Cherry Audio Pro Soloist: the Synth and Software Review

A vintage favorite rises from the grave (and gets a 2020s update)

When the ARP Pro Soloist was introduced in 1972, I was playing bass in a folk-rock lounge band. I’m sure I had heard of synthesizers, but I doubt I had ever seen one. Since then I’ve learned that the Pro Soloist was very popular in the early ’70s. It was heard on records by a lot of important artists, because it sounded good and had some features that were (for that bygone era) very cool indeed.

In designing their software emulation of the Pro Soloist, Cherry Audio has wisely kept the signature features of the original, while adding a big bunch of improvements. You can be as vintage as you dare with this plug-in, but you can do a whole lot more.

The ARP Pro Soloist was a success because it had 30 presets. They weren’t programmable; full programmability wouldn’t hit the scene until six years later. But you could flip a lever and get a new sound instantly, which was a big factor if you were playing live.

It was monophonic, of course, and the keys didn’t sense velocity, but there was a pressure (aftertouch) sensor under the keyboard, which made expressive playing very possible. The pressure sensor could be used to add vibrato, tremolo, a pitch-bend, a volume swell, wah-wah from a resonant filter, or “growl.”

Figure 1: The voice panel

The Cherry Audio Pro Soloist adds polyphony, effects, velocity sensing, a basic arpeggiator, a 6-slot modulation matrix, and full programmability. This is still a one-oscillator synth, but a supersaw/superquare button is available to add richness to the tone.

It also has two separately programmable layers, which can be layered atop one another or split to the left and right sides of the keyboard. Not only that, but each of the layers has an entirely independent set of effects. This is not a feature you see often, and it’s quite useful, especially if you’re planning to gig with your laptop and a MIDI keyboard.

The synth works in VST, VST3, AU, AAX, and stand-alone formats, and costs $49.

User interface. When you launch Pro Soloist, the panel you’ll see looks a lot like the original hardware instrument. On the left are eight on/off switches for routing MIDI keyboard aftertouch to various destinations. To the right are 15 more switches, each of which can select one of two different presets from the original hardware instrument.

Figure 2: the FX panel

Five sliders in the “left-hand” control section govern volume, brilliance (basically, filter cutoff), the amount of aftertouch sensing, portamento speed, and pitch-bend range. There’s also an octave up/down switch with five positions. (Octave up/down on the hardware had only three positions.) In dual voice mode, the upper and lower layer sounds each have their own settings for these controls.

Each layer can be set to mono retrigger, mono legato, or poly mode using buttons in the left-hand area. The one thing that threw me off at first was the three buttons below these. The setting of the Touch Sensor buttons is not stored with the preset, and you wouldn’t want it to be. Use these buttons to tell the Pro Soloist whether your MIDI keyboard has mono or poly aftertouch.

There’s a brilliant innovation lurking here: the Last button is used with monophonic aftertouch, but it causes the Pro Soloist to apply the aftertouch modulation only to the last note you play in a chord. Pedal steel pitch-bends of up to a whole-step are possible, and you can bring out one note in a chord by adding brilliance or vibrato. I’ve never seen anything like this before. Hopefully it’s not patented, because I’d love to see other manufacturers grab the idea and run with it.

Two full panels not found on the hardware Pro Soloist are included. In the Edit panel (see Figure 1 above) are the oscillator controls, a resonator bank with up to five resonators in parallel, a resonant lowpass filter, an ADSR envelope, an AR envelope, and a modulation matrix with six routings. In the Arp/FX panel (Figure 2 above) you’ll find a basic arpeggiator, plus distortion, phaser, flanger/chorus, echo, and reverb.

Voicing. A Pro Soloist layer has only one oscillator, one LFO, and one ADSR, so it’s always going to sound a bit thin compared to a full-featured modern synth. You can spread both layers across the keyboard, so there can be two distinct tones per note, but there’s nothing resembling FM or wavetable modulation. Nonetheless, the instrument has some nice enhancements.

Consider the mod matrix. The LFOs from the phaser and flanger/chorus effects are available as sources even when the effects themselves are switched off, so in fact you have not one LFO but three. Both the frequency and resonance amount of each resonator can be modulated. Noise and stepped random signals can also be used as sources.

You can use the MIDI keyboard (note number, though it’s shown on the panel as CV, an abbreviation for “control voltage”) to make one or more resonators track up or down as you play, so the filtering options are quite extensive. The output of each resonator can be routed into the filter or bypass it, with full control over the amount of each output. This is subtle, but there’s quite a lot of tone-shaping control.

The better known ARP 2600 also had only one ADSR and one AR envelope. As in the 2600, either of these can be used to control either the filter cutoff or the VCA, so if you want to use the ADSR to add pitch modulation to the oscillator for a quick attack transient, you can still have full-power sustaining notes by opening the filter and VCA with the AR envelope. If I could wish for only one change in this synth, I’d love to see a switch that would change the AR (attack-release) envelope to an AD (attack-decay). That would be sweet.

The audio clip. This brief sketch was made using seven instances of Pro Soloist and nothing else, apart from a bit of level automation. (The DAW was Reason 12.7.) It was inspired by the quarter-note riff, which was the first thing my fingers did on the keyboard. This riff strongly implied Phrygian mode. That preset and the pad and bass were not edited, but I did a few things to the lead sound, lowered the pitch of the kick drum preset, and turned off the arpeggiator that was playing the high chimes in the background so I could choose my own notes.

The verdict. I wasn’t expecting much from a single-oscillator synth that debuted 50 years ago, so I was very pleasantly surprised by the Cherry Audio Pro Soloist. Polyphony and added effects are inevitable these days, but the dual layer architecture is an unexpected bonus that adds a lot, as does the mod matrix. Having programmable access to five resonators is a very unusual feature, and the aftertouch sensing is both authentic and very expressive.

There’s a fully functional 30-day downloadable demo, so what are you waiting for?

Price: $49

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