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.
Controls
- Wave switches the oscillator between saw and square.
- Tune shifts the pitch by up to an octave either way.
- Cutoff and Reso set the filter's base frequency and how much it rings. High resonance is where the acid voice lives.
- Env Mod sets how far each note's envelope sweeps the filter above the cutoff, and Decay how long that sweep lasts: short for a percussive blip, long for a sustained sweep.
- Accent sets how strongly hard-played notes lift the filter and level.
- Volume sets the output level.
The second row holds the extended controls:
- FB HP is the high-pass in the resonance path. Around 150 Hz is the classic value; raise it to thin the squelch, lower it to fatten it.
- Acc Decay is a separate filter decay for accented notes, so accents can be snappy while normal notes sustain.
- Soft Atk and Amp Decay shape the level of each note: a softer onset and how long the note rings.
- Slide sets the glide time between notes.
- Drive adds saturation after the filter.
Voice controls above the panel switch between Monophonic (the default), Mono Legato and an eight-voice Polyphonic mode, set which held note wins, and choose when notes slide automatically.
Getting started
Acid Bass plays from your computer keyboard or a MIDI controller. Start with Classic Acid, hold a low note and turn Cutoff and Env Mod while you play. Squelch and Hard Acid push resonance and accent much further; Soft Bass is a rounder, gentler starting point.
The panel also has a 16-step pattern grid with Gate, Note, Accent and Slide rows for sketching a line. For now the pattern stays in the panel and is not saved with presets.
