That the kings of analogue monosynths were the Minimoog and Odyssey is undisputed, but there were others - take ARP's ProSoloist, Roland's SH2000 and Korg's Sigma...

THE SECONDHAND MARKET is an important starting point for many aspiring musicians. Partly for this reason, and partly for pure historical posterity, many old keyboards have appeared on these pages for re-appraisal. Some are notable for being the first of a kind, some produce unique sounds, some are just plain curious. This article throws together three synths from different manufacturers which clearly, in retrospect, belong together as a family. These are the ARP ProSoloist, the Korg Sigma and the Roland SH2000. These were preset monosynths and, although they all sported some degree of synthesis capability, they were specifically designed to make flutes, oboes, violins, trumpets and many other classical instruments available to the synthesist. Originally costing well over £500, they were all monophonic (a Minimoog cost £1200 in those distant days) but, with the exception of the hernia-inducing Yamaha CS80, they were the only synths to offer one facility that we now expect to find on any serious synthesiser: pressure sensitivity.

Pressure sensitivity is an important attribute for a keyboard because it comes closer than any other to imitating the action of a non-electronic musical instrument. Almost any musical effect that occurs after the start of the note (timbral change, vibrato, pitchbend, volume change) can be described in terms of additional pressure on some part of an acoustic instrument. Whilst each of these effects could be created on earlier keyboards using a combination of pitchbend and mod wheels, and on more recent synths using three-way controllers or joysticks, each of these devices requires a free hand, and you don't always have one available. There are very few alternatives; foot controllers are all very well, but not all synths can handle them, and you'll fall over if you try to use two simultaneously; breath control is better, but not everyone can get the hang of it. There has to be a simpler answer, and there is. You simply press the note down harder.

BASED AROUND PRESSURE- (but not velocity-) sensitive, three-octave keyboards, the construction of these synths is very basic. The only significant ergonomic difference between the Roland and the ARP is the position of the switches that select the voices. On the SH2000 these are found in front of, and below, the keyboard rather than behind, and above, it. The ProSoloist's top panel controls may be cheap and insubstantial, but worse than that, the Roland's toggles are badly exposed, and many an SH2000 suffers from broken switches. Luckily, Roland still have spares, and repairing the damage is only 20 minutes work. The Korg is the odd one out: it's beautifully built, bristling with knobs, rockers and joysticks, and its look is distinctly hi-tech. This dissimilarity continues around the back of the synth because - where the ARP's rear panel is simplicity itself, with just low and high audio outputs, and the SH2000 offers nothing more than the single jack socket (with three position output level switch) and a tuning knob - the Sigma is busy with controller inputs for filter modulation, VCO modulation, VCO pitch and trigger In, and outputs for trigger Out, and keyboard voltage Out, plus separate outputs for the two instrument sections (more later). Even a headphone socket is provided on the Korg. Clearly, where Korg saw their machine as a genuine synthesiser, it's quite possible that neither ARP nor Roland envisaged their offerings in this way, but as add-ons for the organ at the local social club.

Consequently, understanding and operating the ProSoloist or the SH2000 couldn't be simpler. The ARP has 30 voices collected into six groups: reeds, woodwinds, brass, strings, percussion, and guitar, selected by 16 toggle switches (15 selectors plus the equivalent of a shift key). There are also 30 voices on the SH2000, but these are grouped into 12 rather looser groups - brass, woodwind, strings, more strings, guitars, keyboards, percussive instruments, four groups of variously silly sounds, and noise.

Almost all the controls on these synths are found to the left of their respective keyboards, and are almost exclusively related to the pressure sensitivity of the instruments. On the ARP these are: pitchbend (approximately a tone if you stand on the key); wow; growl (square-wave type distortion); brilliance; volume; and vibrato (with variable speed). The Roland offers one fewer touch-sensitive parameter than the the ARP; pitchbend, wow, growl, volume, and vibrato. However, instead of the ProSoloist's touch brilliance control the SH2000 sports a rudimentary filter section featuring low-pass cutoff frequency, resonance (which can be driven into self-oscillation) and modulation. Unfortunately, on both synths the depth of each touch-sensitive parameter is only controlled by a global Touch Sensitivity control, so if you want lots of (say) vibrato, you can only have lots of the other effects as well - or none at all. The ProSoloist only has five additional controls: master volume, initial brilliance (a low-pass filter), a three-position octave selector switch, a repeat option (which retriggers the percussive voices at the vibrato speed), and variable rate portamento. The SH2000 offers all of these but also includes pitch control (plus or minus a semitone), hold, and "long sustain" which extends the normal release time of a voice.

