A bandpass filter is a type of algorithm that takes some input sound-file and returns only the information within a certain frequency range, or 'frequency band'. This implementation has six bandpass filters in parallel with flexible centre frequency and bandwidth. This is similar to the comb filter bank in that you can create the 'speaking chord' effect, although the effect is less 'buzzing', and more a kind of 'stroking' effect - rather similar to an Aeolian harp.

Here is a spectral plot of the filterbank effect:

Centre Frequency: Each filter allows a centre frequency to be set (in Hz). By clicking on the piano keyboard icon, this may be set in equal temperament.
Bandwidth: This is the frequency distance with which the filter loses 6dB.