Single chip VC-ADSR idea

[Jeremy Brookes]

I've been looking into doing a VC-ADSR based around a PIC processor,
something like the 16C7x series. These have up to 8 on board ADCs (only
8-bit) and 1 or 2 PWM outputs (10 bit). The ADCs could sample the voltage
for each parameter and then use this to drive the PWM generator. The PWM
output can run at something like 20kHz and with a low pass filter on it at
maybe 10kHz, it should be capable of producing a reasonably fast analogue
voltage. So with a 16C74 (8 x ADC, 2 x PWM), it could be a dual ADSR or
maybe some complex HADSR whatever. Use some of the spare input pins for
selecting different modes, ADSR versus AR, linear vs exponential, a 'punch'
mode like a 10ms plateau after the attack phase but before the decay, it
might be possible to scale the amplitude (overall volume or peak of the
attack phase) with another voltage input. The chips in OTP versions run to
less than 10ukp, maybe as little as 5ukp. So what sort of features should I
think about for these devices?

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