Acid line

The Propellerhead ReBirth TB-303 clone
The Propellerhead ReBirth TB-303 clone

From the squelchy riff throughout Luke Vibert's Analord to the screaming lead of Phuture's Acid Tracks, acid lines are a popular element of many dance songs, even spawning the whole genre of acid house. Most are played on the Roland TB-303 bassline synthesiser or one of its clones, although they are seldom basslines. So what exactly are they?

There doesn't seem to be a clear definition of an acid line, but they tend to share two common characteristics: firstly, they use repetitive notation; and secondly, they employ a filter that has a moving cutoff point.

Acid lines were first played on synthesisers which had step sequencers, and due to the technical constraints of the era in which they were created, the first acid lines tended to be up to sixteen notes or rests in length. Although the technology used to create electronic music has since improved, acid lines often still retain this characteristic simply because it is part of a style that has become very popular.

The other main characteristic of the acid line, the filter, is almost always of the low pass variety. The resulting sound depends on the synthesiser used and the exact type of filter that it has, but in general the effect is of the timbre getting duller as the cutoff point is lowered, and brighter as it is raised. If the filter's resonance is turned up and the synthesiser is overdriven, the effect can be accentuated to the point where it sounds less like an instrument increasing in brightness and more like some kind of twisted machine that's in increasing levels of distress.

The following songs have notable acid lines:

For more examples of acid lines, you can hunt down pretty much any release by Hardfloor, Plastikman, or Luke Vibert. All three have released countless tracks that exemplify the sound.