Andy Honeybone lies down and thinks horizontally. There is more to making a keyboard sound like a guitar than reaching for the right voice. He says.

NO. The series will not continue with a review of five-part left-hand chords. I'm sure they exist but we'll leave them to the likes of Stravinsky. Instead, the time has come to stop thinking in vertical chord blocks.

Thinking horizontally takes us away from keyboard idioms and allows us keyboardists to understand and more sympathetically play synthesised or sampled versions of traditional instruments; composition may also be approached in a more open and, dare I say, minimalist manner.

The realistic acoustic guitar voice on the DX7II sent me scuttling for some real guitar music. One of the most immediate things that struck me was that for a multiphonic instrument, the guitar plays an awful lot of single note lines. In part, this is an illusion due to the simplification required to overcome the cumbersome accurate notation of sustained broken chords. Nevertheless, what the guitar can sustain, the mind can remember, and a complete sense of harmony can be presented as a sequence of single notes. We can take this argument to its logical opposite and also say that the arrival of harmonic clues can be arranged to completely baffle the listener — if ambiguity is the desired intention.

It's a well-known fact that successful synthesis is a combination of both timbral correctness and the phrasing of the notes to bring out the character of the instrument. The notion of idioms is somewhat coloured by association: for example, a synthesised harpsichord will sound correct if either a Scarlatti sonata or the Stranglers' "Golden Brown" is played. The tone colour of some themes is so integral (Captain Pugwash, Dance of the Sugar Plum Fairy, Fossils from Carnival of the Animals, Largo from the Hovis advert, etc) that the tune only needs to be hinted at with a passable voicing and the illusion is complete. Timbral caricature.

Imitating other keyboard instruments is easy, but successful impersonation of entirely different instruments requires more research. Don't expect trombones to trill or flutes to bend notes more than a semitone. A glance at a standard work on orchestration will give you both the correct ranges and a whole string of rules that you can systematically break. After all, half the fun of synthesis is that you can have a bass piccolo and soprano tuba.

Let's stay with the guitar and analyse a few textures. First the guitar is a transposing instrument which sounds one octave lower than written. Its range starts at E below the bass clef and extends to just over three octaves. The DX7II PickGuitar voice is ready transposed and its range is therefore as written from E below middle C. The bass string may be tuned down to a D, as is required for many blues and folk picking styles as well as the first movement of good old Rodrigo's concerto.

The strum is very difficult to reproduce live on a keyboard and most attempts to ripple a chord will end up uneven. The most realistic method is to use a sequencer, and to add each note separately. Assuming you don't quantise, the timing variations should be enough to give a realistic spread. Even in the long gone days of ARP String Ensembles, the advice was to record each line of an arrangement individually. It's the only way you can overcome the preconceptions of polyphonic piano style and concentrate on that most elusive quality, phrasing.

Double and single octave ghostings are evocative of the guitar as are single note runs interspersed with chordal punctuation. Open intervals such as sixths and tenths are more common than tight thirds. Remember the maximum number of notes that can be plucked is five (unless you know any six fingered guitarists). The open bass strings (E, A and D) are often used as pedal tones over which harmonic fragments are suspended. The most difficult concept of 'thinking guitar' is to understand how the physical problems of covering six strings and 20in of fretboard with four fingers and a thumb affects the music produced. As good an example as any can be found in the opening of the Rodrigo concerto.

But back to horizontal thinking. The most common horizontal device is the broken chord or arpeggio (from the Italian arpeggiare, 'to play the harp') which imparts both harmony and motion. An arpeggio is simply some arrangement of the notes of a chord played one at a time in some defined order. Other-hand arpeggio accompaniment is very common in classical piano music, Liszt's Liebestraum, for example. The range of left-hand arpeggios is from way below the bass clef to C-above-middle-C. To avoid an arpeggio which is too bass heavy and muddy sounding, make sure it's only when you're above C-below-middle-C that you use intervals of less than a diminished fifth as adjacent notes. This proviso gives rise to several basic patterns, one of the most common of which can be described as: C, G, E', C', G', B', E'', B' for a major seventh chord (the tick marks indicate the octave relative to the root note). An arpeggio may contain an added sixth as beloved by the French or, in more jazzy pieces, the seventh and ninth.

All this is fine and good, but rather wrapped up in real piano playing. The use of sequencers and electronic tone generators means that anything goes. Nik Kershaw has used sequences of arpeggios on both "Easy" and "The Riddle" at one time one of his trademarks. The Steps Ahead album "Magnetic" contains a track called 'Sumo' starting with a sequence which appears to be a collection of totally unrelated notes. As the track gets going, you realise that it doesn't really matter what the sequencer is doing, it all hangs together anyway. The distinction between an arpeggio and a sequence becomes blurred. They are both linear arrangements of notes, and that's what this piece is about.

Being a chord man myself, I was completely thrown when I couldn't fit a chord to what was going on at one point in a particular song I was transcribing. It wasn't that I didn't know what the chord was; I was floored by the fact that there wasn't a chord at all and it didn't need one. Up until that point there has been plenty of chords but suddenly, the last one decayed away and, for two bars, the piece was coasting along quite nicely with just the bass and a counterpoint line. In a linear sense, the harmony was complete. It had taken me more years than I'd care to admit to appreciate the horizontal.