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At its best, digital technology takes some of the drudgery out of life. (At its worst...well, let's not go there.) The computer can handle all sorts of messy details, leaving us humans free to be creative and have fun.

One of the handier gadgets in computer music is the arpeggiator. While there are lots of variations, the concept is simple enough: You hold a sustained chord on the keyboard, and the arpeggiator steps through the notes of the chord one at a time, repeating the pattern until you release the keys. With an absolute minimum of dexterity, you can create driving rhythms and interweaving counterpoint parts.

Arpeggiators were found on some of the very earliest keyboard instruments that used digital scanning to figure out which keys were being pressed. The Oberheim OB-8 (released in 1983) had one, as did the Korg PolySix (see Figure 1). In recent years, designers of both hardware and software-based synthesizers have taken the arpeggiator concept to new heights. Since I'm not lucky enough to have either an OB-8 or the infinitely more sophisticated Korg Karma, in this article we'll focus on the arpeggiators found in softsynths. We'll cover some basic concepts and also suggest some ways to use an arpeggiator musically. (Jump to the tips.)

The Korg Karma took the arpeggiator concept to new heights of expression by integrating algorithmic and auto-accompaniment music technologies. Developer Stephen Kay offers detailed audio and video examples at Karma-Lab.com.

Figure 1. The arpeggiator section of the Korg PolySix synthesizer (the software version is shown here) has only basic controls, as on the original 1981 hardware instrument. However, the Key button starts the arpeggiator when a MIDI note-on message is received. The original instrument predated MIDI.

Up the Down Staircase: Arpeggiator Basics

The arpeggiator takes its name from the Italian word arpa, which means "harp." A harp often plays rolled chords across several octaves, a technique known in classical music as an arpeggio. In its simplest form, an arpeggiator is a device that plays arpeggios.

The classic synthesizer arpeggiator has several basic features: an on/off switch, a tempo control, a gate-time control, a hold switch, an octave switch, and a mode selector. Often the tempo can be synchronized to the tempo of a master sequencer, and can be set to musically meaningful values such as eighth-notes.

The gate time is sometimes given as a percentage: When it's set to 100 percent, each note in the arpeggio will last until the next note starts. When the gate time is less than 100 percent, there will be a gap between the notes (though the gap may be obscured if the synth preset has a long envelope release time).

When the arpeggiator is first switched on, it does nothing. It sits silently, waiting for you to play something on the keyboard. The moment you play a note or chord, the arpeggiator swings into action. If the hold switch (also called a latch) is off, the arpeggiator will stop generating notes as soon as it sees no keys pressed down on the keyboard. But if the hold switch is on, the arpeggiator will keep going even after you lift your fingers. It will keep producing the same pattern until you play a new note or chord, or until you press the hold or on/off switch to stop the racket.

Because an arpeggiator can remember what notes you played even after your hands have gone elsewhere, it's a great device for producing accompaniments in live performance. An arpeggiator is like an extra hand (or maybe two or three of them).

Arpeggios à la Mode

The most interesting feature of an arpeggiator is its mode selector. You'll be given a choice of at least three modes, and often there will be a dozen or more. The arpeggiators in modern synthesizers, such as the Yamaha Motif series, can have hundreds of modes. Complex arpeggiator modes are more often known as patterns. Some instruments also allow you to program your own arpeggiator patterns, but all of them start with the basic modes:

• Up: The arpeggiator plays the notes in your chord from low to high, then repeats. For example, if you play a C major triad, the arpeggiator plays C-E-G, C-E-G, C-E-G, and so on.
• Down: The arpeggiator plays the notes in the chord from high to low, then repeats (for example, G-E-C, G-E-C, and so on).
• Up-and-down (sometimes called alternating): The arpeggiator rolls the chord back and forth. If you play a C major triad, the arpeggiator plays C-E-G-E-C-E-G-E, and so on. Note, however, that some arpeggiators repeat the top and bottom notes when in up-and-down mode. This would produce C-E-G-G-E-C, C-E-G-G-E-C, and so on. Depending on the type of rhythm you need for the song, the repetition of the top and bottom notes in up-and-down mode can be either a good thing or a bad thing. Some arpeggiators let you choose between the two up-and-down modes.
• As played: In this mode, the playback order depends on the order in which you pressed the keys. To make a slightly more interesting example, we'll use a C7 chord this time. If you play the notes in the order C-G-E-Bb, then the arpeggiator will repeat them in that order. Naturally, if you roll the chord from low to high or high to low when playing it, as played ends up being the same as up or down.
• Random: On each step, the arpeggiator chooses a note from within the chord, but you have no control over its selection.