Compressors are very useful work tools but they can also be playful toys that create exciting sounds. They are available as computer plug-ins or external hardware units.

API compressor

There are two main reasons to use compression. One is to keep the volume of any instrument or vocal at a steady level so that it sits nicely with the instrumental backing.

The second reason is if you want to get “that distinctive compressed sound” which most compressors give. Each unit makes its own “sonic footprint” which can be very desirable.

For example, almost all of the Beatles records carry that sonic footprint that was created by using a Fairchild compressor.

Compression can be applied to a single vocal or instrument, or it can be applied to the complete mix of voices and music.

Different musical instruments require slightly different compressor settings in order for them to work best.

Whichever compressor you use, the principles of how to set it correctly are the same. For general use here’s how you set a compressor:

Chandler compressor

Start off by learning on a simple compressor rather than one which has too many controls.

A simple unit should have these five controls: Input. Output. Attack. Release. Ratio. Plus a meter which indicates how much compression is occurring.

It is good to have a starting point:

Set the Ratio control to 4:1
Set the Attack control to a short setting of about one millisecond.
Set the Release control to a medium setting of about 100 milliseconds.

Make sure that the sound you want to compress is being sent into the compressor.

If the Gain Reduction meter isn’t moving, this means that the threshold is set too low. You need to increase the strength of the input signal.

A rack of compressors

Adjust the Input control until a movement of about 5-7 dB is showing on the meter. (The Input control is also known as the Threshold control.)

Finally adjust the Output control so that a satisfactory level is being sent back out of the compressor to the recorder.

You should experiment a little and see how a lower threshold setting gives you more gain reduction and a higher threshold gives you less. You’ll hear how dramatically the sound can change.

Then play around with the other controls so you can get a feel for their functions.

Finally, try sending different musical instruments through the compressor. You’ll soon discover that each one needs different settings to achieve the desired result that you want.

There are no hard-and-fast rules to follow regarding compression so you can set the unit to work as transparently or dramatically as you wish. It’s usually dependent upon your music. Just make sure that you’re not introducing unwanted distortion. (More in the course).