THE SECOND synth I ever owned was a Sequential Circuits Pro-One. In 1981, it gave me everything I wanted in a monophonic instrument: analog oscillators, a noise generator, a fat lowpass filter, ADSR generators, a choice of LFO waveforms, surprisingly flexible modulation routing, a rudimentary step sequencer, and the first arpeggiator I’d ever used. It had no MIDI and no presets, and it deleted its sequencer data the moment you switched off the power.
Sequential Circuits sold about 10,000 Pro-Ones during four years of production because they sounded so good and they cost just over half a grand. The Pro-One was like a Prophet-5 for those of us who couldn’t afford patch storage or polyphony. Today, a used one in good condition commands as much as $2,000—close to the original price of a new one when you take inflation into account.
Sequential Circuits was founded by Dave Smith, the man who first conceived of MIDI, invented vector synthesis, and launched the first commercial soft synth. His current, eponymously named company recently introduced a direct descendent of the Pro- One, appropriately named the Pro 2. Thirty years after the original ceased production, you’d expect some significant enhancements, and you won’t be disappointed. The Pro 2 blends the rich sound of analog filters with the precision and versatility of digital technology, and it sells for about the same price as a good used Pro-One.
Fig. 1. The Pro 2 offers so many directions for sonic exploration that it could keep you up all night creating new sounds for years to come. The Pro 2 begins with a single Prophet 12 voice and expands on that foundation. It has four digital oscillators, two analog filters, and one of the most sophisticated step sequencers I’ve seen in any instrument. Control-voltage inputs and outputs give it modular compatibility. And although it isn’t a true polysynth, it lets you play four notes at the same time.
Look Around The Pro 2’s black-and-red front panel and wood trim, as well as its user interface and much of its functionality, take their cues from the Prophet 12 (see Figure 1). The Velocity- and Aftertouchsensing keyboard has 44 keys (the same as a Minimoog), and the pitch bend and mod wheels emit a red glow. Above the wheels are two pressure-sensitive, latchable touch sliders (the likes of which first appeared on the company’s Tempest analog drum machine), along with the Volume knob, the Distortion knob, and a few buttons you’d want under your left hand.
Fig. 2. Four rotary encoders and four buttons control whatever parameters are displayed in the OLED. The sharp, 3" x 0.75" OLED display is the same as the Prophet 12’s and can be read from any angle. The soft controls—four rotary encoders and four buttons that flank the OLED—affect whichever parameters are displayed (see Figure 2). Forty-six knobs and dozens of buttons are dedicated to specific functions. Most buttons either illuminate or have LEDs to indicate status. The front-panel layout is consistently logical and easy to learn.
The back panel has two unbalanced 1/4- inch outputs, a 1/4-inch stereo headphone jack, and an unbalanced 1/4-inch mono audio input with its own level knob on the front panel. In the middle are three MIDI jacks (In, Out, and one that’s switchable between Out and Thru), a USB port for MIDI I/O, and 1/4- inch jacks for a footswitch and an assignable pedal. The footswitch can control sustain or toggle the arpeggiator hold on and off. You can reverse the polarity of the footswitch or pedal jack, ensuring compatibility with any brand.
Fig. 3. If you have other instruments or modules with control-voltage connections, the Pro 2 lets you assign any CV input to any destination and any source to any CV output. It can scale and invert control voltages in either direction. Between the audio jacks and the pedal jack are nine minijacks for control-voltage signals— four inputs, four outputs, and a gate output (see Figure 3). Although I wish these had been 1/4-inch jacks so I could interface it to my Moog Voyager without the need for adapters, they are designed for use with Eurorack gear, such as the company’s new DSM01 Curtis Filter module.
Architectural Detail As on the Prophet 12, the oscillators, filters, and amplifiers are monophonic, whereas the delay and output stage are stereo. As with other keyboard synths from Dave Smith Instruments (DSI), the Pro 2’s front panel is divided into functional blocks, with controls for the oscillators, filter, and envelopes in the lower half. You’ll find lots of dedicated controls, with deeper functions never more than two button-presses away.
