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Upwards compression...
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November 10, 2015
12:49 pm
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djfresha
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Hi to all,

Working on a 2-mode compressor which is a bit different from the norm... Most compressors I've seen use downwards compression and then progress to downwards expansion in the same plugin. However, I've gone a bit different and have done the downwards compression part including the softknee which all works fine. I'm now trying to get my head around how to do the upward compression and what detector algo to use. The upwards compressor will trigger between -60dB and the threshold (from -50dB to 0dB), and also include a downwards expander at -60dB downwards, to compensate the lower region and not to raise everything up.

Was wondering how I should go about reading in the value, and what dB should the triggering start? because all the signal below the threshold is technically 'on' and above is 'off', but most audio starts at say -96db and goes upwards, so I would be upwards compressing from the off.

Has anyone had any experience in this or implementing upwards compression code?

November 13, 2015
4:18 pm
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JD Young
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Hi djfresha,

I thought about your question, but your goal is not a 100% clear to me. You say most compressors use downwards compression and progress to downwards expansion in the same plug-in. What do you mean by ‘progress to’? Most compressors I use are capable of downwards compression: ratio > 1, or upwards expansion: 0 < ratio < 1). Here’s an image, just to make sure we’re talking about the same thing: http://stash.reaper.fm/oldsb/3.....81/dyn.png)

Downwards compression: test if the envelope goes over the threshold. NO: do nothing. YES: calculate the gainfactor (0 < gainfactor < 1, or negative dB value).

Upwards compression: test if the envelope stays under the threshold: NO: do nothing. YES: calculate the gainfactor (gainfactor > 1, or positive dB value).

Downwards expansion: test if the envelope stays under the threshold: NO: do nothing. YES: calculate the gainfactor (0 < gainfactor < 1, or negative dB value).

Good luck!

JD

November 13, 2015
9:19 pm
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djfresha
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Apologies - had a typo in the OP.

Yes I mean from downwards compression to upwards....was trying an all in one (so I had 0.14:1 = -7:1 upwards, through to inf:1 for downwards) - your image is right (looking at downards + upwards compression for my query)

For now I've just done downwards to simplify. Was reading up that some people prefer parallel compression (which is what I've already catered for) to get 'similar' sound out, and yes I do know this isn't true upwards compression.

My original question was (reworded).... if we're doing upwards compression on a signal, and say we have a threshold of -10dB and do a -5:1 (aka 0.2:1 ratio) so -20dB becomes -12dB, and say -70dB becomes -22dB, this is all in relation pretty loud comparing original sound to new sound : where would we define the point *ideally* where we say ok don't include a certain range ie from -96dB to maybe -60dB in our upwards, but expand that up to meet our upward compressed so not to cause 'stepped' or zippered sound due to the jump point? also if -96dB (as I read) it hypothetically CD noisefloor (pretty damn close to zero but still 'there') would we want to avoid raising this 'white noise' when doing upwards? Would we sneak in a small expander at the lower levels?

Cheers for the reply, and pointing out my typo (*facepalm*)

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