Electro-Harmonix Mod Rex

The Electro-Harmonix Mod Rex, introduced in 2018 as the Mod Rex Polyrhythmic Modulator, is a digital modulation pedal that puts four independent modulation sections in one box and locks them all to a single tempo¹². Instead of chaining a chorus, a tremolo, a panner and a filter pedal and hoping their rates line up, the Mod Rex syncs its Modulation, Tremolo, Pan and Filter engines in time, each with its own rhythmic subdivision¹².

That sync-first design is the whole point of the pedal. MusicRadar's review put it directly³:

Four modulation sections synced to one tempo

The heart of the pedal is its four independent modulation sections, all synced in time¹. Each section is an LFO-controlled engine, and each can run at a different rhythmic value relative to the master tempo, which is what makes the pedal "polyrhythmic": the sections divide or multiply the same beat rather than each drifting on its own rate⁵.

The four engines are:

• Modulation: Vibrato, Flanger, Chorus or Phaser¹
• Tremolo: a tremolo with a Depth control for intensity¹⁶
• Pan: moves the signal between the left and right outputs¹⁶
• Filter: a modulated lowpass, highpass or bandpass filter¹⁷

Each section's LFO offers four wave shapes: ramp up, triangle, ramp down and rectangle, each individually adjustable⁷. That gives a player the difference between, say, a smooth triangle-wave chorus pulse and a hard rectangle-wave chop, independently per section.

The sections in detail

Mod covers the standard set of modulation effects: vibrato, flanger, chorus and phaser⁷. A Depth knob sets the amount of the effect, and a Feedback control sets the resonance of the Flanger and Phaser¹. The section can also invert the right side in phase, creating a stereo effect from a mono signal⁷.

Trem is a no-frills tremolo whose Depth control moderates intensity¹⁶.

Pan brings stereo movement to the signal, shifting it across the left and right outputs⁶. In mono operation, where only one output is used, the PAN section does not go idle: it acts as another tremolo section, but with all the wave shapes inverted, so a mono rig still gets a second, complementary tremolo¹⁶.

Filter offers a choice of a modulated LPF, HPF or BPF¹. As with the Mod section, the right side can be inverted, and the filter type can be set to lowpass, highpass or bandpass⁷.

The controls

The Mod Rex's tempo, displayed as BPM, is adjustable with the Tempo knob, or set by tapping quarter notes on the TAP footswitch¹². Tempo can also be driven by an expression pedal into the EXP input².

The pedal saves and recalls up to 100 presets and comes from the factory with 20 programs installed¹. An external footswitch can be used to step up and down the bank of 100 presets, which Gearnews noted would be handy in live use⁷.

Stereo, MIDI and expression connections

The Mod Rex features full stereo input and output¹². The rear panel carries:

• MONO/L INPUT for a mono signal or the left channel of a stereo signal¹
• R INPUT for the right channel of a stereo signal¹
• MONO/L OUTPUT and R OUTPUT for mono or stereo output¹
• EXP for an external expression pedal¹
• CLK/FC for an external pulse clock or a foot controller¹
• MIDI IN for MIDI signals¹

MIDI gives full control of all parameters and preset recall¹, and the pedal can be synced to an external device with MIDI Clock or an external pulse clock², so it can follow a sequencer or drum machine rather than its own tap.

Where it came from and what reviewers said

Electro-Harmonix unveiled the Mod Rex in September 2018, and it was available immediately at a US street price of $249²⁴. The maker's current list price is $169.00¹. MusicRadar's review, which put the UK price at £229, acknowledged that the pedal contains "some common effects" but concluded that the synchronization of the four sections makes it greater than the sum of its parts³.

For players weighing the Mod Rex against single-function EHX modulation pedals such as the Neo Clone or the Mod 11, the difference is architectural: those pedals do one modulation voice at a time, while the Mod Rex stacks four synced engines, at the cost of a larger footprint and a digital rather than analog signal path¹².

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