[sdiy] Polymoog resonator question

Mattias Rickardsson mr at analogue.org
Thu Oct 11 11:52:01 CEST 2018


On Tue, 9 Oct 2018 at 00:53, David G Dixon <dixon at mail.ubc.ca> wrote:

>
> Today I made a PCB for a Polymoog resonator with voltage-controlled corner
> frequencies.  I put four resonators on the board.  Three of them I am going
> to stuff so that the manual range of frequencies are the same as the
> original Polymoog (60 to 300 Hz, 300 to 1500 Hz, and 1500 to 7500 Hz).
> However, the fourth I'm thinking about setting up so that it can scan over
> that entire range, so that it can cross over and reinforce each of the
> three peaks from the other resonators.  Does anyone have an opinion on this
> idea?  If so, I'd love to hear it.  Maybe it would be better to break the
> audio range up into four ranges.  I can't decide.
>

Generally speaking in a multi-band parametric eq or resonator like this I'd
definitely want the ranges to overlap more or less - having 60-300 &
300-1500 & 1500-7500 without overlap sounds like a questionable idea from
Moog's side - but on the other hand there can be some problems with huge
amplitudes when peaks collide. In the original old design I guess the
frequency ranges might have been limited to 2,5 octaves partly by the
topology, but in your case with voltage controlled 2164s, is there any
reason not to give the bands much wider ranges - perhaps even the full
10-octave audible range?

In the end, if I'd make something like this I'd probably choose four
limited but overlapping ranges, perhaps 20-400 & 75-1500 & 250-5000 &
1000-20000, and choose components and levels in order to optimize the audio
fidelity for each band.

Having four frequency sliders with "mutually blocking" slider tops like
Korg's old "Traveler" filter solution would also be an interesting take if
colliding peaks would be undesirable. :-)
https://www.sequencer.de/pix/korg/traveller_korg_vcf.jpg

/mr
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