A monophonic acid bass synthesizer in the spirit of the Roland TB-303: one oscillator, a resonant ladder filter that squelches, and the accent and slide that turn a simple bassline into acid.
The idea
The TB-303 was sold in 1981 as a practice bass for guitarists and flopped. A few years later, producers in Chicago found that its resonant filter, swept hard and played with accents and slides, made a sound nobody had heard, and acid house was built on it. Acid Bass keeps that small performance vocabulary.
The oscillator morphs continuously from saw to square. It runs into a four-stage low-pass ladder that saturates as you push it, with a high-pass in the resonance path so the squelch never swamps the fundamental. A decay envelope sweeps the cutoff on every note, and the whole voice runs at four times the sample rate to keep high sweeps clean.
Accent is not just a louder note. Notes played hard open the filter further and get louder at the same time, which gives accented steps their "wow". Slide glides the pitch from one note into the next instead of jumping.
