Knee (Compressor)
Definition
The shape of the transition between the uncompressed and compressed regions of a compressor's gain curve, centered around the threshold. A hard knee applies gain reduction abruptly at the threshold; a soft knee begins applying gain reduction gradually as the signal approaches the threshold, creating a smoother, more natural onset.
In Simple Terms
How abruptly a compressor starts working. A hard knee kicks in sharply — precise and controlled. A soft knee eases in gradually — smoother and more natural. Vocals usually want a soft knee; limiters need a hard one.
In Practice
A hard knee setting on a limiter prevents any signal from exceeding the ceiling with precision. A soft knee on a vocal compressor begins reducing gain gently before the threshold is fully reached, resulting in a more transparent, musical compression that is less audible at the point of engagement.
Common Confusion
Soft knee is not inherently better than hard knee. Hard knee is preferred for precise limiting and transient control; soft knee suits vocals and instruments where a transparent, gradual response is more musical.