Function-specific knobs let you dial in level, tuning, shape, shape modulation, waveform crossfades, and glide amount for each of the four oscillators. Access additional parameters such as FM or AM amount using the four soft knobs and buttons surrounding the display.
Waveform shapes range from 5 virtual analog (including super sawtooth) to 12 morecomplex wavetables, 12 super wavetables, and 3 colors of noise—the same as the Prophet 12 supplies, with the addition of the super waves. Super waves duplicate the standard waves, but additional iterations are stacked and detuned for extra thickness, and their bigger, fatter sound makes an audible difference. A sine-wave suboscillator pitched an octave below Oscillator 1 supplements the four main sound sources.
Filter 1, a 4-pole lowpass that self-oscillates at high resonance settings, is a new design based on the original Prophet 5 (but without using a Curtis chip). Filter 2 is a 2-pole design that effectively emulates the classic Oberheim SEM filter. Like the original, it lets you sweep through lowpass, notch (band-reject), and highpass responses. Pressing the Bandpass button inverts the notch filter, and changes are graphically displayed. Sweeping between responses has always been one of my favorite Oberheim capabilities, and the Pro 2 lets you modulate the sweep with any source.
You can enable just one of the two filters, or use both in series or in parallel. You can even dial in a mix of series and parallel, thanks to a continuously variable knob. Engaging the Oscillator Split button routes two oscillators to one filter and the other oscillators to the other filter.
Although each filter has its own 5-segment (DADSR) envelope generator, dedicated knobs affect only the ADSR segments and the envelope amount; use the soft controls to change the initial delay segment and the effect of Velocity on envelope amount. The amplifier’s envelope generator has the standard four ADSR knobs, with other parameters accessed by the soft controls.
Although the two freely assignable 5-stage envelopes are functionally identical to the filter envelope, you change their settings using the soft controls. Dedicated buttons switch between the two envelope generators. All envelopes are loopable, meaning their attack, decay, and release segments will repeat as long as you hold down a key. Route control signals from any of the five envelope generators to any modulation destination.
In my Prophet 12 review (see the January 2014 issue of Electronic Musician), I wrote that its modulation scheme approaches a modular synth in its flexibility. The same is true of the Pro 2, but the routing possibilities are even more extensive. The Pro 2 allows you to easily patch any of 51 mod sources to 142 destinations. Audio input and output are among the mod sources, and the mix of parallel and serial filter routing is one of the destinations that can be modulated. Twentyfive of the mod routings have fixed sources— LFOs, envelopes, and sequencer tracks—and 16 are freely assignable. When you press the Assign Source or Assign Dest button, all the modulation paths are listed in the display.
The four LFOs let you specify their destinations using a dedicated knob. Each LFO can run freely or sync to the internal sequencer, arpeggiator, or an external clock source. You can also specify that an LFO cycle will be reset whenever you press a key. Settings include phase and slew rate, and LFO frequencies extend into the audio range for some awesome FM sounds.
One Equals Four One of the Pro 2’s most unusual features for a monosynth is its ability to play four notes at the same time. In the 1970s, a monophonic synthesizer that allowed you independently and simultaneously to control the pitch of more than one oscillator with the keyboard was parapolyphonic, which literally means like or almost polyphonic. In very few recent instruments, manufacturers have resurrected the concept and shortened this term to paraphonic. I hope we’ll see other new monosynths with this capability soon.
When you press the Misc Params button and change the key assignment from Low Note, Hi Note, or Last Note to Paraphonic, the keyboard will trigger the four oscillators independently. Only the first key you press triggers the filter envelope; subsequent key presses will trigger notes instantaneously at the current cutoff level, with no filter envelope. Each of the four notes does have its own amplifier envelope, however.
