Delta

A phase-cancellation null-test / difference-checker plugin.

Feed two versions of the same audio (a re-render, a bounce after a plugin change, an A/B of a master) into Delta's main input and sidechain, hit Align, and it finds the sample-accurate timing offset between them automatically via cross-correlation, then outputs only the difference. If the two sources are identical, the output is silence — a perfect null. Anything left over is real, audible, and shown live on a scrolling spectrogram: exactly which frequencies and moments the two sources actually differ at.

Built with JUCE, ships as VST3 / AU / Standalone on macOS and Windows.

⬇ Download the latest beta — macOS and Windows, free during the beta period. · Changelog

Also listed on KVR Audio.

Why this exists

Null-testing is a standard technique (invert one signal, sum it with the other, listen to what's left) but doing it properly requires the two sources to be aligned to the sample — even a 1-sample offset destroys the null and makes two identical signals look completely different. Delta automates that alignment step and gives you a live visual of the residual instead of just a number, so you can actually see where two mixes/renders/masters diverge, not just that they do.

This is a standalone tool aimed at a different audience than typical creative effects — audio engineers doing verification/QA work — so it has its own visual identity: black background, monospace type, a single amber "instrument" accent, a frequency-axis spectrogram instead of a knob.

Status

Early-stage / actively developed, free during the beta period. This repository shows the plugin's architecture: JUCE plugin wrapper with a sidechain input bus, cross-correlation alignment, FFT-based spectrogram pipeline, custom UI. The exact visual calibration (glow strength, colour grading, peak-hold decay curve) used in the shipped/tested build is simplified in Source/PluginEditor.cpp here — that polish is the actual product, not fully open source at this stage.

Features

• Sidechain-based dual input: main = source A, sidechain = source B, output = A − delay-compensated B
• One-click automatic sample-accurate alignment via cross-correlation (± ~5.8ms search window)
• Live scrolling spectrogram of the residual on a logarithmic frequency axis, with a peak-hold contour and a dB colour legend
• Built-in synthetic test signal (no real routing needed to try it out)
• Denormal-safe processing, lock-free audio-thread-to-UI handoff for the spectrogram data (no locks on the audio thread)
• Builds as VST3, AU (passes auval validation), and a Standalone app

Tech stack

• C++17, JUCE (audio processing + UI)
• CMake + Ninja

Building

git clone --depth 1 https://github.com/juce-framework/JUCE.git libs/JUCE
cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build

On macOS, add -DCMAKE_OSX_ARCHITECTURES="arm64;x86_64" to the configure step to build a universal binary (Apple Silicon + Intel) instead of the host-only default. The official beta releases are built this way.

This produces a VST3, an AU component, and a standalone app under build/Delta_artefacts/Release/, and installs the plugin formats into your system's plugin folders automatically (COPY_PLUGIN_AFTER_BUILD).

Project structure

Source/
  PluginEntry.cpp       JUCE plugin entry point
  DeltaProcessor.*       AudioProcessor: sidechain bus, alignment, FFT pipeline
  PluginEditor.*          Custom UI (spectrogram, peak-hold, legend, HUD)
  DeltaLookAndFeel.h      Custom LookAndFeel (monospace, amber, square controls)
CMakeLists.txt

Open items

• Code signing / notarization for both macOS and Windows (current beta requires a one-time manual step on first install)
• Resizable / high-DPI UI
• Automated test suite (headless DSP + UI snapshot tools, private repo)
• Real-world testing in a DAW (Ableton, Logic, FL Studio, etc.) and on an actual Windows machine -- so far only Standalone-on-macOS and CI compile checks
• Licensing gate for the post-beta paid release

License

This repository's source code: MIT — see LICENSE. Covers the architecture shown here (JUCE plugin wrapper, sidechain bus setup, alignment algorithm, UI, build setup). As noted above, the exact visual calibration used in the actual product is not included in this source.

The compiled plugin (downloads / releases): free to use during the beta period, not free to redistribute or resell. See the TERMS.txt included in each release download for the full terms. A paid license will replace this beta terms after the beta period ends.

Also by the same author

Delta is a standalone tool, not part of the Montagem family below — but same author, different audience:

• Montagem 808
• Montagem Finisher
• Montagem Widener
• Montagem Punch

A family of one-knob plugins for funk automotivo / phonk production.