Super Filter = No filter

[Gene Zumchak]

List,

 A recent thread about waveform synthesis reminded me of an  idea I had
about 25 years ago when I was into synths. I wanted to build a single
voice channel (ala Moog).  Since I had visions of commercial
possibilities, I needed to make it without a (patented) Moog VCLPF.  My
background is digital, and the things I did for Moog (like the 960
sequencer) were digital.  I was into microcomputers from the beginning.
(I owned a KIM-1 (6502) serial #000005, which at $250, cost less than an
8080 chip set at the time.)

 My goal was to make the perfect filter.  Imagine a waveform, like a
sawtooth, with a particular spectral recipe, and a filter bank in which
each filter affects only one harmonic.  Each filter would have its own
ADSR generator to control its harmonic.  If the waveform is the sum of
the fundamental and some number of coherently generated harmonics, then
a VCA/ASDR  for each harmonic, prior to the summing will give the
identical effect as a filter bank with individual time control of each
harmonic.  That is, the ideal LP filter would be no filter at all, but a
bank of coherent harmonic generators each with its own VCA and envelope
generator.

 To make the coherent fundamental/harmonic generator, I planned to use
EPROMs tied to DACs for table lookup of sines.  Muxing data  out of a
single EPROM modulo eight, I could supply waveforms for the first eight
harmonics (enough?).

 Needless to say I never built it.  Today it would be a lot easier and
cheaper.  In fact, I might be tempted to calculate everything in the
micro (a 16 MHz 68HC12) and generate the already enveloped, filtered
waveform directly.  Has anyone ever attempted this approach to a single
voice channel?

Gene Zumchak