TB-303 is a synthesiser/sequencer produced by Roland in 1982. The TB-303 had a crucial role in the development of contemporary electronic music. The well-known "acid" sound can be done with a TB-303 by playing a melody while changing the cutoff, frequency, envelope modulation and accent on the filter. The unit used a sine wave or a pulse wave and used a 2-pole lowpass filter. It also featured a simple step-time method of entering note data into the programable sequencer.