[sdiy] SID

[Rainer Buchty]

>     If I remember correctly, the SID has only 3 oscilators, so at best,
> you will get 3 voice polyphony.  The thing only has 1 filter, so in many
> ways, it would be best suited for mono.  A long time ago, I had planned
> on making a 4 voice synth using 4 of the chips...never did anything
> beyound buying one of the chips.  Then they became unavailiable, so I
> gave the chip away....too bad, in a way.

Plus, you have a fourth voice since it had that design bug^W feature
which created an audible click when switching the final VCA's volume. That
way it was possible to play back 4bit samples. There've been players
on the C64 allowing to play back even two sample voices.

Meanwhile, those crazy guys do 3x 12bit sample playback by abusing the
pulse width setting of each oscillator as the sample data register; that
way you will of course hear the carrier frequency.

>     It would be fairly easy to duplicate what this chip did in an FPGA,
> but, that would sortof defeat the simplicity of the whole thing.

And here comes my question to the digital filter gurus: Is it possible to
design something like a tunable digital filter *without* realizing that
tuning through manifold tables of coefficients but just by the digital
counterpart of a CV input? If yes, it'd be great if somebody could direct
me to books to read, web sites to visit, etc.

Rainer

-- 

Rainer Buchty, LRR, Technical University of Munich
Phone: +49 89 289-28401, Fax +49 89 289-28232, Room S3240