Recording Software

What is compression?  Compression helps you tame dynamic (has very loud AND very quiet parts) tracks, shape sounds and add punch to the sound.  What about all the knobs on there and what they do?
First of all, what is a compressor and what does it do? In a nutshell, a compressor will automatically turn down the volume by a certain amount – but ONLY when the audio gets louder than a certain volume. This sort of flattens out the audio’s volume a bit.
I’ve often wanted one of these on my TV! You know how commercials often are much louder than the show? Well a compressor (if you could set it up on your entertainment center) would allow the audio to come across at a certain maximum volume (this knob would be called the “threshold”) without ever turning it down. You decide how loud that maximum volume is. After that, any time the audio exceeds your max setting, the compressor will turn it down by some amount. Again you decide (this knob would be the “ratio” – 1:1 won’t turn it down, and infinity:1 turns it down all the way).
So when those super loud TV commercials come on, they will “trip” that maximum level on the compressor, which will then turn down the volume – but only while the audio is coming in really loud. As soon as your show comes back on with its normal volume, the compressor stops turning things down.
Wow, that is either one of the better metaphors for a compressor that I’ve come up with (not sure the picture above showing a rolling pin “compressing the dough of audio” really works:-P). Either that or you’re more confused than ever. If it’s the latter, please click on any of the links below for a better, more direct explanation.
Ken has written about compression often, since it is such a common and useful – even necessary – audio recording and editing tool. For example, see his posts:

• Improve Or Ruin Your Audio With an Effect Called Compression,
• Should You Use Compression In Audio Recording? and
• Vocal Compression Using Reaper’s ReaComp Effect Plugin.

Those last two have videos to help explain compression. And since a thing is often best understood when explained by different people, below is something to fit that bill. That article gets more into the specific buttons and knobs on your typical compressor.
Watch this video tutorial by Audio Issues for an explanation from someone different.