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MPC OS. This release works on MPC OS 3.x. On MPC OS 2.x it loads and plays from the Q-Links, but its touchscreen page stays empty until a release with a compatible skin is published. The catalog shows which MPC OS each release works on, and the installers warn before putting a 3.x-only plugin on a 2.x device. See MPC OS 2.x vs 3.x in the main repo.
A TB-303-style acid bassline sequencer for the Akai MPC OS built-in plugin host. It generates two bass lines, lets you blend between them, and plays them over MIDI into a synth track. Acid makes no sound itself. It is a native VST2 plugin with a touchscreen skin and Q-Link control.
Version 2.0.0 · GPL-3.0-only · by sd88me
- Add Acid to an instrument track from the plugin browser.
- Acid plays through a MIDI output port named Acid (a second instance is Acid 2). On the track you want to hear it, set the MIDI input to that port and set MIDI CH to the channel that track listens on.
- Press GENERATE on SEQ A, and on SEQ B if you want a second line, then start the transport.
The screen has six tabs: SEQ A, EDIT A, SEQ B, EDIT B, MOD and GLOBAL. The Q-Links follow the tab you are on.
Each line is an independent sequencer of 2 to 32 steps. Both follow the MPC transport: every 16th is placed from the song position, so starting mid-song, looping or locating keeps Acid on the grid. The controls are the same on both pages. Q-Links 1-8 turn the eight knobs in the order they appear (the grid left to right, top row then bottom), then GENERATE, MUTATE, BLEND, MIDI CH, REGEN and DIR.
| Control | What it does |
|---|---|
| GENERATE | Pick a new random seed and start a new pattern. Clears every locked step (see EDIT) |
| MUTATE | Nudge about 25% of the steps in place (rest/note, pitch), keeping the pattern recognisable. Repeat it to keep evolving. Mutated steps are locked, so they survive knob moves |
| DENSITY | Chance that a step is a note rather than a rest |
| ACCENT | Chance that a note is accented (louder) |
| SLIDE | Chance that a note slides into the next step, 303-style. A slide into a rest becomes a plain note |
| OCTAVES | How many octaves above the root the pitches can span, 1 to 3 |
| ALGO | 1 is the classic density/accent/slide model. Higher values blend in a second generator (non-repeating pitches, clustered runs of notes and rests, pyramid accents), up to 16 |
| LENGTH | Steps before the pattern loops, 2 to 32. It takes effect at once. GENERATE to fill a longer pattern with new steps |
| GATE | Note length as a fraction of a step. It is live, and held slides ignore it |
| OFFSET (A) / TUNE OFFSET (B) | OFFSET rotates which step plays without rewriting the pattern. TUNE OFFSET sets B's interval relative to A, ±24 semitones (+7 is a fifth above, -12 an octave below) |
| DIR | Forward, reverse, or pendulum (bounces off each end) |
| REGEN | Re-roll automatically every 1 to 32 bars, or off |
| MIDI CH | MIDI channel the line plays on |
| BLEND A>B | The same control as on GLOBAL |
DENSITY, ACCENT, SLIDE, OCTAVES, ALGO, LENGTH and SCALE reshape the playing pattern live from the current seed, so you can sweep them without losing its character. Returning a knob to the same value gives back the same pattern. Only GENERATE picks a new seed. Patterns saved with 1.0.x will sound different, because the same seed now maps to a different pattern.
Each line has an edit page, next to its SEQ page, with 16 steps at a time. A yellow marker above the step numbers follows the playing step (on the bar you are viewing). The 16 Q-Links turn the 16 NOTE sliders. The STEPS 1-16 / STEPS 17-32 switch picks which bar of a longer pattern you see. Per step:
- ON switches the step between a note and a rest. A rest keeps its note, so switching it on brings the note back.
- NOTE is a vertical slider in scale steps from the root. 0 is the root, in the middle, and the slider reaches two scale octaves (14 steps) above and below it.
- ACC and SLIDE are independent, so a step can be both, as on a 303. GENERATE rolls them independently too.
- LOCK marks a step as hand-edited. A locked step keeps its note, accent and slide when DENSITY, ACCENT, SLIDE, OCTAVES, ALGO, LENGTH or SCALE reshape the pattern. Editing a step locks it. Tap LOCK to hand it back to the knobs.
Locks are saved with the project and cleared by GENERATE and REGEN.
