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<DIV dir=ltr align=left><SPAN class=255581120-27112022>OK, but if you have, say,
a triangle-wave VCO, and you give it a subtle sinusoidal Linear FM modulation,
it will just warble back and forth in time a bit. The amplitudes won't
change.</SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=255581120-27112022></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=255581120-27112022>The way you're describing
it, phase modulation seems identical to frequency modulation. Hence, I
don't see the need for another term -- FM is sufficient.</SPAN></DIV><BR>
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<FONT size=2 face=Tahoma><B>From:</B> Donald Tillman [mailto:don@till.com]
<BR><B>Sent:</B> Saturday, November 26, 2022 12:03 PM<BR><B>To:</B> David G
Dixon<BR><B>Cc:</B> synth-diy mailing list<BR><B>Subject:</B> Re: [sdiy] "FM"
Synthesis (was Re: Buchla 295 10-band comb filter topology)<BR></FONT><BR></DIV>
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<DIV>Mmm, not really.</DIV>
<DIV><BR></DIV>
<DIV>Wave shaping is along the Y axis only. For each cycle, the phase
angles remain as they were, but every given Y value gets warped to the same new
Y value.</DIV>
<DIV><BR></DIV>
<DIV>Phase modulation is shaping along the time axis only. For each cycle,
the Y values are unchanged, but their phase angles are warped to new
values.</DIV>
<DIV><BR></DIV>
<DIV>"Wave Morphing" might include both.</DIV>
<DIV><BR></DIV>
<DIV>The subtle part is that certain kinds of waveshaping (again, Y axis only)
can appear to warp the signal along the time axis, even though that didn't
technically happen. "PWM" is an extreme and familiar example.</DIV>
<DIV><BR></DIV>
<DIV> -- Don</DIV>
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<DIV
style="TEXT-TRANSFORM: none; FONT-STYLE: normal; TEXT-INDENT: 0px; FONT-FAMILY: Menlo; WHITE-SPACE: normal; LETTER-SPACING: normal; COLOR: rgb(0,0,0); FONT-SIZE: 12px; FONT-WEIGHT: normal; WORD-SPACING: 0px; font-variant-caps: normal; -webkit-text-stroke-width: 0px">--<BR>Donald
Tillman, Palo Alto, California<BR><A
href="https://www.till.com">https://www.till.com</A></DIV></DIV></DIV>
<DIV><BR>
<BLOCKQUOTE type="cite">
<DIV>On Nov 26, 2022, at 11:25 AM, David G Dixon <<A
href="mailto:dixon@mail.ubc.ca">dixon@mail.ubc.ca</A>> wrote:</DIV><BR
class=Apple-interchange-newline>
<DIV>
<DIV>OK, I get it. It's just a subtle form of waveshaping. It's
basically<BR>linear FM where the modulating wave is at the same frequency as
the<BR>modulated wave, so that when the waveforms return to the same position
they<BR>are at the same frequency that they started at.<BR><BR>-----Original
Message-----<BR>From: Donald Tillman [<A
href="mailto:don@till.com">mailto:don@till.com</A>] <BR>Sent: Saturday,
November 26, 2022 10:05 AM<BR>To: David G Dixon<BR>Cc: synth-diy mailing
list<BR>Subject: Re: [sdiy] "FM" Synthesis (was Re: Buchla 295 10-band comb
filter<BR>topology)<BR><BR>On Nov 25, 2022, at 5:58 PM, David G Dixon via
Synth-diy<BR><<A
href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</A>>
wrote:<BR>
<BLOCKQUOTE type="cite"><BR>I've struggled with this idea of "phase
modulation" -- I don't really get<BR>it.<BR><BR>[...]<BR><BR>Is any of that
correct? If not, then I'd very much appreciate an<BR>explanation of
phase modulation -- specifically, what the hell is
it?<BR></BLOCKQUOTE><BR>You're way off. Not your fault; the goofy
terminology has made this very<BR>difficult to understand.<BR><BR>Here's my
zen explanation:<BR><BR>You know that "subtractive synthesis" starts with a
harmonically rich<BR>waveform (ie., painfully bright) and runs it through low
pass filters to<BR>shape the spectrum dynamically.<BR><BR>And "additive
synthesis" starts with component waveforms and mixes
them<BR>dynamically.<BR><BR>And "waveshaping synthesis" dynamically distorts
the waveform, or more<BR>specifically warping it along the Y
axis.<BR><BR>Well, "phase modulation" starts with a sine wave and warps the
hell out of<BR>it along the *time* axis, dynamically, with the help of a
second waveform at<BR>the same frequency (or simple ratio).<BR><BR>Warping a
waveform along the time axis means stretching this part of the<BR>waveform,
and squishing the rest. If the effect is subtle it ends up<BR>resembling
a PWM wave.<BR><BR>If the effect is more than subtle, the stretches and
squishes can go over<BR>multiple cycles.<BR><BR> -- Don<BR>--<BR>Donald
Tillman, Palo Alto, California<BR><A
href="https://www.till.com">https://www.till.com</A><BR><BR></DIV></DIV></BLOCKQUOTE></DIV><BR></DIV></BODY></HTML>