Removed Splie interpolation.

Tried another calculation for filter coefficients.

config.h

@@ -57,7 +57,7 @@
 #define USE_XFADE_DATA 1
 // CHORUS parameters
 #define INTERPOLATION_WINDOW_SIZE 5 // use only odd numbers!!!
-//#define INTERPOLATE_MODE 11
+#define INTERPOLATE_MODE 11
 #define CHORUS_WAVEFORM WAVEFORM_TRIANGLE // WAVEFORM_SINE WAVEFORM_TRIANGLE WAVEFORM_SAWTOOTH WAVEFORM_SAWTOOTH_REVERSE
 #define CHORUS_DELAY_LENGTH_SAMPLES (15*AUDIO_BLOCK_SAMPLES) // one AUDIO_BLOCK_SAMPLES = 2.902ms; you need doubled length, e.g. delay point is 20ms, so you need up to 40ms delay!
 

effect_modulated_delay.cpp

@@ -25,7 +25,6 @@
 #include <Audio.h>
 #include "limits.h"
 #include "effect_modulated_delay.h"
-#include "spline.h"
 #include "config.h"
 
 /******************************************************************/
@@ -62,7 +61,7 @@ boolean AudioEffectModulatedDelay::begin(short *delayline, int d_length)
   filter.numStages = 1;
   filter.pState =  filter_state;
   filter.pCoeffs = filter_coeffs;
-  calcModFilterCoeff(5000.0, 0.0, 5.0);
+  calcModFilterCoeff(500.0);
 
   return (true);
 }
@@ -86,13 +85,6 @@ void AudioEffectModulatedDelay::update(void)
     float mod_number;
     float mod_fraction;
 
-#ifdef INTERPOLATE_MODE
-    int8_t j;
-    float x[INTERPOLATION_WINDOW_SIZE];
-    float y[INTERPOLATION_WINDOW_SIZE];
-    Spline s(x, y, INTERPOLATION_WINDOW_SIZE, INTERPOLATE_MODE);
-#endif
-
     // (Filter implementation: https://web.fhnw.ch/technik/projekte/eit/Fruehling2016/MuelZum/html/parametric__equalizer__example_8c_source.html)
     arm_q15_to_float(modulation->data, modulation_f32, AUDIO_BLOCK_SAMPLES);
     arm_biquad_cascade_df1_f32(&filter, modulation_f32, modulation_f32, AUDIO_BLOCK_SAMPLES);
@@ -111,23 +103,8 @@ void AudioEffectModulatedDelay::update(void)
       mod_idx = *mp * float(_delay_length >> 1);
       mod_fraction = modff(mod_idx, &mod_number);
 
-#ifdef INTERPOLATE_MODE
-      // Generate a an array with the size of INTERPOLATION_WINDOW_SIZE of x/y values around mod_idx for interpolation
-      uint8_t c;
-      int16_t c_mod_idx = _circ_idx - int(round(mod_idx)); // This is the pointer to the value in the circular buffer at the current modulation index
-      for (j = ~(INTERPOLATION_WINDOW_SIZE >> 1) | 0x01, c = 0; j <= INTERPOLATION_WINDOW_SIZE >> 1; j++, c++) // only another way to say: from -INTERPOLATION_WINDOW_SIZE/2 to INTERPOLATION_WINDOW_SIZE/2
-      {
-        int16_t jc_mod_idx = (c_mod_idx + j) % _delay_length; // The modulation index pointer plus the value of the current window pointer
-        if (jc_mod_idx < 0)
-          y[c] = float(_delayline[_delay_length + jc_mod_idx]);
-        else
-          y[c] = float(_delayline[jc_mod_idx]);
-        x[c] = float(j);
-      }
-      *bp = int(round(s.value(mod_fraction)));
-#else
       // Simple interpolation
-      int16_t c_mod_idx = (_circ_idx - int(round(mod_idx))) % _delay_length;
+      int16_t c_mod_idx = (_circ_idx + int(round(mod_idx))) % _delay_length;
       float value1, value2;
 
       if (c_mod_idx < 0)
@@ -140,7 +117,15 @@ void AudioEffectModulatedDelay::update(void)
         value1 = _delayline[c_mod_idx - 1];
         value2 = _delayline[c_mod_idx];
       }
-      *bp = mod_fraction * value1 + (1.0 - mod_fraction) * value2;
+      *bp = int(round(mod_fraction * value1 + (1.0 - mod_fraction) * value2));
+      
+#ifdef DEBUG
+      float m = (value2 - value1) / (SHRT_MAX >> 1);
+      if (m > 1.0 || m < -1.0)
+      {
+        Serial.print(F("WARNING m="));
+        Serial.println(m, 4);
+      }
 #endif
 
       bp++; // next audio data
@@ -164,56 +149,39 @@ void AudioEffectModulatedDelay::setDelay(float milliseconds)
   _delay_length = min(AUDIO_SAMPLE_RATE * milliseconds / 500, _max_delay_length);
 }
 
