MI Audio Lo-Fi Delay

The MI Audio Lo-Fi Delay is a compact delay pedal from MI Audio, a maker based in Sydney, Australia. It is built around the PT2399 chip, a digital delay device that emulates an analog or tape delay sound, with custom circuitry around it for modulation and filtering. MI Audio calls it "Warm, warbly, messy goodness. A creative tool for the adventurous."¹

The pedal delivers up to approximately 600ms of delay time, with a REPEATS control that runs from short slapback all the way into self-oscillation, and a modulation section that MI Audio says can do classic modulated delay sounds "but be pushed to do so much more."² The design has a long history at the company: MI Audio showed a prototype Lo-Fi Delay as far back as March 2012, describing careful design work around the PT chip "to give modulation like no other pedal."³

What it does: a modulated PT2399 delay

The PT2399 is a digital delay chip that has become a staple of the lo-fi delay category. GuitarPCB's documentation describes it as providing "smooth delay effects with a maximum delay time of approximately 600 milliseconds," with subtle artifacts at maximum that vary with each chip's tolerance⁴, which is exactly the character lo-fi builders lean into. Delicious Audio's guide to lo-fi pedals groups the MI Audio Lo-Fi Delay among lo-fi delays valued for their digital artifacts rather than clean, pristine repeats⁵.

MI Audio's own description of the pedal is an "analog/digital hybrid design" built around the PT2399 chip¹. What separates it from a basic PT2399 build is the modulation and filtering wrapped around the chip. MI Audio says the pedal offers "modulation like no other pedal, with control over the filtering of the delay signal," and that the filtering control "really gives a new perspective with a flick of the switch"².

The modulation is deep enough to go well beyond chorus-style delay. In square wave mode, MI Audio points to "cool octave skipping sounds"², and the DEPTH control goes from zero at minimum, for an unmodulated delay, to what the maker calls "super warble at maximum"².

The controls

The production pedal carries knobs for input level, delay time, repeats and modulation depth, plus switches for the LFO waveform, filter character and trails behavior².

The INPUT control is worth a note for anyone who has used other PT2399 delays: because it drives the delay line itself, it doubles as a character control, letting you keep echoes clean or push them into overdrive without affecting the dry path¹².

Power and connections

The pedal runs on a 9V battery or a 9VDC power supply, through a 2.1mm jack with negative center, and draws 30mA¹. Input impedance is 500kΩ¹.

For output, there is a stereo output jack that gives access to the delay signal alone via the ring, using a stereo splitter, so the wet signal can be routed elsewhere for further processing¹.

How it compares with other lo-fi delays

The PT2399 lo-fi field is crowded, and the MI Audio stands out mainly for its modulation depth and the wet-only output²¹³.

• The Jeds Peds Lo-Fi Delay is another PT2399 build, using the chip's two on-board amps as input and output mixers.
• The Hochstrasser Electronics Sundial, reviewed by Pedal of the Day, is a PT2399-based digital delay whose feedback control routes the delay back into itself for lush echoes, with self-oscillation past about 2:00 on the dial⁶.
• The Catalinbread EG1 Lo-Fi Delay and Wampler The Doctor Lo-Fi Delay take the lo-fi delay idea in other directions, with the Wampler adding self-oscillating capabilities combined with modulation.

Against these, the MI Audio's distinguishing features are the waveform switch on the modulation, the filter switch for shaping the echo's tone, the INPUT control that can overdrive the delay line, and the ring output for the wet signal alone¹².

Where it came from

The Lo-Fi Delay has been in MI Audio's lineup in evolving forms for well over a decade. The March 2012 prototype page describes the same core idea: a PT2399 chip with careful custom circuitry around it for modulation, including the octave skipping sounds in square wave mode that carried through to the production pedal³. The R&D Lab page on MI Audio's site shows a later development version, described as an "as-of-yet unnamed" MI Effects Lo-Fi Delay, with the REPEATS, TIME, INPUT and DEPTH controls, the square/triangle wave switch, the trails switch, and a LO/HI-PASS mode switch that MI Audio said would probably become a three position filter switch in production². The production pedal as sold carries the two position Hi/Lo filter switch¹.

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