> > No practical filter, digital included, will have a cutoff that sharp. It
> > *could*, but that causes all sorts of other problems (like serious ringing
> > throughout the spectrum).
>
> Are there any rules of thumb for an appropriate frequency range that
> the filter should act on?
Depends on the filter you're using, but for the most part you just have to
evaluate and decide.
FIR filters ring more as they sharpen (and you're already unavoidably suffering
from this to some extent because of the subbanding). It's easy enough to see
by plotting it out...
IIR filters cutoff more sharply with less edge weirdness, but they introduce
phase non-linearity (and additional coder delay).
Simply taking an axe to the frequency spectrum (and dropping the lowest and
second lowest coeffs) will likely cause very nasty edge effects.
Monty
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