[sdiy] Imitating CEMs with PICs

[Antti Huovilainen]

On Sun, 1 Oct 2006, Tom Wiltshire wrote:

> imitate/simulate/copy the unobtainable (or at least extremely expensive) 
> SSM and CEM synth chips that I wanted but can't get.

As far as audio path is involved (VCO, VCF, VCA), you can forget it.

For sub-audio components (LFOs, EGs, lag processors, whatever), the 
situation is more favorably. There you're often better off when you don't 
blindly try to emulate the analog components but instead concentrate on 
getting the same end result.

In a monosynth for example, you'd be best off calculating all modulations 
digitally and then using a multiplexed DAC to produce 8-10 CVs to control 
the VCOs, VCF and VCAs (2x vco freq, pw, 2x vco amp, vcf cutoff, vcf res, 
final vca). Any halfway decent MCU (which rules out most PICs though) 
should be able to calculate those at > 1 kHz rate which removes most of 
the aliasing issues (if you quantize modulation period to a multiple of 
dac update period).

Antti

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