Subdecay M3

The slim group of synth pedals featuring one or more tracking oscillators has just gained a new member: the Subdecay M3.

This monophonic stompbox efficiently tracks your signal, triggering three digitally controlled oscillators in a circuit inspired by the legendary Korg MS-20.

Here’s the pedal’s path, also immortalized in the pedal’s graphics:

3 x Oscillators > 3 x LFOs (PWM & pitch for each oscillator, and the filter) >
Two envelope generators (filter & AMP) > Voltage controlled analog resonant filter >
Voltage controlled amplifier

The Oscillators knob makes the three oscillators interact with each other in 11 different ways, creating different source sounds based on a combination of sawtooth and/or pulse waves.
The Algorithm knob selects filter, amp and LFO settings.

By combining all the possible combinations given by these two knobs you get 121 patches that can be further tweaked through the Resonance and Parameter knobs: the Parameter knob tweaks a different function depending on the selected algorithm, while Resonance adds the classic boost to the sound’s frequency before the filter’s cut.

See description under the video or here for the full list of Oscillator and Algorithm combinations.

Subdecay M3, Builder’s Notes

A Monophonic Guitar Synthesizer

Based on the Korg MS-20, the M3 brings the sounds of 70s monophonic synthesizers without the modular complications.

Instead of dual oscillators, the M3 employs 3 digitally controlled oscillators for super fat synth sounds that never go out of tune.

Eleven oscillator combinations cover string sounds, analog bass, bell tones, fifths and more. The algorithm knob’s eleven settings further shapes the sound controlling everything from the filter, two envelope generators, LFOs, portamento and more.

’70s inspired

The 1970s saw a massive expansion of electronic music instruments. Much like early electric guitars some didn’t know what to make of these electronic synthesizers. Some of these electronic noise makers were almost affordable.  (insert if you can afford a truck, you can afford a synthesizer meme)

Ease of use and portability improved as well, but MIDI wasn’t coming until 1983. Saving patches usually meant writing them down in a notebook. This was still a vast improvement from earlier interconnected cabinets in studios that needed constant tuning and maintenance and were near impossible to use live.

This era created some of the most iconic synthesizers of all time. We’ve packed the essence of 70s analog monosynth into the M3. Don’t let the simplified controls deceive you. The M3 incorporates the following:  (Synth Speak warning)

Control and structure

Three oscillators.
Three LFOs (PWM & pitch for each oscillator, and the filter)
Two envelope generators. (filter & AMP)
Voltage controlled analog resonant filter.
Voltage controlled amplifier

Synths of this era rarely had more than two oscillators per voice. A single LFO was common. Many synthesizers used a single envelope generator to control the filter and the amplifier. So how did we fit all this 70s goodness in a stompbox? We borrowed some tricks from the 80s. As MIDI became a synthesizer standard many of those “analog” synthesizers used digital control. Analog envelope followers and LFOs were replaced with digital technology. The synth world that was still analog moved on from voltage controlled oscillators to digitally controlled oscillators. Often the same processors found in computers were found in synthesizers controlling everything.

User friendly for guitarists-

Essentially the M3 has 121 tweakable patches. The oscillator knob selects between eleven oscillator combinations. The algorithm knob selects filter, amp and LFO settings. The parameter knob allows you to alter each algorithm in different ways.


Each of the M3’s oscillators are capable of sawtooth waves or pulse waves with variable pulse width modulation. One of the LFOs controls the PWM. Another controls the pitch and is used to detune the oscillators for a chorus effect.


Oscillators: This knob sets between 11 different oscillator selections.
A B & C Saw wave ensembles: The basis for the string machines of the past. Can also capture some horn sounds.
D E & F Basses: A mix of lower frequency saw and PWM waves.
G Fifth: Two oscillators track the input pitch with one oscillator offset by a 5th for that classic 5th synth sound.
H Major Triad: This is more of an ode to 90s electronic music than the 70s. We won’t judge you for using it!
I octaves: Stacked octave saw waves.
J: Two square waves and upper octave 5th: This was a common way synthesizers attempted to capture bell and chime timbers, or even electric piano.
K Stacked Squares: All three oscillators run squarewaves in unison. Perfect for synth leads.

Algorithms: This controls everything else. Filter and Amp envelopes, LFOs, portamento and pitch follow for the filter. Additionally one or more setting can be tweaked with the parameter knob.
1 Wide open: Parameter controls filter offset. The envelopes are wide open with moderate release. This is an example of one of the most simply synth settings.
2 String Envelope: Parameter controls filter offset. A moderate attack with high sustain and near reverb like release. Works well with string oscillator settings.
3 portamento: Parameter controls filter offset. The oscillators will glide smoothly from note to note. A classic synth lead trick that never goes out of style.
4 Decay: Parameter controls filter and amp decay length from just a blip to two seconds.
5 Decay/sustain 1: Parameter controls filter sustain. Another common synth sound. A quick decay that doesn’t decay all the way.
6 Decay/sustain 2: Similar to #5, but slower and brighter.
7 Fade: Parameter controls decay. Wide downward filter sweep.
8 Vibrato: Parameter controls Filter LFO speed. Slow decay with filter modulation.
9 Fast Modulation: Parameter controls Filter modulation speed into the audio range from roughly 2 octaves down to two octaves up. This creates a faux ring modulation effect.
10 Slow attack: Parameter controls amp attack. like a reverse or swell effect. the notes fade in instead of out.
11 Filter Rise: Parameter controls the rise rate. Each note triggers a deep rising sweep of the filter. The Amp fades out as the rise peaks.

Volume: You know what this one does, right? Turn it up to make it louder.

Resonance: Controls the resonance of the filter.

Parameter: Control varies depending on algorithm setting.