Move a knob while it loops

The documented origin story of acid house is an instruction manual for this recipe: in Chicago around 1985–87, Phuture (DJ Pierre, Spanky, Herk) let a secondhand TB-303 loop a pattern and turned the knobs while it played — "Acid Tracks" is twelve minutes of that. The lesson generalizes: an acid line is not a melody with a sound; it is a loop plus a hand. The pattern's job is to give the couplings something to chew on — accents for the bloom, slides for the vowels — and the performance is cutoff, resonance, and envmod moving in real time.

Everything measured here is borrowed from the acid machine chapter and its notebooks (tb303.ipynb, step_seq.ipynb).

The scaffold

phasor~ (BPM/240) ──▶ tap.303.seq~ ──pitch──▶ tap.303~ ──▶ out
                                  └──gate───▶   (right inlet)

One bar of 16 steps per phasor cycle (BPM ÷ 240, the drum scaffold's math); ~125 BPM → phasor~ 0.5208. The sequencer's pitch and gate outlets are the voice's own contract — accents ride the gate at 2.0, slides are pitch changes under a held gate, so the voice's ~60 ms RC does the glide.

A line to start from

Program per step (step <n> <pitch> [accent] [slide], rest <n>) or per lane. A serviceable opener in A — and, as everywhere in this part, a starting point, not a transcription:

step:    1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16
pitch:   33 33 45 33 33 36 33 31 33 33 45 47 33 33 31 36
gate:    x  x  x  x  .  x  x  x  x  x  x  x  .  x  x  x
accent:  A  .  .  A  .  .  A  .  .  A  .  .  .  .  A  .
slide:   .  .  .  .  .  .  .  S  .  .  .  S  .  .  .  .

pitches 33 33 45 33 33 36 33 31 33 33 45 47 33 33 31 36
gates   1 1 1 1 0 1 1 1 1 1 1 1 0 1 1 1
accents 1 0 0 1 0 0 1 0 0 1 0 0 0 0 1 0
slides  0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0

The ingredients that make it acid rather than bass: the octave jumps (33 → 45), at least one slide into a note (the flag sits on the target step), rests that let the filter close, and accents placed where the groove leans — not where the melody peaks.

The voice

recall 1 is the factory "squelch" and a fine start. Explicitly:

@waveform saw @cutoff 500 @resonance 0.9 @envmod 0.7 @decay 300 @accent 0.8

Then the moves, in the order a set builds:

  1. Ride cutoff. 300 → 2000 Hz over eight bars and back. This is the genre. Remember the modeled envmod law: 2/3 of the envelope's sweep sits above the knob, 1/3 below, and the resting point shifts as you turn it — the knobs interact like the hardware because the interaction is modeled.
  2. Stack the accents. Runs of accented notes at high resonance are the wow: the C13 capacitor doesn't fully discharge between close accents, and the measured cutoff-peak bloom across a run is ×1.94. Put three accents in a row somewhere and listen to the third one open.
  3. Raise resonance into the break. Past 1.0 is the documented bend territory — a stock 303 never self-oscillates, and neither does this filter until you push it there deliberately.
  4. waveform square for the hollow verse, saw for the drop.
  5. vca warm thickens exactly where the hardware does — measured 5.4 % difference signal on quiet notes, 11.5 % on hot accents.
  6. Transpose, don't re-program: transpose -12 on the sequencer for the sub-drop, +5/+7 for the question-answer sections. It shifts live, like the hardware's transpose mode without the mode.

After the voice

Acid techno's other instrument is the distortion pedal: tap.overdrive~ after the voice, driven hard, is the documented lineage (a 303 into a screaming feedback overdrive is half the harder end of the genre). Keep mute in reach on the sequencer for breakdowns — it drops the gate but the clock keeps running, so the line re-enters exactly in place.

When to leave the recipe

  • You're programming melodies. If the line only sounds right without slides or accents, it isn't an acid line yet — or it wants the generic bass rig (tap.vco~ + tap.svf~ + tap.adsr~) instead of this voice's refusals.
  • You want the filter alone — tap.diode~ gives you the 303's ladder on any source, squelch and all, without the biography.
  • You want hands-free evolution. The 303 rewards a hand on a knob; if the patch must run itself, store extremes in the voice's preset slots and ride timed recall morphs instead — a different instrument, honestly.