Arpeggiator

An arpeggio is a chord played one note at a time. An arpeggiator plays one for you, in time, for as long as you hold the keys. You choose the notes and the arpeggiator decides when each one sounds.

Hold C4, E4 and G4 (a C major chord) with the arpeggiator set to Up and eighth notes at 120 BPM. It plays C, E, G, C, E, G, one note every quarter of a second. Set it to Down and you get G, E, C, G, E, C. Up-down climbs and falls back, and Random picks a new order each time. Change to Am (A, C, E) and the pattern carries on with the new notes, so holding C, G, Am and F in C major turns four held chords into a moving part.

The usual controls:

• Mode sets the order: up, down, up-down, random, or the order you pressed the keys.
• Rate sets how often a new note plays, such as quarter notes, eighths or sixteenths, sometimes with a swing option.
• Range (or Octave) repeats the pattern one or more octaves higher before starting over. With a two-octave range, C4 E4 G4 becomes C4 E4 G4 C5 E5 G5.
• Hold (or Latch) keeps it running after you let go.

Roland’s Juno-6 of 1982 had an arpeggiator built in, and arpeggiated chords drive a lot of synth-pop and trance. Beginners meet one as an Arp button on a synth or keyboard, or as an arp mode in an app.

Gelato Chord has an Arp mode, part of its $4.99 unlock, with up, down, up-down, down-up, random and pick patterns at rates from quarter notes to swung eighths, locked to the tempo. For how the arp fits with the rest of a synth, see how a synthesizer works.