In this article we will first talk about compression in what it is and how it’s used. Then we look at the 4 important things you need to know and understand to use compression in your audio recordings correctly.
When you add compression, you add noise. Why does a compressor add noise?
The purpose of a compressor is to reduce the dynamic range of a track or entire mix. This means it reduces the higher levels and brings them down closer to the lower levels. Basically you’re crushing down the sound and then bringing it all back up again.
Now the problem is the signal sounds quieter because the peak levels were brought down and will need to be brought back up.
Now the signal is as loud as it was before in the peaks, and the lower-level sections are also louder.
Unfortunately the compressor has no way of distinguishing between the low level noise that you don’t want and the low level signal that you do want. Every signal contains some noise. There is no such thing as a noise-free recording.
The job of a good audio engineer is being able to manage all this noise effectively.
When a stereo mix is compressed,, it will be noisier. You can tell how much by looking at the gain reduction meter on your compressor; the maximum gain reduction that it shows is equal in decibels to the amount of noise you have added.
Most recordings use compression. All pop music you hear on the radio uses a lot of compression. Why? Well, we’ve gotten to a point where it’s a competition to see who can make the loudest record!
A good recording engineer can use compression as a very valuable tool, although many musicians that are home recording studio enthusiasts don’t fully understand audio compression and what to do with it.
OK, enough babbling… this is what you need to know:
The 1st thing to look at when working (or playing) with a compressor is the “threshold”.
This is the point at which the compressor kicks in and starts to do it’s thing. If you’re using a plugin which came with your audio recording software program set it to the factory default setting. This will be a medium setting so you can go to either extreme and see how it operates. After it kicks in, it starts turning the overall level, or volume down.
The 2nd thing to look at is the “ratio”.
The ratio will determine how much level is turned down in the threshold. So when your ratio level says 4:1, that means 4 db of signal is going into the compressor and only 1 db is allowed to come out. Typical settings as on the Bombfactory compressor will be 4:1, 8:1, 12:1, and 20:1. The higher the number the greater the compression.
The 3rd thing to look at is the “attack”.
The attack determines how soon the overall level of sound (refer to the “gain reduction” nob) will start to be altered.
The 4th thing to look at is the “release”.
The release time means how long until the unit stops altering the sound. A low attack setting will allow more of the initial signal to get through without being altered.
What about a “limiter”? It’s a compressor as well. The difference being that we use it for controlling occasional peaks of audio rather than compressing constantly for containment purposes as done with a compressor. So the limiter will start at 10:1 and go up from there, So, say you have a track that over peaked in only a couple places in the whole song, you could put a limiter on it and it would only kick in at those peaks and be totally unaffecting the rest of the time.
*Tip for using compression.
A good tip I learned from engineers is not to use compression on your stereo outputs of your mixing board. So, if you see your needles pinning a bit into the red, instead of throwing a compressor on em, look at which individual tracks are responsible instead.
It’s tempting to put the compressor on the overall mix because that’s the easy way, but if you work on containing the individual tracks you will get a more natural musical performance element to your mix and more dynamics too.