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Synth Pedals for Guitarists, Part 2

Marty Cutler



When it comes to good synths in small packages, synth pedals and apps give guitarists and bassists even more choices.

In our first installment, we reviewed four effects pedals that afforded relatively uncomplicated gateways to synthesis for guitarists and bass guitarists. Each device offers the ability to tweak a few selected parameters. In contrast, the devices we survey this time allow full access to their sound engines. Two of the synths discussed here are pedals, as they all were in Part 1, and one of them is an iOS app.

Source Audio C4 ($239)

The C4 patterns itself after Eurorack modular systems. It has stereo input and output, with the inputs assignable to up to four discrete voices and independent signal paths. Each voice has assignable modifiers. You can assign a voice to an oscillator with a choice of sine, square, or sawtooth oscillator waveforms. Other voice selections include monophonic or polyphonic pitch shifting, intelligent harmonizing, and a pair of step sequencers, as well as dry signal to distortion, tremolo, and filter effects. The C4’s synth oscillators do not process the guitar’s timbre; the only information derived from the input signal is amplitude and pitch.

Tracking the input signal is similar to guitar-to-MIDI conversion, but according to Bob Chidlaw, one of the engineers responsible for the C4, it has no MIDI triggering of pitches internally or externally. He explained, “The software inside the pedal is detecting complete periods of the string vibration and noting how long it takes to finish a complete period. The reciprocal of that time is proportional to the pitch. That number is used to control the frequencies of all the synth oscillators inside the pedal. So, it is really doing pitch-to-number. Any more details are ignored.”

You choose two from no fewer than 28 filter types, including phasers and several varieties of lowpass, multimode, notch, peak, and triple-peak filters. Two envelope generators have several preset variations that include traditional ADSR, simple attack/decay, and attack/release envelopes.

Tracking on the C4 is superb—swift and articulate, whether you plug in a guitar or bass. However, playing the pure synthesizer patches requires a bit of extra care, as sounds tend to distort and break up if you accidentally play more than one note at a time. Any voices that use oscillators are monophonic, but you can process instrument signals through filters, pitch shifters, and other C4 synthesizer resources, often blurring distinctions between synthesizer and guitar tones.

Four knobs—Input, Mix, Control 1, and Control 2—flank a three-way toggle switch to access preset banks, and an Alt (Alternative Function) button near the 9V power jack changes each knob’s function, depending on the preset. Better yet, a USB port in the back lets you connect C4 to a DAW or interface with Source Audio’s Neuro Desktop (Mac/Win) or Neuro Mobile (Android/iOS) editor/librarian software for creating and storing your own sounds.

Through Neuro, you can connect with the C4’s user community for sharing patches. The USB port exchanges MIDI System Exclusive and MIDI Clock, along with a boatload of Control Change messages. The 3.5mm Control Input Port connects the C4 to external control devices and pedals. With its powerful 4-voice system and deep modulation capabilities, Source Audio’s C4 is a powerful entrée to guitar synthesis.

Meris Enzo ($299)

Arguably the most complex (and therefore, the most sophisticated) synth of the lot, the Enzo’s layers of programmable parameters are nested beneath six knobs, two buttons, and a pair of footswitches, every one of which has a secondary function. For instance, the Pitch knob offers smooth sweeping between three octaves in semitones, an portamento speed accessed with a press of the Alt button, which can change the synth waveform in conjunction with the bypass pedal.

Four modes—accessed from an illuminated button above the bypass footswitch—determine how the Enzo responds to your playing. Poly tracks polyphonic input, whereas Mono provides a monophonic synth that responds to pitch bending. Arp accesses the pedal’s arpeggiator, and the Tap footswitch (or MIDI Clock) controls the speed. Dry is a bit of a misnomer, as it substitutes the guitar’s signal for the oscillators and routes it through the rest of the synth architecture and effects, including a variety of ladder and state-variable filters and a ring modulator. The Enzo tracks like a beast: cleanly and with no perceptible latency.

