more advanced build script, refactor eqprocessor.cpps functions: process and recomputeBiquad, which were not nice to read. now nicer to read. no need to compile, compile at more major change

src/engine/AudioBuffer.h

@@ -1,6 +1,5 @@
 #pragma once
 #include <vector>
-#include <cstdint>
 
 namespace engine {
 

src/engine/AudioEngine.cpp

@@ -3,8 +3,6 @@
 #include "engine/EqProcessor.h"
 #include "engine/SpectrumAnalyzer.h"
 
-#include <cmath>
-#include <numbers>
 #include <algorithm>
 #include <QThread>
 #include <QMediaDevices>

src/engine/EqProcessor.cpp

@@ -1,7 +1,6 @@
 #include "EqProcessor.h"
 #include <cmath>
 #include <numbers>
-#include <algorithm>
 #include <cstring>
 
 namespace engine {
@@ -33,51 +32,66 @@ void EqProcessor::reset() {
     std::memset(m_state, 0, sizeof(m_state));
 }
 
-void EqProcessor::process(AudioBuffer &buf) {
-    const int channels = buf.channels;
-    const int count    = buf.sampleCount();
-    float    *samples  = buf.samples.data();
+
+void EqProcessor::process(AudioBuffer &a_buf) {
+    const int channels  = a_buf.channels;
+    const int count     = a_buf.sampleCount();
+    float *samples      = a_buf.samples.data();
 
     for (int band = 0; band < BANDS; ++band) {
-        if (std::abs(m_gainDb[band]) < 0.01f) continue;
+        if (std::abs(m_gainDb[band]) <  0.01f) {continue;}
+        
+        const auto& c = m_coeff[band];
 
-        const float b0 = m_coeff[band][0], b1 = m_coeff[band][1], b2 = m_coeff[band][2];
-        const float a1 = m_coeff[band][3], a2 = m_coeff[band][4];
+        for (int idx = 0; idx < count; ++idx) {
+            const int ch = idx % channels;
+            
+            auto &s = m_state[band][ch];
 
-        for (int i = 0; i < count; ++i) {
-            const int ch = i % channels;
-            float &z1 = m_state[band][ch][0];
-            float &z2 = m_state[band][ch][1];
+            const float x = samples[idx];
+            const float y = c.b0 * x + s.z1;
 
-            float x = samples[i];
-            float y = b0 * x + z1;
-            z1 = b1 * x - a1 * y + z2;
-            z2 = b2 * x - a2 * y;
-            samples[i] = y;
+            s.z1 = c.b1 * x - c.a1 * y + s.z2;
+            s.z2 = c.b2 * x - c.a2 * y;
+            
+            samples[idx] = y;
         }
+            
     }
 }
 
 void EqProcessor::recomputeBiquad(int band) {
-    const float sr   = static_cast<float>(m_sampleRate);
-    const float f0   = FREQS[band];
-    const float dBg  = m_gainDb[band];
-    const float Q    = 1.41421356f;           // sqrt(2) , Butterworth Q
-    const float A    = std::pow(10.f, dBg / 40.f);
-    const double w0  = 2.0 * std::numbers::pi * f0 / sr;
-    const double cW  = std::cos(w0);
-    const double sW  = std::sin(w0);
-    const double alp = sW / (2.0 * Q);
+    const double sampleRate = static_cast<double>(m_sampleRate);
+    const double frequency  = FREQS[band];
+    const double gainDb     = m_gainDb[band];
+    constexpr double Q      = std::numbers::sqrt2;
 
-    // Peaking EQ biquad 
-    const double b0 = 1 + alp * A,  b1 = -2 * cW, b2 = 1 - alp * A;
-    const double a0 = 1 + alp / A,  a1 = -2 * cW, a2 = 1 - alp / A;
+    // RBJ peaking EQ gain factor
+    const double A = std::pow(10.0, gainDb / 40.0);
+    const double omega = 2.0 * std::numbers::pi * frequency / sampleRate;
+    const double sinW = std::sin(omega);
+    const double cosW = std::cos(omega);
 
-    m_coeff[band][0] = float(b0 / a0);
-    m_coeff[band][1] = float(b1 / a0);
-    m_coeff[band][2] = float(b2 / a0);
-    m_coeff[band][3] = float(a1 / a0);
-    m_coeff[band][4] = float(a2 / a0);
+    const double alpha = sinW / (2.0 * Q);
+
+    // rbj audio eq cookbook
+    const double b0 = 1.0 + alpha * A;
+    const double b1 = -2.0 * cosW;
+    const double b2 = 1.0 - alpha * A;
+
+    const double a0 = 1.0 + alpha / A;
+    const double a1 = -2.0 * cosW;
+    const double a2 = 1.0 - alpha / A;
+
+    const double invA0 = 1.0 / a0;
+
+    auto &c = m_coeff[band];
+
+    c.b0 = static_cast<float>(b0 * invA0);
+    c.b1 = static_cast<float>(b1 * invA0);
+    c.b2 = static_cast<float>(b2 * invA0);
+    c.a1 = static_cast<float>(a1 * invA0);
+    c.a2 = static_cast<float>(a2 * invA0);
 }
 
 } // namespace engine

src/engine/EqProcessor.h

@@ -1,5 +1,4 @@
 #pragma once
-#include <array>
 #include "AudioBuffer.h"
 
 namespace engine {
@@ -28,10 +27,23 @@ private:
     int   m_sampleRate { 44100 };
     float m_gainDb[BANDS] {};
 
-    float m_coeff[BANDS][5] {};
+    struct BiquadCoefficients {
+        float b0 {};
+        float b1 {};
+        float b2 {};
+        float a1 {};
+        float a2 {};
+    };
+
+    BiquadCoefficients m_coeff[BANDS];
+
+    struct BiquadState {
+        float z1;
+        float z2;
+    };
 
     static constexpr int MAX_CH = 8;
-    float m_state[BANDS][MAX_CH][2] {};
+    BiquadState m_state[BANDS][MAX_CH] {};
 };
 
 } // namespace engine