[music-dsp] [a teeny OT] What is a "filterbank" exactly?

[robert bristow-johnson]

On 04/09/2004 20:31, Nigel Redmon at earlevel at earlevel.com wrote:

> Just quick note in addition to the other comments. The example you are
> using may well be implemented as a serial set of peaking filters
> instead of a parallel set of bandpass filters. This is just an "on the
> way out the door" comment, and not intended to address the "what is a
> filterbank" question, but I'm sure some people aren't aware that you
> can't necessarily sum filters in parallel and get what you expect,
> because of cancellations and peaking due to phase shift from the
> filters.
> 
> For instance, I've seen people take a shelving filter such as 1 + H /
> (s^2 + sqrt(2) + 1) and split the "1" off (direct signal), do the
> low-pass part, and add them back together--but that doesn't work very
> well.

you won't get pretty monotonic behavior, but i remember reading or hearing
somewhere (Digi, Waves maybe?) that this simple shelf (with a dip in it) is
"more musical", whatever the hell that means.

> Similarly, adding a biquad bandpass to a direct signal doesn't
> give you the pretty peaking filter you'd expect.

it doesn't??!!  how can that be?  what am i missing, Nigel?

r b-j