[feat]: Filter (#18)

closes #16

Reviewed-on: #18

src/Filter.cpp

@@ -0,0 +1,36 @@
+#include "Filter.h"
+#include "Settings.h"
+
+Filter::Filter(/* args */) {}
+
+Filter::~Filter() {}
+
+void Filter::CalculateNormals() {
+    m_v = powf(10, fabs(m_order) / 20.0);
+    m_k = tanf(M_PI * m_freq);
+}
+
+void Filter::Trigger() {}
+
+void Filter::Release() {}
+
+float Filter::Process(float in) {
+    // may move to a compile-time dictionary calculation, if needed
+    CalculateCoefficients();
+    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) {
+    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 / SAMPLE_RATE;
+    m_q = res;
+    m_order = q;
+}