bandpass [-c] frequency[k] width[h|k|o|q]
frequency, and (3dB-point) band-width
width. The -c option selects a
constant skirt gain (peak gain = Q) instead of the default:
constant 0dB peak gain. The filter rolls off at 6dB per octave
(20dB per decade).
See also sinc for a bandpass filter with steeper shoulders.