wip: filter (lp, hp, bp)

src/BandPassFilter.cpp

@@ -0,0 +1,17 @@
+#include "BandPassFilter.h"
+
+BandPassFilter::BandPassFilter(/* args */) {
+}
+
+BandPassFilter::~BandPassFilter() {
+}
+
+void BandPassFilter::calculate_coefficients() {
+    Filter::Normals base = calculate_normals();
+    m_norm = 1 / (1 + base.K / m_q + base.K * base.K);
+    m_a0 = base.K / m_q * m_norm;
+    m_a1 = 0;
+    m_a2 = -m_a0;
+    m_b1 = 2 * (base.K * base.K - 1) * m_norm;
+    m_b2 = (1 - base.K / m_q + base.K * base.K) * m_norm;
+}

src/Filter.cpp

@@ -0,0 +1,41 @@
+#include "Filter.h"
+
+Filter::Filter(/* args */) {
+}
+
+Filter::~Filter() {
+}
+
+Filter::Normals Filter::calculate_normals() {
+    Filter::Normals res;
+    res.V = powf(10, fabs(m_order) / 20.0);
+    res.K = tanf(M_PI * m_freq);
+
+    return res;
+}
+
+void Filter::Trigger() {
+}
+
+void Filter::Release() {
+}
+
+float Filter::Process(float in) {
+    float out = in * m_a0 + m_z1;
+    m_z1 = in * m_a1 + m_z2 - m_b1 * out;
+    m_z2 = in * m_a2 - m_b2 * out;
+    return out;
+}
+
+void Filter::Process(std::vector<float>& samples) {
+    calculate_coefficients();
+    for (std::size_t i = 0; i < samples.size(); i++) {
+        samples[i] = Process(samples[i]);
+    }
+}
+
+void Filter::SetParameters(float freq, float res, float q) {
+    m_freq = freq;
+    m_q = res;
+    m_order = q;
+}

src/HighPassFilter.cpp

@@ -0,0 +1,17 @@
+#include "HighPassFilter.h"
+
+HighPassFilter::HighPassFilter(/* args */) {
+}
+
+HighPassFilter::~HighPassFilter() {
+}
+
+void HighPassFilter::calculate_coefficients() {
+    Filter::Normals base = calculate_normals();
+    m_norm = 1 / (1 + base.K / m_q + base.K * base.K);
+    m_a0 = 1 * m_norm;
+    m_a1 = -2 * m_a0;
+    m_a2 = m_a0;
+    m_b1 = 2 * (base.K * base.K - 1) * m_norm;
+    m_b2 = (1 - base.K / m_q + base.K * base.K) * m_norm;
+}

src/LowPassFilter.cpp

@@ -0,0 +1,22 @@
+#include "LowPassFilter.h"
+#include "Settings.h"
+
+LowPassFilter::LowPassFilter(/* args */) {
+    //todo: defaults
+    m_freq = 200.f / SAMPLE_RATE;
+    m_q = 0.707; 
+    m_order = 0;
+}
+
+LowPassFilter::~LowPassFilter() {
+}
+
+void LowPassFilter::calculate_coefficients() {
+    Filter::Normals base = calculate_normals();
+    m_norm = 1 / (1 + base.K / m_q + base.K * base.K);
+    m_a0 = base.K * base.K * m_norm;
+    m_a1 = 2 * m_a0;
+    m_a2 = m_a0;
+    m_b1 = 2 * (base.K * base.K - 1) * m_norm;
+    m_b2 = (1 - base.K / m_q + base.K * base.K) * m_norm;
+}

src/Synth.cpp

@@ -4,11 +4,13 @@
 #include "Logger.h"
 #include "OscillatorType.h"
 #include "Settings.h"
+#include "LowPassFilter.h"
 
 Synth::Synth(/* args */) {
     add_oscillator();
     add_oscillator();
     AddEffect(new ADSR());
+    AddEffect(new LowPassFilter());
     for (size_t i = 0; i < STREAM_BUFFER_SIZE; i++) {
         float sample = 0.0f;
         m_out_signal.push_back(sample);