Prevent occurences of clipping in loud downmixed scenes

The downmixer effect is a mixer, wich, like the platform mixer,
  hard-clips. To prevent clipping during loud scenes across multiple
  chanels, apply a fixed attenuation on the result of the downmix.
  Note that this attenuation is lower the theoretical required
  attenuation (except for quad and surround) but is adequate for
  most content.

Bug 4280902
Change-Id: Iec520e9f1367284d6102633f532429361717692d

1 files changed, 20 insertions, 20 deletions

diff --git a/media/libeffects/downmix/EffectDownmix.c b/media/libeffects/downmix/EffectDownmix.c
index 8735503..5bf052a 100644
--- a/media/libeffects/downmix/EffectDownmix.c
+++ b/media/libeffects/downmix/EffectDownmix.c
@@ -822,9 +822,9 @@ void Downmix_foldFromQuad(int16_t *pSrc, int16_t*pDst, size_t numFrames, bool ac
     if (accumulate) {
         while (numFrames) {
             // FL + RL
-            pDst[0] = clamp16(pDst[0] + pSrc[0] + pSrc[2]);
+            pDst[0] = clamp16(pDst[0] + ((pSrc[0] + pSrc[2]) >> 1));
             // FR + RR
-            pDst[1] = clamp16(pDst[1] + pSrc[1] + pSrc[3]);
+            pDst[1] = clamp16(pDst[1] + ((pSrc[1] + pSrc[3]) >> 1));
             pSrc += 4;
             pDst += 2;
             numFrames--;
@@ -832,9 +832,9 @@ void Downmix_foldFromQuad(int16_t *pSrc, int16_t*pDst, size_t numFrames, bool ac
     } else { // same code as above but without adding and clamping pDst[i] to itself
         while (numFrames) {
             // FL + RL
-            pDst[0] = clamp16(pSrc[0] + pSrc[2]);
+            pDst[0] = clamp16((pSrc[0] + pSrc[2]) >> 1);
             // FR + RR
-            pDst[1] = clamp16(pSrc[1] + pSrc[3]);
+            pDst[1] = clamp16((pSrc[1] + pSrc[3]) >> 1);
             pSrc += 4;
             pDst += 2;
             numFrames--;
@@ -877,8 +877,8 @@ void Downmix_foldFromSurround(int16_t *pSrc, int16_t*pDst, size_t numFrames, boo
             // FR + centerPlusRearContrib
             rt = (pSrc[1] << 12) + centerPlusRearContrib;
             // accumulate in destination
-            pDst[0] = clamp16(pDst[0] + (lt >> 12));
-            pDst[1] = clamp16(pDst[1] + (rt >> 12));
+            pDst[0] = clamp16(pDst[0] + (lt >> 13));
+            pDst[1] = clamp16(pDst[1] + (rt >> 13));
             pSrc += 4;
             pDst += 2;
             numFrames--;
@@ -892,8 +892,8 @@ void Downmix_foldFromSurround(int16_t *pSrc, int16_t*pDst, size_t numFrames, boo
             // FR + centerPlusRearContrib
             rt = (pSrc[1] << 12) + centerPlusRearContrib;
             // store in destination
-            pDst[0] = clamp16(lt >> 12); // differs from when accumulate is true above
-            pDst[1] = clamp16(rt >> 12); // differs from when accumulate is true above
+            pDst[0] = clamp16(lt >> 13); // differs from when accumulate is true above
+            pDst[1] = clamp16(rt >> 13); // differs from when accumulate is true above
             pSrc += 4;
             pDst += 2;
             numFrames--;
@@ -939,8 +939,8 @@ void Downmix_foldFrom5Point1(int16_t *pSrc, int16_t*pDst, size_t numFrames, bool
             // FR + centerPlusLfeContrib + RR
             rt = (pSrc[1] << 12) + centerPlusLfeContrib + (pSrc[5] << 12);
             // accumulate in destination
-            pDst[0] = clamp16(pDst[0] + (lt >> 12));
-            pDst[1] = clamp16(pDst[1] + (rt >> 12));
+            pDst[0] = clamp16(pDst[0] + (lt >> 13));
+            pDst[1] = clamp16(pDst[1] + (rt >> 13));
             pSrc += 6;
             pDst += 2;
             numFrames--;
@@ -955,8 +955,8 @@ void Downmix_foldFrom5Point1(int16_t *pSrc, int16_t*pDst, size_t numFrames, bool
             // FR + centerPlusLfeContrib + RR
             rt = (pSrc[1] << 12) + centerPlusLfeContrib + (pSrc[5] << 12);
             // store in destination
-            pDst[0] = clamp16(lt >> 12); // differs from when accumulate is true above
-            pDst[1] = clamp16(rt >> 12); // differs from when accumulate is true above
+            pDst[0] = clamp16(lt >> 13); // differs from when accumulate is true above
+            pDst[1] = clamp16(rt >> 13); // differs from when accumulate is true above
             pSrc += 6;
             pDst += 2;
             numFrames--;
@@ -1004,8 +1004,8 @@ void Downmix_foldFrom7Point1(int16_t *pSrc, int16_t*pDst, size_t numFrames, bool
             // FR + centerPlusLfeContrib + SR + RR
             rt = (pSrc[1] << 12) + centerPlusLfeContrib + (pSrc[7] << 12) + (pSrc[5] << 12);
             //accumulate in destination
-            pDst[0] = clamp16(pDst[0] + (lt >> 12));
-            pDst[1] = clamp16(pDst[1] + (rt >> 12));
+            pDst[0] = clamp16(pDst[0] + (lt >> 13));
+            pDst[1] = clamp16(pDst[1] + (rt >> 13));
             pSrc += 8;
             pDst += 2;
             numFrames--;
@@ -1020,8 +1020,8 @@ void Downmix_foldFrom7Point1(int16_t *pSrc, int16_t*pDst, size_t numFrames, bool
             // FR + centerPlusLfeContrib + SR + RR
             rt = (pSrc[1] << 12) + centerPlusLfeContrib + (pSrc[7] << 12) + (pSrc[5] << 12);
             // store in destination
-            pDst[0] = clamp16(lt >> 12); // differs from when accumulate is true above
-            pDst[1] = clamp16(rt >> 12); // differs from when accumulate is true above
+            pDst[0] = clamp16(lt >> 13); // differs from when accumulate is true above
+            pDst[1] = clamp16(rt >> 13); // differs from when accumulate is true above
             pSrc += 8;
             pDst += 2;
             numFrames--;
@@ -1130,8 +1130,8 @@ bool Downmix_foldGeneric(
             lt += centersLfeContrib;
             rt += centersLfeContrib;
             // accumulate in destination
-            pDst[0] = clamp16(pDst[0] + (lt >> 12));
-            pDst[1] = clamp16(pDst[1] + (rt >> 12));
+            pDst[0] = clamp16(pDst[0] + (lt >> 13));
+            pDst[1] = clamp16(pDst[1] + (rt >> 13));
             pSrc += numChan;
             pDst += 2;
             numFrames--;
@@ -1159,8 +1159,8 @@ bool Downmix_foldGeneric(
             lt += centersLfeContrib;
             rt += centersLfeContrib;
             // store in destination
-            pDst[0] = clamp16(lt >> 12); // differs from when accumulate is true above
-            pDst[1] = clamp16(rt >> 12); // differs from when accumulate is true above
+            pDst[0] = clamp16(lt >> 13); // differs from when accumulate is true above
+            pDst[1] = clamp16(rt >> 13); // differs from when accumulate is true above
             pSrc += numChan;
             pDst += 2;
             numFrames--;