[sdiy] Fw: Low Cost Comb Filter Methods

[Juan Bermúdez Costa]

Thank you for the profuse explanation and for preserving the moral and legal 
integrity intact ...
Juan Bermúdez

----- Mensaje original ----- 
De: "Ben Bradley" <ben.pi.bradley at gmail.com>
Para: "*SYNTH DIY" <synth-diy at synth-diy.org>
Enviado: lunes, 11 de junio de 2018 4:43
Asunto: Re: [sdiy] Low Cost Comb Filter Methods


>I have these articles (I have a 13-CD set of JAES archives for cheap,
> an amazingly lucky hamfest find). I think I can describe them here
> adequately without running into legal or moral problems.
>
> In short, this "comb filter" is a bunch of spaced-out-in-frequency
> analog bandpass filters, similar to those in graphic equalizers, but
> with substantially higher Q. The thread from last year (see the last
> paragraph below) is, IMHO, actually more informative than both of
> these articles.
>
> The first article describes an op-amp-based bandpass filter with
> trimpots to change frequency and bandwidth. There's a PC board shown
> with a quad opamp and R's and C's making up four such filters (and
> thus 8 trimpots). The author made nine of these boards (I doubt this
> was "low cost" back then), with each filter having different R and C
> values. There's a table giving the resonant frequency and  component
> values for each frequency. The frequencies for the 36 filters range
> from 50Hz to 9000Hz, in an approximate geometric progression so that
> there are about four filters per octave.
>
> The second article describes a clavichord with its output going
> through this filter.
>
> Both articles have references to previous JAES articles, but the
> second one also has this to an article by the author in Electronotes:
> [5] R. W. Burhans, "Non-Uniform Comb Filter Spacings with Respect to
> Equally Tempered Scales," Electronotes, vol. 5, pp. 15-16 (June 20,
> 1974).
>
> There was a discussion on SDIY just last year of this type of filter
> bank (used to simulate the many resonances in an acoustic instrument),
> and many posters had something to say about it. The subject is:
> Resonator type filters, started 6/29/17.
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