Grit — Distortion / Lo-Fi Processor

(TODO: screenshot)

License

MIT License
(c) 2026 Andy Jenkinson (uglifruit) — with ClaudeCode.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Overview

Grit is a four-mode distortion and lo-fi processor. It covers the range from smooth amp-style saturation to hard digital clipping, bit crushing, and sample-rate degradation — all in a single applet slot.

Available as a MONO applet.

Signal Flow

Audio In ──► AudioEffectGrit (distortion + tone) ──► Audio Out

Wet/dry mixing is handled internally. The dry signal is the unprocessed input; the wet signal is the distorted output after tone filtering.

Parameters

Param	Range	CV	Description
Mode	CLIP / SAT / CRUS / DECI	—	Distortion algorithm (see below)
Drv	0–100%	drv_cv	Input gain before distortion. 0% = ×1 (unity), 100% = ×10.
Thr/Kne/Bit/Dec	0–100%	amt_cv	Effect depth — meaning depends on Mode (see below). Label changes with Mode.
Ton	0–100%	tone_cv	Post-distortion lowpass. 0% ≈ 800 Hz (dark), 100% = fully open.
Mix	0–100%	mix_cv	Wet/dry balance. 0% = fully dry, 100% = fully wet.

Modes

CLIP — Hard Clipping

Clips the signal at an adjustable threshold. Amt (Thr) controls the threshold level:

100% — threshold at full scale; no audible clipping (clean pass-through at low drive)
50% — clips loud transients and peaks; adds harmonic distortion
0% — threshold near zero; severe hard limiting

Classic transistor/diode-style distortion at high drive. Use Tone to roll off the harsh high-frequency content that hard clipping adds.

SAT — Soft Saturation

Smooth amplitude-limiting via a rational approximation (x / (1 + |x| × k)). Amt (Kne) controls the saturation knee:

0% — nearly linear; very slight softening at peaks
50% — moderate saturation; warm, tape-like compression
100% — hard saturation; similar to clipping but with a softer transition

Unlike CLIP, SAT never introduces a hard discontinuity. The result is smooth even at high drive settings.

CRUS — Bit Crushing

Reduces the bit depth of the audio signal. Amt (Bit) controls how many bits are discarded:

0% — 16-bit (full resolution); clean
50% — ~8-bit; noticeable quantisation noise and steps
100% — 1-bit; extreme digital grit / square-wave distortion

Low bit depths produce characteristic quantisation noise that sits above the signal. Combine with Tone to tame the high-frequency noise content.

DECI — Decimation (Sample Hold)

Reduces the effective sample rate by holding each sample for multiple output samples. Amt (Dec) controls the hold factor:

0% — 1× hold (full sample rate); clean
50% — ~8× hold; ZX Spectrum / 8-bit computer character
100% — 16× hold; heavy stairstepping, very low perceived sample rate

Decimation produces a characteristic “staircase” distortion that is different in character from bit crushing — it degrades the time resolution of the signal rather than its amplitude resolution.

Controls

Control	Action
Encoder (browse)	Navigate cursor through parameters
Encoder (edit)	Adjust parameter value; on Mode — cycle CLIP / SAT / CRUS / DECI
Button	Enter/exit edit mode; assign CV input when cursor is on a CV slot
Aux button	Cycle mode (CLIP → SAT → CRUS → DECI → CLIP)

Tone

The Tone parameter applies a single-pole lowpass filter to the wet (distorted) signal only. This is useful for:

Taming the harsh upper harmonics added by CLIP and CRUS
Creating a “muffled” or “lo-fi cassette” character when combined with SAT
Blending in a softened, de-emphasised distortion alongside the dry signal with Mix

Tone does not affect the dry signal path.

CV / Gate Inputs

Drv, Amt, Tone, and Mix each have an assignable CV input slot. Mode has no CV. Assign inputs using the in-applet CV input editor (press button when cursor is on a CV label).

Suggested Patches

Warm overdrive

Mode = SAT, Drv = 40%, Amt = 60%, Tone = 70%, Mix = 100%
Drive into saturation, roll off harsh highs with Tone.

Fuzz/hard clip

Mode = CLIP, Drv = 80%, Amt = 30%, Tone = 50%, Mix = 100%
Extreme drive into a low threshold → classic fuzz character.

8-bit digital crunch

Mode = CRUS, Drv = 0%, Amt = 50%, Tone = 60%, Mix = 70%
Mid bit depth; Tone softens quantisation noise; Mix blends back some clean signal.

Lo-fi sample degradation

Mode = DECI, Drv = 0%, Amt = 40%, Tone = 80%, Mix = 100%
Moderate decimation; sounds like a low-quality digital recording.

Parallel grit blend

Any mode, Mix = 30–50%
Mixes a small amount of distorted signal back with the clean source — adds density and presence without overwhelming the original.

Technical Notes

All DSP runs in the audio interrupt (update()). No heap allocation, no buffers — only a few float state variables per instance.
The x / (1 + |x| × k) saturation approximation is a Padé-type rational function. It is continuous and differentiable (no discontinuity), so it adds only even and odd harmonics smoothly rather than the harsh odd-harmonic content of hard clipping.
Tone coefficient is computed at control rate (~150 Hz) using expf() — not in the audio hot loop.
RAM1 impact: negligible.

Files

File	Purpose
`audio_applets/GritApplet.h`	UI and control layer (HemisphereAudioApplet)
`Audio/AudioEffectGrit.h`	DSP engine (AudioStream subclass)