An electro swing workstation with a generative songwriter. The rhythm guitar and the swing kit are sampled — velocity layers and round robins, shipped with the app, so it runs with no network. The upright bass, the sub, the horn section, the clarinet and the keys are generated by a four-operator FM engine. What they go through is modelled: a gypsy-jazz guitar body, microphones, a gramophone horn, vinyl, tape — and the club under all of it.

Quick start

1. Hit Write a Song — it arranges a whole record and plays it.
2. Change Style, Key, Scale, Tempo or Density, then write another.
3. Export it as MP3, WAV or MIDI.

Loop repeats the song; Auto-next writes a new one when it ends, after the ring-out — measured from where you left the delay and reverb, not guessed.

Two records at once

Electro swing is a band from the 1930s and a producer from this century, and every song here is arranged as both. Old-record sections are the band as a gramophone heard it: band-limited, horn-resonant, mono, crackling, the kit keeping time on a ride cymbal and the upright walking. Club sections are the same band with a four-on-the-floor kick under it, the whole band pumping around every kick, the bass bouncing on the off-beats and the horns cut into stabs. Between them is a build: the gramophone opening up over four bars, a riser, a snare roll, and half a beat of nothing for the drop to land in.

The producer's beat is the one thing that never goes through the gramophone, the tape or the pump. That is why the drop sounds like the present arriving: everything else changes, and the beat was already there.

Styles

• Electro Swing — dorian vamps, la pompe, a walking bass that turns into a bounce, horn stabs and a clarinet or trumpet hook.
• Hot Club House — Django's harmonic minor, two Selmers, a gypsy-guitar lead and an accordion under the drops.
• Big Band Boogie — rhythm changes and the blues, a Freddie Green four, stride piano, background figures and a shout chorus.
• Jump Blues — twelve-bar forms, a shuffle, boogie-woogie bass and piano, riffs in unison and a sax out front.
• Noir Swing — the line cliché and the minor-major seventh, brushes, vibraphone, a harmon-muted trumpet, half-time drops.
• Swing Hop — a swung boom-bap under chopped horns, lazy comping and a tine piano.
• Balkan Beats — the phrygian dominant's ♭II over a major tonic, off-beat chops, a brass-band oom-pah and a shout.
• Charleston — the ragtime circle of dominants, the Charleston rhythm, honky-tonk stride and a gramophone horn on the brass.
• Cabaret Lounge — harmonic minor, arpeggiated guitar, accordion, a clarinet and a ride-led drop.
• Electro Dixie — two-beat drums, oom-pah bass, a clarinet trilling over a trumpet and a trombone.
• Swing Step — the same band at 170 over breakbeats, the chords held two bars and a rolling sub.

Scales and changes

The scale writes the melody; the chords come from the style. Swing harmony moves — often twice a bar — and leaves the key constantly, so progressions carry the ii–V inside a single bar, the tritone substitute, the passing diminished, the ragtime circle of secondary dominants and Django's m6 vamps. Triads become sixth chords, because a swing band ends on a sixth. Past the swing vocabulary there are the Hungarian minor, the phrygian dominant, the bebop scale, the blues scales and two symmetric ones for colour.

How a song is put together

An intro — the needle dropping on an old record, a beat with a filtered sample, a horn fanfare, Krupa's floor toms — then a verse on the old record, a build, a drop, a second verse, build and drop, a middle — a break back into the gramophone with a solo over it, a solo over the club, or a big-band shout — a long last drop, and an ending: the turntable brake, the big-band button, the record going back to 1937, or a dead stop.

Every song writes its own fader ride and its own effect lane — where the gramophone closes in, where it sweeps open, how loud the vinyl is, where the brake lands. Your Effects sliders scale that lane rather than replacing it.

Swing

Everything is written on a straight grid and swung on the way out, by one number per style: the band swings its eighths, anywhere from a lilt to a full triplet; the house beat swings its sixteenths, and only a little. A triplet in a solo is written straight, because it already is the swing. The drummer's limbs each keep their own time as well — the ride hand on top of the beat, the hi-hat foot laid back on 2 and 4.

The guitars

La pompe is the engine of gypsy jazz: four downstrokes a bar, the ones on 2 and 4 accented and choked a tenth of a second after they sound, with a ghosted upstroke bouncing off each. The guitar is a recording, so the choke and the dead upstroke are a real hand on real strings. It is voiced the way a hand reaches — root, fifth, sixth or seventh, third — and played by two guitarists, panned apart, a few milliseconds and a few cents from each other.

