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How To Really Use Audio Compression

Audio Compression

Well, you just finished recording your drums, bass, guitars, piano, vocals and whatever other instruments you need. Now the first thing to do is go to each track and put on some compression to reduce those crazy peaks and get some volume too, right? Wrong! Audio compressors are not meant to give volume (limiters anyone?) and there’s a much better way to control peaks, which I may cover in the future (*cough* automation *cough*). So, what are those compressors really for? Believe it or not, much like an Equalizer (EQ), they are also a sound shaping tool.

Often we hear that “compressors are used to control the peaks”. This is completely true, but we fail to see the depth to which this extends. Controlling peaks is not just about reducing their volume or making the track louder. You know how people say we should use audio compression to add more punch? You’re probably wondering what they mean by that since no one actually explains HOW a compressor adds punch. Have you heard about using compressors to fatten up a sound? Same story, no one ever says HOW a compressor does that.

Allow me to offer an explanation on a snare track:

How To Use Audio Compression

See how the beginning of the signal is so much louder than the rest? That’s the peak we can control. The audio compressor can make it quieter, compensate for the volume difference, and then this happens:

Audio Compression
Note: this is an overemphasized example – this is not what a healthy snare track looks like!

When a peak is quieter that leaves room for the tail of the sound (yes, we call that part after a peak the “tail”) to come through. This is how a sound is fattened up. Why? Nerd-moment time:

[box type=”info” align=”” class=”” width=””]There’s always an upper limit, or ceiling, to how loud a track can go. If a peak hits this ceiling then the rest of the signal cannot go higher. Actually it can, but our brain buries it because that peak really sticks out. If we bring down the peak, then the tail can get much closer to the ceiling, letting us hear more of the whole signal making it seem fatter.[/box]

What about giving the signal more punch? It’s the opposite. Now, don’t get confused – we don’t use the audio compressor to make the peaks louder. We use it to make the tail quieter. This makes the peak really jump out and hit you in the face. Why does this give it more punch?

By reducing the tail volume we put more emphasis on the initial burst, making the peak stand out. Punch comes from shorter bursts of sound, while fat comes from a more consistent and lasting sound.

Now that you know this, your next question is: “How do I set my audio compressors to give more punch/fat?” Excellent question, with a not so straightforward answer. Since each recorded signal will always have widely different dynamics from the next I can’t really give you proper numbers. This is something you have to listen for. It’s even more different if you’re using it on a group of instruments (like the drum group or even the mix buss). Instead, I can tell you how attack and release work and then you find your ideal values for each depending on your track.

1. Attack

No nerd-moments this time. I’ll just tell it to you straight: The smaller the Attack the ‘fatter’ the signal. Basically, the “attack” control how quickly the audio compressor activates to turn down the signal. If it starts turning down the signal right away, then the peak is caught, turned down and brought closer to the tail. If the attack is longer, then you get more punch because the peak comes through.

2. Release

This is how quickly the audio compressor stops working or stops turning down the signal. You have to consider release in relation to the attack and your audio. Think about how fast your attack is working and then what you want to achieve. Let’s say you have a nice peak at the start of the signal. Let’s say you caught it with your attack to turn it down. If you want the signal to be fat, you have to adjust release so that the audio compressor stops working once it’s past that peak, i.e. shorter.

Now we want more punch. Let’s say you let that peak come through and the audio compressor is turning down the tail. How long do you want the tail to be turned down to create that separation? Longer, yes, but probably not too long or you’ll lose the bulk of the sound. My head’s spinning, can you simplify? Of course!

Here’s a setting used to give more punch to a kick drum:

Kick Drum Audio Compression

This is what I used to fatten up the bass line that goes with it:

Kick Drum Audio Compression
“Release” is the same so that the two can work together and stay tight with the song tempo.
[box type=”info” align=”” class=”” width=””]If you want a fatter sound then go with a shorter attack and if you want more punch go for a longer attack. Release is completely dependent on the audio you have. That’s about it for sound shaping. There’s still a question of how much, but that’s another story starring threshold and ratio. I may cover it in the future, but there’s already a mountain of information available on it.[/box]

Keep in mind that this is an advanced approach to audio compression. It’s not just about volume anymore, it’s about sound shaping and completely relative to the audio you have. You need to learn to listen and it will take time, but it will vastly improve your mixes in the end.

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