# Gelyk EQ

![Gelyk](gelykshot.png)

A minimalist **7-band parametric equalizer** with a cyber/neon UI, built on
[JUCE](https://juce.com) (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.

---

## 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.

---

## 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.

---

## 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).

---

## Building

### Requirements

- **CMake 3.15+** and a C++17 compiler (Clang, GCC, or MSVC).
- [JUCE 8.0.7](https://github.com/juce-framework/JUCE) - 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

```sh
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:

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

### Linux / Artix note (no GTK or WebKitGTK headers required)

The plugin **does not depend on GTK or WebKitGTK developer headers**, so it
builds cleanly on minimal/headless-flavored distros such as **Artix** - no
`webkit2gtk`, `gtk3`-devel, `libsoup` or `jsc` packages needed.

This is guaranteed in `CMakeLists.txt`:

```cmake
target_compile_definitions(GelykEQ PRIVATE JUCE_WEB_BROWSER=0)
```

JUCE's Linux `FileChooser` in JUCE 8 no longer links GTK either - it shells out
to `zenity`/`kdialog` at runtime, and Gelyk never opens a native file dialog.
Disabling `JUCE_WEB_BROWSER` removes the WebKitGTK-backed `WebBrowserComponent`
(which Gelyk does not use), eliminating the entire GTK/WebKit include chain.

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

---

## License

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