Module A-128 (Fixed Filter Bank) is a filter bank, made up of 15 parallel band pass filters, all with fixed middle frequencies and bandwidth (50 Hz / 75Hz / 110Hz / 150Hz / 220Hz / 350Hz / 500Hz / 750Hz / 1.1kHz / 1.6kHz / 2.2kHz / 3.6kHz / 5.2kHz / 7.5kHz / 11 kHz).

Each band pass filter has its own amplitude control knob, with which that frequency band can be attenuated. The bandwidth of each of the filters is approximately half an octave.

The signal at the output of the A-128 contains a mix of all the filters, depending on the position of each one's amplitude control knob.

The filter bank's main job is to emphasise individual sections of the whole audio frequency range.