Ian Gardiner explains this most arcane of musical skills.

Hands up, who remembers the Mellotron? Thirteen years ago this mythological instrument was capable of conjuring up vast caverns of string orchestras via a keyboard, operating a Heath Robinson contraption of tape loops, and no self-respecting Art-Rock band could successfully explain the meaning of the universe without one. Since it passed away we have had a procession of keyboards in its wake attempting to recreate string sounds, from string machines, through polyphonic analogue synths of increasing complexity, up to today's digital sampling instruments. Looping problems aside, the veracity of, say, the string orchestra sample on the Kurzweil 250 is extraordinary, but... not quite the same as the real thing. Which probably explains why, over the past few years, there seems to have been an increase in the use of real acoustic strings in the mix of various Rock and Pop productions, and indeed they appear to have become an essential part of the fabric of bands such as Lloyd Cole and the Commotions, judging from their album, Rattlesnakes. Even the arrangers are getting credits on the record sleeve! So for those of you in pursuit of the tasty string arrangement, here is a user's guide.

Modern Western bowed instruments come in four sizes: violin, viola, cello, and double bass, together covering a range of over five octaves. Example one shows the sounding ranges. There are two slight complications to be found when writing for these instruments, since viola players insist on reading parts written in the obsolete alto clef, and double bass parts are written an octave higher than they sound to save ink!

Like guitars the different strings of each instrument have different qualities, with the sound becoming brighter the higher the pitch of the string you play. For instance, the highest string on the cello (the A string) is very bright and penetrating, and is therefore a good register for solo passages, whereas the lower strings, though less responsive, are richer and more mellow.

Now, in terms of register, most guitar-based Rock music is bass heavy, with most of the sound being centred around and below middle C, and this makes the bowed double bass, for example, difficult to integrate into such a set-up as it treads the same territory as the electric bass or synth bass. The cello and viola share a similar relationship with the guitar so that unless a 'space' is built into the arrangement for them, they cut through most cleanly in their middle to upper registers. Violins are therefore the most exposed of the family and normally dominate any string ensemble, but by adjusting for these limitations in register in the production, however, it is possible to create a unique and unusual sound, as in Nicky Holland's quirky arrangements for the Fun Boy Three that set lugubrious cellos and trombone against a rolling tom-tom based beat.

All string instruments are very homogeneous, blending well with themselves in whatever combination, and the two most common groupings are the string quartet (two violins, viola, cello), and the string orchestra, numbering from 14 to over 50 players, in which all the instruments are combined.

The Beatles must have been the first band to utilise a quartet behind their songs, the most obvious examples being George Martin's arrangements for Yesterday — a discreet, 'Classical' backing for Paul McCartney plus acoustic guitar — and for Eleanor Rigby, which dispensed with any Rock instruments altogether, instead giving the quartet the chugging chords and bass lines, and getting them to play loudly and with heavy accents in order to build a punchy, propulsive sound. Generally, however, the allusion to classical music styles is difficult to avoid when using the quartet in such isolated surroundings, but its intimate 'chamber music' quality is very effective in backing a reflective type of solo song, as exemplified by Elvis Costello's Shipbuilding, or Judie Tzuke's For You which offsets her acapella vocals against a sophisticated and beautiful quartet arrangement by Paul Hart.

The string orchestra has occupied a more central position in the lighter side of commercial music for some time (checkout Radio 2's 'String Sound'!), and in the Sixties, when British Pop producers tended to have a background in commercial arranging, a lot of records were made into more wholesome family entertainment through the inclusion of jolly strings. It is, nevertheless, a much more flexible medium than the quartet, being capable of a wide range of dynamics and colours. There are no hard and fast rules as to intermediary combinations between quartet and orchestra; the mellow sound of six violas may be exactly what you're searching for.

So, having decided what number of what instruments you're going to use, what do you write for them? Here are a few possibilities.

