Added spline interpolation functions.

UI.hpp

@@ -418,7 +418,7 @@ const char effects_text11[] PROGMEM = "Rev. Damping";
 const char effects_text12[] PROGMEM = "Rev. Level";
 const char effects_text13[] PROGMEM = "Chorus Freq.";
 const char effects_text14[] PROGMEM = "Chorus Delay";
-const char effects_text15[] PROGMEM = "Chorus Intensity";
+const char effects_text15[] PROGMEM = "Chorus Intens.";
 const char effects_text16[] PROGMEM = "Chorus Level";
 const char effects_text17[] PROGMEM = "Bass LR Level";
 const char effects_text18[] PROGMEM = "Bass M Level";

config.h

@@ -61,6 +61,7 @@
 #define SAMPLE_RATE 44100
 #define REDUCE_LOUDNESS 0
 #define USE_XFADE_DATA 1
+#define SPLINE_WINDOW_SIZE 7 // For chorus, only odd numbers!
 
 //*************************************************************************************************
 //* DEBUG OUTPUT SETTINGS

effect_modulated_chorus.cpp

@@ -24,6 +24,8 @@
 #include <Arduino.h>
 #include "limits.h"
 #include "effect_modulated_chorus.h"
+#include "spline.h"
+#include "config.h"
 
 /******************************************************************/
 
@@ -67,10 +69,10 @@ void AudioModulatedEffectChorus::update(void)
   short *bp;
   short *mp;
   float mod_idx;
-  int x1;
-  int x2;
-  int y1;
-  int y2;
+  /* int x1;
+    int x2;
+    int y1;
+    int y2;*/
 
   if (l_delayline == NULL)
     return;
@@ -113,32 +115,70 @@ void AudioModulatedEffectChorus::update(void)
 
   if (block && modulation)
   {
+    uint8_t j;
+    int16_t spline_idx;
+    Spline modulation_spline;
+    modulation_spline.setDegree(Catmull);
+
     bp = block->data;
     mp = modulation->data;
 
     for (int i = 0; i < AUDIO_BLOCK_SAMPLES; i++)
     {
+      float x[SPLINE_WINDOW_SIZE];
+      float y[SPLINE_WINDOW_SIZE];
+
+      // write data into circular buffer
       if (l_circ_idx >= delay_length)
         l_circ_idx = 0;
       l_delayline[l_circ_idx] = *bp; // write signal into circular buffer
 
+      // calculate modulation index
       mod_idx = float(*mp) / SHRT_MAX * delay_length_half + l_circ_idx; // calculate index with modulation as a float
-
       if (mod_idx > delay_length)
         mod_idx = mod_idx - delay_length;
       else if (mod_idx < 0)
         mod_idx = delay_length + mod_idx;
 
-      // linear interpolation
-      x1 = int(mod_idx);
-      y1 = l_delayline[x1];
-      if (x1 + 1 >= delay_length)
+      // get value with spline interpolation
+      for (j = 0; j < SPLINE_WINDOW_SIZE; j++)
+      {
+        spline_idx = mod_idx + (SPLINE_WINDOW_SIZE / -2) + j;
+        if (spline_idx > delay_length)
+          spline_idx = spline_idx - delay_length;
+        else if (spline_idx < 0)
+          spline_idx = delay_length + spline_idx;
+
+        x[j] = spline_idx;
+        y[j] = l_delayline[spline_idx];
+
+        Serial.print(j, DEC);
+        Serial.print(": X=");
+        Serial.print(x[j], DEC);
+        Serial.print(" Y=");
+        Serial.println(y[j], DEC);
+      }
+      modulation_spline.setPoints(x, y, SPLINE_WINDOW_SIZE);
+      *bp = int(modulation_spline.value(mod_idx) + 0.5);
+
+      Serial.print(" SPLINE=");
+      Serial.println(*bp, DEC);
+      delay(200);
+      /*
+
+        // linear interpolation
+        x1 = int(mod_idx);
+        y1 = l_delayline[x1];
+        if (x1 + 1 >= delay_length)
         x2 = 0;
-      else
+        else
         x2 = x1 + 1;
-      y2 = l_delayline[x2];
+        y2 = l_delayline[x2];
+
+         bp = (int((float(y2 - y1) / (x2 - x1) * (mod_idx - x1) + y1) + 0.5) >> 1); // mix original signal 1:1 with modulated signal
+
+      */
 
-      *bp = (int((float(y2 - y1) / (x2 - x1) * (mod_idx - x1) + y1) + 0.5) >> 1); // mix original signal 1:1 with modulated signal
       bp++;
       mp++;
       l_circ_idx++;

spline.cpp

@@ -0,0 +1,124 @@
+/*
+  From: https://raw.githubusercontent.com/kerinin/arduino-splines
+*/
+
+#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

@@ -0,0 +1,45 @@
+/*
+  From: https://github.com/kerinin/arduino-splines
+
+  Library for 1-d splines
+  Copyright Ryan Michael
+  Licensed under the LGPLv3
+*/
+
+#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