Arpeggios, Arpeggiators and Sequences

A held chord is a block. It sounds, it sets up a harmony, but it doesn't move. A lot of electronic music prefers to run through the notes of the chord one by one, quickly and in rhythm: the shimmer of a trance synth, the bouncing pluck in house, the hypnotic line in techno, or the piano notes picked out one at a time in lo-fi. All of these lines rest on the same idea, the arpeggio.

One chord, two ways to play it

Listen to the A minor chord played as a block, then the same notes played one after another.

These are exactly the same notes, so the same harmony. But the second version creates rhythm and movement where the first one just held still. Playing the notes of a chord one after another rather than together is called an arpeggio, from an Italian word that brings the harp to mind.

Which way it goes

An arpeggio is defined first by the order in which it runs through the notes. The simplest one goes up: A, C, E, then starts over. It can also go down, or go up and then come back down, which is called up and down. Look at the rising version over one bar of sixteenth notes.

Notice a detail on the grid: the arpeggio has three notes, but the bar divides into groups of four sixteenth notes. So the A3 doesn't land in the same spot in every beat. It falls on the first beat, just before the second, in the middle of the second, just after the third, on the fourth, then just before the next bar. This offset between a pattern of three and a grid of four is what gives arpeggios their hypnotic side; you've already come across it with polyrhythms.

Add the octave, A4, and the pattern becomes four notes: now it lines up exactly with the beats. The same goes for up and down, if you don't repeat the top and bottom notes: A3, C4, E4, C4, then start over, with a wave-like motion.

Compare the two figures by ear. The rising version turns endlessly and never seems to land in the same place; the up and down version breathes on every beat, calmer and more regular.

The arpeggiator and its settings

Writing these notes one by one is possible, but slow. That's why most DAWs offer an arpeggiator: a MIDI effect that takes the chord you're holding and plays it as an arpeggio, automatically and at the track's tempo. You write or play a simple held chord, and the arpeggiator does the rest. Four settings show up almost everywhere.

• The mode chooses the order of the notes: up, down, up and down, random, or the order in which you played the notes. Depending on the arpeggiator, up and down may or may not repeat the top and bottom notes.
• The rate sets the length of each note in the arpeggio: 1/8 for eighth notes, 1/16 for sixteenth notes, and often triplet values, like 1/16T.
• The octave range replays the pattern one, two or three octaves higher before coming back to the start, which widens the line a lot.
• The gate sets the length of each note relative to the rate, often as a percentage. A short gate gives you clipped, punchy notes; a long gate gives you smooth, connected ones.

Try a simple experiment in the workshop: keep Am in up mode, and move the gate from very short to very long. With a pluck sound, the short gate brings house and electronic pop to mind; the long gate, with a pad sound, suggests trance or ambient textures instead. The mode and the gate often change a line's character more than the choice of notes does.

Arpeggios over a chord progression

An arpeggiator follows the chords you give it. If you hold Am, then F, each bar plays the notes of the new chord in the same order and the same rhythm. So the line keeps its identity while changing color. Here's the rising version over these two chords, with the octave added.

Voicings matter here as much as they do for held chords. If you move between chords that sit close together, the arpeggio glides smoothly from one to the next; if you jump from one register to another, it jumps too. Here, A and C belong to both chords, which makes the change very smooth.

The step sequence

An arpeggio takes its notes from a chord. A step sequence works differently: you write a note, or a rest, directly into each step of the grid, often sixteen steps per bar. That's how the sequencers of the first electronic machines worked, and it's still the method behind a lot of acid bass lines and techno patterns. A sequence can skip steps, repeat a note, accent certain steps, or slide one note into the next.

Listen to this original sixteen-step sequence in A minor. It leans mostly on the root, with a few other notes of the scale and rests that give it all its rhythm.

A sequence like this often runs unchanged for minutes on end, while the sound around it evolves, for example by slowly opening a filter. Theory plays a discreet but decisive role here: the chosen notes, mostly the root here, with the third, fourth, fifth and seventh, set the minor color of the whole section.

The ostinato, the pattern that stays put

One last technique, and not the least: the ostinato, a short pattern repeated stubbornly, unchanged, while the harmony changes around it. Unlike the arpeggiator, which adapts its notes to each chord, the ostinato keeps its own. So it's each new chord that changes the way you hear it.

Listen to this four-note pattern, C5, E5, G5 and E5, repeated without change over Am, F, C and G. Over Am, the G colors the chord with a seventh. Over F, the E adds a major seventh and the G a ninth. Over C, the pattern blends into the chord. Over G, the C and the E create a tension that releases when the loop comes back to Am.

This technique is precious in production: a single pattern, programmed once, is enough for a whole loop, and the chord progression takes care of keeping it fresh. You hear it in a lot of melodic electronic music, played by a pluck or a piano, and it's also an excellent starting point for a hook.

With the bass, the chords, the melody and now the arpeggios, your loop is starting to fill up. The next lesson helps you give each part its own place in pitch, so everything can be heard.