER apply an effect without deciding first that you need that effect.
Now go record some awesome voice overs!
Here are some of my other articles on using compression:
Compression: What Needs It And What Doesn’t?
Improve Or Ruin Your Audio With an Effect Called Compression
Should You Use Compression In Audio Recording?

What Is A Side Chain In Audio Recording?

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You may have heard of the term, “side chain” or “sidechain” in audio recording. As with so many things in the audio recording realm, the term sounds more complex than what it actually means.

So what DOES “sidechain” mean already?

Okay, let’s start with a basic description of how an effect (think compression or EQ) is applied to an audio track.
Let’s say you want a compressor (see my post “Should You Use Compression In Audio Recording?“) on your musical instrument track. You would connect the compressor by sending the music on a round trip from the music track to the compressor. When the music comes back FROM the compressor, it is now compressed. See pic below.

 

How a compressor knows what to do

A compressor only applies its effect when it is told to by the incoming audio. For a review on this see my post Vocal Compression Using Reaper’s ReaComp Effect Plugin. For example, it will compress only if and when the incoming audio gets louder than a certain “threshold” volume. At all other times, the compressor does nothing.
Now usually the sending and receiving signals are from the same track – instruments from the instrument track go into the compressor and compressed instruments go back to the instrument track.

But what if you fed the compressor a DIFFERENT input?

Say you could get the compressor to compress the vocal track based on instructions from a track that is NOT the vocal? whoa, that’s some mad scientist stuff right there! But maybe you could do some cool things.
Let’s say you have music on a second track. What if you sent THAT audio into the compressor to control how the voice is compressed? Well. that is exactly what happens when you “duck” an audio signal. When the voice is singing/talking, it pushes the music out of the way. You guessed it. I have a post on ducking too:) – What is Ducking In Audio Recording?
You still have the instrument track sending the music on a round-trip to the compressor. But the compressor no longer takes orders from the instruments. It listens to a new master whose input comes in a side door:). Hence the moniker “side chain.”
That side door is where you send the signal from the vocal track. So the instruments still get compressed (turned down when the control signal gets loud enough), but it’s now the vocal volume acting as the control. So when the vocal goes above the threshold, the compressor turns the volume down on the instruments. Pretty cool huh?

Other cool things you can do with side-chaining

  • Make a tempo-based tremolo by sending the side chain of a gate effect a click track so the gate on an instrument track opens and closes in time with the click track
  • Make pumping dance tracks by putting a compressor on to the bass and sidechain the kick, so the kick will push through the bass every hit
  • Put a compressor on the bass track and then have the kick drum activate the compressor via a sidechain. When the kick drum hits it will dip the bass line in the mix, allowing the kick to cut through the mix and sound more clear
  • Anything your imagination can come up with

Hopefully this gives you an idea what sidechain (side-chain, or however you spell it) in audio recording means.

Use Ducking For Electronic Dance Music Effect

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DJ EDM and DuckingI originally wrote this article in September of last year – before I saw the movie, “Now You See Me.” I’m updating it because we just watched that excellent movie, and the effect I describe below for using ducking in electronic music can be clearly heard in the soundtrack at the end of the movie, during the credits. On the soundtrack album, the song is track number 8, “Now You See Me – Robert DeLong Remix.” It’s an electronic variation of the “Now You See Me” theme composed by Brian Tyler. Take a listen at the iTunes store here.
Ducking in audio recording is a really useful effect for any number of things. The basic idea is that when the audio on one track (you need multi-track recording software for this) gets louder, the audio on another track (or even all the other tracks) get less loud. It’s like one track pushes the other track(s) down and out of the way. Or put another way – the other track(s) “duck” out of the way of of the controlling track.
I wrote about how to do this using Reaper multi-track software in my article What is Ducking In Audio Recording? The object is most commonly to allow a single voice to be clearly heard over some background music. So whenever the audio on the vocal track is sounding, the volume on the music track gets correspondingly less loud. When listening to JUST the music track in that case, it sounds a bit weird. But when combined with the vocal track, you don’t even notice that the music is getting softer at those points because the voice fills in the void.
The way that one track controls another is by use of something called “side-chaining,” which just means that you send some of the output of one track to another track. In ducking, you put a compressor effect on the track that you want to do the ducking – the music track in the above example. But instead of the music controlling the action of the compressor, you bring in the audio from a different track (the vocal track in our example) to feed/control the compressor on the track doing the ducking.
But remember that I said ducking can be used for a lot of different effects? And remember when I said that listening to JUST the track doing the ducking can sound weird, since it is inexplicably lowering and raising its volume at seemingly random times? Well we can use THAT in Electronic Dance Music (EDM).
The idea is to set up a music track with a pad (synthesizer playing a long, sustained sound – a note or chord), and then to cause the the volume of that music to drop almost completely out periodically – typically to the rhythm of the song. So you set up a drum track to be the controlling track, and whenever a drum hit happens, the volume of the music track drops, gving out a sort of pulsing, throbbing sound perfect for EDM. Then just mute the drum track, and you have a very rhythmic and dance-to-able synth pad track.
The following article shows you how to do the EDM ducking thing using Cakewalk’s Sonar X2 Producer software. Of course you can do the same thing in Reaper using the same technique I described in the article linked at the top of  the page.
Red that article here: http://blog.cakewalk.com/edm-ducking-synth-melodies/

Using Compression To Punch Up The Kick and Snare Drums

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punchCompression is an effect often used to add punch and power to kick and snare drums, especially in pop and rock music. Adding compression to the drums in your recordings is a simple matter nowadays (yes, I’m still all geeky about how much easier it is to do recording now that everything is software – even 15+ years since I was able to make the transition from analog tape).
Anyway, the process of adding the compressor effect (now usually a plugin on the tracks in your software) is the same with pretty much all recording software. Below is an article showing you how to do it using Cakewalk’s SONAR X2 Producer software. I did a video showing you how to add compression in Reaper using the built-in compressor plug-in, “ReaComp” in my post, Vocal Compression Using Reaper’s ReaComp Effect Plugin.
Read the article on drum percussion in Sonar here: http://blog.cakewalk.com/make-kick-and-snare-sound-more-aggressive/