What does the mix knob on a compressor do?

What it does and does not change

The mix knob does not change how the compressor works. Threshold, ratio, attack and release behave the same at any setting. It changes only what leaves the device: a crossfade between the processed signal and the signal that went in.

Why blend at all

Hard compression makes a sound dense and even, and it flattens the attack of each note. The untouched signal has the attacks and none of the density. Mixed together, the quiet parts are raised by the compressed signal while the peaks are still set by the dry one. The effect is the opposite of ordinary compression: the loud moments are left alone and the quiet ones come up.

Starting points

• Drums: a high ratio, a fast attack, 10 dB or more of gain reduction, mix at 20 to 40 percent. The kit gets weight and sustain and keeps its crack.
• Vocals: a moderate ratio, 6 to 10 dB of reduction, mix at 30 to 50 percent, to hold a vocal forward without the sound of a compressor working.
• Bass: 30 to 50 percent, to even out notes and keep the pluck.

Set the compressor harder than you would for normal use. The mix knob is what makes it subtle.

Match the level before judging

Adding a compressed copy makes the track louder, and louder sounds better. Compare with the device bypassed at the same loudness before deciding the blend is an improvement. Makeup gain applies to the compressed signal, so it changes the blend as well as the level.

In Zammoth

The Compressor's Mix runs from 0 to 1 and starts at 1, fully compressed. Any setting below 1 is parallel compression inside one device, with no second track or bus to set up. For a whole group, put the compressor on the group's bus. See the Compressor reference.