Every time the word Minimoog appears in an interview, an ARP Odyssey fan gains another grey hair; once considered the Minimoog's rival, the Odyssey seems to have been forgotten by modern music.

MANY YEARS AGO, when I believed Keith Emerson talked to God, I'd lie awake at night wondering why the sounds I got from my primitive Korgs, Rolands, and Crumars paled in comparison to those of the professional keyboard "wizards" of the time. I managed to discover part of the answer in time to convince myself that it wasn't just my playing style that was at fault.

The missing element was class: that elusive sound quality that makes certain keyboards into Instruments in much the same way that orchestral instruments have their own characters. Although the "rock" keyboard has only been with us for 20 years or so, several classic keyboards have been created in that short time - the Mellotron, the Minimoog, Prophet 5, and the ARP Odyssey to name but a few.

Now, I wouldn't expect anyone who considers the original DX7 an old instrument to agree with me, but I feel that many modern synthesisers could learn a lot from the Odyssey. We're talking about a machine that could imitate classical instruments with convincing passion and excite with new and innovative sounds. It's only monophonic of course (actually it's duophonic, but we'll come to that later), but when did you last hear a polyphonic flute or saxophone? For me the thing that sets the Odyssey apart from other synths is a sound quality unsurpassed in some areas by even the most sophisticated digital keyboards.

ENOUGH OF THE lyrical waxing. Just who were ARP and what was the Odyssey? Well, ARP were an American synth manufacturer named after their founder, designer Alan R Pearlman. My own Odyssey previously belonged to Robert John Godfrey of The Enid. As a long-time owner of ARP keyboards I asked him about their background.

"In the early 70s there were only two serious manufacturers of synthesisers", he told me, "Moog and ARP. Both companies were at the forefront of development of the wall-to-wall modular systems of the time such as the ARP 2500 and the later ARP 2600 series, and they were the first two companies to produce small synths that sounded good."

To bear this out there's a huge ARP modular synthesiser to be seen in the "mothership" scenes of Close Encounters of the Third Kind. I asked Godfrey when and why he bought his first Odyssey. "In 1975", came the reply, "specifically because I didn't want two Minimoogs".

Recalling the cost of both instruments at the time - around a grand - this may seem a touch facile, but then I realised it was actually pretty astute. The Odyssey has a unique character as a keyboard, producing a "live" sound - sharp, resonant and with something I can only describe as tremendous "zing". For the rock bands of the time, this gave a wide range of textures produced by combining the Odyssey with another, warmer synth - typically a Minimoog, but occasionally ARP stablemate, the Pro-Soloist. You can find examples of this on Jean-Michel Jarre's Oxygene and ELO's Out of the Blue. Dave Lawson of Greenslade, Don Airey in his Colosseum II days also used the Minimoog and Odyssey combination to great effect. And, of course, there was The Enid.

THE ODYSSEY IS not a particularly large synthesiser but it did manage to combine some features in a way that hadn't been seen before. The keyboard is three-octaves C-to-C giving a total range, with octave switching, of seven octaves, and with broad tuning, a range from sub- to super-sonic. There is, of course, no velocity or pressure sensitivity. All the controls are positioned on the top panel, which was white on early models but changed to gold on black or orange on black on later ones. On the early models the underside of the case extended under the keyboard, but later models (sometimes called the Odyssey 2) had a less robust case which left the last inch or so of the keys totally exposed. This may have been alright in a studio situation but it was definitely a backward step for the gigging musician - an alarming number were soon to be seen with broken keys as a result. Another nice touch on the early models which was subsequently abandoned was a system of colour coding the panel controls to aid programming.

With the exception of pitch-bend and octave up/down, all the controls are either sliders or two-position selector switches. Part of the attraction for many players was the logical layout of the controls which enabled even the most reticent synth player to understand and experiment with sounds. The importance of this back in 1975 is not to be underestimated - remember that there were no patch memories then and all voice modifications were carried out "live" - often halfway through a song under stage-lit conditions.

