Fast VCOs/V->F converters

[Martin Czech]

> More on accuracy, some comments on digital waveform generation, and
> expectations...
> 
> When evaluating pitch accuracy in musical applications there are two
> important factors: absolute (isolated note) pitch accuracy and relative
> error (two or more notes).  Of the two, relative is hardest to hit because
> of the small error required but in many ways easiest to implement because
> all that is really important is that all of the VCOs do the same thing -
> this is referred to "tracking".
SNIP



True.



> When one flirts with the digital domain as in this application another area
> needs to be looked at: short-term phase jitter.  Like it or not, playing
> back a waveform from memory with a VCO still is subjected to all of the
> realities of sampling.  What you are creating is a variable sample rate
> system where the VCO frequency sets the sampling rate.  All of the Nyquist
> nasties apply, but one of the worse and most subtle is what happens when the
> sample rate jitters.  Small, fast changes in the phase of the sampling clock
> cause the modulation of the spectrum of the sampled waveworm and as a result
> produce all sorts of sideband frequencies, most of which are inharmonic -
> digital grunge in other words.  Grudged that our hears really, really hate
> (and probably why any of you are making analog synths in the first place)> quite the same twice (the edge uncertainty is roughly less then their tim




Also good point.



> Since I bopped into this thread a bit late I'd like to ask a question about
> the end goal here for the waveform table lookup VCO.  What is the
> expectation that this design will produce in the way of sonic diversity?
> The practical answer may be startling!  How many table locations are being
> considered?  Will waveform sequencing be possible?  Are we trying to
> reinvent the PPG?
> 


As *I* have a microwave allready, there seems to be no reason to reinvent
the PPG today. But someone asked for possibilities of hf-vco/wavetables.
I simply tried to give an answer.

I would say: a circuit for a modular that leads a bit away from the
usual harmonic wave stuff like saw , tri , sqa etc. is wellcome, and if
there are some artefacts, well, better then nothing.  Some might say:
We live in the times of lo-fi and grungelizers ;->. If you are out for
something perfect, use a sampler and/or a program to compute waves. This
is a clean, but also timeconsuming method.

m.c.