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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'>Not really. It’s a full-wave
rectifier followed by a standard LP filter stage tuned to about 1/4 of the
expected incoming frequency followed by a notch filter tuned to twice the
incoming frequency. I also use a full wave rectifier instead of the
normal half wave rectifier, because I figure this gives faster integration. This
is why the ripple is at twice the incoming frequency, and a notch filter knocks
it out nicely. Through the judicious choice of gain at the LP filter, the
envelope follows the waveform tops more or less exactly, and comes up to full
strength within two periods of the incoming waveform, with ripple which is
inconsequential. For a 10Vpp waveform coming in, the envelope rides at
5V, which will turn on my favored linearized 2164 VCA design to unity gain.<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'> David Moylan
[mailto:dave@expeditionelectronics.com] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Saturday, August 31, 2019
5:26 AM<br>
<b><span style='font-weight:bold'>To:</span></b> David G Dixon<br>
<b><span style='font-weight:bold'>Cc:</span></b> synth-diy@synth-diy.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [sdiy] vocoder
filters</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'>Curious about this envelope follower you mention. Trade secret?<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'><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'>On Aug 31, 2019 03:48, David G Dixon <<st1:PersonName w:st="on">dixon@mail.ubc.ca</st1:PersonName>>
wrote:<o:p></o:p></span></font></p>
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<div>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Well, I know that the higher-Q filters have a longer delay,
so that they take longer to respond to the incoming waveform. I’m
thinking that a Q of about 3 is probably about right, and with that, only a
4-pole filter is required.</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>I’ve got a nice design for an envelope follower which
responds quickly and has little or no ripple, so that’s not a problem.</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>On a related note, does anyone here have problems getting the
Bode plotter in Multisim to work consistently? I am finding with this
simulation that sometimes if I change the component values, the Bode plotter
doesn’t work at all. Also, for some simulations, changing the component
values doesn’t change the filter response at all. Multisim is sure
glitchy. It’s very frustrating. I can sometimes fix it if I
erase all of the passive components and load new ones with the new values,
rather than just changing them, but that sort of thing is just complete
bullshit. Multisim is a sad excuse for a professional program.
There must be something better out there (?).</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
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<p><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'> Paul Perry
[mailto:paulfrancisperry@gmail.com] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Friday, August 30, 2019
10:22 PM<br>
<b><span style='font-weight:bold'>To:</span></b> David G Dixon<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [sdiy] vocoder
filters</span></font><o:p></o:p></p>
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<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>I don't
think there is a "right" answer. To my mind, it depends on what one
wants to do with the unit. Think about what will happen when a single swept
tone is used to modify white noise. The low pass filter on the VCAs probably
has a significant effect as well.<o:p></o:p></span></font></p>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>paul
perry <st1:City w:st="on">Melbourne</st1:City> <st1:country-region w:st="on"><st1:place
w:st="on">Australia</st1:place></st1:country-region><o:p></o:p></span></font></p>
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<p><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><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>On Sat,
31 Aug 2019 at 14:50, David G Dixon <<a href="mailto:dixon@mail.ubc.ca">dixon@mail.ubc.ca</a>>
wrote:<o:p></o:p></span></font></p>
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<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Well, I think I might have answered my own question.
Looking again at the JH Living Vocoder, since Jurgen Haible’s filter
responses overlap at about the 8dB mark, it really should not matter at all
what’s going on around the skirt of the response, and higher-Q filters
with two 2-pole stages should give very similar results to low-Q filters with
four 4-pole stages (and be much much cheaper to build).</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>I’d still appreciate if anyone has any specific
insights into this problem. Cheers.</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
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<p><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:<a
href="mailto:synth-diy-bounces@synth-diy.org">synth-diy-bounces@synth-diy.org</a>]
<b><span style='font-weight:bold'>On Behalf Of </span></b>David G Dixon<br>
<b><span style='font-weight:bold'>Sent:</span></b> Friday, August 30, 2019 9:05
PM<br>
<b><span style='font-weight:bold'>To:</span></b> <a
href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</a><br>
<b><span style='font-weight:bold'>Subject:</span></b> [sdiy] vocoder filters</span></font><o:p></o:p></p>
</div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Hey
SDIY Team!</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>I’m
thinking about building a vocoder, and I have a general question about the
bandpass filters.</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>I’ve
looked at Jurgen Haible’s Living Vocoder, and he used 8-pole filters with
low Q. These give a reasonably broad band with fairly steep slopes.
He makes the filters from two pairs of LP and HP.</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>I
was thinking about using BP filter sections, but just 4-pole, and with higher Q
(around 10). This gives a somewhat narrower band, and the slope is steep
near the corner, but fairly shallow around the skirt. This idea uses a lot
fewer components (about half as many).</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>What
I’m asking is, does anybody here have any insight into what the
“proper” approach to vocoder filters would be? What is the
design goal? Do you want significant overlap from one band to the next,
or should they be fairly distinct? I guess I’m just looking for
some general guidelines and conventional wisdom.</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> </span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Cheers,</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>Dave
Dixon</span></font><o:p></o:p></p>
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<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>_______________________________________________<br>
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