On the extreme left of the panel is a pitch-bend knob - unfortunately devoid of a central default position - a slider to control the portamento time, a switch to set the whole instrument two octaves up or down, and a white/pink noise selector. The portamento on the Odyssey always struck me as non-linear - that is, the glissando starts slowly but accelerates towards the end - unlike the mechanical, linear glides found on so many synthesisers. The unconventional and unpopular pitch-bend knob was replaced on the Odyssey 2 by an equally unconventional and unpopular pressure pad arrangement called Proportional Pitch Control. Three pads sat under three fingers of your left hand and gave pitch-bend up, pitch-bend down, and vibrato, each effect proportional to the pressure applied to the pad. Personally I found this arrangement extremely playable, perhaps because it was a forerunner of today's pressure-sensitive keyboards. The idea was never picked up by other manufacturers and so has disappeared completely.

The synthesiser's two VCOs both have coarse and fine tuning sliders and VCO2 has a sync switch to lock it to VCO1. When not locked the oscillators are entirely independent (although only one trigger is provided which re-initialises all VCOs and envelope generators) and the synth can be played duophonically. Also, VCO1 can be used as an LFO in addition to the dedicated LFO. Both VCOs have extensive frequency modulation: for VCO1 sine and square wave LFO can be added as well as ADSR and Sample and Hold (S/H) tracking. VCO2 has LFO sine and pedal modulation, as well as ADSR and S/H tracking. The outputs of both oscillators may be either sawtooth or square wave, so in addition, pulse-width modulation is available independently for each VCO. Pulse-width varies from approximately 5% up to a 50% square wave. PWM may be modified (again independently) by LFO or ADSR. These facilities give the "big" sound now associated with the analogue synths of yesteryear. The oscillators sound fat without any further modification or modulation, let alone chorusing.

OVER THE YEARS much has been made of oscillator stability (or instability) in early synthesisers. In my experience the Odyssey, once set up, remains just about perfectly pitched throughout a 90-minute set in all conditions from humid bars to sub-zero (well, it felt like it) outdoor stages. Whether this is due to design or some clever tampering by the previous owner I do not know. However, it's also believed that a little instability (not to be confused with tuning drift) can add a touch of random harmonic variation, much like a naturally occurring sound.

"In live performance the Odyssey allows expression even without velocity and pressure sensitivity - but in the best tradition of synth posturing you do need to use both hands."

The Odyssey's LFO is a simple 0.2-20Hz slider, and a S/H mixer. Sample and Hold voltage may be obtained from VCO1 square wave, VCO1 sawtooth, VCO2 squarewave, or the noise generator. Triggering is by LFO or keyboard, and an uncalibrated output lag can be inserted between voltage sample and output.

The largest area of panel-space is devoted to the audio mixer, filters and amplifier. The mixer is a fairly straightforward affair, mixing VCO1, VCO2, and the noise generator together. Ring modulation can be added to VCO1 and VCO2 in varying degrees if the noise generator is sacrificed. There are two filters, a low-pass VCF with VCF resonance, and a simple high-pass VCF. Both filters are infinitely variable from 16Hz-16kHz and the resonance is variable from zero to self-oscillation. The low-pass filter can be modified in no less than seven ways, of which three can be active to any degree simultaneously. These are: keyboard CV (infinitely variable) or S/H mixer or footpedal (wah-pedal synthesiser); S/H or LFO sine wave; envelope one (ADSR) or envelope two (AR). This sounds impressive even by today's standards but remember two further things: firstly, that this machine was freely available in 1975, and secondly that the parameters were infinitely variable with no quantisation into half-a-dozen or so pre-selected levels. The filters are four stage with 24dB/octave cutoff adding considerably to the "meatiness" of the sound.

The Odyssey's envelope generator is a traditional ADSR and the AR is a simple attack, sustain-whilst-the-key-is-depressed, release time generator. Both can be triggered from the keyboard (gate) or by LFO squarewave. In addition, the ADSR repeat can be switched between keyboard and auto repeat.

