800px-TB303 Front View

Front panel of the TB 303.

The Roland TB-303 'Bassline' Synthesizer is a monophonic synthesizer produced by from 1981 to 1984. Although originally designed for accompaniment to guitarists, it was often used to create a harsh acid like sound generated by playing a repeating note pattern and modulating the cutoff, frequency and resonance.

Today the TB 303(and its clones) are most often used for the production of Psytrance and Acid House.