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Source/Sampler/Effects/BandEQ.h

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+/*
+  ==============================================================================
+
+    BandEQ.h
+    Created: 2 Jan 2024 5:02:27pm
+    Author:  binya
+
+  ==============================================================================
+*/
+
+#pragma once
+#include <JuceHeader.h>
+
+#include "Effect.h"
+
+/** This is a sample 3-band EQ effect, inspired by the Kiloheart's free 3-Band EQ plugin. */
+class BandEQ final : public Effect
+{
+public:
+    void initialize(int numChannels, int fxSampleRate) override
+    {
+        sampleRate = fxSampleRate;
+
+        juce::dsp::ProcessSpec spec{};
+        spec.numChannels = numChannels;
+        spec.sampleRate = sampleRate;
+        filterChain.reset();
+        filterChain.prepare(spec);
+    }
+
+    void updateParams(float lowFreq, float highFreq, float lowGain, float midGain, float highGain)
+    {
+        // This possibly has an issue where the frequencies are outside of range on plugin initialization
+        auto coeffLow = juce::dsp::IIR::Coefficients<float>::makeLowShelf(sampleRate, lowFreq, Q, juce::Decibels::decibelsToGain(lowGain));
+        auto coeffMid1 = juce::dsp::IIR::Coefficients<float>::makeHighShelf(sampleRate, lowFreq, Q, juce::Decibels::decibelsToGain(midGain));
+        auto coeffMid2 = juce::dsp::IIR::Coefficients<float>::makeHighShelf(sampleRate, highFreq, Q, juce::Decibels::decibelsToGain(-midGain));
+        auto coeffHigh = juce::dsp::IIR::Coefficients<float>::makeHighShelf(sampleRate, highFreq, Q, juce::Decibels::decibelsToGain(highGain));
+        *filterChain.get<0>().state = *coeffLow;
+        *filterChain.get<1>().state = *coeffMid1;
+        *filterChain.get<2>().state = *coeffMid2;
+        *filterChain.get<3>().state = *coeffHigh;
+    }
+
+    void updateParams(const SamplerParameters& samplerSound, bool) override
+    {
+        updateParams(
+            samplerSound.eqLowFreq->get(), samplerSound.eqHighFreq->get(), 
+            samplerSound.eqLowGain->get(), samplerSound.eqMidGain->get(), samplerSound.eqHighGain->get()
+        );
+    }
+    
+    void process(juce::AudioBuffer<float>& buffer, int numSamples, int startSample = 0) override
+    {
+        juce::dsp::AudioBlock block{ buffer.getArrayOfWritePointers(), size_t(buffer.getNumChannels()), size_t(startSample), size_t(numSamples) };
+        juce::dsp::ProcessContextReplacing context{ block };
+        filterChain.process(context);
+    }
+
+    juce::Array<double> getMagnitudeForFrequencyArray(juce::Array<double> frequencies)
+    {
+        std::array filters{
+            &filterChain.get<0>(),
+            &filterChain.get<1>(),
+            &filterChain.get<2>(),
+            &filterChain.get<3>()
+        };
+
+        juce::AudioBuffer<double> magnitudes{1, frequencies.size()};
+        magnitudes.clear();
+        bool empty{ true };
+        for (const auto& filter : filters)
+        {
+            juce::AudioBuffer<double> temp{ 1, frequencies.size()};
+            filter->state->getMagnitudeForFrequencyArray(frequencies.getRawDataPointer(), temp.getWritePointer(0), frequencies.size(), 48000);
+            if (empty)
+            {
+                magnitudes.addFrom(0, 0, temp.getReadPointer(0), frequencies.size());
+                empty = false;
+            }
+            else
+            {
+                for (int i = 0; i < temp.getNumSamples(); i++)
+                    magnitudes.setSample(0, i, magnitudes.getSample(0, i) * temp.getSample(0, i));
+            }
+        }
+
+        return juce::Array<double>{magnitudes.getReadPointer(0), frequencies.size()};
+    }
+
+private:
+    using Filter = juce::dsp::ProcessorDuplicator<juce::dsp::IIR::Filter<float>, juce::dsp::IIR::Coefficients<float>>;
+    using FilterChain = juce::dsp::ProcessorChain<Filter, Filter, Filter, Filter>;
+
+    static constexpr float Q{ 0.6f };  // Magic number I saw online for the response curve
+    
+    int sampleRate{ 0 };
+    FilterChain filterChain;
+};