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

[rburnett at richieburnett.co.uk]

It should work Aaron. Some thoughts..

Get the PWM carrier frequency as high as you can (well above the audio 
range) so that you can heavily attenuate the switching frequency with a 
low-pass filter whilst still getting a sufficiently fast slew-rate for 
sounds that need a fast attack.

If you get the switching frequency up into the low hundreds of kHz, then 
any intermodulation products produced in the VCF or VCA due to residual 
PWM carrier ripple should be well above the audio band.

You might want to look at using a 2nd or 3rd order low-pass filter for 
the PWM carrier suppression because higher order can give you better 
suppression at the PWM carrier frequency (and its harmonics) for a given 
step-response setting time.  With just 1st order RC it might be a 
difficult tradeoff, that becomes easier if you move to 2nd order.

If you've got lots of PWM channels available there are other fancy 
things you can do with multiple channels running at different switching 
rates, or in anti-phase to reduce the ripple at the switching frequency. 
  Not sure how beneficial they are in practice.

Sounds like a fun project!

-Richie,



On 2022-11-05 02:05, Lanterman, Aaron D via Synth-diy wrote:
> It’s been a while since I’ve done a synth design video:
> 
> https://youtu.be/RYA_k1I47l8
> 
> I have a senior design team working on a hybrid synth (digital
> oscillators, analog VCFs and VCAs), which got me thinking about
> minimalist control schemes that wouldn’t need an op amp. Not sure if
> this is a good idea or not.
> 
> Aaron Lanterman, Prof. of ECE, Georgia Tech
> My blog on Education and Innovation:
> https://edupocalypsenow.wordpress.com
> My blog on Electronics and Programming:
> https://lantertronics.blogspot.com
> My YouTube channel on Electronics and Programming:
> https://www.youtube.com/c/lantertronics
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