Discomfort Designs Riemann's Grave Octave Bit Crusher Distortion Filter

The Riemann's Grave Octave Bit Crusher Distortion Filter is a stereo filter pedal from Discomfort Designs that combines a multi-mode filter with a three-way distortion section. At its core it is a stereo filter pedal whose cutoff can be modulated by a random sample and hold wave or a Wandering Sine, and whose Zeta Function stage adds distortion by wave folding, bit crushing, or octave up distortion¹. Delicious Audio describes it as more than a simple distortion pedal: "a powerful, self-contained workstation for timbral sculpting"².

The pedal is named for Bernhard Riemann, a German mathematician who made contributions to analysis, number theory, and differential geometry³. Discomfort Designs also makes the Black Tooth Doom Octave Distorter and the Doomsailor Distortion.

A stereo modulated filter with three distortion modes

The circuit is built around a curated trio of biquad filters paired with a sample rate reducer². Two low pass filters sit at the heart of the design, and you can apply modulation randomly or with precision³. The pedal runs as a dual-engine system, with distortion on the right and filter on the left².

The filter section is a state-variable design you sculpt with Frequency and Resonance controls, and a three-way switch toggles between Band Pass, Low Pass, and High Pass modes². The distortion side is the Zeta Function, which can add mild saturation or distortion in three ways: wave folding, bit crushing, or octave up distortion¹.

Not just for guitar, the effect works on drums, synths and any other input signal you can think of³.

The modulation sources and the Zeta Type switch

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 it moves². The three positions on the modulation switch are Random Sample & Hold, Static, and Wandering SineWave⁴.

On the distortion side, the Distortion / Zeta Type switch selects between Wavefolder, Bitcrusher, and Octave Distortion⁴. Higher Zeta Function settings will mangle and crush, and create some wonderfully ugly atonal messy sounds, which Delicious Audio notes drums love².

A wavefolder and a bitcrusher work differently. A wavefolder folds the waveform back on itself as the level rises, adding harmonics through folding rather than clipping. A bitcrusher, as used here through the sample rate reducer, drops the sample rate so the signal breaks into coarse, lo-fi steps. The original version's second filter, also a resonant LPF, had its cutoff modulated by a curvy sine wave or a pointy ramp wave LFO, with a rate knob for speed, one toggle for the LFO shape, and another choosing constant or random modulation².

The compact version

In October 2025, Discomfort Designs shrank the original 1590BB Edition into a compact stereo device⁴. The pedal is named for a dead mathematician⁴. The enclosure is baby blue¹.

What reviewers said

Pedal of the Day reviewed the original Modulated Allfilter version in 2022, calling it "an effects unit that defies all logic and convention" and describing how it transforms the input into "a fury of bits, bleeps, pops and more"³.

On the compact version, the same site found it "a fun little thing that has a mind of its own," flipping the script on what normal effects should be, and concluded that "this one will keep a smile on your face and innovation in your playing" thanks to its wide array of controls, knobs and switches¹.

Guitar Pedal X found the sum of the parts gives a range of useful textures, from robot-talk through various fluttery, zithery, and swooshy textures allied to lo-fi distortion flavors⁴.

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