JH's VCO, wavetable source

[mbartkow at ET.PUT.Poznan.PL]

Grant,

thanks, but ...

> I have to point out that the most elegant solution to
> wavetable generators is an analog to digital converter.

...I don't think so. I personally don't like the idea of 
converting an analogue signal into digital domain and
back.

> A high frequency VCO clocking a counter, has no
> advantages over an analog to digital converter
> used as an address generator.

I would say there are some subtle pros and cons. First
of all, ADC is prone to quantization errors which accumulate
with the nonlinearity errors and scale mismatch of the input
saw waveform. Moreover, I think that the requirement of a
precise and sufficiently fast ADC makes this approach more 
expensive one.
 
> The use of the ADC gets you two additional operating modes,
> namely arbitrary scale quantization and non-linear synthesis
> (we recently hand traced the transfer functions of the Serge
> Wave Multipliers into a wavetable, sounds the same but with
> eight bit grunge).
> 
> Additionally the software to generate the 256 sample wavetables is
> available for download with a shareware price of a measly $20.
> http://www.wiard.com

These features are related to the wavetable idea, not to the use 
of ADC. I cannot see, why quantization could not be berformed by 
dropping some bits at the wavetable output. OTOH, nonlinear synthesis 
requires extremely fast (and expensive) ADC (maybe a flash one)
to instantly deal with feedbacks one might patch.

BTW, there might be a piece of RAM instead of the EPROM and
a local microcontroller responsible to fill up the RAM with the
transfer curve (my idea for a module - put some pots and an algorithm
within a microcontroller generates a curve according to the position
of the pots. For example some polynomial stuff.) You are not limited
to fixed wavetables in this way.

regards,

mb


--

Maciej Bartkowiak, PhD
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