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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.)

Korg Karma

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.

Fig. 1: Korg PolySix

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:

Bells & Whistles

Every synthesizer designer seems to put a bit of fresh spin on the arpeggiator concept. While almost all arpeggiators have the basic features discussed above, you may conceivably find some fascinating extras.

These days, there's some overlap between the arpeggiator and a related device called a step sequencer. To some extent it's a matter of semantics whether a device is called an arpeggiator or a step sequencer, and some devices can function in either manner (see Figure 2). In a step sequencer, it's always possible to program a series of steps so that they'll have different pitches—that is, different transpositions of the MIDI notes. Some arpeggiators will do this; others won't.

Fig. 2: VirSyn Tera

Figure 2. The arpeggiator in VirSyn Tera is also a complex step sequencer. You can choose patterns from the palette at upper left and insert them in the sequence grid at upper right. When a channel is set to "arpeggio," as with the top line here, Tera steps through the pattern whenever one or more keys are pressed. The pattern editor has data fields for a controller output, note transposition, chords, step mute and skip, and other functions. (Click to enlarge.)

Generally speaking, a step sequencer responds to only one key on the keyboard at a time, or responds to the keys separately: When you play a key, the sequence will be transposed so that it starts on that key. If you play multiple keys, either the step sequencer will ignore all but one of them (the more common situation), or it will play a separate sequence based on each key (as in Steinberg Xphraze). In contrast, an arpeggiator generally plays only one pattern at any given time, but that pattern can utilize (in some manner) two or more notes that are being held on the keyboard.

For example, let's suppose you've programmed a four-step pattern with note transpositions of 0, 2, 5, and –2. If you hold only one key on the keyboard, such as a D, the pattern will produce the series D-E-G-C. But when you hold a D minor triad (D, F, A), the arpeggiator will apply a different transposition to each note in the arpeggio. This table shows the result:

Chord Note Transposition Output
D 0 D
F 2 G
A 5 octave D
D –2 C
F 0 F
A 2 B
D 5 G
F –2 Eb
A 0 A
D 2 E
F 5 Bb
    etc.

This type of transposition can be heard at the end of the audio example "steps.mp3" (see the Examples sidebar).

Fig. 3: AAS UltraAnalog

Figure 3. In the arpeggiator in Applied Acoustic Systems UltraAnalog, the arrow in the top line controls the length of the pattern. Clicking in any of the green boxes causes a step to be a rest. The Range parameter is for choosing the number of octaves, and the Latch checkbox puts the arpeggiator in hold mode.

Arpeggiators are sometimes tricked out with features such as the following:

Fig. 4: LinPlug Sophistry

Figure 4. The arpeggiator in LinPlug Sophistry provides velocity/modulation values for each step as a series of numbers. The VEL knob mixes the programmed step velocities (A) with the keyboard velocities (K), but the values in the series are always available as a separate modulation source independent of velocity. A special "mod-only" mod allows keyboard performances to be played normally while the arpeggiator produces a cycle of modulation values.

Some arpeggiators, such as the one in Cakewalk Z3ta+, can be programmed with complex patterns by recording and editing short Standard MIDI Files (SMFs). After saving the SMF, you can access it in the arpeggiator's pattern list (see Figure 5).

Fig. 5: Cakewalk Z3ta+

Figure 5. The arpeggiator in Cakewalk Z3ta+ shares panel space with the low-frequency oscillators (LFOs). You can store patterns as Standard MIDI Files and load them from the Pattern menu.

Steppin' Out: Arpeggiation Tips

An arpeggiator is primarily a device for creating rhythmic parts that have an element of motion. When programming an arpeggiator track, you'll probably want to consider adding other elements to the synth preset that add still more motion. There are several ways of doing this:

Stereo delay effects, which are included in many synths, can turn a simple arpeggio into a massive wall of moving notes—listen to "delay.mp3." The delay should be synced to the same master clock as the arpeggiator. (Synchronization is often switched on by default.) I like to set one side of the delay to quarter-notes and the other side to another value, such as dotted eighths.

A synced LFO can be an excellent source for modulating filter cutoff or an oscillator waveform while the arpeggiator runs. If your synth has several LFOs, set each to a different rhythm value and use them to modulate different parameters.

A "trancegate" effect, which switches the sound on and off in a rhythmic way, works extremely well when combined with an arpeggiator and a delay. If your synth doesn't have this effect, you may be able to apply it in the host sequencer. In this case, you'll also want to put the delay effect in the host, because delay generally works better when it's after the rhythmic gate in the signal path.

Now let's look at some performance techniques.

