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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>The reason is because you don’t want
the base pitch to shift as a result of the Linear FM signal input. Linear
FM is a good way to get subtle vibrato effects, and obviously, this should be around
the base pitch.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Having said that, I never AC couple my
linear FM inputs. It has never been a problem, probably because I take
pains to ensure that none of my VCO or LFO outputs have offsets.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Synth-diy
[mailto:synth-diy-bounces@synth-diy.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>Pete Hartman<br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, February 02, 2020
4:07 PM<br>
<b><span style='font-weight:bold'>To:</span></b> synth-diy@synth-diy.org DIY<br>
<b><span style='font-weight:bold'>Subject:</span></b> [sdiy] Why is Linear FM
usually (always?) AC Coupled?</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>I was just discussing this with a friend, and his speculation was that
it would prevent any DC component from shifting the center of the modulation
away from the note that was being played. And while that seems plausible,
I've never heard anyone explicitly say that was why. To be fair I don't
think I've heard anyone explain why.<br>
<br>
So: is there a reason linear FM inputs are typically AC coupled? Have we
stumbled on the right answer?<br>
<br>
And if so, why would Exponential FM be left DC coupled? So you could transpose?<br>
<br>
Thanks<br>
<br>
Pete<o:p></o:p></span></font></p>
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