[sdiy] Driving SSI2144 freq control with PWM from a microcontroller

[Mike Bryant]

Don't you mess up the effects of any log element that way ?

But definitely works for a linear synth.  My first microcontroller based synth (a Z80) in the early 80s used PWM for VCFs and VCAs.
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Neil Johnson via Synth-diy <synth-diy at synth-diy.org>
Sent: 07 November 2022 09:52
To: Lanterman, Aaron D <lanterma at ece.gatech.edu>
Cc: synth-diy mailing list <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Driving SSI2144 freq control with PWM from a microcontroller

Hi all,

Genuinely curious question: since you're driving a low-pass filter
anyway, why not dispense with filtering the PWM and, assuming the PWM
clock is way above audio, just drive the frequency control pin
directly?  You'll be driving the transistor ladder directly from PWM
so it would behave more as a switched-capacitor filter rather than in
linear mode, but it might work.
For the SSI2144 that would be, say, +/- 90mV pulse waveform.

Neil
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