[sdiy] Chopper circuits for audio and CV?

Mike Bryant mbryant at futurehorizons.com
Wed Jun 2 12:02:45 CEST 2021


A lot, lot more than just leaving the signal in digital and processing it that way :-)

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of cheater cheater via Synth-diy
Sent: 02 June 2021 10:41
To: Roman Sowa
Cc: synth-diy
Subject: Re: [sdiy] Chopper circuits for audio and CV?

If you wanted to use ADAT or something similar, how much do you think it could cost if you had 50 outs and 50 ins, where each one has to convert 16 analog synth channels to digital, or back from digital to
16 analog channels? Assume something competent like 16-bit audio and 18-bit CV*

And what if you scaled this up by 100?

* actually I'm not sure - what's a competent bit depth for CVs? Say for something like pitch tracking on a self-oscillating filter.

Cheers

On Wed, Jun 2, 2021 at 11:30 AM Roman Sowa <modular at go2.pl> wrote:
>
> That was covered on this list inside out. There were ideas for using 
> band shifting aka AM, and also pulse displacement technique known from 
> RC toys, and I'm nearly sure TDM was also discussed few times. 
> Everytime the outcome was: it's easier to do in digital and results of 
> doing it in analog are far from satisfactory, not to mention insane 
> complexity of the circuit.
>
> Of all methods discussed so far TDM seems like most natural and 
> easiest to do. Done in every polysynth known to mankind in terms of 
> CV, but for audio - that could get tricky. You'd need sample&hold 
> circuits able to track and settle in less than 1us and still expect a 
> lot of noise and possibly distortion. And that's for mere 48ksps of audio channel.
> No need for separate clock cable, you can regenerate clock from TDM 
> signal. Might even add some pattern to it to mark synchronization of 
> 16 channels.
>
> Why not use something like ADAT instead?
>
> Roman
>
> W dniu 2021-06-02 o 09:58, cheater cheater via Synth-diy pisze:
> > Hi all, I was wondering if anyone ever tried using a chopper circuit 
> > to put 16 voices of full bandwidth audio over one 1/4" cable. Also, 
> > the same thing goes for CV. Is that a feasible use case? What are 
> > the biggest problems that could be encountered here? I assume that 
> > the chopper clock can be distributed separately using a 50 ohm 
> > terminated distribution.
> >
> > Thanks
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