Horizont

A stereo algorithmic reverb audio plugin (VST3 / AU) for macOS, built with JUCE and C++17.

It pairs a Schroeder/Moorer-style reverb core - a diffusion allpass section and a bank of parallel damped combs whose gains are derived from an RT60 time - with a feedback pitch-shifting loop: each pass through the reverb is recirculated through a granular crossfade pitch shifter, so the tail climbs or descends in pitch on every echo. The UI is a dark teal hardware-rack style skin with skeuomorphic rotary knobs and a live wet-spectrum analyser.

Screenshot

Features

• 9 fully automatable, host-saveable parameters in an AudioProcessorValueTreeState
• Stable, self-scaling reverb: comb gains are computed from RT60 so the loop never diverges, and every delay length / filter / window scales with sample rate
• Per-sample parameter smoothing (juce::SmoothedValue) - no clicks, no allocation in the audio callback
• Granular pitch shifter with seamless crossfade; bypasses transparently at 0 semitones
• Feedback loop routing the wet signal back through the pitch shifter and diffusers
• Dark themed GUI: skeuomorphic knobs, glass panel highlights, animated spectrum display
• Factory presets exposed through the host's program mechanism
• VST3 and Audio Unit formats; plain make build + install on macOS

Controls

Control	Range	Default	Notes
Low Cut	20 – 500 Hz	40 Hz	Input high-pass filter
High Cut	800 Hz – 20 kHz	14 kHz	Input low-pass filter
Decay	0.2 – 10 s	3.5 s	RT60 of the comb bank
Size	0.4 – 2.0	1.0	Room size scaling of comb delays
Diffusion	0 – 1	0.6	Input allpass diffusion depth
Brightness	0 – 1	0.75	High-frequency damping of the tail
Feedback	0 – 1	0.6	Recirculation through the pitch shifter
Pitch	-12 – +12 st	0 st	Pitch shift applied per feedback pass
Dry/Wet	0 – 1	0.35	Dry / wet mix

DSP architecture

 input -> [low-cut HP] -> [high-cut LP] -----> feedback node
                                                 |      ^
                                        (pitch shifter) |
                                                 |  wet tail
                                    [2 cascaded allpass diffusers]
                                                 |
                                  8 parallel combs (damping + RT60 gain)
                                                 |
                                        wet sum -> dry/wet mix -> output

• Diffusers shape the early reflections before the diffuse tail.
• Combs each use a different prime-based delay length; their loop gains are 10^(-3 * delaySeconds / decaySeconds) so the composite RT60 tracks Decay.
• Pitch shifter runs on the wet feedback path. Grains are windowed and crossfaded; the read point moves at a rate proportional to the shift, with sample-rate-scaled window lengths and a 32-sample crossfade.
• The wet output passes through a DC blocker, and the whole engine is sample-rate independent.

Requirements

• macOS with Xcode Command Line Tools (xcode-select --install)
• CMake >= 3.22
• git, make, codesign (all ship with the command line tools)

Build & install

From the repository root:

make            # fetches JUCE 8.0.15 into ./JUCE, configures and builds
make install    # installs into ~/Library/Audio/Plug-Ins/VST3 and .../Components

make is fully self-contained: if ./JUCE is missing it clones a pinned, stable JUCE release into the current directory, then builds the plugin. The resulting bundles land in build/Horizont_artefacts/Release/.

Other targets:

make uninstall  # remove installed copies
make clean      # delete the build directory
make help       # list targets

If you prefer to manage JUCE yourself, either check it out as ./JUCE next to this repo, or point CMake at it with -DJUCE_ROOT=/path/to/JUCE.

Note: JUCE 9 / master refactored the LookAndFeel API and is not yet supported - a JUCE 8.0.x release tag is required.

After installing, ask your DAW / Audio Unit host to rescan plug-ins (or run auval to validate the component). Installed bundles are ad-hoc code-signed.

Project layout

CMakeLists.txt          build configuration
Makefile                one-command build/install on macOS
Source/
  PluginProcessor.*     processor, APVTS, state save/load, program (preset) handling
  PluginEditor.*        layout, panels, preset combo box
  HorizontEngine.*        the reverb DSP core
  PitchShifter.*        granular crossfade pitch shifter
  HorizontLookAndFeel.*   dark teal theme, skeuomorphic rotary knobs
  Knob.*                knob component (slider + caption + value readout)
  SpectrumDisplay.*     animated wet-spectrum analyser
  Presets.h             factory presets

License

This project is released under the GPL v3 - the standard license for JUCE projects that use the open-source JUCE distribution. You may additionally use it under the terms of a JUCE commercial license if you hold one.