Strings are good sustaining instruments, and sustained notes or a sustained counter-melody can thicken a texture or add that final touch of gloss. To amplify this effect the notes or lines can be doubled at the octave (or doubled twice over two octaves) on instruments above or below, or they can be split into two parts in parallel intervals, like multitracked vocals — parallel thirds or sixths have a warm and smooth quality, whereas fourths and fifths are more open and harder edged, or with more instruments (or with overdubbing) the two can be combined, as in Example Two.

Sustained chords are obviously effective, but h ave to be treated with more care since overdoubling too many notes can make the overall sound very opaque, and in voicing string chords the lower notes need to be spaced further apart than those at the top. See example three.

In soupier harmonic contexts higher notes of a chord can be effectively sustained above the simpler basic harmony — the ninth, eleventh and/or thirteenth over a minor seventh, for example — and placed in the upper registers this has become a common practice in Jazz Funk/Soul recordings, as on, say, Al Jarreau's single Mornin'.

These days it's not so usual to find strings doubling the vocal line, but more often they'll double inner instrumental lines or guitar/bass guitar riffs. Ann Dudley's arrangements for Lloyd Cole exploit this device to the point of defining an integral part of the band's sound — she uses a small body of strings playing louder to get a harder tone, doubling the lines in unison or with an octave higher, to achieve a perfect foil for those fashionable jangly guitars. Adding inner lines or figures of their own can be effective also. Remember that whiplash string figure in the middle of the chorus of Michael Jackson's Billie Jean! If strings are being used behind a song they can be useful in providing an instrumental link, or an introduction, or even as an alternative to the shout chorus or the fade ending, a coda maybe.

It's largely unrecognised in most arrangements that string instruments are capable of a far wider range of sounds than just the normal bowed tone. Plucked notes ('pizzicato') have occasionally been reserved for songs with 'rain' in the title — 'It might as well rain until September', plink, plink, plink, plink — but they can be used also for interesting rhythmic and percussive effects, as can hitting the strings with the wood of the bow ('col legno'). The bow can also be drawn across the strings very near the bridge to obtain a glassy, trebly tone ('sul ponticello'), or a mute placed on top of the bridge to make the instrument quieter but sweeter. Two adjacent strings can be bowed simultaneously ('double stopping') and this produces a strident, nasal quality that can be used quite aggressively. Michael Nyman's score for The Draughtsman's Contract creates an original, sharp-edged sound by multitracking a close-miked single violin using this technique, in a style that fuses the phrases of English Baroque composer Henry Purcell, Rock riffing, and the repetitive patterns of systems music (a kind of Purcell automatic?). Also, as on a guitar, sustained harmonics can be produced at the relevant places on the string, and I even know a cellist who has developed a nifty line in 'hammering on' a la Eddie Van Halen! All these techniques are commonly found in 20th century 'classical' music and, as an aside, it's intriguing how many 'serious' composers are crossing over to arrange in the Pop music world, like David Bedford for Madness and Elvis Costello, Dominic Muldowney for Sting and Michael Berkeley for Kate Bush.

Hopefully the digital sampling keyboards will not eventually supersede the use of the real instruments, and as each have their own characteristics, it should become possible to work the two in tandem. And mentioning Kate Bush, it is worth noting that she successfully marries Fairlight string samples with a real string sextet on her recent single Cloudbusting. I followed a similar approach in arranging the beginning of a song for a forthcoming album by Drum Theatre, on which, instead of the Mellotron, a multitracked Kurzweil weaves a dense web of chords, analogous to the sound of a vast string orchestra, and out of this a real string quintet (muted) gradually take over as the song begins, creating a dramatic spatial contrast. Using both media exposes the other's limitations, as it would have saved a fair amount of time if we could have MIDI-ed up the quintet to obtain the correct synchronisation, but there again it proved amazingly difficult on the Kurzweil, even with its velocity sensitivity, to play even the simplest phrases with the natural expressive control of a string player. It is important when combining the two, also, to make sure the keyboard is very accurately in tune, since string players develop an advanced sensitivity to intonation and find it hard to adjust to anything outside of the true concert pitch.