Compressors are great helpers to help us maintain the balance of our sound. Depending on how we set it, a compressor can increase the volume of silent notes, decrease the volume of loud notes, or do both simultaneously.
This article is a general compression guide for beginners.
There are expensive studio compressors, affordable compressor pedals, DAW compressor plug-ins, etc. In this article, we will be focusing on simple every day compressor pedals.
Although I am a bass player, the principles in this article can be applied to any instrument.
What Is A Compressor?
“A compressor is basically a pedal to balance the volume of your signal. When a signal is too loud, a compressor limits or squishes this spike to a more reasonable level. When a signal is too soft or starts to fade, a compressor can boost the signal to even out dynamics.” (Reverb)
The terms change from pedal to pedal, but here is a general overview of the controls we have on a typical compressor.
Threshold determines the scope of compression. A low threshold rate means that the compressor will cover silent notes. A high threshold rate means that the compressor will ignore silent notes and focus on louder notes only.
Attack time determines how fast the compressor will react after we play a note exceeding the threshold. A fast attack time means that the compressor will react as soon as it hears the note. A slow attach time means that; after hearing the note, the compressor will let the attack & note ring a little, and activate afterwards.
Release time lets us determine how fast the compressor will deactivate. A fast release time means that, when it hears just a few notes outside of the threshold, the compressor will deactivate itself. A slow release time means that, even after hearing notes outside the threshold, the compressor will stay activate a little longer.
Rate determines the force of compression. 2:1 is a light compression rate of 50%. “It indicates that a signal exceeding the threshold by 2 dB will be attenuated down to 1 dB above the threshold, or a signal exceeding the threshold by 8 dB will be attenuated down to 4 dB above it.” (UAudio) Following the same logic, 4:1 is a medium compression rate, 8:1 is a strong compression rate, 20:1 / ∞:1 can be considered as a brick wall limiter.
How I Use Them
How you would use a compressor depends on your purpose.
One of my purposes is to achieve a constant, ever-flowing bass sound without any volume deviation – imagine typical Muse or electronic bass lines. For this purpose;
- Threshold should be very low, because I want to cover every single note
- Attack time should be fast, because I am aiming at a sustained constant volume; I don’t want any peaks when I attack the strings
- Release time should be slow, because I don’t want to deactivate the compressor due to some silent notes in-between
- Rate can be set medium / high
Another purpose is to use the compressor as a limiter to prevent volume peaks due to technique, slapping or mischievous pedals.
- Threshold should be high, because I’m focusing on volume peaks only
- Attack time should be as fast as possible, because I want to “catch” the peak
- Release time can be relatively fast; because after catching the peak, things can get back to normal
- Rate should be as high as possible, because I’m willing to create a volume cap
As an example; here are the steps I follow to setup my MXR Bass Compressor as a limiter:
- I turn off any pedals between my bass and the compressor.
- I set Ratio to 20, Output all the way down and everything else all the way up.
- I start plucking my bass strongly, preferably on the lower notes. The gain-meter will probably go crazy and react to everything. While plucking my bass and keeping my eye on the gain-meter, I gradually set the input down until the pedal reacts just a little to only my highest peaks.
- I start plucking my bass normally, and turn the pedal on & off while gradually increasing the output level until I hear no volume difference between the on/off states.
- I decrease the release level to taste.
In a typical setting with my passive P-Bass; I would have release at 14:00, input at 14:00, output at 10:00 and attack & ratio maxed out. Input & output would obviously depend on the output power of your bass.
This setting enables me to tame the signal while leaving my clean dynamics unaffected. The compressor will happily limit the peaks caused by adrenaline, slapping or former pedals.
Another purpose is to even out the strings and notes on the bass without eating the tone and dynamics too much. For this purpose;
- Threshold should be medium, because I want to keep some of my dynamics
- Attack time should be medium for the same reason
- Release time should be medium for the same reason
- Rate can be low, around 2:1 or 4:1
A compressor is an optional, but very welcome addition to my pedalboard setup. If I have free space, I feel safe having a compressor set to “limiter” mode; and the sound guys enjoy the controlled bass sound.
My compressors of choice can be seen on my bass gear list.
For further reading, check What Is Audio Compression where Scott Wiggins shares a deep insight on compressing, supported by the math behind.