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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'>So, today I have done some simulations,
and have discovered that I can replicate the frequency response and delay
characteristics of Jurgen Haible’s 8-pole (4-stage) BP filters with my
own 4-pole (2-stage) BP filters with a Q of about 3 (for each stage). The output
frequency responses look virtually identical, and given an input sine wave (or
square wave) at the filter’s corner frequency, the output signal is up to
full amplitude within 5 or 6 periods, for both filters. When the input signal
is turned off, the ringing characteristics of both filters are also essentially
identical, with the signal dying away within 5 or 6 periods.<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'>From this, I conclude that I can get the
same results that Jurgen Haible got with about half of the filter hardware, as
I suspected. This is nice, since I have already laid out and built a PCB with
12 of these 4-pole BP filters on it for a fixed filter bank, and I can use the
exact same layout for the vocoder.<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 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weight:bold'>From:</span></font></b><font
size=2 color=black face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
color:windowtext'> Synth-diy [mailto:synth-diy-bounces@synth-diy.org] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Magnus Danielson<br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, September 01, 2019
11:25 PM<br>
<b><span style='font-weight:bold'>To:</span></b> synth-diy@synth-diy.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [sdiy] vocoder
filters</span></font><font color=black><span style='color:windowtext'><o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
<p><font size=3 color=black face="Times New Roman"><span style='font-size:12.0pt'>Dear
David,<o:p></o:p></span></font></p>
<p><font size=3 color=black face="Times New Roman"><span style='font-size:12.0pt'>Many
other vocoders used higher Q setups, and Jürgen and I agreed that you need to
avoid that. The reason is that higher Q gets you into higher group delay,
making the filter more sluggish to respond and rings longer after the end of a
sound. It also causes different time-shifts between bands to become bigger than
if you use low Q.<o:p></o:p></span></font></p>
<p><font size=3 color=black face="Times New Roman"><span style='font-size:12.0pt'>Jürgen
was inspired by the EMS3000 vocoder until I sent him the EMS5000 manual and
schematic, which derailed the project a little. :)<o:p></o:p></span></font></p>
<p><font size=3 color=black face="Times New Roman"><span style='font-size:12.0pt'>So,
it is not recommended to go for higher Q, and I think you get why.<o:p></o:p></span></font></p>
<p><font size=3 color=black face="Times New Roman"><span style='font-size:12.0pt'>Cheers,<br>
Magnus<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>On 2019-08-31 06:05, David G Dixon wrote:<o:p></o:p></span></font></p>
</div>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt' type=cite
cite="mid:A31B78DEC0A64298AE8ACA5A1D3F182D@david78c70950b">
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'>Hey SDIY Team!<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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).<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black 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.<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'>Cheers,<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'>Dave Dixon<u1:p></u1:p></span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><br>
<br>
<o:p></o:p></span></font></p>
<fieldset class="mimeAttachmentHeader"></fieldset><pre><font size=2
color=black face="Courier New"><span style='font-size:10.0pt'>_______________________________________________<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>Synth-diy mailing list<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'><a
href="mailto:Synth-diy@synth-diy.org">Synth-diy@synth-diy.org</a><o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'><a
href="http://synth-diy.org/mailman/listinfo/synth-diy">http://synth-diy.org/mailman/listinfo/synth-diy</a><o:p></o:p></span></font></pre></blockquote>
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