[sdiy] Pink?

[mskala at ansuz.sooke.bc.ca]

On Fri, 17 Aug 2018, Mattias Rickardsson wrote:
> So, why aren't VCOs and VCFs more spectrally pink?

I'm not sure I understand what you mean by "more pink".  If you just mean
that raw VCO outputs have more harmonic content than you want, well, of
course they do, that's by design.  Standard subtractive synthesis starts
with a signal that has lots of harmonic content and then you remove some
with a filter to reach the desired level.  In order to get the right
amount of harmonic content by removing some, you have to start with *more*
than the right amount, and that's what the VCO produces.  VCOs designed
for this application are not meant to sound good alone without a filter.

But any low-pass VCF with at least one pole will roll off the high end at
at least 6dB/octave in the limit of high frequencies, which is already a
sharper roll-off than traditional 3dB/octave pink noise.  So if the output
of the VCF still sounds too bright for you (too much high-frequency
content) and you want a sharper roll-off, I'm not sure what to tell you
except to try a sharper filter.  And if you don't like the sound of a lot
of resonance, try using less resonance.

If you want a filter with specifically a 3dB/octave roll-off, such things
do exist (for instance, they're used in some pink noise generators;
typically it's a many-pole filter set up to simulate the slow roll-off of
less than one pole over the part of the slope that is audible) and in some
sense the result might be called the most "pink" filter response
possible... but it'll be a lot brighter, with more high-frequency
content in the output, than we usually expect of VCFs, so it's unlikely to
be what you want if you're listening to more standard filters and thinking
them too bright.

> Have there been any attempts historically to alter their characteristics a
> bit in synths? :-)

There's been plenty of experimentation with different filter curves.

-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before principles.
http://ansuz.sooke.bc.ca/