Using the knee on your compressor

There is a lot of confusion regarding the knee setting on compressors. Low end outboard compressors usually don’t have a knee setting, but since most of you are using a DAW with built-in software compressor/limiters you will most definitely find a knee setting lingering on your plug-ins, just waiting for your confused fiddling.

What does the knee do?

Bluntly, it smooths out the ratio in regard to how much of an a signal gets over the threshold. It’s a relationship between the threshold and intensity of the signal.

• A hard knee applies the ratio directly when the signal passes the threshold

• A soft knee applies the ratio exponentially as the signal gets closer to the threshold.

Applies compression before the threshold?

You see, if the threshold it set to -10dB and the ratio to 1:4, the signal that will surpass the threshold will gradually reach the 1:4 ratio going from 1:1 – 1:2 – 1:3 until it reaches the threshold.

A hard knee setting wouldn’t do anything until the signal reached the threshold, where it would clamp down on it immediately.

So which should I use? Soft knee or hard knee?

This varies from instrument to instrument.

• Vocals can benefit from a soft knee approach, and generally drums can be put on a hard knee attack.

• A soft knee on snare can be a good idea, and a hard knee on rock vocals can also be fine.

Feel free to experiment and see what suits your style. Just remember to use your ears and not follow some website's advice blindly.

I hope you can squeeze something useful from this for your audio experiments. No pun intended.

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