A compressor is nothing more than an automated level control that uses the input signal that determines the output level. You can think of compression as a man standing in front of the volume faders/console and reducing the volume only to the louder parts of a song so that we can have a more “constant” volume throughout the whole song.
When the volume surpasses a particular volume level then the compressor starts compressing/reducing it in order to match it with the volume of the other parts.
Ratio – controls how much the output level the compressor will increase compared to the level that’s been fed to the input. Usually this is calibrated in a ratio that goes anywhere from 1-1 to 100-1, what that means is, if the ratio says 4-1, every 4dB that’s coming into the compressor, only 1dB will go out through the output.
Threshold – Determines the signal level where the compression actually begins. Below the threshold point, no compression occurs. Above the threshold is when all the compression occurs. Many compressors are calibrated in dB, so setting it at -5 means that when the level reaches -5 in the input meter, the compression begins to kick in.
Attack and Release – Not all compressors have attack and release parameter controls, these controls determine how fast or how slow the compression reacts to the beginning or end of the signal envelope. The beginning is the attack and the end is the release. The attack and release controls are the key to proper compression set up.
Gain – Sometimes called make-up gain. When a compressor begins to compress, it actually attenuates the signal. So in order to boost the signal, back up to where we were when we first started, we use the gain control, which adds some additional gain to the signal.
The gain reduction meter is an indication of just how much compression is occurring in any given moment. Some devices you’ll see a VU meter, or peak meter but it reads backwards.
How to use a compressor
1. Open your favourite compressor as an insert on the track that needs a compressor.
2. Adjust the Threshold so that the Peaks (sudden volume changes or “spikes” that need to be reduced) will surpass the Threshold narrowly.
3. Make the Ratio and the Threshold work together. Ratio is purely configured depending on the sound source but here’s some nice starting points:
Bass – 4:1 – 8:1, Drums Group: 2:1, Vocals: 2:1 – 4:1, Electric Guitars: 2:1-6:1.
Each sound source is different so this is only a guide.
4. Adjust the Attack and Release buttons, following the guidelines that I gave you above.
Too fast Attack will reduce the dynamics and kill the “feeling” of the song.