Sometimes when you’re playing paraphonically, it’s easy to forget that the Pro 2 isn’t truly polyphonic. The playing technique is different enough that I’d be hard-pressed to reproduce some of the paraphonic sounds with a true polyphonic instrument. And it sounds so analog, I occasionally forgot I was playing a synth with digital oscillators.
Fig. 4. The refined step sequencer gives you as many as 31 tracks that serve as independent modulation sources, enabling performance capabilities that would be impossible on most synths. Everything in Sequence The Pro 2’s internal sequencer borrows its design from the analog step sequencers in modular synths of the 1960s and ’70s (see Figure 4). You get a choice of either an 8-track sequencer with a maximum of 32 steps or a 16-track sequencer with a maximum of 16 steps. Although the first track always controls oscillator pitch, you can route other tracks to any modulation destination you wish. That means you can automate as many as 31 parameters—filter cutoff, amplifier attack, pitch bend, or whatever—so that their values change with every step.
Record a sequence of notes simply by entering sequencer mode, selecting 16x16 or 8x32, and playing one note at a time. The notes you played will be shown in the display, along with their Velocity, and the LED for each step will illuminate. You have the option of changing the tempo, turning off notes to create rests (by pressing the button for that step), or changing a note’s pitch or Velocity. You can tie two or more notes by holding down the button for one step while pressing the button for a subsequent step. You can also slide between notes by selecting a note and turning the Slew knob. While you’re viewing the track, soft knobs let you view and alter the pitch, Velocity, slew, and length of each note.
Because the sequencer accommodates rests and ties, notes in a sequence can be of different lengths, yielding more musical results than the constant barrage of eighth or sixteenth notes typical of some step sequencers. And because it also lets you program sequences of any length up to the maximum, you can easily create ostinato patterns in odd time signatures. Having so much versatility enhances the Pro 2’s sequencer considerably. However, although the sequencer can play up to four pitches simultaneously, you can’t record chords using real-time or step recording. To sequence chords, you’ll need to layer notes one track at a time.
To record step-by-step parameter changes, choose a destination, press and hold a step’s button, change the parameter’s value, and your change will be stored and displayed. To record parameter changes in real time, press the Record button while playing a note sequence and change the parameter’s value as the sequence plays. Each time you change a different parameter, your changes will automatically be recorded on the next available track, and the value for each step will be displayed. If you want to smooth the transition between values, increase the slew amount.
Each preset can store a different sequence, which can be triggered from the keyboard or by pressing the Play/Stop button when the sequencer is enabled. In many of the factory presets, you’ll notice illuminated LEDs in the Sequencer section, indicating that a sequence has been preprogrammed and is waiting for you either to press a key, press Play/Stop, or both. Even if no LEDs are lit, pressing the Sequencer button will often reveal a hidden sequence.
The very handy Cue feature lets you select a sound, play its associated sequence, and then select another sound to finish the current sequence before progressing to the next sound’s sequence without interruption. Cue allows you to string one sequence after another, using different presets or copies of the same preset with alternate sequences, to play a complete song in real time.
Chain of Effects If you’re familiar with the Prophet 12, you may already know about the Pro 2’s breadth of effects processing. Like its 12-voice counterpart, the Pro 2 offers four stereo delays, tuned feedback, distortion, and DSI’s unique Character processing.
In the Delay section, three of the processors offer standard digital effects, and the fourth emulates an analog bucket brigade. Each lets you specify the delay amount, feedback, and time (up to 1 second). By enabling Sync, you can set the delay time to a multiple of the tempo for note values ranging from a sixtyfourth to a whole note. You can pan each delay to any position and apply lowpass and highpass filtering. These four delays offer enough flexibility that you can impart discrete echo, slapback, flanging, chorus, or simulated reverb to every user preset you create.
Feedback routes each voice’s amplifier output to a tuned delay. The delay’s output is mixed with the oscillator output, resulting in a feedback loop. The feedback frequency tracks the keyboard and is quantized by semitones over a 4-octave range, allowing you to play the feedback melodically. Tuned feedback gives DSI synthesizers a quality that distinguishes them from other instruments.
