Initial Gelyk EQ plugin

Source/EqualizerDSP.h

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+#pragma once
+
+#include <JuceHeader.h>
+
+namespace gelyk
+{
+
+// A single peaking/shelf filter band with smoothed coefficients.
+struct FilterBand
+{
+    enum class Type
+    {
+        lowShelf,
+        peak,
+        highShelf
+    };
+
+    Type type = Type::peak;
+    float gainDb = 0.0f;   // target gain in dB
+    float freq = 1000.0f;  // centre/corner frequency
+    float q = 1.0f;
+
+    void prepare(double sampleRate, int blockSize);
+    void reset();
+    void process(juce::dsp::AudioBlock<float>& block);
+
+    using Filter = juce::dsp::IIR::Filter<float>;
+    using Coeffs  = juce::dsp::IIR::Coefficients<float>;
+
+    Filter left, right;
+};
+
+// Simple background "realtime" analyser: it keeps a circular ring buffer
+// of the most recent input, computes an FFT magnitude spectrum periodically
+// in a background thread, and exposes the result thread-safely for the UI.
+class SpectrumAnalyser : public juce::Timer
+{
+public:
+    SpectrumAnalyser();
+
+    void prepare(double sampleRate, int maxBlockSize);
+    void push(const float* const* channels, int numChannels, int numSamples);
+
+    void startBackground();
+    void stopBackground();
+
+    // Copies the latest spectrum into `dest` (size destSize) with equal
+    // log-spaced bands, returning the number of bins written.
+    int copySpectrum(juce::Array<float>& dest, juce::Array<float>& freqBins,
+                     int maxBins) const;
+
+    void setEnabled(bool enabled);
+
+private:
+    void timerCallback() override;
+
+    void runAnalysis();
+
+    mutable juce::CriticalSection spectrumLock;
+    juce::Array<float> readySpectrum;   // dB magnitudes per bin
+
+    juce::AudioBuffer<float> ring;
+    int ringFill = 0;
+    int ringChannels = 0;
+    double sampleRate = 44100.0;
+
+    std::atomic<bool> enabled { true };
+};
+
+} // namespace gelyk