[sdiy] Polyevolver internals

[Antti Huovilainen]

On Tue, 29 Dec 2009, Eric Brombaugh wrote:

> Depends on how long a delay you need - If you're willing to strap on an 
> external SRAM you can get quite long delays from a dsPIC, even at decent 
> sample rates. If you're trying to get by only with internal RAM though 
> it is pretty limited. Really only good for phaser/chorus ranges.

If you're willing to sacrifice bandwidth (you could just call it "analog 
modelled delay"), you can fit up to 0.5 secs mono delay in a single dspic 
(assuming you don't need the sram for anything else). Whether 0.5s is 
enough for much usable is another thing though.

> No idea how well it would work to have both DCOs and digital oscillators 
> running simultaneously though. Could end up with some IRQ contention if 
> the DCO hardware needs much babysitting.

I don't see much point in using DCOs when you can simply add more dsp
oscillators and mix them in software.

dsPIC with integrated audio DAC should work as a pretty nice two voice 
chip for building polysynths (or monosynths). Use SPI to control N dspics 
and mix the separate voice outputs together in analog. IIRC, they cost 
about 6e / part for the 28 pin dip versions. I'm planning to try this 
early next year.

Antti

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