[sdiy] Generating a large number of CV outputs

[Mike Bryant]

Yes the key thing about PDM over other methods is it doesn't have to have a fundamental fairly low sampling rate like PWM or D-S.  This gives it much faster response time to requested changes.  One way to think of it is that PWM and D-S have a low pass filter on their feedback loops, which D-S actually does have, whilst PWM sort of has in the lag of changing the M-S ratio.

This, and the fact that you get far less energy at the sampling rate, is why many digital microphones have moved to using PDM, and of course most new MCUs now support this mode.

________________________________
From: mskala at northcoastsynthesis.com <mskala at northcoastsynthesis.com>
Sent: 08 December 2023 03:30
To: Mike Bryant <mbryant at futurehorizons.com>
Cc: Danjel van Tijn / intellijel <danjel at intellijel.com>; SDIY <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Generating a large number of CV outputs

On Fri, 8 Dec 2023, Mike Bryant wrote:

> I just had a read of this and generally very well put.  However you seem to
> miss out mentioning PDM  between the sections on PWM and Delta-Sigma.  This
> gives faster settling time of DC voltages than PWM, as well as other
> advantages when producing audio as its easier to push the noise out of
> band.

I'm not sure PDM is meaningfully different from delta-sigma at the level
of detail I included in the posting.  The things I would want to say about
it would be the same things I did say about delta-sigma.  Is there an
important example of a PDM scheme that is not a form of PWM nor
delta-sigma modulation?

--
Matthew Skala
North Coast Synthesis Ltd.
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