The Doepfer A-128 is a fixed filter bank for the Eurorack A-100 system. It is made up of 15 parallel band pass filters, each with their own attenuation control. Each of the bands is extremely narrow which means the overall tonality of a signal can be finely tweaked through to extreme effects such as bandwidth limiting like a telephone through to vocoder like effects. It’s basically an EQ that can attenuate most parts of the signal, leaving only a narrow portion of the signal left on any one of the fixed frequencies between 50Hz and 11kHz.
