A great deal of research has recently gone into making the guitar synthesiser perfect, and the Shadow GTM6 Guitar-to-MIDI system is one of the first designs to make use of that research. Does it cure all the problems?

Over the last few years a number of successful guitar synth designs have appeared. Successful, that is, in the sense that some people have managed to use them to make music. Sales have never been great, so refinement has been slow. But there's been a steady improvement in the performance and capabilities of each new model. Latest in the line is a unit from Shadow Electronics, the West German pickup manufacturer; all in, it'll set you back about £1000.

For the sake of comparison, the Shadow system is a little cheaper than the Roland (even at its lowest price) and about the same price as the Ibanez. Both of these Japanese systems include a guitar; the Roland also has a built-in synth (basically a JX3P) but is less instant in its response than the newer Ibanez and Shadow. The Shadow is built into the guitar of your choice, and it has a built-in sequencer, but more of that later.

Now, a lot of 'traditional' music people, retailers and musicians alike, are reluctant even to try (let alone buy) a hi-tech instrument like this. It's partly fear of the unknown, partly fear of looking stupid, and partly lack of imagination.

To get over that level of market resistance, a guitar synth has to be a) instantly playable by any punter in any music shop, b) not too temperamental, c) fairly responsive to normal guitar technique, and d) based on a nice instrument to start with.

The Shadow MIDI system consists of a pickup and a 19" 2U rack-mounted unit, with a small three-pedal board. A variety of pickups can be fitted to any guitar of your choice, but for review purposes, I was provided with the system on a Squier Strat, which was a pleasant instrument to play. A Shadow locking tremolo system was fitted to the guitar, and the pickup sat beneath this; consequently there were two distinct audio output signals available, as well as the output to synth. This facility in itself makes the Shadow system attractive, with a range of extra tones available from the 'acoustic' pickup off the bridge, as well as the full range of Strat tones from the five-way selector on three single-coil pickups.

The guitar is connected to the unit by a stereo jack cord, which goes into the top left-hand corner of the front of the unit. Just below this is a five-pin DIN socket for the footpedal unit. Next along we come to the main control panel, which is also detachable for use as a remote control. This has a total of 13 pushbuttons and an LED display, which will be detailed later. Next along are six string sensitivity adjusters and an overall sensitivity pot, and an on/off switch.

The back panel has two output jack sockets, one for acoustic guitar transducer signals and one for electric guitar pickup signals. Beneath these are two MIDI Outs.

On powering up, the module is immediately ready for action. However, if you haven't used it before, the best way of beginning is to do a 'Cold Start'; this clears the memory and sets all the parameters at default levels. From here on, all manner of subtle adjustments can be made to suit your personal use of the system. I don't propose to discuss them in too much detail (I could write a book...), but a brief overview of what the unit does, and how it does it, may be useful.

First of all, it's necessary with any MIDI controller to establish contact with the synth you're controlling. The best way of doing this, according to Shadow, is to ask the built-in sequencer to punch out some music so that you can make sure the synth and amp are on, and then adjust the volume. The piece they've chosen is 'The Dwarf's Dance' by Grieg. I suppose any robotic music would have the same effect after the fifth or sixth hearing, but not only did I consciously avoid pressing 'Sequencer Play' at this stage, I also began having nightmares about the piece starting up at just the wrong moment. You know the problem: you go back to the unit to check your tuning, press the wrong button and suddenly the PA erupts with a jaws rhythm and a tune like an elephant's mating dance.

To ensure that the unit interprets the guitar signals correctly, the first procedure you must go through is Tuning. This is an easily accomplished and remarkably user-friendly process. The left-hand column of buttons has two LEDs above it, one marked Play, the other Program. The top button selects between these two options.

Tuning is performed in the Program mode, by pressing the bottom button marked (logically enough) Tune. The display then shows two horizontal lines until you pluck a string, at which time one or other of the LEDs below the display indicates whether that string is flat or sharp, and the display indicates by how much.

Turning to performance, it's fair to say that all pitch-analysis systems produced so far introduce some kind of delay. The delay on the Shadow system is quoted as being 6 milliseconds or two cycles, whichever is longer. That's pretty short, and frankly you don't notice it too much above the pitch of the open D string. Below that, the delay is obtrusive, and (as on the other systems) you have to cover up the delay with guitar sound. However, with the possible exception of the Ibanez, the Shadow's is the best all-round triggering I've heard to date on this sort of system.

As already mentioned, a lot of guitar synth sales are lost by the fact that you can't just pick them up and play them. Systems that use a hex pickup need to be adjusted for sensitivity to suit each individual player. On some designs, this involves electronic programming or fine adjustment of small hidden screws - not the sort of task many musicians are capable of performing at short notice.

