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<div><span style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" class="elementToProof">That's one way of doing it, but still locks you into a lower sampling rate. Often better
to just sample at a very high rate (as fast as your logic allows) and just decide do I need to output a '1' now or not.<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Richie Burnett <rburnett@richieburnett.co.uk><br>
<b>Sent:</b> 08 December 2023 10:47<br>
<b>To:</b> Mike Bryant <mbryant@futurehorizons.com>; mskala@northcoastsynthesis.com <mskala@northcoastsynthesis.com><br>
<b>Cc:</b> SDIY <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] Generating a large number of CV outputs</font>
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<div class="PlainText">I forget, is PDM equivalent to PWM but with the ramp counter bit-reversed
<br>
before it gets compared with the reference? So the overall ratio of 1's to <br>
0's in one period of the bit sequence is the same as PWM, but the 1's and <br>
0's are scattered around the period, instead of having all of the 1's <br>
grouped at the start of the period and all of the 0's grouped together at <br>
the end of the period. Am I right?<br>
<br>
-Richie,<br>
<br>
<br>
<br>
-----Original Message----- <br>
From: Mike Bryant<br>
Sent: Friday, December 8, 2023 9:34 AM<br>
To: mskala@northcoastsynthesis.com<br>
Cc: SDIY<br>
Subject: Re: [sdiy] Generating a large number of CV outputs<br>
<br>
<br>
Yes the key thing about PDM over other methods is it doesn't have to have a <br>
fundamental fairly low sampling rate like PWM or D-S. This gives it much <br>
faster response time to requested changes. One way to think of it is that <br>
PWM and D-S have a low pass filter on their feedback loops, which D-S <br>
actually does have, whilst PWM sort of has in the lag of changing the M-S <br>
ratio.<br>
<br>
<br>
This, and the fact that you get far less energy at the sampling rate, is why <br>
many digital microphones have moved to using PDM, and of course most new <br>
MCUs now support this mode.<br>
<br>
<br>
<br>
<br>
From: mskala@northcoastsynthesis.com <mskala@northcoastsynthesis.com><br>
Sent: 08 December 2023 03:30<br>
To: Mike Bryant <mbryant@futurehorizons.com><br>
Cc: Danjel van Tijn / intellijel <danjel@intellijel.com>; SDIY <br>
<synth-diy@synth-diy.org><br>
Subject: Re: [sdiy] Generating a large number of CV outputs<br>
<br>
<br>
On Fri, 8 Dec 2023, Mike Bryant wrote:<br>
<br>
> I just had a read of this and generally very well put. However you seem <br>
> to<br>
> miss out mentioning PDM between the sections on PWM and Delta-Sigma. <br>
> This<br>
> gives faster settling time of DC voltages than PWM, as well as other<br>
> advantages when producing audio as its easier to push the noise out of<br>
> band.<br>
<br>
I'm not sure PDM is meaningfully different from delta-sigma at the level<br>
of detail I included in the posting. The things I would want to say about<br>
it would be the same things I did say about delta-sigma. Is there an<br>
important example of a PDM scheme that is not a form of PWM nor<br>
delta-sigma modulation?<br>
<br>
-- <br>
Matthew Skala<br>
North Coast Synthesis Ltd.<br>
<br>
<br>
<br>
<br>
<br>
<br>
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