Acid Line Generator
Squelchy 303-style lines with slides, accents and octave jumps. Generate one, tweak the steps and the filter, then take the MIDI to your 303 plugin.
Steps
Click a note to step it up the scale, Shift-click (or right-click) to step it down, or hover and use the mouse wheel. On plays the step, Oct jumps an octave up or down, Acc accents it and Slide glides into the next note.
Sounds to load your MIDI into
Supersaw Essentials: 25 free trance presets for Vital, the free synth. Leads, plucks, pads and gated stabs, voiced for every tool on this site.
How an acid line works
The acid sound comes from the Roland TB-303: one oscillator, a resonant low-pass filter and a short envelope that snaps the filter open on every note. What makes a line squelch isn't the notes so much as three things on each step.
Accent hits the step harder: louder, with the filter thrown further open and closing faster, so it barks. Slide holds the note into the next one and glides the pitch across, without retriggering the filter, which gives acid its rubbery, talking quality. Octave jumps move a step up or down an octave for bounce.
Most of the movement in a real acid track comes from turning the cutoff, resonance and env mod while it plays. Switch on Filter sweep to hear the cutoff open and close over four bars, then automate the same thing in your DAW.
Using the MIDI with a 303 plugin
Accents are exported as velocity 127 and normal steps as velocity 90. Slides are notes that overlap the next one, which is how most 303 emulations (ABL3, Phoscyon, TB-303 plug-outs, TAL-BassLine-101 in mono legato mode) read a slide. Set your plugin's accent to respond to velocity and its glide to legato, and the line plays as it does here.
No 303 plugin? Use any mono synth with a single saw, a resonant 24 dB low-pass, a short filter envelope and legato glide. The free Vital Preset Generator's rolling bass makes a decent start: open the resonance and shorten the decay.
Questions
Which styles can it make?
Acid trance (rolling 16ths with plenty of slides), tech trance (sparser, harder accents and octave jumps), psy acid (busy, root-heavy and in the Phrygian scale) and classic 303 (the wandering, jacking lines of the late 80s).
Why does my plugin not slide?
Most 303 emulations only slide when notes overlap and the synth is in mono or legato mode. Check that legato or glide is on, and that your DAW hasn't trimmed the overlapping notes when you dropped the MIDI in.
What key should an acid line be in?
The same as the rest of the track. Most acid lines sit on the root and jump to the octave, the fifth or the minor third, so they work over almost any trance progression in that key.
Can I use these lines in released music?
Yes. The MIDI you export is yours to use however you like.