How Does A Compressor Make An Audio Track Louder?
By Brandon Drury

So you want to learn how to use a compressor? Well good luck. It takes years to get even a decent feel for a compressor. I'm just now getting where I feel that a compressor will tolerate me playing with it's settings. In the past, it was just laughing and mocking me because I just didn't understand how to use it to improve my recordings.

So let's talk about how a compressor can make an audio tracker louder. Ironically, a compressor actually knocks the volume down on a track, but then has a makeup gain knob that boosts it back up. To understand how a compressor can make something louder, you need to understand the difference between peak loudness and average loudness (also called RMS). A peak is just what it says it is. It's a spike. The signal starts very low and goes very high. A good example of peak loudness is a snare drum hit. Average loudness is sound that occurs over time. Imagine hitting a low E on a bass guitar and letting it sustain. This is an almost constant sound.

One other concept is the volume ceiling. In other words, in digital audio we have a volume limit. It's called zero. For whatever reason they measure volume in negative numbers with 0dB being the absolute loudest. If a track has a peak that jumps up to zero, we can not push the volume up on that track even if the other portions of the track are very low in volume (without volume automation).

Now let's take an audio track that can be both peaky and constant. A vocal track is a great example. A vocal can jump up very quickly but it can also sustain. Let's say it hits 0db at one point, but most of the track is sitting well below that. You'll find that when the vocal is set at maximum gain before clipping, the many of the words are unintelligible. This is because they are simply too quite. Assuming there are no extreme problems, the first thing I'll usually do is grab a compressor. I'm go ahead and smash those peaks down and then I'll push the volume back up with the make up gain on the compressor. Now the vocal is evened up quite a bit. The vocal will sit in the track much better and will sound fuller.

When mastering a record, compression is almost always used to make the volume of the cd louder. Most of the time, the cd is already hitting zero, so it's peak volume will not increase. However, it's RMS or average volume can increase substantially. When we put a compressor on stereo mix, we can smash the song down into a smaller dynamic range. It uses up less volume. While this can be a bad thing as the dynamics are decreased, these days overall volume seams to be more important (I'm not sure who decided this). After the compressor does it's thing, the makeup gain is used to boost the level of the track up the desired amount.

When you are learning the audio mixing process, I recommend using more compression than you think you need. Hit everything very hard. If it sounds distorted, back off. I think that compression is the opposite of reverb. While many beginning home recording enthusiasts will use too much reverb, they often times, do not use as much compression as the big boys. Experiment. This is different for everyone.

In summary, a compressor is used to to knock off the top (loudest parts) of an audio signal and then uses it's makeup gain to push the volume back up. It takes lots of time to master using a compressor. Keep in mind that you can do much more with a compressor than make things louder. As always, don't be afraid to experiment.

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