create object files

src/effect_anttimoog.cpp

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+// Houtson 2020
+//
+// Implementation of the Moog ladder filter based on the work of Antti
+// Huovilainen, described in the paper "Non-Linear Digital Implementation of the
+// Moog Ladder Filter" (Proceedings of DaFX04, University of Napoli). Adapted
+// from a Reaper JS source file at
+// http://ajaxsoundstudio.com/cookdspdoc/moog.html
+//
+//
+
+#include "effect_anttimoog.h"
+#include <Arduino.h>
+
+#ifndef TEENSY_ANTTI_FILTERCPP_H
+#define TEENSY_ANTTI_FILTERCPP_H
+#define DIAG_PER_SAMPLES 0  // set to 0 for no DIAG or >0 for "print some diag every x samples" e.g. 500
+
+AudioEffectAnttiMoog::AudioEffectAnttiMoog(float sampleRate) {
+  filter_y1 = filter_y2 = filter_y3 = filter_y4 = filter_y5 = filter_out = 0;
+  srate = sampleRate;
+  filter_nylimit = srate * 0.49;
+  filter_z = 1.0 / 40000.0;  // twice the "thermal voltage of a transistor"
+  SetCutoff(1000.0f);
+  SetResonance(0.1f);
+  compute_coeffs(filter_freq, filter_res);
+};
+
+void compute_coeffs(float freq, float res) {
+  float f_, fc_, fc2_, fc3_, fcr_, acr_;
+  if (freq < 1) {
+    freq = 1;
+  } else {
+    if (freq > filter_nylimit) freq = filter_nylimit;
+  }
+  if (res < 0) {
+    res = 0;
+  } else {
+    if (res > 1) res = 1;
+  }
+  filter_freq = freq;
+  filter_res = res;
+  // srate is half the actual filter sampling rate
+  fc_ = filter_freq / srate;
+  f_ = 0.5 * fc_;
+  fc2_ = fc_ * fc_;
+  fc3_ = fc2_ * fc_;
+  // frequency &amp; amplitude correction
+  fcr_ = 1.8730 * fc3_ + 0.4955 * fc2_ - 0.6490 * fc_ + 0.9988;
+  acr_ = -3.9364 * fc2_ + 1.8409 * fc_ + 0.9968;
+  filter_scl = float((1.0 - exp(-2 * AM_PI * f_ * fcr_)) / filter_z);  // filter tuning
+  filter_r4 = 3.96 * filter_res * acr_;                                // filter feedback
+};
+
+void SetCutoff(float freq) {
+  if (freq != filter_freq) compute_coeffs(freq, filter_res);
+};
+
+void SetResonance(float res) {
+  if (res != filter_res) compute_coeffs(filter_freq, res);
+};
+
+virtual void Process(float *samples, uint32_t n) {
+  for (uint32_t s = 0; s < n; ++s) {
+    for (int a = 0; a < 2; a++) {
+      filter_y1 = filter_y1 + filter_scl * (tanh((samples[s] - filter_r4 * filter_out) * filter_z) - tanh(filter_y1 * filter_z));
+      filter_y2 = filter_y2 + filter_scl * (tanh(filter_y1 * filter_z) - tanh(filter_y2 * filter_z));
+      filter_y3 = filter_y3 + filter_scl * (tanh(filter_y2 * filter_z) - tanh(filter_y3 * filter_z));
+      filter_y4 = filter_y4 + filter_scl * (tanh(filter_y3 * filter_z) - tanh(filter_y4 * filter_z));
+      filter_out = (filter_y4 + filter_y5) * 0.5;
+      filter_y5 = filter_y4;
+    }
+    samples[s] = filter_out;
+  }
+};
+
+void AudioEffectAnttiMoog::update(void) {
+  uint16_t sample_data_unsigned;
+  audio_block_t *block;
+
+  block = receiveWritable(0);
+  if (!block) return;
+
+  for (uint32_t s = 0; s < AUDIO_BLOCK_SAMPLES; ++s) {
+    float current_sample = block->data[s] * INV_WAVE_AMP;
+    for (int a = 0; a < 2; a++) {
+      filter_y1 = filter_y1 + filter_scl * (tanh((current_sample - filter_r4 * filter_out) * filter_z) - tanh(filter_y1 * filter_z));
+      filter_y2 = filter_y2 + filter_scl * (tanh(filter_y1 * filter_z) - tanh(filter_y2 * filter_z));
+      filter_y3 = filter_y3 + filter_scl * (tanh(filter_y2 * filter_z) - tanh(filter_y3 * filter_z));
+      filter_y4 = filter_y4 + filter_scl * (tanh(filter_y3 * filter_z) - tanh(filter_y4 * filter_z));
+      filter_out = (filter_y4 + filter_y5) * 0.5;
+      filter_y5 = filter_y4;
+    }
+    block->data[s] = filter_out * WAVE_AMP;
+  }
+
+  // print some diags
+  if (DIAG_PER_SAMPLES && diag_count > DIAG_PER_SAMPLES) {
+    diag_count = 0;
+  }
+  if (DIAG_PER_SAMPLES) diag_count++;
+
+  transmit(block);
+  release(block);
+}
+#endif

src/effect_anttimoog.h

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+// Houtson 2020
+//
+// Implementation of the Moog ladder filter based on the work of Antti
+// Huovilainen, described in the paper "Non-Linear Digital Implementation of the
+// Moog Ladder Filter" (Proceedings of DaFX04, University of Napoli). Adapted
+// from a Reaper JS source file at
+// http://ajaxsoundstudio.com/cookdspdoc/moog.html
+//
+//
+
+#include <math.h>
+#include <stdint.h>
+#include "AudioStream.h"
+
+#ifndef TEENSY_ANTTI_FILTER_H
+#define TEENSY_ANTTI_FILTER_H
+
+#define AM_PI 3.14159265358979323846 /* pi */
+#define WAVE_MAX 32768.0
+//=====================================================
+// amplitude of signal. Should be less than WAVE_MAX
+#define WAVE_AMP 32000.0f
+// From martianredskies
+#define INV_WAVE_AMP (1.f / 32000.0f)
+
+
+class AudioEffectAnttiMoog : public AudioStream {
+ public:
+  AudioEffectAnttiMoog(float sampleRate) : AudioStream(1, inputQueueArray) {}
+  void compute_coeffs(float freq, float res);
+  void SetCutoff(float freq);
+  void SetResonance(float res);
+  virtual void Process(float *samples, uint32_t n);
+  virtual void update(void);
+
+ private:
+
+  audio_block_t *inputQueueArray[1];
+  int16_t *sample_bank;
+  int16_t nibble_effect_mode;
+  int16_t prev_input;
+  uint16_t bitmask_mute;
+  uint16_t bitmask_invert;
+  uint16_t bitmask_squeeze;
+  bool waveform_negative;
+  int diag_count = 0;
+
+  float srate;
+  float filter_scl, filter_z, filter_r4, filter_res, filter_y1, filter_y2, filter_y3, filter_y4, filter_y5, filter_out, filter_freq, filter_nylimit;
+  uint32_t count = 0;
+  bool print_out = false;
+};
+#endif
+
+