[sdiy] Tracking Generators?

[jh.]

> Has anybody taken a shot at implementing a "Tracking generator" like in
the
> Oberheim Xpander?

I think my Interpolating Scanner should cover that application:
http://home.t-online.de/home/jhaible/jh_ipscan.html
(Scroll down to "... And A Piecewise Linear Voltage Controlled Waveshaper
(2)")
You don't even need the OTAs - just sum up all the control currents over
potentiometers with an opamp.
(If anybody wants to build it, the usual "for private use only" applies.)

> OK Why? We were talking about harmonic generators, Steve Curtin pointed
out
> that a harmonic generator by itself is practically useless since static
> harmonics are boring. So each harmonic needs a VCA and envelope, which is
a
> lot of circuitry. However, if there was a simple enough non-linear
function
> generator, then a single envelope could be twisted into many envelopes and
> used to control the harmonic VCAs, giving animation to the sound with
about
> half the parts hopefully.

In practice, it can be even easier than that. Set up an arbitrary
nonlinearity, use
an input signal which is envelope-shaped already and/or a VCA for additional
control, and use a second CV to create a variable DC offset for the input
signal.
With 8 breakpoints, the two parameters input level and input offset, and a
selection
of basic VCO waveforms you can spend days to come up with ever new sounds.

JH.