[sdiy] vocoder filters

David G Dixon dixon at mail.ubc.ca
Sat Aug 31 06:46:18 CEST 2019

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).


I'd still appreciate if anyone has any specific insights into this problem.



From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of David
G Dixon
Sent: Friday, August 30, 2019 9:05 PM
To: synth-diy at synth-diy.org
Subject: [sdiy] vocoder filters


Hey SDIY Team!


I'm thinking about building a vocoder, and I have a general question about
the bandpass filters.


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.


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).


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.



Dave Dixon

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