[sdiy] Why Bands for String Filters and Narrow and Numerous

[Elain Klopke]

Most certainly interested :)

On Fri, Jun 30, 2017 at 1:11 PM, Bernard Arthur Hutchins Jr <
bah13 at cornell.edu> wrote:

> Tom Asked Fri, 30 Jun 2017 : Is there some reason why string filters use
> a large number of fixed bands, rather than fewer variable ones?
>
>
> Simply, the filters are sharp (narrow), so you need a lot of them (say
> 40) to span (overlap) a wide enough processing bandwidth. So (you rightly
> demand!) why do they need to be sharp? For achieving dynamics, either the
> filter frequencies or the input frequency typically needs to move.  (Else
> you are merely waveshaping one boring fixed shape to another.) Moving all
> the filter frequencies is of course impractical while moving the input
> is basically just FM of a VCO.  If you have only a few broad filters,
> AND FM depth is small (typically achieving an animated dynamic sound like
> tremolo), very little equivalent AM (harmonics moving up and down BP
> slopes) is achieved. With lots of sharp filters, lots of relatively large
> motions are achieved (some up, some down, some flat).
>
>
> The other application is as a formant filter.  (That is, not FM, but
> note-to-note spectral shape changes.)  The ability to get lots of detail
> (with adjustable depth) is useful, and variable Q, ALL 39 filters with
> one control (overall feedback), was demonstrated in my
> Electronotes EN#115 filter bank. I will see if I can post this if anyone is
> interested.
>
>
> -Bernie
>
>
>
>
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