ADDAC303 Muscle Sensing

Plug yourself in: this Eurorack module turns muscle flexes into control voltage, turning your body into a synth interface.

Overview

The ADDAC303 Muscle Sensing isn’t just another CV source—it’s a bridge between your nervous system and your modular rig. Built by ADDAC System of Lisbon, Portugal, this compact 4 hp Eurorack module uses electrode pads to detect muscle tension, translating physical movement into usable control signals. It’s part of the ADDAC300’s Expressive Controls Series, a line focused on expanding how we interact with modular systems beyond knobs and keyboards. Instead of playing notes, you’re conducting your own physiology—clenching a fist, tapping a foot, or tensing a forearm becomes a gesture that shapes sound in real time.

This isn’t gimmickry; it’s a legitimate, if niche, performance tool. The module ships with reusable electrode pads, so you’re ready to go out of the box. Just stick them on your arm, flex, and you’ve got an envelope. Pair it with a drum module and it’s an organic trigger source—raw, human, and slightly unpredictable. One user noted it’s “good for drums, probably bad/limited for flute unless you were tapping your foot along,” which sums up its strengths and limits neatly. It doesn’t read fine motor control; it reads effort. That makes it better suited for rhythmic or gestural expression than melodic precision.

It’s also part of a broader vision. ADDAC had already released the ADDAC307 Heart Sensing module before this, which they called “the second module we make to take advantage of the physical body as a control source”—implying the Muscle Sensing was the first. That’s significant. In a world where most modular gear is about precision and repeatability, ADDAC leaned into the messy, variable nature of the human body. The Muscle Sensing, along with the Light to CV and Heart Sensing modules, forms a suite for “greater expression and sonic exploration,” as described by users and the manufacturer alike.

Specifications

Manufacturer	ADDAC System
Product type	Eurorack module
Width	4 hp
Depth	4 cm
Max current	60ma
Bus board cable	8 × 2 idc (doepfer style) connector
Output voltage range	±10v
Offset range	±10v

Key Features

Body as interface

The core idea is radical in its simplicity: your muscles become controllers. By attaching electrode pads to your skin and flexing a muscle, you generate a bio-signal that the module converts into control voltage. This isn’t MIDI aftertouch or ribbon controllers—it’s direct physiological input. The signal path starts with raw muscle activity, which the module conditions into a usable envelope. You’re not just playing the synth; you’re part of the circuit.

Envelope shaping and smoothing

Once the signal is captured, the module gives you hands-on control. The gain knob adjusts sensitivity—how much flex translates to how much voltage. The offset knob shifts the baseline, letting you set the resting level of the CV output. There’s also a smooth switch that toggles between hard and soft smoothing of the raw sensor output. This lets you shape the response: a sharp, percussive envelope for drum triggers, or a slower, more gradual rise for filter sweeps or volume swells.

Dual CV and gate outputs

The ADDAC303 provides both a positive and an inverted CV output, so you can use the same muscle movement to simultaneously open one parameter while closing another—say, brighten a filter while darkening a second oscillator. It also includes a comparator gate output with an adjustable threshold knob. This turns your muscle flex into a digital on/off signal, perfect for triggering sequencers, drum modules, or sample players. Set the threshold high and only strong clenches will fire it; set it low and even subtle twitches can trigger events.

Designed for performance

The module ships with reusable, replaceable electrode pads, meaning you can swap them out when they wear down or reposition them mid-performance. It’s built for experimentation—stick them on your arm to trigger beats, on your leg to tap tempo, or even on another musician in the band, turning a drummer’s hit or a bassist’s pluck into a control signal. Perfect Circuit calls it “perfect as a non-traditional interface for your modular,” and that’s exactly the niche it fills: not for every patch, but for moments when you want the machine to breathe with you.

Historical Context

The ADDAC303 Muscle Sensing was the first module in ADDAC System’s push toward body-driven control. It preceded the ADDAC307 Heart Sensing, which the company later described as their second module “to take advantage of the physical body as a control source.” That makes the Muscle Sensing a pioneer in their Expressive Controls Series, a line that also includes the ADDAC308 Light to CV. Together, these modules represent a deliberate shift away from traditional control methods, embracing environmental and biological inputs as valid sources of musical expression. While the broader Eurorack world was busy multiplying oscillators and filters, ADDAC was asking: what if the controller wasn’t a keyboard, but your heartbeat? Your movement? Your tension? This module is one answer.