feat: add basic lp filter

core/Filter.cpp

@@ -0,0 +1,49 @@
+#include "Filter.hpp"
+#include <cmath>
+
+Filter::Filter(float initCutOff, float initSampleRate)
+    : cutOff_(initCutOff), feedback_(0.0f), alpha_(0.0f),
+      sampleRate_(initSampleRate), zL_(0.0f), zR_(0.0f) {
+  recompute();
+};
+
+void Filter::process(const float *in, float *out, uint32_t frames) {
+  filter(in, out, frames, &zL_);
+};
+void Filter::processStereo(const float *inLeft, const float *inRight,
+                           float *outLeft, float *outRight, uint32_t frames) {
+  filter(inLeft, outLeft, frames, &zL_);
+  filter(inRight, outRight, frames, &zR_);
+};
+
+void Filter::filter(const float *in, float *out, uint32_t frames, float *z) {
+  for (uint32_t i = 0; i < frames; ++i) {
+    float feedbackInput = in[i] + (feedback_ * (*z));
+    *z = *z + alpha_ * (feedbackInput - *z);
+    out[i] = *z;
+  }
+}
+
+void Filter::recompute() {
+  float fc = std::fmax(cutOff_, 1.0f);
+  float rc = 1.0f / (2.0f * M_PI * fc);
+  float val = 1.0f - std::exp(-1.0f / (rc * sampleRate_));
+  alpha_ = std::fmin(val, 0.999f);
+};
+
+void Filter::setCutOff(float newCutOff) {
+  cutOff_ = newCutOff;
+  recompute();
+}
+float Filter::getCutOff() const { return cutOff_; }
+
+void Filter::setFeedback(float newFeedback) {
+  feedback_ = std::fmin(std::fmax(newFeedback, 0.0f), 0.99f);
+}
+float Filter::getFeedback() const { return feedback_; }
+
+void Filter::setSampleRate(float newSampleRate) {
+  sampleRate_ = newSampleRate;
+  recompute();
+}
+float Filter::getSampleRate() const { return sampleRate_; }

core/Filter.hpp

@@ -0,0 +1,33 @@
+#ifndef FILTER_HPP_INCLUDED
+#define FILTER_HPP_INCLUDED
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+#include <cstdint>
+
+class Filter {
+public:
+  Filter(float initCutOff = 1.0f, float initSampleRate = 48000.0f);
+  void process(const float *in, float *out, uint32_t frames);
+  void processStereo(const float *inLeft, const float *inRight, float *outLeft,
+                     float *outRight, uint32_t frames);
+
+  void recompute();
+  void setCutOff(float newCutOff);
+  float getCutOff() const;
+  void setFeedback(float newFeedback);
+  float getFeedback() const;
+  void setSampleRate(float newSampleRate);
+  float getSampleRate() const;
+
+private:
+  void filter(const float *in, float *out, uint32_t frames, float *z);
+  float cutOff_;
+  float feedback_;
+  float alpha_;
+  float sampleRate_;
+  float zL_;
+  float zR_;
+};
+
+#endif // FILTER_HPP_INCLUDED