band [-n] center[k] [width[h|k|o|q]]
width parameter gives the slope of
the drop. The frequencies at center + width and center - width will
be half of their original amplitudes.
band defaults to a mode oriented to pitched audio, i.e. voice,
singing, or instrumental music. The -n (for noise) option uses
the alternate mode for un-pitched audio (e.g. percussion).
Warning: -n introduces a power-gain of about 11dB in the filter,
so beware of output clipping. band introduces noise in the
shape of the filter, i.e. peaking at the center frequency and
settling around it.
See also sinc for a bandpass filter with steeper shoulders.