Corrected interpolation

synth_sin_cos_f32.cpp

@@ -31,6 +31,8 @@
  * SOFTWARE.
  */
 
+// Rev 10 March 2021 - Corrected interpolation formula  Bob L
+
 #include "synth_sin_cos_f32.h"
 
 // 513 values of the sine wave in a float array:
@@ -80,7 +82,7 @@ void AudioSynthSineCosine_F32::update(void) {
           /* Read two nearest values of input value from the sin table */
           a = sinTable512_f32[index];
           b = sinTable512_f32[index+1];
-          blockS->data[i] = amplitude_pk * (a + 0.001953125*(b-a)*deltaPhase);  /* Linear interpolation process */
+          blockS->data[i] = amplitude_pk * (a + (b-a)*deltaPhase);  /* Linear interpolation process */
  
           /* Shift forward phaseS_C  and get cos. First, the calculation of index of the table */
           phaseC = phaseS + phaseS_C;
@@ -90,7 +92,7 @@ void AudioSynthSineCosine_F32::update(void) {
           /* Read two nearest values of input value from the sin table */
           a = sinTable512_f32[index];
           b = sinTable512_f32[index+1];
-          blockC->data[i] = amplitude_pk * (a + 0.001953125*(b-a)*deltaPhase);  /* Linear interpolation process */
+          blockC->data[i] = amplitude_pk * (a + (b-a)*deltaPhase);  /* Linear interpolation process */
         }
     }
     AudioStream_F32::transmit(blockS, 0);

synth_sin_cos_f32.h

@@ -2,6 +2,7 @@
  *   AudioSynthSineCosine_F32
  * 
  * Status: Checked for function and accuracy.  19 April 2020
+ * 10 March 2021  Corrected Interpolation equations.  Bob L
  *
  * Created: Bob Larkin 15 April 2020
  *