ACID

Acid house is a variant of house music characterized by the use of simple tone generators with tempo-controlled resonant filters. It began in the mid-1980s, when producers of house music discovered that they could create interesting sounds with the Roland TB-303 analogue bass synthesizer by tweaking the resonance and frequency cut-off dials as they played. Acid house music became a central part of the early rave scene in the U.K., and the yellow smiley became its emblem.
There are conflicting accounts about how the term "acid" came to describe this new style of house music. Some believe the term refers to LSD, and that early producers of the music, as well as people at clubs where the music was played, enjoyed the drug and its interaction with the music. Others say that the term was used in Chicago at the time as a term for the squelchy sounds of such bass synthesizers such as the TB-303, and has no connection to drugs at all. Some claim that the acid house scene did have a connection to psychoactive drugs, but that the substance of choice was Ecstasy (MDMA), not LSD.