[sdiy] AS3397 what is it?

[Tom Wiltshire]

Hi Benjamin,

The chip has most of the waveshaping parts of two DCOs, followed by a filter and VCA as you assumed. The mixer has been simplified down to a "Balance CV" which sets the balance between to the two DCO signals.
 I wouldn't call it a synth voice on a chip because there's no envelopes or LFOs or anything. The idea is that those parts you generate digitally and the analog path is controlled by a few basic CVs: Waveshaping, Balance, Filter cutoff and resonance, and VCA volume.

The important bit of the DCOs is that what you have is an integrator and some waveshaping. What you *don't* have and are expected to provide is some timing (reset) pulse and some amplitude control. That's what makes it like a DCO for me. Roland described their Juno106 chip as a "waveshaper", and it was much like this one, although not as versatile, and it similarly needs amplitude control. In Roland's case the timing was provided by 8523 16-bit counters, but these days you'd probably have timers on a microprocessor that you could use. Whether that was what was intended for the original CEM chips, I couldn't say. What does the Prophet 800 do? Didn't it use these chips?

It's pretty flexible, but there's quite a lot of work has to be done "off chip" in the processor to make it behave properly. Have a read about the Roland DCOs and you'll start to get the idea of what it's expecting and what you're required to do to make it work:

https://blog.thea.codes/the-design-of-the-juno-dco/

HTH,
Tom



> On 17 Jan 2025, at 23:21, Benjamin Tremblay via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> Hello,
> I’m intrigued by what the AS3397 chip appears to be. But exactly what does it do? Reading old threads about it and the CEM3396 leave me scratching my head.
> 
> It’s a what… Wave-shaper that takes a computer-generated square wave and gives it personality? 
> 
> What are the correct inputs? I’m assuming it has traditional voicing like a vcf/vca stage and a mixer. 
> 
> Do I need to code up one or more computer waves to send into it, and what is the relationship between the input and the output? 
> 
> Thanks,
> Benjamin 
> 
> Benjamin Tremblay
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