-void AudioEffectModulatedDelay::calcModFilterCoeff(float32_t cFrq, float32_t gain, float32_t width)
+void AudioEffectModulatedDelay::calcModFilterCoeff(float32_t cFrq)
 {
-  /* Calculate intermediate values */
+  const float sqrt2 = 1.4142135623730950488;
-  //  float32_t A = sqrt(pow(10, gain / 20.0f));
-  //  float32_t w0 = 2.0f * PI * cFrq / ((float32_t)AUDIO_SAMPLE_RATE_EXACT);
-  //  float32_t cosw0 = cos(w0);
-  //  float32_t sinw0 = sin(w0);
-  //  float32_t alpha = sinw0 / (2.0f * width);
-
-  /* Calculate coefficients */
-  //  float32_t b0 =  1.0f + alpha * A;
-  //  float32_t b1 = -2.0f * cosw0;
-  //  float32_t b2 =  1.0f - alpha * A;
-  //  float32_t a0 =  1.0f + alpha / A;
-  //  float32_t a1 = -2.0f * cosw0;
-  //  float32_t a2 =  1.0f - alpha / A;
-
-/* https://stackoverflow.com/questions/20924868/calculate-coefficients-of-2nd-order-butterworth-low-pass-filter/20932062
-    ff=cutoff_frq/sample_rate=AUDIO_SAMPLE_RATE_EXACT/1000
-    const double ita =1.0/ tan(M_PI*ff);
-    const double q=sqrt(2.0);
-    b0 = 1.0 / (1.0 + q*ita + ita*ita);
-    b1= 2*b0;
-    b2= b0;
-    a1 = 2.0 * (ita*ita - 1.0) * b0;
-    a2 = -(1.0 - q*ita + ita*ita) * b0;
-
-    ff=1000/44117.64706=0.02266666666
-    ita=804.60898525
-    q=1.414213
 
- */
+  float QcRaw  = (2 * PI * cFrq) / AUDIO_SAMPLE_RATE_EXACT; // Find cutoff frequency in [0..PI]
-  // 1kHz 2nd order Butterworth lowpass filter coefficients
+  float QcWarp = tan(QcRaw); // Warp cutoff frequency
+
+  float gain = 1 / (1 + sqrt2 / QcWarp + 2 / (QcWarp * QcWarp));
+  filter_coeffs[2] = (1 - sqrt2 / QcWarp + 2 / (QcWarp * QcWarp)) * gain;
+  filter_coeffs[1] = (2 - 2 * 2 / (QcWarp * QcWarp)) * gain;
+  filter_coeffs[0] = 1;
+  filter_coeffs[3] = 1 * gain;
+  filter_coeffs[4] = 2 * gain;
+
+  /*
+    // 1.1kHz 2nd order Butterworth lowpass filter coefficients
     // calculated with Iowa IIR FIlter Designer 6.5
-  float32_t b0 = 0.124589380980617656;
+    float32_t b0 = 0.072959657268266670;
-  float32_t b1 = 0.124589380980617656;
+    float32_t b1 = 0.072959657268266670;
     float32_t b2 = 0.0;
     float32_t a0 = 1.000000000000000000;
-  float32_t a1 = -0.750821238038764660;
+    float32_t a1 = -0.854080685463466605;
     float32_t a2 = 0.0;
 
-  /* Normalize so a0 = 1 */
+    // Normalize so a0 = 1
     filter_coeffs[0] = b0 / a0;
     filter_coeffs[1] = b1 / a0;
     filter_coeffs[2] = b2 / a0;
     filter_coeffs[3] = -a1 / a0;
-  filter_coeffs[4] = -a2 / a0;
+    filter_coeffs[4] = -a2 / a0; */
 }
 
-void AudioEffectModulatedDelay::setModFilter(float cFrq, float gain, float width)
+void AudioEffectModulatedDelay::setModFilter(float cFrq)
 {
-  calcModFilterCoeff(cFrq, gain, width);
+  calcModFilterCoeff(cFrq);
 }

effect_modulated_delay.h

@@ -26,9 +26,9 @@
 
 #include "Arduino.h"
 #include "AudioStream.h"
+#include "config.h"
 
 /*************************************************************************/
-
 //                A u d i o E f f e c t M o d u l a t e d D e l a y
 // Written by Pete (El Supremo) Jan 2014
 // 140219 - correct storage class (not static)
@@ -45,16 +45,17 @@ class AudioEffectModulatedDelay :
     boolean begin(short *delayline, int delay_length);
     virtual void update(void);
     virtual void setDelay(float milliseconds);
-    virtual void setModFilter(float cFrq, float gain, float width);
+    virtual void setModFilter(float cFrq);
 
   private:
-    virtual void calcModFilterCoeff(float32_t cFrq, float32_t gain, float32_t width);
+    virtual void calcModFilterCoeff(float32_t cFrq);
 
     audio_block_t *inputQueueArray[2];
     int16_t *_delayline;
     uint16_t _circ_idx;
     uint16_t _max_delay_length;
     uint16_t _delay_length;
+
     // filter data
     arm_biquad_casd_df1_inst_f32 filter;
     float32_t modulation_f32[AUDIO_BLOCK_SAMPLES];

