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E-RM Polygogo

Eurorack Module By Rory Dow
Published October 2021

E-RM Polygogo: 32HP, +12V 110mA, -12V 15mA.E-RM Polygogo: 32HP, +12V 110mA, -12V 15mA.

Interesting and unique synthesis techniques seem to be plentiful of late, and the E‑RM Polygogo is no exception. It’s also one of a growing number of modules that are stereo, plus it may just be the best looking module I’ve ever seen.

The Polygogo uses a digital synthesis method invented by E‑RM called Polygonal Synthesis. This works by plotting the X and Y position of drawn polygons. If, for example, you draw a circle, and you plot the amplitude of one axis over time, you get a sine wave. The speed of the drawing dictates the frequency and by changing the shape and rotation, a huge variety of stereo waveforms can be generated.

A beautiful OLED yellow‑on‑black screen shows you the drawing plot and updates in real time as you change parameters. The graphics are the exact polygonal plot that is output from the X and Y (left and right) outputs. It’s hard to convey in words just how nice this screen looks, and the polygon plotting is rather mesmeric.

Most of the slider controls are focused on manipulating the polygon shapes and every parameter can be CV controlled. The knobs above each slider change from fine‑tuning controls to bipolar CV attenuators when a cable is plugged into the CV input. Order sets the number of corners the polygon will have, from two (a straight line) to 28 (a near perfect circle). You can switch ‘regular’ mode off to allow for a non‑integer number of corners, which will create extra harmonics when the plotting scans a ‘broken’ edge. With the Cycle button, you can also toggle whether the polygon is always drawn from the same spot, or whether it begins drawing from the last position. This has the effect of ‘spinning’ the polygon and creating additional stereo movement.

Teeth will take the sides of the polygon and tilt them inwards creating disruptions and overtones in the waveforms. Roll rotates the polygon which causes the waveforms and relative phase relationship between the X and Y outputs to constantly shift, creating spacial movement. The final two sliders change the ratio and FM amount of an internal operator (there is an additional exponential FM input too, with attenuator). The frequency of the internal operator can be smooth, or quantised depending on the status of the ‘OP ratio’ button. Frequency modulation is represented nicely on the display.

As well as the wide range of stereo synth‑tones that the Polygogo can generate, I found a much pleasurable distraction using it as a modulation source.

Fold will push the waveform out of the edges of the screen and into the opposite side, adding harmonics at low levels and extreme crushing and distortion effects at higher levels.

The Polygogo is not difficult to master. You quickly become accustomed to connecting the visual to the audible. Smooth circular shapes make sine waves. Jagged shapes add more harmonics. Spinning shapes will have more stereo movement. And if the screen looks chaotic, the sound will be too.

As well as the wide range of stereo synth‑tones that the Polygogo can generate, I found a much pleasurable distraction using it as a modulation source. The X‑Y outputs make an excellent modulation pair. Sort of like having your own automated joystick controller continually drawing complex repetitive patterns. Although I don’t have the hardware to test it out, I imagine the Polygogo would make an excellent controller for lasers or oscilloscope art.

I’m not sure the Polygogo really generates anything that a flexible oscillator can’t already. The stereo aspect is definitely a big part, but the raw tones sound much like sawtooths and sine‑waves being sync’ed, FM’d, bit‑crushed, wave‑folded, etc. It does however offer a very unique approach to making these sounds and taking a different path to a familiar destination can offer as much joy as going somewhere new. In the end, the Polygogo is well built, innovative and fun to use and I can’t think of much higher praise than that.