Because of its deep architecture, spartan user interface, and nested parameters, programming and saving patches and global settings can be time-consuming. Many involve pulling and reinserting the plug to power up and play. You’ll need a control pedal to cycle through presets or MIDI connectivity to send patch changes, because you have no other way to access to the Enzo’s presets.

Without the presets, you will need to familiarize yourself with the unit’s nested functions and design your own patches from scratch every time. Fortunately, a jack on the Enzo’s rear accommodates an expression pedal, and it can also transmit and receive MIDI through a TRS cable and an intermediary device such as the Meris MIDI I/O ($89). The Enzo supports MIDI Control Changes for all parameters, sending and receiving System Exclusive, and syncing to MIDI Clock. An expression pedal or footswitch can move through presets once they are stored.

You will be rewarded for your extra effort and expense. The Enzo is capable of producing sounds of great beauty and animation—thick, billowing, resonant pads; flute-like leads; fat, quacking brass; processed, pitch-shifted guitars that sound like woodwinds; dissonant, metallic, ring-modulated tones; and synthy arpeggios that respond to playing dynamics.

Thanks to Elliot Garbus, you can download Enzo Edit, a free editor/librarian (Mac/Win) whose UI reflects the hardware’s work surface. The software has a novel patch generator with seven different randomizing techniques to choose from.

Despite its challenging workflow and extra cost (you should budget for a Meris MIDI I/O and a control pedal), the Enzo is deeply satisfying for guitarists who want to expand the guitar’s sonic landscape.

Yonac Roxsyn (iOS, $9.99)

To my way of thinking, Yonac Roxsyn is more of an electric guitar- and bass-oriented signal processor than a dyed-in-the-wool synthesizer. It hearkens back to the early days of the Roland GR-500, which applies waveshaping and clipping to the guitar signal as part of its sound-voicing scheme. Its programming interface is designed to resemble a modular analog synthesizer, making the iPad’s touchscreen an ideal medium for exploring and creating new sounds. To use the app, you will need an iOS-compatible audio interface and a USB-to-Lightning adapter. Once your guitar is connected, you can adjust the threshold and dynamics settings to accommodate your guitar’s pickup output.

Roxsyn divides its five pages into Synth, Mod/Arp, FX, Prefs, and Tape, in which you can load backing tracks or record your own synth parts. The Synth page’s upper portion deals with adjusting and balancing your guitar signal in the left three columns and voicing the oscillators (Shapes, in Roxsyn lingo) on the right. The window’s lower half presents two filters, each with four types—lowpass, highpass, bandpass, and a formant filter—an envelope generator for each filter, and a single amplitude envelope. A few nice touches include the ability to apply either or both filters to any voice and to press the amp envelope into modulating either or both filter inputs.

Although Roxyn’s envelope generators follow the contours of your guitar’s or bass’s signal, you can also trigger programmable envelopes for the amp and filter. They’re fundamentally ADSR envelopes with an additional rate from the decay to the sustain stage. As with all the hardware devices here, Roxyn uses the signal from the guitar’s pickups rather than MIDI notes to drive the synth.

Roxsyn’s three voices provide five different Shapes. To my ear, these sound like overdriven, band-limited versions of the live guitar signal. Most everything, especially the pads and lead patches, retains audible traces of the input instrument’s timbre. When combined with widespread over-application of effects, this tends to impart a sameness to the instrument textures. The Arpeggiated patches fare better because of the staccato nature of the sounds. Likewise, basses are fat and squelchy.

Roxsyn needs a global transpose feature; a good many of the patches sounded muddy in the middle-to-low-registers but clear and articulate when I moved individual voices up an octave. In general, be prepared to dial back the effects, and get ready to tweak. Fortunately, if you know anything about synthesizer signal flow, Roxsyn is a breeze to program.

Event Horizon

Boss recently announced the release of the SY-1000, a new guitar synth that furnishes a hefty supply of guitar, bass, and other instrument and synthesizer models. Among several new synth engines is one that Boss calls a Dynamic Synth, which responds to input from a standard ¼-inch guitar cable, alongside the standard 13-pin cable/divided pickup system and MIDI I/O. Look for an in-depth review here in Synth and Software in the near future.

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