The compressor is next to the EQ perhaps the most used tool in mixing. The basic principle behind it is easy to understand from the name: it compresses the audio signal, and thus reducing the dynamics. The purposes for this are more than one.
1. It can make the sound “sit better” in the mix.
2. It can lower the volume.
3. It can in the end make the overall volume louder.
What? Louder? Shouldn’t compressing lower the volume? Well, it does, but by lowering the loudest part, while keeping the quieter parts intact you can raise the overall volume. There have been many heated discussions on compressing, as overuse of it completely destroys the dynamics of the audio. This is usually called squashing.
Please don’t squash your material.
Believe it or not, but the human voice is actually what I compress most often. While this is mostly when I mix music, the principles are the same for spoken word. Consider this scenario: You have recorded yourself speaking but realize that at several times you’re speaking to low and at other times you’re talking to loud. You now have two options:
1. Ride the fader, a term used to describe automation of the volume.
2. Apply a compressor and let it do the work and even things out.
The basics controls
The controls of compressors can vary both in name and numbers, sometimes they include more controls and sometimes they include less. Anyway, here’s the basics.
Threshold sets the value from which the compressor starts to work. Usually shown in negative dB, for instance -15dB. The higher the negative value (i.e., the lower the value) the more of the signal will be compressed.
Ratio determines how much compression is applied. It usually is set like a scale, for instance 2:1, 4:1 etc. If the signal exceeds the threshold it will be compressed (lowered in volume) by the set ratio.
Attack is a timing parameter, usually set in milliseconds, that determines how long it takes for the compressors total effect to take place.
Release is another timing parameter, and as you might guess it decides how long the compression is applied. A short release time might make the signal “pump” while a long release time can hold the signal down for a longer time.
Knee decides how hard the compression will be applied at the threshold value.
Gain simply raises or lowers the volume.
These controls might seem hard to understand just from reading about them, so my advice is to experiment with a compressor in front of you while learning what these do. The compressor can be hard to understand but it is close to an invaluable tool once you do.
If you have any kind of audio editing software then you should have a compressor available. Consult the product manual for this. There are a huge amout of compressors on the market, pretty much every software compressor is in plug-in format, so you’ll have to see if it’s compatible with the software that you’re using. You can of course also use a hardware compressor if that’s your cup of tea.