By contrast, the Shadow system is pretty much instantly playable. It's as well to be aware that your fingerpicking might be a little too light for the pickups, but to solve that, you need only to tweak one of the Sensitivity pots on the front panel. If the synth you're playing is velocity- or touch-sensitive, you can adjust the Dynamics control to use those parameters effectively.

On the MIDI side, the Shadow transmits only the following information: Key On, Key Off, Key Velocity, Pitch Bend, and Program Change. What this means in plain English is that you can control up to eight synths independent of each other; one for each string, one for the Sequencer and one using the Hold function. This is done by assigning each synth to a separate MIDI channel. You can also, of course, use the Shadow unit to change patches on your synths remotely.

Now, as MIDI is generally keyboard-oriented, each semitone on the keyboard is assigned a MIDI number. In order to get the subtle pitches in between these semitones, which guitarists take for granted when they bend a string, MIDI contains a parameter called Pitch Bend. However, on most keyboards, and therefore on most MIDI systems, there's only one pitch-bend. This can cause problems if you bend more than one note at once on the guitar which is common practice, really), and with some guitar-synth configurations in the past, whole chords have been transposed when the player only bent one string.

The GTM6 responds to string-bending in one of three ways, each of which you may find useful.

In Trigger mode, every time you reach a semitone above or below the previous recognised pitch, a new note is started. That is, it starts the envelope again, as if you'd played a new note. As the handbook says, the result sounds as if a pianist were trying to imitate a guitarist.

In Quantize mode, the unit again responds only when a new semitone pitch is reached, but this time without starting a new envelope. The note is still dying away, but the pitch changes in semitone steps.

In Bend mode, the synth follows your bend exactly. Problems arise, as I've suggested, when you pluck two strings and bend one or both. If you're using one synth for each string it's fine, because each synth can respond to an individual pitch-bend command. But if you're only using one or two synths, the Shadow reverts to Trigger mode until you play monophonically again. The range for pitch-bending is four or eight semitones up and down.

More drastic changes of pitch are accommodated on the Shadow by transposition. It's possible to transpose any of the strings up or down by a maximum of three octaves, which opens up mind-boggling possibilities. The idea of using a variety of tunings is certainly appealing, and the opportunity of playing some of Stefan Grossman's rags on detuned steel-strung acoustic, with a honky-tonk piano sound on the synth, is very welcome. Well, it is to me anyway.

Three pedals are supplied with the system, and these are connected to the front panel with a standard MIDI lead, as it happens. The first (starting from the left) is called Rec-Play/On-Off, which as its designation suggests turns the synth sound on and off. This plays a key role in operating the sequencer, too.

The middle footpedal is Hold. You can use it in one of two ways; either a) to hold a chord on the synth sound while you solo over it with the guitar sound, or b) to switch between two synthesiser sounds.

The third pedal controls the Chain function. This allows you to step through a pre-programmed sequence of patches, to change the Bend, Quantize or Trigger options in each case, and even to store individual chains of presets for the Sequencer or Hold facilities as well.

The Sequencer is simultaneously an exciting and frustrating addition to the Shadow system's armoury. Frustrating because it's one of those that literally accepts the information it's given. That might sound stupid, but what it means is this. Having selected the Sequencer option on the main unit, you stamp on the Rec/Play pedal to start the recording. Play the sequence, and as soon as you've finished, press the pedal again. If you happen to stand on the pedal at just the right moment, the sequence will be perfectly in time. If, on the other hand, you get it slightly wrong, then your 16-bar blues sequence will turn out to be 15.9 or 16.1 bars long, and will go round and round with a permanent limp.

All in all, though, the Shadow system has a number of benefits to recommend it. To start with, you can have it fitted to any guitar of your choice; I've heard it on several different electric and acoustic guitars, and have as yet witnessed no 'glitching' problems (caused by the hex pickups responding to resonances in the body) at all. You can also use it with any MIDI synth, too, which could be handy if there's more than one keyboard in your band, for instance.

Technically, I reckon this is the fastest pitch-analysis system I've heard; it's a compact unit which is very easy to use, and it has a built-in sequencer which some may find useful, though it is difficult to get absolutely spot-on.

Also against the Shadow is the fact that there's still something of the delay that seems to characterise all these systems, and some guitar players will undoubtedly find that difficult to live with.

Price GTM6 rack unit £899; pickups for a variety of guitars are available from £75 for a standard acoustic transducer, to £140 for the Shadow locking trem unit fitted to the review Strat

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