Gelyk EQ

A minimalist 7-band parametric equalizer with a cyber/neon UI, built on JUCE (JUCE 8). It ships as an AU and VST3 plugin.

This README is intentionally verbose: it covers what the plugin is, how it is structured, how every band behaves, and how to build it from source on any platform - including Linux/Artix without the WebKitGTK/GTK developer headers.

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What it is

Gelyk EQ is an audio effects plugin for mixing and mastering. It provides seven independent EQ bands covering the full ~20 Hz – 20 kHz spectrum, plus a master output gain, wrapped in a dark, glowing "neon" interface.

Rather than a dense wall of identical knobs, each band is laid out as a large drag-to-shape fader (the "gain curve") in a shared visualiser. Dragging gives you one-glance sight of the summed response you are actually shaping.

The band layout

Seven filters run in series, logarithmically spaced across the spectrum:

Band	Filter type	Default frequency	Default Q
0	Low shelf	60 Hz	0.71
1	Peak/parametric	160 Hz	1.0
2	Peak/parametric	400 Hz	1.0
3	Peak/parametric	800 Hz	1.0
4	Peak/parametric	1.6 kHz	1.0
5	Peak/parametric	4 kHz	1.0
6	High shelf	10 kHz	0.71

Parameter ranges

Parameter	Range	Default
Gain (per band)	−24 … +24 dB	0 dB
Frequency	20 … 20,000 Hz	per band (skewed, centre 1 kHz)
Q (per band)	0.1 … 6.0	per band
Master	−24 … +24 dB	0 dB

All parameters are smoothed per-block to avoid zipper noise, and remember their state between sessions via a JUCE AudioProcessorValueTreeState.

On-screen controls

• The visualiser - the main field shows:
  • the live input spectrum (a realtime FFT analyser), drawn as a glowing, filled waveform;
  • the static summed EQ curve (the actual filter response), overlaid on the same log-frequency axis so peaks line up with their bands;
  • the neon 0 dB centre line and reference grid.
• Per-band faders - drag a band vertically to change its gain, horizontally to move its frequency, or use the mouse wheel to nudge its Q. The knobs and numeric readouts below each fader are permanently linked to it.
• LEVEL / FREQ / Q knobs - an alternative, precise way to edit the currently hovered band.
• MASTER fader - output trim.
• SENS slider - vertical offset for the live spectrum trace (how visually "hot" the analyser appears; the display is pre-tuned to real per-FFT-bin levels, so it reads meaningfully without touching this).
• WAVE slider - opacity of the live spectrum waveform.
• HUE / SAT / BRI sliders - recolor the entire palette (colour-shift, global saturation and brightness) for a custom neon look.
• SCALE selector - fractional UI scaling for high-DPI or small screens.
• A status bar shows the build version and, when the plugin is built from a git checkout, the current branch/commit and dirty state.

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Controls at a glance

Control	Mouse down / drag	Mouse wheel
Band fader	Vertical = gain	Adjusts band Q
	Horizontal = frequency
Per-band knobs	Rotate = value	-
Master fader	Vertical = output gain	-

Double-click any knob or fader to reset it to its default value.

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Project structure

Source/
  PluginProcessor.h/cpp   AudioProcessor, parameter layout, state + audio pipeline
  PluginEditor.h/cpp      The neon UI: visualiser, faders, knobs, color controls
  EqualizerDSP.h/cpp      FilterBand IIR biquad + the background SpectrumAnalyser (FFT)
  GitInfo.h.in            Template for the git build-info header, filled by CMake
CMakeLists.txt            Build configuration (JUCE 8, AU + VST3, CMake 3.15+)
Makefile                  Convenience wrapper: build, install, codesign

DSP highlights (EqualizerDSP)

Each FilterBand is a set of JUCE IIR biquad coefficients, recalculated cheaply whenever gain/frequency/Q change and continuously smoothed toward the target. The channels run stereo-locked so the summed response is identical on left and right.

The SpectrumAnalyser runs on a background thread: it fills a circular ring buffer from the input, and periodically Hann-windows the most recent 4096 samples and runs a realtime FFT to produce the magnitude spectrum the editor renders (aggregated into log-spaced bins from 20 Hz to 20 kHz).

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Building

Requirements

• CMake 3.15+ and a C++17 compiler (Clang, GCC, or MSVC).
• JUCE 8.0.7 - fetched automatically by CMake via FetchContent when JUCE_ROOT is not set. To reuse an existing checkout, configure with -DJUCE_ROOT=/path/to/JUCE.

Configure & build

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --config Release -j$(nproc)

The plugins are placed in build/GelykEQ_artefacts/<config>/AU (and VST3).

On macOS the bundled Makefile also installs both formats into your user plugin folders and refreshes the system registry:

make            # configure + build
make install    # copy into ~/Library/Audio/Plug-Ins and codesign

Linux / Artix note (no GTK, WebKitGTK, curl or GTK file selector needed)

Gelyk builds on minimal/headless-flavored distros such as Artix without any of the usual JUCE baggage: no webkit2gtk, gtk3, libsoup, jsc, libcurl or file-selector development packages. This is pinned in CMakeLists.txt:

NEEDS_CURL        FALSE   # juce_add_plugin: never link libcurl
NEEDS_WEB_BROWSER FALSE   # juce_add_plugin: never link WebKitGTK

target_compile_definitions(GelykEQ PRIVATE
    JUCE_WEB_BROWSER=0
    JUCE_USE_CURL=0
)

• JUCE_WEB_BROWSER=0 removes WebBrowserComponent from the compile, which is the only thing in juce_gui_extra that #includes <gtk/gtk.h>, <webkit2/webkit2.h>, <jsc/jsc.h> and <libsoup/soup.h>.
• JUCE_USE_CURL=0 matters just as much. JUCE's Linux default is 1, which makes juce_core #include <curl/curl.h> and compile juce_Network_curl.cpp. Nothing would link libcurl (NEEDS_CURL is FALSE), but its headers would still be a hard requirement. Gelyk never touches URL/WebInputStream, so nothing is lost.
• File dialogs are not a GTK dependency. JUCE 8's Linux FileChooser shells out to zenity/kdialog at runtime, and Gelyk never opens a native file dialog anyway.
• X11's multi-monitor/DPI extensions (Xrandr, Xinerama, Xshm, Xcursor) are dlsym()ed at runtime by JUCE, so their headers are treated as optional: CMakeLists.txt probes for each and sets JUCE_USE_XRANDR / JUCE_USE_XINERAMA / JUCE_USE_XSHM / JUCE_USE_XCURSOR accordingly. A distro carrying just libX11 still builds, minus multi-monitor reporting.

What is still required is JUCE's own Linux baseline, checked at configure time with a helpful error instead of a raw pkg-config failure:

pkg-config	Arch / Artix	Debian / Ubuntu
alsa	alsa-lib	libasound2-dev
freetype2	freetype2	libfreetype6-dev
fontconfig	fontconfig	libfontconfig1-dev
X11 headers	libx11 (libxext for Xshm)	libx11-dev (libxext-dev)

None of them drag in GTK.

If you ever do need native file dialogs at runtime (outside Gelyk), install zenity or kdialog.

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License

See the JUCE license for the framework; the Gelyk EQ source follows the same licensing model. (Adjust per your chosen licensing.)