How exactly Knee works on Compressor?

Hi guys, I was reading the Live manual yesterday and I found something that I really could not understand. It's how Knee works on Compressor.

At the manual (page 284), it says this: "For example, with a 10db knee and a -20 db threshold, subtle compression will begin at -30db and increase so that signals at -10db will be fully compressed."

 

Ok, I understood that Knee is used for gradually compression and with a 10db knee it will start at -30db. But why would it go to -10db if my threshold is set to only -20db? That's what I'm not understanding.

Can someone please explain the Knee fuction more detailed please?

Thanks

4 followers

claudioferrari 2 years ago | 1 comment

2 answers

  • Dennis DeSantis Ableton staff
    contribution
    33 answers
    187 votes received
    9 votes

    With a Knee of 0, you can think of the Threshold as being a single point. When the input level is below this point, the compressor does nothing. As soon as the input level is at or above this point, the compressor becomes fully active. With a ratio of 4, for example, this might look like:

    • signals below the Threshold are uncompressed (ratio of 1:1)
    • signals at or above the Threshold are fully compressed (ratio of 4:1)

    When you set a Knee value, however, you can think of the Threshold as a range, rather than one point. For input levels below this range, the compressor does nothing. As you enter the range, the compressor will become gradually more active, until it is fully "on" at the top end of the range. Thus:

    • signals far below the Threshold are uncompressed (ratio of 1:1)
    • signals a bit below the Threshold are a bit compressed (ratio of 2:1)
    • signals at or right around the Threshold are more compressed (ratio of 3:1)
    • signals far above the Threshold are fully compressed (ratio of 4:1)

    Notice that as you turn up the Knee, two vertical lines move outwards from the Threshold point in the graph. This visually indicates the expanded threshold range.

    2 years ago | 1 comment
  • Mage2k
    contribution
    2 answers
    1 vote received
    2 votes

    To follow on what Dennis DeSantis said, the range is then +-knee.  So, that's why the compression starts at -30dB in your example, -20dB -10dB = -30dB, and why it doesn't reach it's max compression ratio until -10dB, -20dB + 10dB = -10dB.

    2 years ago | 0 comments

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