In simple terms ATOM's Compressor helps reduce the dynamic range of your sound, meaning the loud parts aren't quite as loud and the quiet parts aren't as quiet. This makes for a more normalized result, which can be very useful in mixing your sound into your song because its loudness is consistent.

The Compressor FX unit can be found in the FX section of ATOM:

The unit begins as the fourth FX unit from the top, and can be turned on by clicking the top right power icon of the Compressor section or the left-side light in the Compressor module of the fx rack section:

If the orange on/off button is activated it means the Compressor is active.

"Threshold," refers to the point at which the compressor will begin working. Signals above the threshold value will be compressed, whereas signals below it will not.

"Ratio," determines how much the signal will be compressed if it goes above the threshold value. A higher ratio value means more extreme compression.

"Knee," applies a subtle smoothing to the compression essentially by determining how quickly the signal gets compressed. Higher knee values mean the compression applies more quickly but in a more subtle way than the "Attack," parameter will allow.

"Attack," determines how fast the compression applies. High attack values mean the compression applies slower. "Release," is the same but for when the compression stops. High release values mean the compression will stop more slowly.

"Gain," allows you to boost the overall signal of the compressed audio. This is often needed to bring the overall volume back to its original levels before it was compressed.

"Mix," is essentially a dry/wet knob for the Compressor. A Mix of 0 means no Compression effect is applied, while a Mix of 100 means the entire signal is run through the Compressor.

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