4ms Looping Delay ()

Name: 4ms Delay
Brand: 4ms

Clock-synced delay with up to 87 seconds of looping space and precise timing. Modular's answer to infinite echo without the tape hiss.

Overview

Tap the Ping button and the 4ms Looping Delay is running. It doesn't fade in or warm up. Every repeat is quantized and locked to the clock. This isn't the smeared, warbling echo of tape or the gritty PT2399 chip. It's clean digital delay, built for players who want rhythmic precision without giving up depth. You can stretch a loop out to 87 seconds in mono mode, or run stereo at 43 seconds. That's enough room to build whole ambient movements or layer polyrhythmic textures that evolve over minutes. Because it's clock-synced, every repeat lands where it should, which made it a favorite for live performers who need reliability.

The Looping Delay blurs the line between delay and looper. Flip on Infinite Hold and the module stops recording, locking whatever is in the buffer into a loop. From there you can reverse playback, scrub through the loop with the Feedback knob while holding Infinite, or modulate the timing with CV for rhythmic shifts. The manual calls this "windowing." It seems obscure until you use it to isolate a single transient or stretch a vowel into a pad.

The interface stays simple. No menus, no OLED screens, no nested functions buried under button presses. Everything is on the front panel: Time, Feedback, Mix, and Delay Feed, each with CV inputs so you can modulate them from an LFO, envelope, or sequencer. The Time knob works in musical divisions - whole notes, eighth notes, dotted values - thanks to a toggle switch that lets you add 16 beats, set exact values, or divide by eight. It rewards musical thinking over technical tweaking, though it does assume you're comfortable with basic rhythm math. Patch a fast LFO to the Time CV and the delay stutters and pitch-bends in rhythmic bursts. Slow it down and the shifts become glacial. There's no internal reverb or filtering. The Send/Return jacks let you route the loop through a filter, phaser, or another delay for cascading effects.

Specifications

Manufacturer	4ms
Production Years
Original Price	$275.00
Format	Eurorack
Module Width	10 HP
Depth	25mm (0.98")
Power Consumption	+12V: 188mA max, -12V: 48mA max
Sampling Rate	48kHz
Bit Depth	24-bit sampling, 16-bit recording
Maximum Delay Time	87 seconds (mono), 43 seconds (stereo)
Frequency Response	0Hz to 24kHz
Audio Input	DC-coupled (jumper selectable), 16.8V p-p max before clipping
Audio Output	0Hz to 24kHz, ±10.5V max, soft limiting
Clock Input	Accepts external clock or tap tempo via Ping button
Clock Output	Main Clock Out, Loop Clock A, Loop Clock B
CV Inputs	Time, Feedback, Mix, Delay Feed, Hold, Reverse
Controls	Time knob, Feedback knob, Mix knob, Delay Feed knob, Ping button, Infinite Hold button, Reverse button
Connectors	Input, Output, Send, Return, Clock In, Clock Out, Loop Clock A, Loop Clock B, and CV jacks for all parameters
Firmware Updates	Field-upgradable via audio file playback
Assembly Options	Available as DIY kit or pre-assembled unit

Key Features

Time Control with Musical Intelligence

The Looping Delay speaks clock. The Time knob isn't a continuous sweep. It's divided into 17 steps representing musical divisions, from 1/8th notes up to 32-bar phrases. The three-position Time switch changes how those values are read: center for direct beat counts, up for adding 16 beats (good for long loops), and down for dividing by eight (good for fast subdivisions). You think in bars and beats instead of dialing in milliseconds. Hold the Infinite button and turn the Time knob, and you enter Unquantised Time Mode. The delay time becomes fully variable, useful for gliding between rhythmic values or diving into audio-rate delays for Karplus-Strong synthesis. Patch a square wave from a VCO into the Time CV input and the delay line becomes a resonant filter bank, tunable via 1V/octave in audio-rate mode.

Infinite Hold and Loop Manipulation

The Infinite Hold button is the looper side of the module. When engaged, recording stops and feedback locks at exactly 100%, so the loop plays indefinitely. You can still work the loop in real time. While holding Infinite, turning the Feedback knob shifts the start and end points of the loop. That's the "windowing" mentioned above, and it lets you explore fragments of audio, isolate transients, or create rhythmic variations without re-recording. Reverse mode flips playback direction, with a twist: newly recorded material continues forward, so old and new move in opposite directions. Exit Reverse and those forward-recorded segments play backward. That can catch users off guard, but it opens up complex phasing effects when chained with other modules.

Send/Return for External Processing

The Send/Return jacks are among the most underrated parts of the module. Many delays only allow wet/dry mixing. This one lets you route the entire delay path through external effects. Patch the Send to a filter, then return it, and every repeat gets filtered, not just the input signal. That makes it a processing hub, able to build evolving textures with resonant filters, granular processors, or even another delay. Some users have installed alternate firmware (like the v5-Send-Return-Pre-Loop mod) to place the Send/Return before the memory buffer. Effects then shape the input before it's recorded, so every generation of the loop carries the same processing. It assumes you're deep in the patch bay.

Historical Context

The 4ms Looping Delay arrived in the mid-2010s, when modular synthesis was moving from boutique curiosity to mainstream tool for electronic musicians. At the time, most digital delays in the format were either lo-fi emulations or basic buffer-based designs. The Looping Delay embraced its digital nature instead of disguising it. It was inspired by late-'70s and early-'80s digital delays like the Lexicon PCM42, and it skipped pitch-shifting and tape degradation in favor of clean, sample-accurate repeats. The module filled a gap for composers who wanted long, stable loops without the mechanical fragility of tape or the memory limits of early samplers. It also reflected 4ms's design philosophy: functional, DIY-friendly, and well integrated with the modular ecosystem. The company's earlier Dual Looping Delay (DLD) packed two channels into 20HP. The Looping Delay is a streamlined, single-channel version, more accessible in both price and complexity. It became a favorite among performers who needed reliability in live sets, as well as sound designers exploring generative composition. Mutable Instruments' Clouds offered granular manipulation, while the Looping Delay went for rhythmic precision and tight control - less about texture, more about timing.

Collectibility & Value

The 4ms Looping Delay isn't a rare bird, but it's not generic either. It's a staple in many Eurorack systems and holds steady resale value - typically between $225 and $275 for used units in good condition, with pre-assembled versions commanding a slight premium over DIY kits. The kit version remains popular among builders. It uses through-hole parts with minimal surface-mount components, which makes it a realistic project for beginners. Owners should know a few potential failure points. The most common issue is firmware corruption, which can keep the module from booting. Users have reported dimly lit buttons or unresponsive controls after failed updates. In most cases you can fix it by re-flashing the firmware from an audio file, though that takes a computer and a working power supply. Some early adopters using older Doepfer PSU2 power supplies noted boot issues after firmware updates, which suggests sensitivity to power-on transients. It's not widespread, but it matters when buying used.

Another quirk: all CV inputs are unattenuated, so a 10V LFO will fully sweep a parameter unless you patch through an attenuator. That isn't a flaw, but it assumes a well-equipped system. On used units, check the jacks and knobs for physical damage and verify that all buttons respond correctly. The Ping button, used frequently for tap tempo, can wear out over time. The module is still in production and supported by 4ms, so parts and documentation are readily available, which helps keep repair costs low. Older units can be upgraded by firmware via audio file. New features like de-jitter modes and quantized change settings have been added since launch.