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November 10th, 2016, 05:51 PM   #1
Joined: Nov 2016
From: Portugal

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Need Help with audio compression equation!

Hi guys, so, i'm building an audio compressor and i ALMOST got it, but i'm having a really hard time coming up with an equation for the "knee".
If you're not familiar with audio compression and are curious, look it up for more detail, but the essential thing is:

-apply a 1:1 function below the threshold
-apply a ratio:1 funtion above the threshold
-have an (optional) interpolation zone between these two functions around the threshold value, this is called the "Knee" and here is where my problem is.

I eventually got to an equation for the knee region that is pretty close to interpolating those two functions but, as much as i tweak it, i CANNOT get it to do it perfectly! (it actually does it if the Ratio is 0 or 1 but not any value in between)

Instead of explaining the math here, here's the link to where i'm actually making said functions, so it's easier to understand my problem:

The equation for the knee is K (4th from the top)

R is the Ratio
W is the Knee width
T is Threshold

Can someone please help me???
It doesnt even have to derive from the existing function, it can be ANY function as long as it merges the two others flawlessly, the slope is irrelevant.

Thanks guys!
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December 12th, 2016, 12:13 AM   #2
AshBox's Avatar
Joined: Oct 2016
From: labenon

Posts: 33
Thanks: 4

Hello Alexrodi,

There is two type of knee range you can derive. Hard and Soft Dynamic Range Compression. Which one you want to implement? I am not getting you question exactly.

Last edited by AshBox; December 12th, 2016 at 12:19 AM.
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