Cherry Audio Pro Soloist

Cherry Audio have resurrected the venerable ARP Pro Soloist in software.

I make no bones about my love for the ARP Pro Soloist, and I wouldn’t be surprised if there were secret cabals in SOS‑land who regularly take the piss out of me for referring to it in reviews of other equipment. I don’t care. Every time that Korg have hinted at another recreation of a vintage ARP, or Arturia have teased their next slew of soft synths, my fingers and toes have been crossed in the hope of an accurate recreation of this funny little preset monosynth. And, finally, it’s arrived. But it’s come from elsewhere...

You might be wondering what made the Pro Soloist special, and why I think that it remains so. To answer this, let’s return to 1971, a year in which changing from one synthesized sound to another was an activity that could at best be described as hit‑or‑miss. Most of the time it involved repatching, although, on the new‑fangled Minimoog that was just about to appear, a pre‑defined signal path meant that you needed only press a few switches and twist a bunch of knobs to obtain something that — if you were lucky — approximated the sound you wanted. But this was also the year in which ARP released the Soloist, a small synth that allowed you to jump from any of its 18 preset voices to any other at the flick of a toggle. Not only did this sound great, it introduced something revolutionary that we now take for granted. Despite Cherry Audio’s website and manual claiming otherwise, the Soloist boasted aftertouch with up to six simultaneous destinations: pitch, vibrato, wow, growl, brilliance and volume.

You might be wondering what made the Pro Soloist special? To answer this, let’s return to 1971... the year in which ARP released the Soloist, a small synth that allowed you to jump from any of its 18 preset voices to any other at the flick of a toggle.

The Soloist was a marvel but, sadly, it was flimsy and prone to failure. So, the following year, ARP release the Pro Soloist. This also had its shortcomings, but it exuded one quality that overrode any criticisms: its 30 presets could sound amazing. But how? Surely, it’s just a single‑oscillator preset monosynth with a signal path comprising nothing more than a VCO, VCF and VCA, right?

No. Wrong. Very wrong. In many ways the Pro Soloist was the most innovative of all ARP’s synthesizers, and much of its architecture was unique, including a digital keyboard scanning system and a fascinating audio generator that comprised a high‑frequency oscillator driving a logic counter, which in turn produced a stream of pulses that were used to generate the initial waveforms. Then there was the way that ROM chips were used as switch matrices to change the voicing when you selected a new preset. Furthermore, there were multiple signal paths through the synth, one of which passed the oscillator’s output to three filter banks containing 10 tuned resonators. When you selected a voice, a bunch of digital gates directed the signal through (up to) five of these resonators to obtain complex timbres that, even today, can be produced on little short of a modular synth or its software equivalent. Not only could the Pro Soloist produce orchestral sounds that were more accurate than anything else of its era, its aftertouch made it one of the most expressive synths ever produced, and some of its sounds remain revered to this day, especially amongst fans of mid‑’70s Genesis [check out Tony Banks' 'Riding The Scree' synth solo, from The Lamb Lies Down On Broadway album, for a great example of the Pro Soloist's capabilities - Ed]. The Pro Soloist was itself superseded by the Pro/DGX in 1977, but later versions of this replaced the revered ARP4012 filter of the Soloist and ARP4034 of the Pro Soloist and early Pro/DGXs with the ARP4075, and were considered (perhaps rightly) as inferior, so we’ll say no more about it.

Standing On The Shoulders Of Giants

The Performance screen of Cherry Audio’s Pro Soloist looks much like the original synth, although a closer inspection reveals that it’s a hybrid of the Pro Soloist and the Pro/DGX and offers several new features, including aftertouch‑controlled wah‑wah and tremolo. Since the GUI is too small to contain everything that the soft synth offers, a second screen provides access to all of the hidden goodies of the Pro Soloist and then adds many more. For example, you can now program the sync’able LFO and both contour generators, access all of the wave generation in the oscillator (which now offers a Super Wave option), and determine how much of which waveform (or waveforms) passes down each of the audio paths. You can also program the all‑important filter emulation, and this now boasts an unusual feature: you can change the polarity of its output to create frequency cancellations and reinforcements when you mix it with the other audio paths through the synth, and this greatly extends the sound design potential. In addition, Cherry have replaced the original resonator banks with five programmable resonators rather than 10 fixed ones. Happily, each of the original curves is available as a preset, thus making it possible to obtain any of the original voices. There’s also a six‑slot modulation matrix. Each slot contains a source, a ‘via’ and a destination. (A via allows you to control one modulation source using another.) There are 22 sources, 22 vias, and 57 destinations on offer and, since most things can be controlled using Cherry’s usual MIDI Learn system, it’s immensely powerful.

Unlike the original, Cherry Audio’s Pro Soloist gives you full control over the synth from the second screen Edit page.

The third screen allows you to polish your sounds with five dedicated effects sections that can be sync’ed to master clock and MIDI Clock where appropriate. Distortion offers a choice of tube and fuzz modes; the phaser offers a choice of poles for a range of famous phasing effects; the flanger/chorus offers a selection of modulation waveforms; the echo has digital, tape and ping‑pong modes plus stereo spread; and the reverb offers five modes with high‑pass and low‑pass filters to sculpt the reverberated signal. The results are not as whooshy (or as noisy) as passing the output from an original Pro Soloist through a Big Muff, Phase 100, Electric Mistress and Space Echo, but they extend the capabilities of the soft synth without tying up your plug‑ins or external boxes, and that’s no bad thing. The final feature is a sync’able arpeggiator with up to three octaves’ range and up, down, up/down and random modes.

The third screen is dedicated to the built‑in effects and an arpeggiator.

