4ms PEG

A dual envelope generator that follows your clock, not your DAW's timeline

Overview

Tap it, ping it, clock it. However you trigger it, the 4ms PEG sets the envelope length from the time between pings. It is not a standard ADSR sitting in the corner of a patch with a predictable rise and fall. It is built around the idea that envelope timing should sync to a beat instead of floating in free time. Plug in a clock, tap the button, or send a trigger, and the envelope's duration locks to the incoming pulse. A snappy decay on a kick works. So does a slow, creeping swell on a pad that matches your tempo. From there you can warp it further.

It's a dual module, with two independent envelope generators on a single 20HP panel. That's compact by Eurorack standards, but not minimalist. Each side has division and multiplication of the incoming clock, a shape knob with CV input, skew control, and multiple trigger modes. You can run one side to sync a filter sweep to your sequence, use the other to modulate amplitude in a polyrhythmic pattern, or patch them together for cascading, self-generating rhythms. You don't need a sequencer to get evolving modulation. Feed it a clock, turn the div/mult knob, and you're off.

It's digital under the hood, running firmware that's been updated over the years (v4.3 for PCB v2.x, v4.2 for v1.x). It doesn't feel cold or clinical, though. Owners report that the internal sampling rate keeps a certain "analog" responsiveness, even though the math is happening in code. Not everyone is charmed. Some purists on forums like Mod Wiggler have griped that the envelopes "feel digital in a bad way" next to the smoother, more organic response of modules like MakeNoise's Maths. That's a matter of taste. The PEG isn't trying to emulate vintage voltage control. It's built around timing precision and rhythmic flexibility, not analog warmth.

It encourages happy accidents. Patch the End-of-Rise (EOR) or End-of-Fall (EOF) gate outputs to other modules and the envelope triggers other events, makes feedback loops, or drives secondary sequences. The OR output takes the higher of the two envelope voltages, which turns the two channels into a kind of dynamic mixer. Set one side to fast, staccato bursts and the other to slow, sweeping arcs, then let the OR output pick which one dominates in real time. It rewards patching blind, just to see what happens when a knob goes all the way up.

Specifications

Key Features

Tempo-Locked Envelopes That Think in Beats

The PEG's whole approach is that envelopes should be rhythmic. Traditional envelope generators fire once per trigger and decay at a fixed rate. The PEG treats the incoming clock as the master metronome. The time between pings sets the total envelope duration, whatever shape you've given it. If your clock slows down, the envelope stretches. If the clock speeds up, it tightens. Your modulation stays locked to the grid, which suits syncopated filter sweeps, tempo-matched plucks, and drone textures that move with the beat. Since you can divide or multiply the clock from /32 to x16, polyrhythmic variations are easy - say, a hi-hat pattern that triggers every third ping, or a bass swell that only happens on every 16th beat.

Shape, Skew, and the Art of Asymmetry

The shape knob isn't a simple sweep from linear to exponential. It cycles through 17 distinct curves, some symmetrical, some wildly asymmetrical. At the extremes you get sharp ramps or long tapers, and in the middle, smoother arcs. The skew control adjusts the ratio between rise and fall times without changing the overall envelope length. Turn it and you can go from a fast attack and slow decay to a slow attack and fast decay, with the total duration still locked to the incoming clock. That makes a snare hit that starts slow and snaps shut, or a pad that swells in quickly but lingers. Both shape and skew have CV inputs, so you can modulate them in real time and have envelopes that change with each cycle.

Generative Patching with Gate Outputs and OR Logic

The PEG outputs events as well as envelopes. The EOR (End-of-Rise) and EOF (End-of-Fall) gate outputs fire when those phases begin or end, so you can chain envelopes, trigger other modules, or make feedback loops. Patch EOR from one channel to the ping input of the other and you have a self-oscillating rhythm generator. The OR output continuously outputs the higher voltage of the two envelope channels. That makes the PEG a kind of dynamic logic module, where the loudest or most active envelope takes control. It works for call-and-response patches, or for feeding a VCA so the more aggressive envelope dominates.

Historical Context

The 4ms PEG came out during the mid-2010s Eurorack boom, when modular synthesis was shifting from boutique curiosity to mainstream creative tool. Envelope generators at the time were mostly variations on the classic ADSR - predictable and reliable, but limited in rhythmic flexibility. Modules like MakeNoise Maths had already begun to blur the lines between envelope, LFO, and logic, but the PEG took a different approach: full tempo synchronization as a first-class feature. Maths offered more analog character and more complex looping modes. The PEG leaned into digital precision and immediate rhythmic utility. It was an alternative for producers who wanted envelopes that locked to a beat without external quantizers or complex clock dividers.

4ms, known for designs like the Spectral Multiband Resonator and the Dual Looping Delay, had a reputation for modules that felt both experimental and practical. The PEG fit that mold. Its release coincided with a growing interest in generative music and algorithmic composition, where modules that could create evolving patterns without constant manual intervention were highly prized. With its dual channels, tap tempo, and feedback-friendly outputs, the PEG became a favorite for people building self-playing systems or exploring rhythmic complexity beyond standard sequencing.

It also arrived just before the wave of "pingable" or "clockable" envelope designs that would later appear in modules like the Acid Rain Maestro or Mutable Instruments Tides (in certain modes). Those modules added more features, including multiple lanes, memory, and complex modulation chains. The PEG stayed notable for its simplicity and directness.

Collectibility & Value

The 4ms PEG isn't rare, but it's not common enough to be a commodity. It's still in production, available both as a pre-built module and as a DIY kit from retailers like Thonk, so you won't find it commanding vintage premiums like a discontinued Doepfer or a rare Analogue Solutions unit. It does hold its value. New units typically sell for around $300 - $350, and used ones go for $200 - $275 depending on condition and seller. The kit version is significantly cheaper, which appeals to builders who want to save money or enjoy the assembly.

It's a modern digital module with firmware updates, so condition is less of a concern than with analog gear. There are no capacitors to dry out and no pots to crackle - just a PCB, a few jacks, and a microcontroller. The main failure points are mechanical: damaged jacks from over-tightened patch cables, or problems with the power jumper if it's set incorrectly. The faceplate is FR4 with a conductive backing for shielding. It's durable but can scratch if mishandled. Firmware can be updated, so even older units can run the latest code (v4.3 for PCB v2.x).

If you're buying used, check that both channels respond to pings, that the tap tempo buttons work, and that the CV inputs modulate as expected. The module relies on precise timing, so any jitter or missed triggers could point to a firmware or hardware issue. Owners report years of trouble-free use. The Mini PEG, a single-channel version with extended div/mult ranges, also exists, but many users still prefer the full dual-channel layout for its flexibility.

Source Documents

Original source documents linked below - references to publicly-available technical documentation, not rehosted.

• Service Manual: User Manual - 4ms Pedals — 1 MB — archive.org

eBay Listings

4ms PEG Pingable Envelope Generator Eurorack Module Dual Env

$300

4ms PEG Pingable Envelope Generator Eurorack Module Dual Env

$300

4MS MINI PEG : NEW : [DETROIT MODULAR]

$159

4MS PINGABLE ENVELOPE GENERATOR (PEG) : NEW : [DETROIT MODUL

$345

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