VCDO - asking again + new idea, wave shaping

[mbartkow at ET.PUT.Poznan.PL]

> Let's say we have an audio range VCO producing a positive sawtooth, with
> a freq range from 0 to
> 20 KHz. As it ramps up periodically, the sawtooth is sampled through a
> fast ADC, the 6 MSB
> from the ADC are used to adress a ROM where various waveforms are stored
> (64 bytes for each).
> Of course, the most significant adress bits of the ROM are used for
> waveform selection. Then the data
> output of the ROM are sent to a fast DAC.
> In order to still have 64 samples for the highest freq (20 KHz), the
> sawtooth must be sampled at
> 1.28 MHz min. In the Farnell catalog I found a 6 bits ADC (CA3306CE by
> Harris) with a typical
> conversion time of 0.1 us. Then we need a fast 8 bits DAC, and there are
> plenty of those.
[...]

I think the best solution is to avoid sampling since it involves possible
aliasing and strange effects related to random sampling of the falling edge 
of the saw. So contiously working ADC (flash or tracking ADCs come to mind) 
might directly address the wavetable ROM. I am not shure 6-bit resolution 
for the waveshape is enough.

***

Since this touches waveshaping, which is what fascinates me for years,
I would like to ask if anybody has an idea for a universal analogue
waveshaping circuit which is simply controlable using possibly few 
parameters (knobs or voltages) yet it allows to achieve a variety of 
"heavily twisted" shapes. 
I must say I *dream* about a shaper circuit for Tshebyshev 
polynomials or Bessel functions - only two parameters and soo much 
possible functions.



regards,

--

Maciej Bartkowiak
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