Intended primarily for electric guitar and bass, the Synth9 Synthesizer Machine from Electro-Harmonix is a polyphonic pedal designed to turn the sound of your instrument into a classic, vintage synthesizer—or more accurately, one of nine such synths, as the pedal offers nine different presets for achieving these tones. It’s suitable for effecting anything from buzzy synth-lead timbre, an atmospheric pad, or a synth bass.

Emulations of the Oberheim OB-X, the Prophet-5, various Moogs, and other classic synths are provided, and control over these synths is possible through the CTRL 1 and CTRL 2 knobs. In and of themselves, these dials have no endemic function, but once a preset is selected, they automatically control preset-specific parameters such as octave selection, sweep time of filters, vibrato, depth, and more. The DRY VOL knob will control the amount of unprocessed, untreated signal passing through the output jack, while the SYNTH VOL knob, with rare exceptions, controls the overall level of the emulated synth.

A single 1/4' input is provided, but to facilitate multiple routing methods, you’ll find two output jacks—one for dry signal, and the other for effect signal. It’s worth noting that this pedal works best when placed first in your signal chain, as distortion and modulation effects might muddy up the tracking algorithms, making precise note detection much harder to accomplish. It’s also recommended that you use this pedal with your guitar’s bridge pickup whenever possible, with the instrument's volume control cranked all the way.

A compressor has been built into the unit, and is constantly active on the synth emulations. The synths are capable tracking notes up to the 23rd fret of the high-E string and down to the low, open-A string of a bass guitar. Included with the pedal is an Electro-Harmonix 9.6DC-200BI power supply.