Old 06-09-2017, 08:46 PM   #1
LefIllegal
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Default Interesting Compression Results, Why?

I decided to build a multiband comp using reaper plug ins. I built two variations. The first is a 3band comp, the other is a 5band comp. Whats interesting is, both have the same exact settings(default), yet when i run audio through the 5band comp, i get appox. .8db-1.1db in gain reduction from out of nowhere with no additonal processing or adjustments. Also there is no perceptable loss in volume, only in the meters readout can this .8db reduction be spotted. I consider this a good thing. Could anyone explain why this is happening and whether it is actually good or not?
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Old 06-09-2017, 08:57 PM   #2
Lokasenna
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My first guess is that your crossovers aren't perfect and are either producing some weird aliasing, or just plain losing a tiny bit of content in those areas.
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Old 06-09-2017, 09:09 PM   #3
LefIllegal
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Lokasenna, thanks for the reply, anyways im not complaining i just found it interesting. Im going to go with your crossover theory as it seems the most appropriate explanation for now. As i said the difference is not audible(at least on my set up), i would consider this reduction a good thing. Until i run into a problem or told to do otherwise, i guess ill run audio thru the 5band.
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Old 06-10-2017, 10:12 AM   #4
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Most filters introduce frequency-dependent phase shifts. The phase-shift by itself isn't a problem. But if you make a high-pass and a low-pass filter and then you re-combine (sum) the two outputs, you don't get the original signal back.

For example - A speaker crossover usually introduces a phase-lag for the woofer (more lag at higher frequencies) and a phase-lead for the tweeter (more at lower frequencies).

...If (at the crossover frequency) you have a -90 degree lag for the woofer and a +90 degree lead for the tweeter, the two drivers are 180 degrees out-of-phase at the crossover point and you get some cancellation of the sound waves and a dip in frequency response. So, it's common practice to reverse the tweeter connection in a 2-way speaker or reverse the midrange connection in a 3-way speaker.
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Old 06-11-2017, 01:43 AM   #5
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this isn't so much about cross-overs as it is about minimum phase filters in general.
since summing/joining happens after the compressors, the extra gain reduction is not from the summing of the split bands, but from the splitting of the bands.
(as a note, the JS splitter/joiners sum to the original perfectly, if that's what you are using...)
if you were to use a linear phase splitter, you would not have the issue of level change due to phase shift.
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Old 06-11-2017, 02:37 AM   #6
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Copy the audio to a new track - without any plugins on that track. Flip the polarity (with the phase switch) - hit play - and you'll hear how the multiband set-up is changing phase relationships at crossover points.
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