I think you answered your own question. Normal arrays of 2 pole
bandpass filters would have a large amount of band overlap due to
their rather gentle slopes . If you use an array of high Q filters,
the bands would be so narrow that you'd have to use a zillion of them
to cover the spectrum. A good compromise is to use a 2 pole filter in
the center of the band, with a high Q filter at the upper and lower
edge of each band to "square the corners" and maximize the separation.
Moe
>>>>>
Out of curiosity, what sort of response is this and why is it good for
vocoders? (I would guess that for vocoder channels you'd want plenty
of discrimination between channels.)
<<<<<
>
> A typical BPF (like the Emu UAF, Oberheim SEM filter in BPF mode,
> and many many similar filters) are two pole designs. For a good
> vocoder filter (a single vocoder BPF!) you'd connect 3 such filters
> in series, two of them with the same Q factor, the 3rd with a
> different Q, and center frequencies spread such that the "middle"
> filter is halfway between the "outer" filters on a log frequency
> scale. Two such blocks are needed for analysis and synthesis of one
> channel, and 20 channels were a good choice for the "classic"
> Sennheiser vocoder.