Jazz generator

How to use it

Press Play. The band starts a new tune straight away: it picks a key and a chord sequence, plays it through two to four times, then moves on to another tune with a new title. Watch the chords go by at the top, and the notes scroll past underneath: gold for the piano, green for the bass, cream for the lead instrument and dots for the drums.

Each room is a starting point. The Study is a quiet, slightly mysterious piano trio with rain on the windows. The Library is slow and hushed, with a clarinet. The Cellar Bar swings harder with sticks, a muted trumpet and an old record’s crackle, and the Ballroom is quick and bright. Change anything once it’s playing: the room changes to Your own mix, and Copy a link to this sound saves it so you can come back to it or send it to someone.

What the settings do

• Mood chooses the kind of chord sequences. Warm uses major keys and the classic II–V–I cadences of swing-era standards. Blue uses minor keys, including a minor blues. Mysterious uses minor keys with a slowly falling inner line (a sound you may know from film-noir and detective scores), tense altered chords, and chords borrowed from a half step above the key.
• Tempo is in beats per minute. Below about 80 the bass plays “in two” (two notes a bar) like a ballad. Faster than that it walks, four notes to the bar. Below 130, the first eight bars of each new tune are played in two, the way a band often states a tune before it starts to swing.
• Swing is how lopsided the eighth notes are. Straight plays them evenly, as in a bossa nova or a pop song. Medium is the long-short triplet feel of most jazz, and Heavy leans further into it.
• How busy changes how much everyone plays: longer or shorter phrases from the lead, more or fewer piano chords, and how often the drummer adds snare accents and fills.
• Key fixes the key if you want to play along. Leave it on A new key for each tune for variety.
• Lead picks who improvises the melody. Choose None for just the rhythm section, which is less distracting while you work or read.
• The mix sets the volume of each part. Room size goes from a small, dry room to a large hall with a long echo.

How it makes the music

There are no recordings inside. Each part follows a set of musical rules, with chance deciding the details. The bass walks between the chords, stepping by a half step into the next chord. The piano plays chords without the root (the bass already has it), choosing the shape that moves least from the last one, the way a jazz pianist keeps the chords flowing. The drummer swings on the ride cymbal or sweeps the brushes, and often adds a fill at the end of an eight-bar phrase (more often when it’s busier). The lead makes up a short idea, repeats it with small changes, aims for the notes that fit each chord, and ends each phrase on a note that sounds settled.

Every instrument is made from scratch with the Web Audio API built into your browser, so no sound files are downloaded. That’s why it works offline and costs almost nothing in data, and why the instruments sound warm but simple next to a real recording.

Ideas for using it

• Background music while you work, study or read, with no ads and no repeats.
• Music for a game night, a dinner party or a quiet shop, with the sleep timer to fade it out at closing time.
• Practising your own instrument: fix the key, choose None for the lead, and take the solo yourself.
• A soundtrack for a video or stream: press Record, let it play, and press it again to download what you heard.

Frequently asked questions