A band-pass is two boundaries at once: a center frequency, a bandwidth, and everything outside the window fades. Voices through old telephones are the canonical sound, all body and air removed.
For analysis, a bank of band-passes is the classic way to split music into bands without a full FFT: eight filters, eight envelope followers, eight control signals. Analog light organs of the 1970s did precisely this in hardware, three filters driving three lamp colors.
Modern visualizers mostly get bands by grouping FFT bins instead, but the band-pass mental model survives because it is the right way to think about the routing: this slice of the spectrum drives that element of the image.