Last night About2Flip commented on the Intro to Compression video:

Again Great Video!!! But what does KNEE do? I have been searching for almost a year now.

The knee function on a compressor is not as important as the ratio, attack or release functions. However, it can still be a useful tool, and it deserves a little attention. Thanks for asking, About2Flip.

Take a look at this screenshot of a compressor plugin:

knee-1

The orange vertical line is the threshold. The diagonal line to the left of the threshold represents the signal before compression is applied. The line to the right of the threshold represents the signal after it crosses the threshold. The higher the ratio, the more compression occurs, and the “flatter” this line becomes.

In case you haven’t guessed yet, the knee of this diagram is where the white line meets the orange threshold line. The white line begins to bend at this point, and it kind of looks like a bent knee.

The knee allows you to determine how curved this transition is. In the picture above, you see that the knee is set to zero, this means there is an immediate transition from no compression to 13.7:1 compression.

But what if you wanted the compression to slowly kick in? What if you wanted it to only compress the signal a little bit when it first crosses the threshold and compress it progressively more as it gets louder? That’s where the knee comes in.

Notice in this picture I’ve cranked up the knee control. As you can see, the “bend” in the line is much more curved, indicating a slow, smoothe transition into “full compression” mode.

knee-2

This is the kind of thing you’ll need to play around with, but basically, if you want the compressed sound to “sneak up” on you a little more, try increasing the knee. That way there won’t be an obvious transition from the uncompressed to the compressed sound.

I like a softer knee on things like vocals and piano. However, on more percussive, choppier tracks, like drums or strummed guitar, a low knee tends to work better.

Does that help? Do you use a “hard” or “soft” knee when compressing? Leave a comment.