Two LFOs, each with two modulation slots. Per LFO: SHAPE (sine, triangle, saw, square or sample and hold), RATE (0.05 to 20 Hz) or, with SYNC on, a cycle of 1/4 note up to 16 bars locked to the song position. Each slot has a destination and an AMOUNT from -100 to +100. Destinations are DENSITY, ACCENT, SLIDE, OCTAVES, LENGTH, GATE and OFFSET on either line, plus BLEND. Your knob values are never changed, so the knobs and the saved project show your own settings. The pattern follows the modulation, so the edit pages move while an LFO is on density, accent, slide, octaves or length. Q-Links 1-8 are LFO 1 and 9-16 are LFO 2.
| Control | What it does |
|---|---|
| SCALE | Scale both lines quantise to: Minor, Phrygian, Harmonic Minor, Minor Pentatonic, Dorian, Major, Phrygian Dominant, Locrian, Whole Tone, Hungarian Minor, Minor Blues or Chromatic (no scale) |
| ROOT | The key both lines play in, C to B |
| SWING | 16th-note swing from 50% (straight) to 75%, shared so the lines stay locked |
| JITTER | Chance per step of perturbing which step plays, never when: skip a step, repeat the last one, or jump to a random one. 0 is off |
| RESET ALL | Every 1, 2, 4 or 8 bars, snap both patterns back to step 1 together. Off lets patterns of different lengths drift as a polymeter |
| BLEND MODE | How A and B merge into one mono line, decided step by step (see below) |
| BLEND A>B | Sweeps from A to B, from -63 (A only) to +64 (B). How it acts depends on BLEND MODE |
| CV MODE | Sends both lines to a Force CV track for external CV/Gate hardware instead of a MIDI synth |
Except in LAYER, A and B are merged into one mono line, so a synth on a single track plays one note at a time. The other line is muted on each step, so notes never overlap. BLEND A>B sweeps in a fixed, evenly spread order, so the hand-over is repeatable rather than random.
| Mode | Result | BLEND A>B |
|---|---|---|
| LAYER | Both lines play together as two voices, crossfaded by velocity. It is the only mode that isn't a single mono line | Fades the velocity from A to B |
| MORPH | Each step comes from A or B | -63 is A only, +64 is B only |
| SPLIT | Rhythm, slide and accent from A, pitch from B | -63 is A only, +64 is all pitches from B |
| FILL | A plays, and B fills A's rests | -63 is A alone, centre is the fill result, +64 is B alone |
| XOR | Plays only where exactly one line has a note: interlocking, syncopated | Same sweep as FILL |
| LOCK | Plays only where both lines have a note: sparse and tight | Same sweep as FILL |
| CHAIN | Call and response: A plays a full pass, then B answers with a full pass | Snaps to real pass ratios, 8:1 down to 1:1 and on to 1:8, plus A only and B only. A readout above the knob shows the current ratio |
Settings are saved with your project.
- A first-generation MPC OS standalone device (32-bit ARM): Force, MPC Live / Live II, One, X or Key 61. Tested on a Force. Newer models are untested.
- Root SSH access to the device. Stock MPC OS doesn't offer it, so this is for modded units.
- Installing plugins this way is unofficial. Back up first and use it at your own risk.
- Download
Acid-<version>-mpc-armv7.zipfrom the Releases page and unzip it. - Copy the folder to the device:
scp -r Acid-2.0.0 root@<device-ip>:/tmp/ - Run the installer:
ssh root@<device-ip> sh /tmp/Acid-2.0.0/install.sh
The installer stops MPC (save your project first), copies the plugin and skin, backs up
MPC.settings, registers the plugin and restarts MPC. Run it again to upgrade in place. Add -y to skip
the confirmation. uninstall.sh in the same folder removes it. INSTALL.md in the zip covers
installing by hand.
vst/build.sh # armhf build in Docker: vst/build/acid.so, the skin, pluginlist-entry.xml
vst/test.sh # offline x86 host test under ASan/UBSan; must print OK / PASSED
Both need sd88me/mpc-vst-plugins checked out next to this repo (../mpc-vst) or MPC_VST=/path set, for the
shared skin tools. Releases are built by the "VST release (draft)" GitHub Actions workflow using
mpc-vst-plugins' shared vst-release.yml.
src/: the generation engine (acid_core.c/.h), vendored fromsd88me/force-acid(seesrc/VENDORED.md)vst/: the plugin (acid_vst.cpp, MIDI out over ALSA seq), skin config (vst.json,layout.conf,module.json,skin.css,fonts/) and the build and test scripts
Acid is the MPC counterpart of the Force Shadow addon in sd88me/force-acid and uses the same engine.
- Pattern model: the density / accent / slide / octave generator (ALGO 1) is a port of the TB-3PO model, via
schwung-tb3poand the Phazerville TB_3PO applet. - Second generator: ALGO values above 1 blend in a generator inspired by the Sting.amxd Max for Live device (non-repeating pitch draw, a random walk that clusters notes and rests, and the "VelPyra" accent shape).
GPL-3.0-only. See LICENSE.