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PostPosted: Wed Jan 04, 2017 1:27 pm 

Joined: Sun Feb 03, 2013 2:39 pm
Posts: 228
Is it possible to get the same gain reduction with the SB compressor for sine waves with the same amplitude but different frequencies?

With attack/release shape = 1 it seems that setting peak mode = release_time/attack_time gives an approximation for that or maybe it's just a coincidence.


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PostPosted: Fri Jan 06, 2017 6:36 pm 
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Joined: Tue Mar 17, 2009 2:56 pm
Posts: 3166
It should work like that already. it's WB. However check sidechain PEQ is it ON with some settings!

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PostPosted: Sat Jan 07, 2017 12:03 pm 

Joined: Sun Feb 03, 2013 2:39 pm
Posts: 228
Bojcha wrote:It should work like that already.
That's only true for attack_time = release_time because auto shapes will be the same in that case, too. However with attack_time != release_time attack and release behave differently enough to settle far away from the theoretical target.
Setting shapes = 1 and peak mode = release_time/attack_time or shapes = 500 and peak mode = 1 seems about to work.
I've only tested analog RMS mode with auto shape on so far.

Here are plots for easier comparison. They show the level computed from input and output (samples vs percentage). The used signals are sine waves with amplitude 1 and frequency as stated below, so they all should've produced the same output. The SB compressor uses threshold = -20 dB, ratio = 2, attack time = 20 ms, release time = 60 ms, knee = 0 dB, mode = RMS and auto fix shape = on. The rightmost plot is from a model compressor.
Image


Last edited by \_/ on Sun Jan 08, 2017 9:27 am, edited 1 time in total.

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PostPosted: Sun Jan 08, 2017 1:43 am 
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With an attack time that's close to the frequency of a tone (100 Hz -> 10 ms, vs 20 ms), it kinda makes sense that the level it reaches can be a bit different (for example, the release could get an effect on the quieter parts of the waveform). The 1000 and 10000 tones are pretty close, not sure why they are sligtly different. So I would expect that you get better results if you increase both the attack and release times (by the same amount, relatively, so for example 200 and 600 instead of 20 and 60). In the theoretical model the lowest tone is also on top, the difference is just smaller.

I'm also not sure what happens with the 10 kHz tone at Shape=500 - that seems odd.


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PostPosted: Sun Jan 08, 2017 9:23 am 

Joined: Sun Feb 03, 2013 2:39 pm
Posts: 228
As requested the same plots but with (attack, release) = (200 ms, 600 ms). They look pretty much the same.

Why does the leftmost plot settle at a different target? The input is the same everywhere.

Image


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PostPosted: Wed Feb 22, 2017 9:17 am 

Joined: Sun Feb 03, 2013 2:39 pm
Posts: 228
I re-did the first measurement now with detection type = peak (all other settings same as here). Not sure if this is looking good. :?
Image


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PostPosted: Sun Jun 11, 2017 10:04 pm 

Joined: Sun Feb 03, 2013 2:39 pm
Posts: 228
Tested new real RMS mode as of ST 8.40, settings as above. No suprises.Image


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PostPosted: Tue Jun 13, 2017 11:45 am 
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Posts: 8818
Looks better than before!


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