Phuture - Acid Tracks
At about 1:10, the acid bass, produced with a TB-303, enters the song.
Roland released a bass synthesizer with a built-in sequencer in 1981. It was a monophonic, monotimbral synthesizer called the Roland TB-303 Bass Line, and it came with several dials for things like its low pass filter. The TB-303 was instrumental to the development of house music, influencing Chicago house. But its famous acid bass sound became a staple of acid house, which used this specific sound quite loyally.
The acid bass is mostly a square wave based plucking-stylized synth, although some renditions may incorporate sawtooth, as well. The defining characteristic of the synthesizer is the progression of the filter as it is applied to the synth. Gradually the low pass filter swallows the boop-like drone of the square wave when its cutoff is low. But because of the resonance of the filter being so high, the acid bass can express its secondary squelching trait by turning the cutoff back high. Acid musicians would modulate these settings throughout their song through gradually-changing envelopes or with rapid movements in sequencers.
Recreations[]
The acid bass is made of such fundamental components that it can be remade in nearly any synthesizer.