[sdiy] Weird Vocoder project

[JH.]

The "better" Vocoders used even higher order filters:
Sennheiser: 6-pole (3 detuned BPF-filters per channel)
EMS 2000 / 3000: 6-pole (detuned)
EMS 5000: 8-pole (probably detuned)
Synton (big one): 8pole (not detuned)

JH.


----- Original Message ----- 
From: "Ian Fritz" <ijfritz at comcast.net>
To: "Magnus Danielson" <magnus at rubidium.dyndns.org>; <tom at electricdruid.net>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Monday, May 28, 2007 6:00 PM
Subject: Re: [sdiy] Weird Vocoder project


At 09:22 AM 5/28/2007, Magnus Danielson wrote:

>A typical vocoder analyzer channel will use a dual-resonance (4-pole) 
>bandpass
>filter where as a graphical EQ uses typically a single-resonance (2-pole)
>bandpass filter. The dual-resonance peaks are spread such that you acheive 
>an
>approximation of a flat pass-band with a little responce-dip inbetween. The
>slopes at the resonances are steeper than the bandpass roll-offs would 
>allow,
>and since the non-resonant gain is set to damping, those slopes is
>considerably
>below the detection level. Those, response-wise they are quite different
>animals.

Yes, this is a very important point.  If you use hi-Q but low-order filters
you may run into a problem because the low-order filter response has fairly
strong tails away from the resonant frequency.  When you have 30 of these
piled up you get a significant background signal.  I learned this from my
36-stage fixed frequency filter bank. :-(

   Ian

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