Interfacing on the earliest models was virtually non-existent. Later models incorporated CV In and Out connections, Gate In and Out, and Trigger In and Out. An External Audio Input was also provided on the Odyssey 2 for processing anything you could put down a standard quarter-inch jack lead.

THE ODYSSEY HAS two areas of great musical strength - the imitation and exaggeration of orchestral instruments, and the creation of effects. Impressions of brass and flutes can be obtained very easily, and with a cutting edge to the voicing that is missing from so many other keyboards. In live performance the layout allows modification of the sound harmonically or with modulation to give expression even without velocity and pressure sensitivity. However, in the best tradition of analogue synth posturing - you do need to use both hands to obtain the best from the system. The modulation facilities and envelopes are as good as any ever offered on an analogue monosynth and are surely responsible for the fact that this was the only machine ever to rival the Minimoog as a lead synthesiser. In addition, the inclusion of S/H, pitch and envelope following, variable PW and PWM gave the Odyssey spectacular sound effect creation abilities only previously associated with modular synths.

If there is a criticism it must lie in how difficult it is to obtain warm, mellow voices. It is possible with great care and delicate balancing of the filters and modulation to approach the sound of a richer synthesiser, but the results lack the characteristic warmth of the Minimoog. Impressive, perhaps, but cold, distant, and featureless by comparison. The Odyssey's voicing, despite its ascendancy in some areas, can be quite limited in others, and for this reason, perhaps, the synthesiser never quite penetrated the market as much as it really deserved.

A lesser-known quality of the Odyssey is the simplicity of its internal architecture. With no more than a screwdriver the whole machine can be disassembled down to board level. There's no digital circuitry to fall foul of, and the system can be understood with even a limited knowledge of electronics. Inevitably, this led to some people modifying their Odysseys in rather interesting ways. My personal Oddy has seen the business end of a soldering iron on many occasions: currently it has an input for a guitar (although other sources could be used) which cuts out the internal oscillators while leaving the rest of the synthesiser fully operational, and the whole range of VCF, VCA, ADSR, and AR effects can be applied to the source material. A second input allows a conventional footpedal to control the filters. You may by now have gathered that this particular Odyssey has been adapted to act as a 24dB per octave wah-pedal - with resonance. There's no accounting for taste.

SO WHY DID such a flexible and playable instrument fall into disuse? Again, I asked Godfrey for his thoughts.

"We stopped using the Odyssey in about 1982", he recalls, "although we have used it once or twice since then. Round about that time we became interested in new things, new technologies, and we produced an album that simply did not require it."

ARP then went very much the same way as their most popular synthesiser. Following the successes of the Odyssey and the much revered Solina string/brass synthesiser, and to a lesser extent the Pro-Soloist, they managed to produce a sequence of progressively less and less popular keyboards. Anyone remember the Omni, Omni2, or the Quartet (also known as the Siel Orchestra)?

A polyphonic combination of various ARP machines, the Quadra, achieved limited success around 1980, but by this time the Prophet 5 had captured the imagination of the rock world and ARP had nowhere to go. Their associations with Siel and Solina had done nothing to enhance the image of the company, and the Japanese giants moved in for the kill. I believe the last machine that they ever built was the Chroma - a hybrid analogue/digital polysynth that was researched and designed by ARP but picked up by Rhodes after their demise. The development effort broke the company and it quietly disappeared from the scene.

Fashion is an important influence in modern music and many good instruments have fallen due to the incessant clamour for new sounds and greater facilities. Nevertheless, if you're an aspiring keyboard virtuoso, and you can't quite get the lead sound you want from your DX7, DW8000, D50 or ESQ1, I recommend that you scan the free ads regularly. Odysseys occasionally appear for about £250, and if you think that's a bit much to pay to play one note at a time, go and talk to a flautist or saxophonist. You'll learn that it's not how many notes you play, it's the notes you choose and the sound that you produce that determine the reaction you get from your audience. Essentially - there's no substitute for class.