spline.cpp

@@ -1,120 +0,0 @@
-#include "Arduino.h"
-#include "spline.h"
-#include <math.h>
-
-Spline::Spline(void) {
-  _prev_point = 0;
-}
-
-Spline::Spline( float x[], float y[], int numPoints, int degree )
-{
-  setPoints(x, y, numPoints);
-  setDegree(degree);
-  _prev_point = 0;
-}
-
-Spline::Spline( float x[], float y[], float m[], int numPoints )
-{
-  setPoints(x, y, m, numPoints);
-  setDegree(Hermite);
-  _prev_point = 0;
-}
-
-void Spline::setPoints( float x[], float y[], int numPoints ) {
-  _x = x;
-  _y = y;
-  _length = numPoints;
-}
-
-void Spline::setPoints( float x[], float y[], float m[], int numPoints ) {
-  _x = x;
-  _y = y;
-  _m = m;
-  _length = numPoints;
-}
-
-void Spline::setDegree( int degree ) {
-  _degree = degree;
-}
-
-float Spline::value( float x )
-{
-  if ( _x[0] > x ) {
-    return _y[0];
-  }
-  else if ( _x[_length - 1] < x ) {
-    return _y[_length - 1];
-  }
-  else {
-    for (int i = 0; i < _length; i++ )
-    {
-      int index = ( i + _prev_point ) % _length;
-
-      if ( _x[index] == x ) {
-        _prev_point = index;
-        return _y[index];
-      } else if ( (_x[index] < x) && (x < _x[index + 1]) ) {
-        _prev_point = index;
-        return calc( x, index );
-      }
-    }
-  }
-  return (0.0);
-}
-
-float Spline::calc( float x, int i )
-{
-  switch ( _degree ) {
-    case 0:
-      return _y[i];
-    case 1:
-      if ( _x[i] == _x[i + 1] ) {
-        // Avoids division by 0
-        return _y[i];
-      } else {
-        return _y[i] + (_y[i + 1] - _y[i]) * ( x - _x[i]) / ( _x[i + 1] - _x[i] );
-      }
-    case Hermite:
-      return hermite( ((x - _x[i]) / (_x[i + 1] - _x[i])), _y[i], _y[i + 1], _m[i], _m[i + 1], _x[i], _x[i + 1] );
-    case Catmull:
-      if ( i == 0 ) {
-        // x prior to spline start - first point used to determine tangent
-        return _y[1];
-      } else if ( i == _length - 2 ) {
-        // x after spline end - last point used to determine tangent
-        return _y[_length - 2];
-      } else {
-        float t = (x - _x[i]) / (_x[i + 1] - _x[i]);
-        float m0 = (i == 0 ? 0 : catmull_tangent(i) );
-        float m1 = (i == _length - 1 ? 0 : catmull_tangent(i + 1) );
-        return hermite( t, _y[i], _y[i + 1], m0, m1, _x[i], _x[i + 1]);
-      }
-  }
-  return (0.0);
-}
-
-float Spline::hermite( float t, float p0, float p1, float m0, float m1, float x0, float x1 ) {
-  return (hermite_00(t) * p0) + (hermite_10(t) * (x1 - x0) * m0) + (hermite_01(t) * p1) + (hermite_11(t) * (x1 - x0) * m1);
-}
-float Spline::hermite_00( float t ) {
-  return (2 * pow(t, 3)) - (3 * pow(t, 2)) + 1;
-}
-float Spline::hermite_10( float t ) {
-  return pow(t, 3) - (2 * pow(t, 2)) + t;
-}
-float Spline::hermite_01( float t ) {
-  return (3 * pow(t, 2)) - (2 * pow(t, 3));
-}
-float Spline::hermite_11( float t ) {
-  return pow(t, 3) - pow(t, 2);
-}
-
-float Spline::catmull_tangent( int i )
-{
-  if ( _x[i + 1] == _x[i - 1] ) {
-    // Avoids division by 0
-    return 0;
-  } else {
-    return (_y[i + 1] - _y[i - 1]) / (_x[i + 1] - _x[i - 1]);
-  }
-}

spline.h

@@ -1,42 +0,0 @@
-/*
-  Library for 1-d splines
-  Copyright Ryan Michael
-  Licensed under the GPLv3
-*/
-#ifndef spline_h
-#define spline_h
-
-#include "Arduino.h"
-
-#define Hermite 10
-#define Catmull 11
-
-class Spline
-{
-  public:
-    Spline( void );
-    Spline( float x[], float y[], int numPoints, int degree = 1 );
-    Spline( float x[], float y[], float m[], int numPoints );
-    float value( float x );
-    void setPoints( float x[], float y[], int numPoints );
-    void setPoints( float x[], float y[], float m[], int numPoints );
-    void setDegree( int degree );
-
-  private:
-    float calc( float, int);
-    float* _x;
-    float* _y;
-    float* _m;
-    int _degree;
-    int _length;
-    int _prev_point;
-
-    float hermite( float t, float p0, float p1, float m0, float m1, float x0, float x1 );
-    float hermite_00( float t );
-    float hermite_10( float t );
-    float hermite_01( float t );
-    float hermite_11( float t );
-    float catmull_tangent( int i );
-};
-
-#endif