@unstable said:
Hey I got a question. in the compression patches I can kind of get my head around the amp factor section. But I don't get any of the att/rel section. Can anyone explain what that sgn~ (signum) is/does ? Secondly I can see the table is effected by the release but not really on the attack. I can hear the attack. The block size is 2. I'm guessing if the default block size is 64 samples then 2 means 128?? Or is it actually 2 ? This outputs a frequency between 0.019 and 57 into a VCF along withe the original amp factor. Any advice ?
ok, so the [amp-factor] stage is giving the amplitude of the signal, scaled according to our threshold and ratio settings. This will either be positive if the amplitude is rising, or negative if it's falling.
next we go into the [att-rel-filtering] section, where we separate the attacks (positive) from the releases (negative)
[block 2] really does mean that the blocksize is only 2 samples. This is so that the [tabsend~] and [tabreceive~] objects deal with packets of two samples at a time,
giving us a sample delay between the input signal and the signal received by [tabreceive~]. If the blocksize were the default of 64, then we would have a 64 sample delay, and our compressor would not work at all well.
sgn~ just gives the sign of the signal, so -1 for negative numbers and 1 for positive ones. note that we are dealing now with just the AMPLITUDE of the signal, which has been scaled in the [amp-factor] section so that rising amplitude (ie, attack) is positive and falling amplitude (release) is negative.
that is then split apart using [max~ 0] with attack sent to the left outlet and release sent to the right outlet. The attack and release stages are both scaled separately (attack scaled by 0.019 to 57, and release by, i think, 0.00019 to 5.7) (and i don't know exactly WHY 57 was chosen, i'm sure the patch would work just as well with 50 or 60)
then we go through the [vcf~]. Although vcf~ is normally used to shape the frequency content of a wavform, in this case, it has a different use. It is smoothing the amplitude signal. So, if we set a fast attack, then the vcf~ will have a cutoff of 57hz, and our compressor will attack within 20ms. if we set a slow attack, then the vcf~ will have a frequency of 0.019hz, and the compressor will take a few seconds to fully attack.
finally, the original signal is multiplied by the compression factor, and sent along its way.
There are some quick mods you can do to this patch, too. A sidechain compressor, essential for any sort of 'french' electro sound, can be made by adding another inlet~ for a second audio signal, and taking the inverse of the compression factor, like this:
[pd att-rel-filtering]
|
[-~ 1]
|
[*~ -1]
and then multiply your second signal by that.
also, it is fun to take the compression factor output to its own [outlet~] and use it as a modulation source for filter cutoffs for synth sounds, etc.
anyway, hope that clears things up a bit?
have fun!
