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Arpeggio is the musical term for the playing of a chord as a rapid succession of notes, rather than simultaneously. The word is derived from the Germanic arpa, meaning harp.  So literally, arpeggio means as played on a harp.  Arpeggiators were first used on electronic musical instruments as a way of simulating this effect. When a chord is pressed on the keyboard, the notes come out one at a time instead of all at once. Over the years arpeggiators have gotten more sophisticated, many features have been added, and the arpeggiator function has become a staple of electronic music. Today's arpeggiators can do much more than separate the notes of a chord. In a musical composition they might contribute elements ranging from rhythm to pattern generation, counterpoint, and even melody.

In a typical electronic music configuration using MIDI (Musical Instrument Digital Interface), there are control devices such as keyboards and sequencers, as well as sound sources (e.g. synthesizers).
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The arpeggiator function can be embedded in a keyboard, a sound source, or inserted in between. When an arpeggiator is part of a keyboard MIDI controller, it responds to chords pressed on the keyboard by sending out a stream of MIDI note events. Outboard arpeggiators, such as the Oberheim Cyclone, can be inserted after the keyboard and do essentially the same thing. Some downstream devices, or sound modules have built in arpeggiators that respond to the incoming MIDI stream and produce patterns of notes instead of chords.

Timing is critical to an arpeggiator, as it needs some kind of clock to tell it when (how fast) to send out the individual notes. Usually there is an internal clock that can be set anywhere from a few to hundreds of beats per minute. Also there must be an option to synchronize the arp to other devices in the studio, so they can all follow the same rhythm. The MIDI protocol includes clock signals that allow this synchronization. In a MIDI studio there is generally one master clock, and everything else is externally synced to that. The syncing may take place at various ratios, so for example, the arpeggiator may send out quarter notes, eighth notes, sixteenth notes, etc.

functions that are often found in arpeggiators
pattern generation Notes of the chord are played out in a repeated pattern, such as up, down, up&down, as played, random.
cycling The pattern may be transposed or inverted each time it is played, usually up one or two octaves.
rate Notes are clocked out at a rate determined by the system clock (bpm), and the note type (quarter note, sixteenth note triplets, etc.)
velocity Velocity of the individual notes (which usually translates to volume) can be fixed, repeated as played on the keyboard, or programmed in some pattern.
note order Pattern generation assumes an order to the notes in the chord, usually low to high, but can also be in the order played.
gate time The duration or gate time of each note can be set, usually as a percentage of the time between notes.
step programming In more sophisticated arpeggiators, the individual steps of the pattern can be programmed as to which note, the velocity, gate time, etc. With a polyphonic arpeggiator, a single step could play multiple notes.
panning The sounds can be panned from left to right as the notes are played out.
latch (hold) Latching allows the arpeggio to continue playing after the keys are released.

What makes a good arpeggiator? Timing, programming, and dynamics. Proper timing allows the arp to keep up with a fast rhythm. Also there should not be any lag between when a key is pressed and the first note of the arp sounds. Timing problems may not be the fault of the arpeggiator, but could be caused by an overloaded MIDI chain. Programming allows more flexibility in creating custom patterns, more variety, polyphony, syncopation. Dynamics are what keep an arpeggio from getting boring - this means that the individual notes can have different velocities, gate times, and panning.

some creative ideas for arpeggiators
melody line A slow moving random pattern, perhaps with a little portamento, superimposed over a faster rhythm, can create some unpredictable but interesting melodies.
counterpoint Arpeggios that follow the chord structure of a tune are an easy way to inject counterpoint. Leave the latch off and play at strategic moments.
pattern generator Play with different settings until you get a pattern you like, then latch it and move to a second arpeggiator to find something that complements it. If you have enough arpeggiators, you can continue this indefinitely.
rhythm machine Use a random pattern that has some rests or syncopation in it to play a drum kit. If your arpeggiator doesn't have rests, try setting the note range on your sound module to be silent for some of the notes the arp is playing.
variation Arpeggiators are by nature repetitive (which is part of their appeal), but you can minimize the annoyance factor by using random patterns or by changing the chords that are playing frequently.
sound effects Weird noises and other sound effects often have a completely different result when played through an arpeggiator. The first part of the sound plays repeatedly (avoid sounds with a slow attack). Experiment!
 

arpeggiator product reviews

Kawai K5000

Emu Proteus 2000

Korg Z1

Korg Karma

Oberheim Cyclone

Waldorf Gekko

Kurzweil PC88

Kurzweil ExpressionMate

Waldorf Microwave XT

Yamaha RM1x

Akai ME20A MAM MAP1

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updated  October 22, 2004     --- egw ---