[sdiy] Making an 8038 not suck

[Antti Huovilainen]

On Fri, 24 Nov 2006, Paul Perry wrote:

> and it isn't even cheap! once one accepts that micros with 10 bit A to D
> won't cut it.

For a modular you obviously can't use an MCU. Then again, for a modular 
you might as well use expensive ICs since your panel and other costs are 
going to swamp the cost of bit fancier electronics.

For a full synth the reality is that using an MCU and 14-16 bit serial DAC 
will eliminate half of the circuitry and make the rest simpler. You can 
also get stepless fast modulations easily - I estimate a typical monosynth 
could get 1-2 kHz update rate which would allow stepless smooth 
modulations and very fast envelope / lfo times.

Modern MCUs (meaning AVR and ARM, not 8051, pic and other ancient designs) 
are pretty fast and have very good free optimizing C compiler (gcc) 
available. Calculating the modulations at say 2 kHz rate is trivial even 
on a slowish 8 MHz AVR.

Plus there's a nice trick that allows very close approximation of smooth 
modulation waveforms even at almost maximum LFO/envelope speed - time to 
dig out highschool math books and reread the part about first order 
differential equations (RC smoothing filter = 1st order lowpass filter).

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
  -- Lt. Cmdr. Ivanova