Spectral Forge

May 8, 2026 · View on GitHub

0.15 is now merged to the Master branch. An extensive update with dozens of new processors, modular routing, presets, host automation, a new more modular codebase, etc. I will tweak the things before a release since some of the new processors still lack DSP, and none of them have really had their parameter ranges and DSP tuned for usability and interesting outcomes. Work with the missing DSP for some of the new modules will go on in parallel in the dev branch.

A spectral compressor and modular effects processor for Linux/Windows, implemented as a CLAP plugin. Designed for Bitwig Studio.

Patent-safe design — does not use the Hilbert/convolution approach from oeksound's patents.

The dynamics section is functional. The modular multi-fx routing system is under active development — expect things to be unfinished or experimental on the main branch. If you just want to use this, stick to the releases.

Contributors and AI assistants: the design specs and implementation plans under docs/superpowers/ include historical, in-progress, and deferred work. Check docs/superpowers/STATUS.md before following any of them — several are SUPERSEDED.

Screenshot_20260421_115617

Building and installing

Requirements: Rust stable toolchain, Cargo. clap-validator is optional for testing.

# Debug build
cargo build

# Release build
cargo build --release

# Bundle as .clap
cargo run --package xtask -- bundle spectral_forge --release

# Install to Bitwig's default search path
cp target/bundled/spectral_forge.clap ~/.clap/

After installing, rescan plugins in Bitwig (or restart). The plugin appears as Spectral Forge under CLAP instruments/effects.

Quick start

  1. Insert Spectral Forge on any audio track.
  2. Play audio through it — the spectrum display will show your signal in real time.
  3. The threshold curve (selected by default) controls where compression begins. Drag nodes to shape the threshold across the frequency range.
  4. Increase the Ratio curve to set compression depth per frequency band.
  5. Use Attack and Release curves to control how fast each band responds.

Interface overview

Top bar (row 1 — curve selectors)

Adaptive curve selector buttons show the curves available for the currently selected slot. A Dynamics slot shows THRESHOLD / RATIO / ATTACK / RELEASE / KNEE / MIX; a Gain slot shows GAIN / PEAK HOLD; a Freeze slot shows LENGTH / THRESHOLD / PORTAMENTO / RESISTANCE; and so on. Clicking a button makes that curve active for editing.

To the right: Floor and Ceil drag-values set the dBFS range of the spectrum display. Falloff sets the peak-hold decay time in ms.

Top bar (row 2 — FFT and scale)

FFT buttons (512 / 1k / 2k / 4k / 8k / 16k) set the FFT window size, trading frequency resolution against latency. Scale buttons (1× – 2×) set the UI zoom.

Curve display

The large centre area shows:

  • Spectrum gradient — the pre-FX signal (teal line) and post-FX signal (pink line) with a filled gradient between them showing the amount of processing.
  • Response curves — coloured polylines for each of the current slot's curves. The active curve is brighter; inactive ones are dimmed.
  • Node handles — only for the selected curve. Circles for bell-type nodes; triangles (▶ / ◀) for shelf nodes.
  • Graph header — top-left overlay reads "Editing: {slot name} — {channel target}". Click it to rename the slot.

Node interaction

ActionEffect
Drag nodeMove frequency and gain
Scroll wheel over nodeCoarse Q (bandwidth) adjustment
Hold both mouse buttons + drag up/downSmooth Q adjustment (500 px = full range)
Double-click nodeReset node to default position

Bottom strip — control knobs

SC assignment (per slot): SC1 / SC2 / SC3 / SC4 / Self buttons assign the current slot's sidechain input. Active inputs light up green.

GainMode (Gain slots only): Add / Subtract / Pull buttons appear when a Gain module is selected.

Global row:

ControlRangeDescription
IN±18 dBInput gain
OUT±18 dBOutput gain
MIX0–100 %Global dry/wet
SC±18 dBSidechain input gain
AUTO MKon/offAuto makeup gain — long-term GR compensation
DELTAon/offDelta monitor — hear only what is being removed

Dynamics + per-curve row:

ControlRangeDescription
Atk0.5–200 msGlobal attack time base
Rel1–500 msGlobal release time base
Sens0–1Sensitivity — how selectively peaks are targeted
Width0–0.5 stGain-reduction mask blur radius (semitones)
Offset±3Additive offset for the active curve
Tilt±3Spectral tilt for the active curve, pivoting at 1 kHz

DELTA is the fastest way to verify the plugin is targeting what you intend — it outputs the removed signal.

Routing matrix

Below the curve editor, the slot routing matrix shows up to 9 processing slots:

  • Diagonal cells — the module assigned to each slot. Click to select that slot for curve editing.
  • Off-diagonal cells — send amplitudes between slots. Default routing is serial: slot 0 → 1 → 2 → Master (slot 8).
  • Right-click a diagonal cell to change the module type.

Available module types: Dynamics (spectral compressor), Freeze, Phase Smear, Contrast, Gain, Mid/Side, T/S Split, Harmonic.

FFT Size

Selectable from 512 to 16384. Larger sizes give better frequency resolution and higher latency. The default 2048 gives ~46 ms latency at 44.1 kHz and ~21 Hz per bin.

Sidechain

Up to 4 auxiliary sidechain inputs are supported. Route any source to an aux input (Bitwig: enable aux inputs in the track header). Each slot can be independently assigned to a sidechain input via the routing matrix.

Running tests

cargo test            # all tests (28 total across 5 test files)
cargo test engine     # engine contract tests only
cargo test stft       # STFT roundtrip test only
cargo test module     # SpectralModule trait compliance tests

Credits

Built on nih-plug (Robbert van der Helm), realfft (Henrik Enquist), triple_buffer, and the CLAP plugin standard (Alexandre Bique et al.). Phase vocoder algorithm references from pvx (Colby Leider). See CREDITS.md for full details.

License

The original source code in this repository is dedicated to the
public domain under the                                        
[Creative Commons Zero v1.0 Universal (CC0-1.0)]
(https://creativecommons.org/publicdomain/zero/1.0/legalcode).
To the extent possible under law, the author has waived all copyright                                         
and related or neighbouring rights to this work.                     
                                                
### Third-party components
                          
The compiled plugin binary links against third-party libraries that
retain their own licenses. Distributions of the compiled binary must
preserve their notices:                                             
                       
| Library | License |
|---------|---------|
| [nih-plug](https://github.com/robbert-vdh/nih-plug) | ISC |
| [egui](https://github.com/emilk/egui) | MIT OR Apache-2.0 |
| [realfft](https://github.com/HEnquist/realfft) | MIT |     
| [triple_buffer](https://github.com/HadrienG2/triple-buffer) | LGPL-3.0 | (I need to check the exact requirements for this)
| [parking_lot](https://github.com/Amanieu/parking_lot) | MIT OR Apache-2.0 |
                                                                             
Run `cargo license` in the repository for the full dependency list.