OneKnob — one-knob JUCE tape plugin

A single-knob audio plugin built on JUCE 8. The lone Amount parameter drives a coherent tape-character chain — soft saturation, gentle tilt EQ, post-saturation HF roll-off, subtle wow & flutter, and an automatic loudness compensation so the knob actually colours instead of just turning up.

Format	VST3, Standalone, AU (macOS)
DSP	4× oversampled tanh saturator + tilt EQ + wow/flutter + loudness comp
Latency	Reported via setLatencySamples() (oversampler latency, ~5–10 samples)
C++	C++20
JUCE	8.0.12 (fetched automatically by CMake)

Repository layout

Source/
  PluginProcessor.{h,cpp}     # AVTS, processBlock, latency, state I/O
  PluginEditor.{h,cpp}        # modern minimal UI with amber halo
  dsp/
    AmountMapper.h            # Amount ∈ [0,1] → coherent coefficient struct
    OnePoleFilters.h          # DcBlocker, OnePoleLpf, OnePoleShelf
    Saturator.h               # tanh + asymmetric (in OS domain)
    TiltEQ.h                  # low shelf 200 Hz + high shelf 8 kHz
    WowFlutter.h              # Lagrange3 delay + dual-LFO + jitter
    LoudnessComp.h            # makeup gain with linear ramp
    TapeProcessor.{h,cpp}     # orchestrator + 4× oversampling
  lookandfeel/                # custom LookAndFeel, fonts, palette, knob component
  resources/                  # 10 PNG knob frames (animated rotary)

CMakeLists.txt                # primary build
CMakePresets.json             # ninja-debug/release/relwithdebinfo, vs2022, xcode
OneKnob.jucer                 # Projucer project (legacy, kept in sync)

Requirements

• CMake 3.22+
• A C++20 toolchain
• Internet on first configure (to fetch JUCE)
• Optional: Ninja generator, a plugin host for testing

Per-platform prerequisites

Windows

• Visual Studio 2022 (MSVC 19.3+) or newer, with the "Desktop development with C++" workload.
• The bundled Ninja in the VS Developer Command Prompt is sufficient — no separate install needed.
• Run all CMake commands from a VS Developer Command Prompt (vcvars64.bat) so cl.exe and ninja.exe are on PATH.

macOS

• Xcode 14+ with command-line tools: xcode-select --install.
• Optional: brew install cmake ninja if you don't already have them.

Linux

A recent Clang or GCC plus the JUCE GUI runtime dependencies. On Debian/Ubuntu:

sudo apt update && sudo apt install -y \
    build-essential cmake ninja-build pkg-config \
    libasound2-dev libjack-jackd2-dev \
    libcurl4-openssl-dev \
    libfreetype6-dev libfontconfig1-dev \
    libx11-dev libxcomposite-dev libxcursor-dev libxext-dev \
    libxinerama-dev libxrandr-dev libxrender-dev \
    libwebkit2gtk-4.1-dev libgtk-3-dev

On Fedora the equivalents are alsa-lib-devel, jack-audio-connection-kit-devel, libcurl-devel, freetype-devel, fontconfig-devel, libX11-devel, libXcomposite-devel, libXcursor-devel, libXext-devel, libXinerama-devel, libXrandr-devel, libXrender-devel, webkit2gtk4.1-devel, gtk3-devel.

Note: libcurl and webkit2gtk are required only because JUCE links them by default; we already disable both via JUCE_USE_CURL=0 / JUCE_WEB_BROWSER=0, but the linker still needs the libraries present for the JUCE static modules that probe them.

Build

The repository ships a CMakePresets.json. JUCE is pulled in automatically via FetchContent (default tag 8.0.12, override with -DJUCE_TAG=...).

