Riemann's Grave is a stereo modulated filter pedal from Discomfort Designs, a maker whose output sits firmly on the experimental end of the board. At its heart is a trio of biquad filters paired with a sample rate reducer, the component that gives the pedal its bit-crushed, lo-fi character1. Pedal of the Day's 2022 review of the original Modulated Allfilter described the result as "a fury of bits, bleeps, pops and more"2. Later versions add a three-way distortion section, making it a filter, bit crusher and distortion in one box.
What it does to your signal
The pedal operates as a dual-engine system, with distortion on the right and filter on the left1. The filter side is a state-variable filter you sculpt with Frequency and Resonance controls1. A central switch routes either static, random, or a wandering sine wave to modulate the filter's frequency, with an adjustable modulation Depth control setting how far the modulation travels1. On the 2025 version, Pedal of the Day describes a multi-mode filter that can be modulated by a random sample and hold wave or a Wandering Sine3.
The distortion side, which Discomfort Designs calls the Zeta Function, can add mild saturation or distortion in three ways: wave folding, bit crushing, or octave up distortion3. Guitar Pedal X lists the Distortion / Zeta Type switch as Wavefolder / Bitcrusher / Octave Distortion4.
The original Modulated Allfilter
The first version, reviewed by Pedal of the Day on 31 October 2022, was built around two low pass filters, and you could apply modulation randomly or with some precision2. The 2025 product page details how those filters work:
- Theorem 1: a resonant 24 dB per octave low pass filter. With toggle 1 pointing down, the cutoff frequency is fixed, clockwise closes and counterclockwise opens. With toggle 1 up, random modulation is applied to the cutoff frequency, and clockwise controls how rapidly a new cutoff frequency is selected1.
- Theorem 2: a second filter, also a resonant LPF, with cutoff modulated by a curvy (sine wave) or pointy (ramp wave) shaped LFO. A rate knob controls LFO speed, Toggle 3 selects the LFO wave shape, and Toggle 4 chooses constant (down) or random (up) modulated LFO1.
Pedal of the Day summed up the original as "an effects unit that defies all logic and convention", with each twist and turn of a knob or flick of a switch resulting in an abstract display of auditory prowess2.
Versions and enclosure
Pedal of the Day described the Riemann's Grave as a pedal whose knobs and switches twist, wrench, pull and shift the input signal in many ways, "each twist and turn of a knob or flick of a switch resulting in an abstract display of auditory prowess"2.
The 2025 compact version keeps the stereo filter and adds the Zeta Function distortion section. Pedal of the Day's review of that version, published 16 October 2025, describes it as, at its core, a stereo filter pedal, finished in baby blue3.
What reviewers said
- Pedal of the Day (2022) on the original: "this pedal encapsulates each and every one of those things with flying colors", referring to transformation, experimentation and having a great time2.
- Pedal of the Day (2025) on the compact version: "this one will keep a smile on your face and innovation in your playing", calling it a fun little thing that has a mind of its own3.
- Guitar Pedal X's Stefan Karlsson (2025): "as you get a range of useful textures - from robot-talk through various fluttery, zithery, and swooshy textures - allied" to lo-fi distortion flavors4.
The namesake
The pedal is named for Bernhard Riemann, a German mathematician who made contributions to analysis, number theory, and differential geometry2. Delicious Audio's page puts it plainly: "It's also named for a dead mathematician."1
Videos
Discomfort Designs
The Pedal Zone
Signal Path
Questions
Does Riemann's Grave work on synths and drums?
Yes. Pedal of the Day's 2022 review of the original Modulated Allfilter notes that it is not just for guitar: the effect works on drums, synths and any other input signal you can think of. That makes it a candidate for processing drum machines, modular gear and keyboards as well as guitar and bass.
What does the Riemann's Grave sound like?
Reviewers describe it as an experimental, unpredictable effect. Pedal of the Day called the original a fury of bits, bleeps, pops and more, while Guitar Pedal X's Stefan Karlsson heard a range of useful textures from robot-talk through fluttery, zithery and swooshy textures, allied to lo-fi distortion flavours. It is a pedal for sound design rather than a transparent filter.
Who was Riemann, the pedal's namesake?
The pedal is named for Bernhard Riemann, a German mathematician who made contributions to analysis, number theory and differential geometry. Delicious Audio's product page puts it plainly: it is named for a dead mathematician.
Is Riemann's Grave available in a smaller enclosure?
Yes. Guitar Pedal X reported in October 2025 that Discomfort Designs had shrunk the original 1590BB Edition into a compact stereo device, available in two editions at £295. The compact version keeps the multi-mode stereo filter and the three-way distortion section.
Sources (4)
- Discomfort Designs Riemann's Grave V2, Delicious Audio, 2025-10-14
- Discomfort Designs Riemann’s Grave Modulated Allfilter, Pedal of the Day, 2022-10-31
- Discomfort Designs Riemann's Grave Octave Bit Crusher Distortion Filter, Pedal of the Day, 2025-10-16
- Guitar Pedal X, Guitar Pedal X, 2025-10-17