When it comes to distortion, the Pro 2 lets you choose your weapon. Using the dedicated Distortion knob, you can set the amount of analog amplifier overdrive to create effects ranging from subtle warmth to nasty clipping. Increasing the filter’s Boost value overdrives the filter to increase harmonic distortion, as well.
The Character section is a collection of five parameters for customizing sounds. Whereas the Prophet 12 has dedicated knobs for these parameters, on the Pro 2 you press the Character button and use soft knobs. If amplifier and filter distortion aren’t enough, use Decimate to reduce the digital sampling rate, Hack to reduce the bit depth, or Drive as yet another distortion source. Two spectral parameters, Girth and Air, boost the low and high ends.
It’s the Sound Unlike some recent synths, the Pro 2 makes it obvious Smith and company didn’t pinch pennies when it came to hiring good sound designers and giving them the resources they needed to come up with some truly inspiring sounds. These are the best bunch of presets I’ve ever heard from any DSI synth. They do an excellent job of taking advantage of the modulation capabilities, too. Wheels, touch sliders, and Aftertouch breathe life into many of the sounds and give them nuanced expressivity.
The Pro 2 stores 792 programs in 4 factory banks and 4 user banks. The Bank Select knob scrolls through the eight banks, and the Program Select knob scrolls through the selected bank’s 99 presets. You can’t rewrite the factory banks, but the rewritable user banks duplicate the factory banks, giving you 396 locations to store programs you’ve created, modified, or downloaded.
The factory sounds are about half monophonic and half paraphonic. Each preset retains its own volume level independent of the master volume, and most presets include preprogrammed sequences, arpeggios, or both. The Play List function lets you organize groups of 16 presets into 4 Sets, which are useful for quickly recalling favorites during a performance or studio session.
The Pro 2’s timbral richness and abundant modulation paths certainly inspired the people who programmed its factory presets. Remarkably, the Pro 2 has some of the fattest tones I’ve ever heard from any synthesizer, thanks in part to its exquisite filters, stacked super waves, and sine-wave suboscillator, which reinforces fundamental frequencies more effectively than a typical square-wave suboscillator. That’s no small feat for a synth with digital oscillators.
You Know You Want It Rather than a synthesizer that emulates acoustic instruments, the Pro 2 is a traditional electronic musical instrument. It lets you assemble sounds from the ground up using raw waveforms and timbre-shaping tools that give it a distinctive character—one that would be impossible to achieve with other synths. Despite its finite set of tools, it is a portable sound designer’s workshop that suggests (dare I say it) seemingly infinite possibilities.
Like the Prophet 12, the Pro 2 is loaded with features that simplify programming. Its intuitive nature streamlines your workflow and invites you to explore. I’m sure I’ve barely scratched the surface of what it can do. I look forward to discovering the kinds of sounds I can coax from its circuitry, what it can do when it’s connected to other control-voltage gear, and what happens when I dive deeper into recording sequences with multiple layers of modulation.
Despite three decades having passed, the Pro 2 is well-positioned as a successor to the Sequential Circuits Pro-One. The Pro-One’s appeal was that it did as much or more than its competitors at a lower cost, and it sounded terrific. Can anyone say the same of the Pro 2? Lots of new monosynths cost less, but from what I’ve seen, none offer the Pro 2’s versatility and depth. In fact, I can’t think of any other keyboard instrument that delivers so much for such a reasonable price.
The Pro 2 exudes quality, thanks to its solid construction, sophisticated user interface, and luxurious sound. Few of its competitors could make that claim so convincingly.
Geary Yelton has been reviewing synthesizers for Electronic Musician since its very first issue.
STRENGTHS: Spectacular sound. Impressive programming depth. Intuitive user interface. Excellent analog filters. CV connectivity. First-rate construction.
LIMITATIONS: Monophonic signal path. No balanced audio I/O. Can’t sequence chords in real time.