"But just as you're about to write the Sigma's Synthe section off, you discover the ring modulator"

The Sigma, meanwhile, offers two distinct sound creation sections - Instrument and Synthe. Only the Instrument section corresponds to the ARP and Roland, and this offers just 11 voices, grouped in footages rather than instrumental families. Selected using rocker switches situated on the control panel behind the keyboard itself, each voice has a single variable parameter for greater flexibility. For example, you can alter the filter cut-off frequency on the tuba, change the pulse width of the clavi, and modify the attack of the strings. Although there are fewer basic voices to be found on the Sigma, the performance controls which affect them are, at least on the surface, more advanced than those of the other synths. Octave up/down, portamento and keyboard pressure sensitivity are to be found as expected, but two joysticks are also provided. Only one of these works on the Instruments, but this offers both vibrato and pitch shift. Unfortunately, the pressure sensitivity capability is much more limited than that of the ProSoloist and SH2000 and can only be directed to the joystick parameters (and even those can't be used together). On the other hand, the Sigma offers delayed vibrato (with variable depth, speed and delay), multiple triggering, and key hold, plus "quarter tone" which, when a note is held, re-scales the keyboard in quarter tones rather than semitones. Curious.

In addition to the Instrument section, the Sigma boasts the intriguing Synthe department. There are eight Synthe voices, which include square, PWM, and sawtooth waveforms of various footages ranging from 32' to 4', as well as Sample & Hold, and Noise. As with the Instruments, each of these are limited to a single variable parameter: five waveforms have variable A/R times and two have variable decay. Only the S&H has a different structure - its variable is Clock Rate. But just as you're about to write Synthe off, you discover the ring modulator. This modulates the sum of the Synthe voices selected against the sum of the Instruments. Some huge analogue sounds can be conjured from this, especially since the Synthe section can be detuned against the instruments. There are also several performance controls (in addition to those controlling the Instruments) which act exclusively upon Synthe. Primary among these is the filter joystick. This (supposedly) preset keyboard possesses both low-pass and high-pass 12dB/octave filters, and these are controlled by a single two-dimensional joystick. The second performance control is the combined vibrato/noise depth/pitchbend joystick and, since the pitchbend range of Instrument and Synthe may be independently set, this offers even more interesting possibilities. Finally comes portamento. The flexibility offered by combining Instruments, Synthe, ring modulation and detuning, can make the Sigma sound like a very much bigger instrument. Never was there a more curious synthesiser than this.

DESPITE ITS LIMITATIONS, the ProSoloist became a highly-respected and widely-used synth. It comes as no surprise, then, that it doesn't sound good - it often sounds fantastic. A wide range of waveforms has been coaxed out of its single analogue oscillator, but the real secret of the ProSoloist undoubtedly lies with its filter. The range of textures produced is remarkable, and the musical quality of the filter modulation is unsurpassed even (some would say especially) today. Given such limited controls, the 30 basic sounds can be manipulated into a wide range of timbres from the softest warm tones to screeching excesses. Indeed, the ProSoloist flute has the sort of sound that gives human flautists a bad name. The tuba is good but in it, transposed up with the filter wide open and maximum growl, lives the brassiest brass you're ever likely to hear. The cello is haunting, the bassoon is woody... All the voices give you some degree of inspiration, and although many of them are as dated as 26-inch bell-bottoms, the essential appeal of the sound has survived the years. As a counterpoint or accompaniment to the relative sterility of, say, a DX7, the ProSoloist is magick.

"Plug an SH2000 into a Roland Space Echo and the harmony lines of a dozen 70s albums leap out of the monitors."

