Slightly blend left and right audio channels

Author: Hanicef

libraries/audio/src/AudioSRC.cpp

@@ -963,6 +963,8 @@ void AudioSRC::convertOutput(float** inputs, int16_t* output, int numFrames) {
 
     } else if (_numChannels == 2) {
 
+        __m128 d8 = _mm_set1_ps(8.0f);
+        __m128 m7 = _mm_set1_ps(7.0f / 8.0f);
         int i = 0;
         for (; i < numFrames - 3; i += 4) {
             __m128 f0 = _mm_mul_ps(_mm_loadu_ps(&inputs[0][i]), scale);
@@ -972,6 +974,10 @@ void AudioSRC::convertOutput(float** inputs, int16_t* output, int numFrames) {
             f0 = _mm_add_ps(f0, d0);
             f1 = _mm_add_ps(f1, d0);
 
+            // blend left and right slightly to make headphones less painful to use
+            f0 = _mm_add_ps(_mm_mul_ps(f0, m7), _mm_div_ps(f1, d8));
+            f1 = _mm_add_ps(_mm_mul_ps(f1, m7), _mm_div_ps(f0, d8));
+
             // round and saturate
             __m128i a0 = _mm_cvtps_epi32(f0);
             __m128i a1 = _mm_cvtps_epi32(f1);
@@ -1243,6 +1249,10 @@ void AudioSRC::convertOutput(float** inputs, int16_t* output, int numFrames) {
             f0 += d;
             f1 += d;
 
+            // blend left and right slightly to make headphones less painful to use
+            f0 = f0 * (7.0f / 8.0f) + f1 / 8.0f;
+            f1 = f1 * (7.0f / 8.0f) + f0 / 8.0f;
+
             // round and saturate
             f0 += (f0 < 0.0f ? -0.5f : +0.5f);
             f1 += (f1 < 0.0f ? -0.5f : +0.5f);