Quickstart

# All platforms (Ninja, Release)
cmake --preset ninja-release
cmake --build --preset ninja-release

Windows (VS Developer Command Prompt)

:: Ninja (recommended — fast, generator-agnostic)
cmake --preset ninja-release
cmake --build --preset ninja-release

:: Or Visual Studio solution
cmake --preset vs2022
cmake --build --preset vs2022-release

macOS

# Ninja
cmake --preset ninja-release
cmake --build --preset ninja-release

# Or Xcode project (multi-config)
cmake --preset xcode
cmake --build --preset xcode-release

Linux

cmake --preset ninja-release
cmake --build --preset ninja-release

Available CMake options

Pass with -D<name>=ON|OFF at configure time:

Option	Default	Description
ONEKNOB_BUILD_VST3	ON	Build the VST3 plugin.
ONEKNOB_BUILD_STANDALONE	ON	Build the standalone host application.
ONEKNOB_BUILD_AU	ON (Apple)	Build the Audio Unit (macOS only).
ONEKNOB_ENABLE_LTO	ON	Link-time optimisation in Release.
ONEKNOB_WARNINGS_AS_ERRORS	OFF	Treat warnings as errors.
ONEKNOB_COPY_PLUGIN_AFTER_BUILD	OFF	Install the plugin to the system VST3/AU path after building.
ONEKNOB_COMPANY_NAME	Borato Company	Vendor string shown by the host.
ONEKNOB_BUNDLE_ID	com.oneknobaudio.OneKnob	Reverse-DNS bundle id (must be unique per plugin).
JUCE_TAG	8.0.12	JUCE git tag/branch/commit to fetch.

Build artefacts

Outputs land in build/<preset>/OneKnob_artefacts/<Config>/:

• VST3 bundle: VST3/OneKnob.vst3
• Standalone: Standalone/OneKnob[.exe|.app]
• AU bundle (macOS): AU/OneKnob.component

Install (VST3)

Copy the built .vst3 bundle to one of:

• Windows (system): C:\Program Files\Common Files\VST3
• Windows (user): %LOCALAPPDATA%\Programs\Common\VST3
• macOS (system): /Library/Audio/Plug-Ins/VST3
• macOS (user): ~/Library/Audio/Plug-Ins/VST3
• Linux (user): ~/.vst3
• Linux (system): /usr/lib/vst3 or /usr/local/lib/vst3

Then rescan in your host. On macOS, AU bundles go to /Library/Audio/Plug-Ins/Components (system) or ~/Library/Audio/Plug-Ins/Components (user). Setting ONEKNOB_COPY_PLUGIN_AFTER_BUILD=ON copies the artefacts automatically.

Build with Projucer (legacy)

OneKnob.jucer is kept in sync with the CMake build. Open it in Projucer, set the JUCE modules path, save, and build in the generated IDE project. Prefer the CMake flow for CI and reproducibility — the Projucer-generated JuceLibraryCode/ and Builds/ directories are listed in .gitignore.

DSP overview

Amount ∈ [0, 1] maps coherently onto seven independent coefficients in AmountMapper::mapAmount. The pipeline (per stereo block):

in
 → DC blocker (HPF ~10 Hz)            base rate
 → WowFlutter (Lagrange3 delay + LFOs) base rate
 → TiltEQ (low + high 1-pole shelves)  base rate
 → upsample 4×
   → Saturator (tanh + asymmetry)      4× rate (only stage that aliases)
 → downsample
 → 1-pole LPF (post-saturation taming) base rate
 → LoudnessComp (makeup gain)          base rate
out

Drive and makeup gain ramp linearly across each block to avoid zipper noise on coefficient changes from AmountMapper. The Amount parameter itself is smoothed via juce::SmoothedValue with a 30 ms ramp before reaching the mapper.

Customising

• Sound character — tweak AmountMapper::mapAmount curves, Saturator::asymmetry, shelf frequencies in TiltEQ, and the LFO rates in WowFlutter.
• Plugin metadata — change PRODUCT_NAME, COMPANY_NAME, PLUGIN_CODE, and PLUGIN_MANUFACTURER_CODE in CMakeLists.txt. Plugin codes must be unique per plugin to avoid host collisions.
• Knob art — replace the 10 PNGs in Source/resources/. Frame order is set in OneKnobLookAndFeel::loadKnobFrames.

Testing tips

• Use JUCE's AudioPluginHost or your DAW to validate parameter automation and state save/restore.
• Sanity-check loudness with pink noise at –18 dBFS RMS at Amount=0 vs Amount=1. Adjust makeupDb in AmountMapper if you measure more than ±0.5 LU.
• For THD inspection, feed a 1 kHz sine at –6 dBFS and run an FFT on the output. At full Amount the 2nd harmonic should sit around –25 to –35 dBc (knob of asymmetry = 0.04 in Saturator.h).

License

No license is provided here; add your own LICENSE before distributing.