To be honest I thought the Chroma was pretty much a dead loss when I first met it. Artful demonstrations at exhibitions started to win me round, though they were always accompanied by loads of ancillary gear and apologies that this elaborate gadget wouldn't be available in Britain for some months.

Finally I spent a day with one and many, though not all of my reservations slipped out the door.

The Chroma was originally designed by ARP, the firm absorbed by CBS in America to form a partnership with their Fender Rhodes division.

It's a strange looking device. There are no obvious controls but a series of 50 pressure switches that show on the black front panel as small numbered squares. They serve a double purpose, calling up memorised sounds or allowing access to parts of the electronics.

A single slider called a Parameter control acts in a similar way to the Incrementor knob on the Moog Source. Suppose you want to change the filter resonance. First press the parameter select button which converts the panel to its second level, hit the appropriate square according to the detailed instruction manual (in this case 38) and the slider becomes the filter resonance control.

It's not quite that simple of course. The Chroma is computer based — a tired phrase these days, but apt in this situation. Each square has a series of steps within it, shown in an LED readout as figures. The filter resonance has eight steps from minimum to maximum (not really a fine enough division, I feel) whereas the tune button has 64 and the modulation depth controls a total of 126 — the LED reads -64 through 0 up to 63.

In certain cases those numbers don't represent grades but different functions. Take square three, the keyboard "organiser". A zero means polyphonic, whereas the figures 4 to 9 switch in six different forms of monophonic playing, 10 to 13 are individual arpeggio patterns, 14 is a sequencer and 15 is random.

The computer control has practically isolated every section of the Chroma's electronics, almost like a modular synth. Instead of using leads to connect them in the desired order, the links are made by these numerical instructions.

The advantage is, you can virtually construct the synthesiser YOU want. The disadvantage is that the machine itself gives no clues on how it's set up. There's just a set of numbers and without the instruction manual you're totally sunk.

The potential as a player's instrument is remarkable. The Chroma has a piano weighted, wooden, touch sensitive keyboard, two pedals and two modulation levers at the left of the 64-note E-to-G keyboard. They can be patched in to control virtually any of the Chroma's facilities — volume, filter, cut-off, attack and decay times, etc.

With all that potential, it's a shame they didn't spend a few more bob on decent modulation wheels instead of the cramped and awkward levers. What's that about a ha'peth of tar?

The Chroma has two oscillator banks coupled with independent filter and VCA sections. A maximum of 16 notes will sound at once or eight if you want to double up for a thicker sound. Certain of the factory programme were set to four notes with the extra oscillators jacked up in pitch to provide additional rich harmonics.

The Chroma keyboard can be split anywhere and the individual halves then taken up or down an octave. It can provide different sounds at each end or overlay two memories throughout the entire range, still retaining eight notes. Polyphonics like the Roland Jupiter 8 and OBX, have to drop to four notes when they pull off this trick.

It does require a re-think. For example the envelope generators are attack, decay and release, there's no sustain. Instead you have to think about how the touch sensitivity is connected up and what modulation is operating over the final volume.

The Chroma shares the clean, spikey quality associated with digital instruments and is better making true, acoustic sounds rather than big, squelchy synthesiser classics. It also manages to be its own effects unit capable of generating phasing or flanging effects by the proper alignment of cross modulation and filters.

The modulation facilities are extensive and inventive, accounting for much of the Chroma's internal flip flopping. Many of the settings triumph because of their unusual harmonic or dynamic inversions — a bit "alien". For example the modulation waveform shapes include sine, cosine, off-set sine, half sine, sawtooth, triangular square, lag square and random, plus six patterns of higgledy piggledy ups and downs that take the Chroma on a round trip of the Hebrides.

There are some oddities within the machine. The sequencer will remember how hard you hit the notes, but not the timing. Everything is reproduced in a metronomic beat. There are only sawtooth and pulse width waveforms on the oscillators, though to be fair the saws can be distorted to alter the harmonic structure. I think it LOOKS naff with a metal strip holding the front panel together, also the pressure switches are nowhere near as easy to trigger as you'd think. A light touch is not enough.

But there are more opportunities for creative and personalised patching than on any similarly priced rival. It requires knowledge and practise to draw the best from it, and the Chroma is not a fast machine to set up. The memory positions are therefore essential and 50, these days, is quite a low number, though a fast tape dump system can save and load in new sounds in less than a minute.

It's an excellent touch sensitive keyboard, and another version with second touch facility to bring in effects is on the way. The pedals are also cleverly arranged.

It's expensive, and I think it will appeal to a limited audience. My major remaining reservation is its positioning — halfway between a standard poly synth and a fully fledged computer, too pricey and complex for some, not powerful enough for others.

£3800