One of the best known modular systems is probably Roland's System-100m , which was built from 1979 to 1984. The manageable number of modules and especially the presence of several functions per module made it an attractive instrument for many users. Behringer has transferred the classic dimensions to the compact Eurorack format and has taken great care to ensure that sound and function are in no way inferior to the cult object.

The Behringer 121 Dual VCF is a double 24 dB lowpass filter with a resonance-free highpass filter. The HPF cuts off at 1 KHz, 2 KHz or 5 KHz and of course can be deactivated. The three signal inputs are the audio mixer before the filter. The filter can be modulated via three control voltage inputs.