spu: fixed Exponential decrease ADSR computation

JaCzekanski · Mar 23, 2020 · 8e03583 · 8e03583
1 parent c17fb01
commit 8e03583
Showing 1 changed file with 5 additions and 1 deletion.
diff --git a/src/device/spu/voice.cpp b/src/device/spu/voice.cpp
@@ -65,7 +65,11 @@ void Voice::processEnvelope() {
             cycles *= 4;
         }
         if (e.direction == Dir::Decrease) {
-            step = step * adsrVolume._reg / 0x8000;
+            // Note: Division by 0x8000 might cause value to become 0,
+            // using right shift by 15 ensures that minimum it can go is -1.
+            // Games affected: Doom (when paused music does not fade out)
+            // Little Princess - Marl Oukoku no Ningyou-hime 2 (voices stop playing after a while)
+            step = (step * adsrVolume._reg) >> 15;
         }
     }