The Sound Of History

Although I was nowhere near my studio when Cherry Audio sent me the soft synth, I couldn’t resist launching it, selecting the Tuba, pushing it up an octave and... Oh my word! Even when played from my computer keyboard and monitored through headphones, it farted at me in exactly the way that it should. This was a great start! Later that evening, I liberated a Pro Soloist from storage and compared the preset sounds of the soft synth with those of the original. Did I expect them to be identical? No, I didn’t, and neither should you, because not all Pro Soloists sound the same. If the components in one unit differ from those in another so that (for example) the centre frequency of a given resonator strays by a few percent, the two sound slightly different, because there’s nothing that you can do to bring them into line with one another. So was I concerned by the small differences that I discovered when comparing the soft synth with my Pro Soloist? Not at all. On the contrary, I was impressed. I sometimes had to make small adjustments in the soft synth to match the two but, as often as not, all that was needed was a tweak of the Brilliance to make the two functionally identical.

My favourite brass sound of the ’70s was the Pro Soloist’s Tuba transposed up an octave with Growl, Brilliance and Volume controlled by aftertouch. Again, the soft synth recreated this perfectly.

The soft synth retains and extends the Pro Soloist’s pressure‑sensitive capabilities, now offering channel and poly aftertouch as well as an innovative ‘last note’ mode that, when receiving channel aftertouch, controls the modulation of just the last note played. This makes it possible to emulate some of the things that you might wish to do with polyphonic aftertouch even if you don’t have a suitable controller to hand. I tested all of this, and was again impressed. I have always loved the Flute preset with the Volume and Vibrato controlled by aftertouch, and the soft synth recreated it with ease. Likewise my favourite brass sound of the ’70s was the Pro Soloist’s Tuba transposed up an octave with Growl, Brilliance and Volume controlled by aftertouch. Again, the soft synth recreated this perfectly. By this time, I was confident that all of the other voices would respond much as expected, and so it proved.

It was now time to play the soft synth in anger, so I set it up to respond to my playing in the way that I wanted. When using it as a monosynth, you can select between low‑, high‑ and last‑note priority with a choice of single‑ or multi‑triggering. Alternatively, you can turn it into a polysynth with a maximum of 16 voices per layer. Hang on a sec... Polyphony? Per layer?

Everything that I’ve described so far is but half of the soft synth because it offers Upper and Lower layers that duplicate everything: sound generation, performance settings, MIDI control, effects and arpeggiation. You can split and layer these to create two independent monosynths or two independent polysynths, or one mono and one poly, or bi‑timbral sounds, the last of which allows you to create some huge basses and lead‑synth patches. When programming, you can Solo either layer in place to check that it’s doing what you think that it should, and a small utility menu allows you to do useful things such as copying, swapping, importing and exporting. The only thing that’s global when you use it in this way is the limiter found on the FX screen, which ensures that you don’t distort one sound by pushing the other too hard. Hmm... that’s not quite true; if you want to weld two disparate sounds into a coherent whole, you can select a Global FX mode that causes both layers to pass down a single effects path to help glue them together.

Bi‑timbral Polysynth?

So how good is a Pro Soloist as a bi‑timbral polysynth? I must admit that — yet again — I was impressed. Monosynths can sometimes be overpowering when turned into polysynths because there’s too much heft behind each note, but the Pro Soloist survives the transition to polyphony in rude health, and I found it simple to program warm strings, pads, brass ensembles and choirs. It’s not a synth you’d choose for things such as chimes and pianos, because the lack of oscillator sync and FM largely precludes these but, in contrast, I was surprised by the ease with which I could obtain the floaty Vangelis‑esque sounds that pour out of it. It’s also capable of a surprising range of off‑the‑wall sounds and effects, courtesy of the modulation matrix. Nonetheless, the Pro Soloist’s forté remains orchestral sounds and, whether my target was a solo flute above an Oxygene‑inspired string accompaniment, or brass solos and stabs, or dual‑layered ensembles, the results were almost always superb.

Before finishing, I tried performing live (admittedly, with no‑one watching) with the soft synth. Controlling it from the GUI is clunky but I soon found that, in addition to the expected MIDI control and automation, I could assign each voice tab to a fader on my MIDI controller and then move the appropriate one up or down to select the upper or lower voices depicted on the GUI. Once I had programmed this, I was then able to recreate the famous solo from ‘The Cinema Show’ by Genesis. This is perhaps the definitive demonstration of the Pro Soloist, and famous for the way that Tony Banks flicks between presets as he plays. (OK, that doesn’t sound particularly impressive in 2024, but it was gob‑smacking in 1973.) Since MIDI maps can be programmed on a per‑patch basis, it’s even possible to allocate different presets to different faders for different tracks, which makes things even better for live performance. For the fourth time, I was impressed.

Finally, I should also note that all of the housekeeping (patch management, GUI settings, audio and MIDI set-up, oversampling settings, and so on) is common with other Cherry Audio soft synths, so I hope that you won’t mind that I’ve skipped these here.

...whereas the originals are constrained by their preset nature, the extended capabilities of the soft synth take it far beyond anything envisaged by ARP’s engineers in 1972.

Cherry Pro Soloist Conclusions

Hardware Pro Soloists are rare, and those that are still fully functional are even rarer. Nevertheless, the character of these unassuming little monosynths means that their reputation has survived for more than half a century — and not just among keyboard players in Genesis tribute bands. Cherry’s Pro Soloist mimics them with remarkable accuracy but, whereas the originals are constrained by their preset nature, the extended capabilities of the soft synth take it far beyond anything envisaged by ARP’s engineers in 1972. Well done, Cherry Audio.