Roland TB-303

The TB-303 was a synthesiser/sequencer produced by the Roland corporation in 1982 that had a crucial role in the development of contemporary electronic music. The well-known "acid" sound can be produced with a TB-303 by playing a melody while changing the cutoff[?], frequency, envelope modulation[?] and accent controls on the filter.

The unit used a half cosine wave[?] (i.e. from 0 to 180 degrees repeating) or a square wave[?] (which is actually not really a square but an alternation between a regular saw and a saw upside down) (switchable between the two) and used a lowpass filter[?] with a rolloff of -18 dB per octave.

It also featured a 'simple' step-time method for entering note data into the programmable sequencer. This was notoriously difficult to use, and would often result in entering a different sequence than the one that had been intended - some users also take advantage of the quirky fact that when the batteries are removed for a certain period, patterns that are programmed in memory begin to vary in random ways - one of the factors that helped to create the randomish "Acid" sound.