The horns

FM, and not as a compromise: a modulator whose envelope rises a little behind its carrier is the blat of a brass attack, and a modulator at twice the carrier's pitch is a clarinet's odd-harmonic bore. Each horn adds the fixed resonances of its own bell and bore, a tongued note is lipped up to pitch in its first few milliseconds, a slurred one arrives without a fresh attack, and breath noise swells in with each note. The section's three players each have their own intonation and land a few milliseconds apart. The section is a trumpet, an alto and a trombone, voiced close from the top down and placed in front of one microphone. They fall off the ends of phrases, swell into pads, and play riffs in unison. A lead horn scoops into notes, shakes long ones, runs enclosures into chord tones in a solo, and anticipates the bar line. A harmon mute is a filter in front of the bell.

The bass

An FM upright, played pizzicato. It walks — the root on one, an approach into the next chord on four, chord tones between, a triplet skip-note before the beat — or plays two to the bar, oom-pah, boogie-woogie, or the producer's bounce on the off-beats. Under the club sections a sub holds each chord's root on its own direct line, where no amplifier can touch it.

Channels

Each channel is an input filter, a preamp or amp, a tone stack and a resonator. The resonator is the interesting part: a Selmer body — a small oval soundhole that honks around 1 kHz — for the rhythm guitars, a speaker for an archtop or a tweed amp, a gramophone horn for a 1920s brass sound, or none for a ribbon or condenser microphone. All of them are built by modal synthesis, identical every run, which is what lets an export match what you heard.

Effects

Pump is the sidechain, scheduled from every house kick rather than detected, so an export pumps exactly as playback did. Vinyl is dust, hiss and the odd pop, generated deterministically. Gramophone is a high-pass, a low-pass, a horn resonance and a fold to mono, all riding one number. The lead and the horns take only a third of the pump, so a melody does not lose its attacks under every kick. Tape Wow drifts the band's pitch; the beat is delayed to match, so the two stay locked. Chorus is on the guitars, Tremolo on the keys, and the Spring on the lead and horns, returned into the band so a gramophone section band-limits the reverb as well.

The drums

Sampled from Karoryfer's Big Rusty Drums, a vintage Polish kit with a big kick, a deep snare and a washy 22" ride: four velocity layers, three takes each. Played as a swing drummer plays — ride spang-a-lang, hi-hat foot on 2 and 4, a feathered kick, ghosted snare comping and the odd dropped bomb. Brushes are always synthesized. Turn Sampled kit off for the synthesized kit, which also stands in for any recording that cannot be reached. The house beat — kick, clap, snaps, hats, shaker, riser, impact — is synthesized, on purpose.

Chaos Engine

• ρ Lorenz — the pitch attractor behind the hook and the solo. Low circles one shape, ~28 is the butterfly, high leaps between registers.
• Chaos ↔ Taste — 0 lets the learned policy pick every note, 1 hands it to the attractor.
• Temperature — low is greedy and repetitive, high explores.
• r Logistic — the drummer's ornaments and the comping. Below 3.57 bars repeat; toward 4.0 no two are alike.

The policy's reward table is tuned for swing: the thirds and the major sixth score highest, the step and the fifth close behind, and the minor second is allowed, because a chromatic approach into a chord tone is half of how this music moves.

Keyboard & Stab Sequencer

Both play the band live through the same channels the song uses. Mute chokes a guitar chord and puts a harmon mute in a horn. The sequencer has its own Swing switch, using the same warp as the song writer.

Seeds

Every song comes from a seed. Each press rolls a new one; close the lock beside it (or type a seed) to keep it — the same seed rebuilds the identical song, so you can change the rig against an arrangement you already like.

Master & exports

The desk: a hall, the drum room, a tape delay synced to swung time, a chorus, a tone sweep and a mix-bus compressor. MP3 and WAV render offline — faster than realtime and sample-deterministic, vinyl and pump and brake included. Either asks how to write it out:

• Single file — the whole mix, with your levels and mutes applied.
• Separate instruments — one file per part, named after the seed, lined up sample-accurately for a DAW.

MIDI writes one track per part — the lead with its own instrument's program — and puts the swing kit and the house beat on channel 10.

Credits & licence

Created by: Wilfredo Bigol Jr

Contact

Licence

The music is yours. All generated and exported audio is released under the Creative Commons CC0 1.0 Universal Public Domain Dedication. You may copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.

The engine is not. The Chaos Engine — the generative system behind this app — is the intellectual property of Wilfredo Bigol Jr. Reproducing, distributing or modifying it, in whole or in part, without permission is prohibited.

The drums are Karoryfer Big Rusty Drums, with the tambourine and cowbell from the Versilian Community Sample Library, and the guitar is Karoryfer Emilyguitar — all CC0 1.0. The bass, horns, clarinet and keys are not recordings at all — they are generated by a four-operator FM engine shared with the sibling 1981 FM Synth Studio. Everything ships with the app, so it runs with no network; samples/CREDITS.md records what was done to each.

MP3 encoding by LAME (lamejs 1.2.1), used under the LGPL-3.0 and kept as a separate, replaceable file.