In contrast, the SH2000 is the poor relation of the three synths. It neither possesses the powerful voices of the ARP, nor the expansive potential of the Sigma's synthesis. Yet switch one on, plug it into a Roland RE201 Space Echo and the harmony lines of a dozen 70s albums leap out of the monitors at you. While none of the voices grab you in the way that some of the ProSoloist voices do, experience shows them to be very usable. Nevertheless, as a soloing instrument, the SH2000 is a disappointment, largely because it lacks the punch of a pukka lead-synth. The strictly single-oscillator voices are thin and pure, and seem to have been designed to be a pleasant, perhaps even unexciting, accompaniment alongside other, more powerful instruments. In that role the Roland excels and although that sounds like damning with faint praise, there is often a place for such an instrument. Unfortunately, that place doesn't really lie within the current music scene.

The Sigma is again the odd one out. For example, it possesses the ability to play more than one Instrument or Synthe patch at once. Whereas the ARP (and the Roland) can only produce one voice at a time, the Korg will allow you to depress as many voice switches as you like - 19 quite different sounds produced simultaneously every time you press a key - and although it doesn't possess 19 oscillators, the resulting noise is both loud and monstrous - a real mix destroyer. Unfortunately, the Instrument voices played on their own are a disappointment. Neither gutsy like the ARP, nor clean and precise like the Roland, the voices are thin, bland imitations of their orchestral inspirations. So it's just as well that the Synthe can be tuned independently of the Instruments, enabling chorusing as well as split-pitch playing.

The ARP ProSoloist never looked like a serious synthesiser, but it's slowly becoming a bit of a collector's item, commanding £150 or more. Despite professional recognition and a face-lift in 1980 (to the semi-digital Pro/DGX sporting ARP's latter-day black and orange livery), it never received in its own lifetime the public acclaim that it deserved. Significantly less prestigious than the Minimoog or its more famous ARP sibling the Odyssey, the ProSoloist nevertheless created some of the most memorable sounds of the 70s - Genesis, Wings, Joe Zawinul, and The Enid were users amongst many others. But perhaps the main appeals of the ProSoloist are the ease with which it can be used, and the range of expression that can be coaxed from six parameter pressure sensitivity. Despite the fact that it can't easily be MIDI'd (no CV and gate), it's monophonic, and it sounds like a Genesis LP, you could do a lot worse than to snap a cheap one up. Where the ARP has a gutsy sound which will survive well beyond 1991, the SH2000 shows its Reginald Dixon heritage all too clearly. Although the inclusion of a resonant filter is a definite plus point, and the filter modulation, no matter how limited, makes the range of timbres and effects obtainable from each voice quite wide, it would take a resurgence of interest in "comfortable" 70's bands like Camel and Caravan to rekindle interest in these sounds, and that's not really on the cards right now. As a consequence, the value of the SH2000 is approximately zero. If you do see one for sale, the asking price should be very low - probably well below £50. The only moral that comes to mind is that of Roland's TR303 Bassline: until acid house caused them to change hands for the best part of 200 quid, you couldn't give them away. At the moment, however, you'll either find the SH2000 bland, or a refreshing change from the usual fare.

When the Sigma came out in 1979 alongside the Korg Lambda and Delta, its design and facilities put the older ARP and Roland to shame. Yet the Sigma never caught on, and within a few years it had vanished. And that's a shame, because the range of possibilities contained within its weird architecture is huge, despite the obvious limitations of the Instrument section. Consequently, its resale value is pretty low - shop prices below £100, private sales around the £50 mark. Who knows, if a bit more fuss had been made of the original Sigma rather than focussing on its limitations, there may have been a Sigma II, and that could have been a very weird and interesting synthesiser indeed.

IT WOULD BE usual to conclude by suggesting which of these instruments offers the best sounds and facilities, and which is the best secondhand buy. But there is a more fundamental issue here: the facilities which we now take for granted - 16-bit sampling, digital effects, multitimbrality and so on - allow anyone to create fantastic sounds and even attain commercial success without much musical creativity. A T3 or a D70 can give you the feeling that you're creating something wonderful, but then you discover that there's no musical substance to it. It's a bit like a drug high: easy to achieve but ultimately worthless. So perhaps the real value of these old synths is that they help you to get closer to the music itself. It's no coincidence that the majority of voices on all of them are orchestral. There are 400 years of tonal development wrapped up in those sounds - sounds which have the ability to stir feelings. The better the imitation then, in theory, the more effective the voice becomes. And an effective instrumental voice demands playing expression. Which brings us back to pressure sensitivity - which is where we started.