[sdiy] Simple DSP as VCO substitute (was Re: CEM3340 reissue)

Tom Wiltshire tom at electricdruid.net
Tue Jun 14 19:40:46 CEST 2016


On 14 Jun 2016, at 16:44, Tim Ressel <timr at circuitabbey.com> wrote:

> Speaking of doable, it should be possible to take a DSP chip and mimic the function of a 3340. Yes I know, the 3340 has "that sound". But it also has "that price". I'm thinking the DSPIC33FJ128GP802. It comes in a 28 pin dip and has built-in audio DACs. Might be interesting.


The idea had occurred to me too, for the same reasons - the dsPIC 33FJ128GP802 is about the right size and format to make a good analog oscillator substitute. It has two DAC channels, so maybe even a dual oscillator would be possible.

There are definitely limitations with the chip (only six 12-bit ADC inputs when using the DAC, for example), and moving to a digital chip implies doing certain things differently (you won't get multiple waveform outputs in parallel, for instance). It's a good idea, and one I've played with quite often, but never been happy enough with the result. That won't stop me trying again though.

In some ways, I think it might make more sense to go in the direction of my 8-bit PIC VCDO and give up with pure virtual analog and accept that you can do a better job if you don't try and be something you're not. Perhaps it should be a voltage-controlled digital oscillator chip, doing a few of the interesting things you can do digitally instead of trying to do anti-aliased analog waveforms with hard sync and PWM and so forth.

Tom





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