Correct the timing. When recording a MIDI sequencer track that will play the arpeggiating synth, it's almost always desirable to quantize the note-ons so that they start on the beat. This will keep the arpeggiator in sync with the rest of the music.

Arpeggiate your fingers. It can also be useful to roll your chords slightly when recording the track. With some arpeggiator patterns, the note order makes a difference. Though it may not be intuitively obvious when you look at a piano-roll edit window, even after a chord is quantized so that all of the notes start on the same clock tick, they're still listed in the track data in a linear order, one note at a time. Whichever note you played first will still be first, even after quantizing. (Unfortunately, some arpeggiators lack a reset-on-stop feature. If the pattern doesn't reset, then the first note heard will depend on what step the pattern had reached when you last stopped the transport in your host program.)

Starve the delay. If you're using a rhythmic delay, you'll probably want to end the held chord a beat or so before any harmony change, to give the audio in the delay line time to "clear out." This will help ensure a clean transition to the new chord.

Shift the beat. By pressing and releasing single keys within a chord while the arpeggiator plays, you can change both the melodic shape of the arpeggio and its rhythm. Depending on the pattern or mode you've chosen, the rhythm will be affected because more or fewer notes are being arpeggiated. For instance, if a four-note chord generates an arpeggio that lasts for exactly two beats, adding a fifth note will cause the pattern to be two and a half beats long.

Drum up (and down). Don't think arpeggiators are just for pitched sounds; you can get some very interesting grooves by arpeggiating a drum kit patch, in which each note triggers a different drum sound.

Multiply the effect. Some instruments allow several arpeggiators to run at once. The way to set this up will differ from one instrument to another, but in most cases the instrument will be in multitimbral mode. Different presets will be assigned to the layers of the multi. The arpeggiator programming may be handled in the presets, or it may be handled within the parts of the multi. In any case, such a setup can create massive and hypnotic walls of rhythmic sound. Adding modulation to the layers (stereo panning, for instance, and filter cutoff sweeps) will cause the arpeggiations to weave in and out of one another.

What Goes Up Must Come Down

The insistent rhythm of an arpeggiator is best deployed in highly electronic styles, from ambient new age to 1980s synth-pop. In theory, an arpeggiator doesn't do anything that you couldn't do with your fingers if you were willing to take the time to record and edit a sequencer track. But setting up an interesting arpeggio pattern first and then experimenting with chord voicings is a lot faster than reprogramming a MIDI sequence track one note at a time.

Also, the factory patterns included with many arpeggiators can be a source of inspiration. Just lay your hands on the keyboard, and you may find that the arpeggiator has fired up your imagination.

If you're up for it, get down with it.

Audio Examples

To demonstrate some of the possibilities of arpeggiators, I chose U-He Filterscape VA, whose arpeggiator you can see in Figure A. This synthesizer is one of the three plug-ins included in the Filterscape package; the other two are filter effects. After downloading the demo version, which produces occasional noise bursts until you buy the product, you can install these example presets I made (12KB Zip file). In Windows, you should copy them to C:\Program Files\u-he\Presets\FilterscapeVA.

Fig. A: Filterscape Arpeggiator

Figure A. The U-He Filterscape VA arpeggiator has pop-up menus for rhythm value, gate time (shown), number of notes to be included in that step, and note transposition. The strip along the bottom outputs a line of controller data.

 

"Basic Arp" provides a very simple arpeggio in "up" mode. The clock moves in steady 16th-notes, and all of the gates are the same length. The only extra programming trick used here is a two-measure LFO sweep of the filter to add a little animation:

In "ArpAccents," the length of the pattern is five notes. I used three different gate lengths. In addition, Filterscape's "Arp Modulator" output modulates both the oscillator waveform and the filter cutoff to provide accents. If you play this arpeggio while holding anything other than five notes on the keyboard, you'll hear the rhythmic pattern shift across the pitch pattern:

"Arp Delay" uses the same underlying arpeggiation as the Accents preset, but the stereo delay line has been turned on, creating a much more animated sound. Note that the arpeggiator is still playing only one note at a time:

This patch becomes even more interesting when you click the ON button in the parametric EQ section, located to the left of the central wheel, adding tone-shaping:

"Arp Rhythm" uses two of Filterscape's more specialized features. One of the steps is set to an eighth-note rather than a 16th, so that the seven-note pattern lasts for two beats. In addition, two of the steps play three-note chords rather than single notes:

Finally, "Arp Steps" uses the arpeggiator as a step sequencer. If you hold one note, you'll hear a dominant seventh chord pattern. Holding more than one note at a time will create a more complex and probably less interesting pattern:


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