Fixed stereo panning.

MicroDexed.ino

@@ -5,7 +5,7 @@
    Dexed ist heavily based on https://github.com/google/music-synthesizer-for-android
 
    (c)2018-2021 H. Wirtz <wirtz@parasitstudio.de>
-                M. Koslowski <positionhigh@gmx.de>
+   (c)2021      M. Koslowski <positionhigh@gmx.de>
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by

effect_stereo_panorama.cpp

@@ -68,7 +68,19 @@ inline float mapfloat(float val, float in_min, float in_max, float out_min, floa
 
 void AudioEffectStereoPanorama::panorama(float p)
 {
-  pan = mapfloat(p, -1.0, 1.0, 1.0, 0.0);
+  //pan = mapfloat(p, -1.0, 1.0, 1.0, 0.0);
+  if (p == 0.5)
+    pan_l = pan_r = 1.0;
+  else if (p > 0.5)
+  {
+    pan_r = 0.5 - abs(0.5 - p);
+    pan_l = 1.0 - pan_r;
+  }
+  else
+  {
+    pan_l = 0.5 - abs(0.5 - p);
+    pan_r = 1.0 - p;
+  }
 }
 
 void AudioEffectStereoPanorama::update(void)
@@ -92,17 +104,16 @@ void AudioEffectStereoPanorama::update(void)
     arm_q15_to_float(in[0]->data, in_f[0], AUDIO_BLOCK_SAMPLES);
     arm_q15_to_float(in[1]->data, in_f[1], AUDIO_BLOCK_SAMPLES);
 
-    float fsin = arm_sin_f32(pan * PI / 2.0);
-    float fcos = arm_cos_f32(pan * PI / 2.0);
-    int16_t* out_p[2] = {&out[0]->data[0], &out[1]->data[0]};
-
     for (uint16_t n = 0; n < AUDIO_BLOCK_SAMPLES; n++)
     {
-      out_p[0][n] = int16_t(in_f[0][n] * _pseudo_log * fsin * SHRT_MAX);
+      out_f[0][n] = in_f[0][n] * pan_r;
-      out_p[1][n] = int16_t(in_f[1][n] * _pseudo_log * fcos * SHRT_MAX);
+      out_f[0][n] += in_f[1][n] * pan_l;
-      out_p[0][n] = int16_t(in_f[0][n] * _pseudo_log * fcos * SHRT_MAX);
+      out_f[1][n] = in_f[1][n] * pan_r;
-      out_p[1][n] = int16_t(in_f[1][n] * _pseudo_log * fsin * SHRT_MAX);
+      out_f[1][n] += in_f[0][n] * pan_l;
     }
+
+    arm_float_to_q15(out_f[0], out[0]->data, AUDIO_BLOCK_SAMPLES);
+    arm_float_to_q15(out_f[1], out[1]->data, AUDIO_BLOCK_SAMPLES);
   }
 
   if (in[0] != (audio_block_t*)&zeroblock)

effect_stereo_panorama.h

@@ -35,7 +35,8 @@ class AudioEffectStereoPanorama : public AudioStream
     AudioEffectStereoPanorama(void):
       AudioStream(1, inputQueueArray)
     {
-      pan = 0.5;
+      pan_l = 1.0;
+      pan_r = 1.0;
     }
 
     virtual void update(void);
@@ -45,7 +46,9 @@ class AudioEffectStereoPanorama : public AudioStream
     audio_block_t *inputQueueArray[2];
     audio_block_t *out[2];
     float in_f[2][AUDIO_BLOCK_SAMPLES];
-    float pan;
+    float out_f[2][AUDIO_BLOCK_SAMPLES];
+    float pan_l;
+    float pan_r;
     const float _pseudo_log = 1048575 / (float)(1 << 20);
 };