1 files changed, 58 insertions, 64 deletions

diff --git a/Alc/effects/compressor.c b/Alc/effects/compressor.c
index 4ec28f9a..a5f1953b 100644
--- a/Alc/effects/compressor.c
+++ b/Alc/effects/compressor.c
@@ -27,6 +27,13 @@
 #include "alu.h"
 
 
+#define AMP_ENVELOPE_MIN  0.5f
+#define AMP_ENVELOPE_MAX  2.0f
+
+#define ATTACK_TIME  0.1f /* 100ms to rise from min to max */
+#define RELEASE_TIME 0.2f /* 200ms to drop from max to min */
+
+
 typedef struct ALcompressorState {
     DERIVE_FROM_TYPE(ALeffectState);
 
@@ -35,9 +42,9 @@ typedef struct ALcompressorState {
 
     /* Effect parameters */
     ALboolean Enabled;
-    ALfloat AttackRate;
-    ALfloat ReleaseRate;
-    ALfloat GainCtrl;
+    ALfloat AttackMult;
+    ALfloat ReleaseMult;
+    ALfloat EnvFollower;
 } ALcompressorState;
 
 static ALvoid ALcompressorState_Destruct(ALcompressorState *state);
@@ -55,9 +62,9 @@ static void ALcompressorState_Construct(ALcompressorState *state)
     SET_VTABLE2(ALcompressorState, ALeffectState, state);
 
     state->Enabled = AL_TRUE;
-    state->AttackRate = 0.0f;
-    state->ReleaseRate = 0.0f;
-    state->GainCtrl = 1.0f;
+    state->AttackMult = 1.0f;
+    state->ReleaseMult = 1.0f;
+    state->EnvFollower = 1.0f;
 }
 
 static ALvoid ALcompressorState_Destruct(ALcompressorState *state)
@@ -67,11 +74,17 @@ static ALvoid ALcompressorState_Destruct(ALcompressorState *state)
 
 static ALboolean ALcompressorState_deviceUpdate(ALcompressorState *state, ALCdevice *device)
 {
-    const ALfloat attackTime = device->Frequency * 0.2f; /* 200ms Attack */
-    const ALfloat releaseTime = device->Frequency * 0.4f; /* 400ms Release */
-
-    state->AttackRate = 1.0f / attackTime;
-    state->ReleaseRate = 1.0f / releaseTime;
+    /* Number of samples to do a full attack and release (non-integer sample
+     * counts are okay).
+     */
+    const ALfloat attackCount  = (ALfloat)device->Frequency * ATTACK_TIME;
+    const ALfloat releaseCount = (ALfloat)device->Frequency * RELEASE_TIME;
+
+    /* Calculate per-sample multipliers to attack and release at the desired
+     * rates.
+     */
+    state->AttackMult  = powf(AMP_ENVELOPE_MAX/AMP_ENVELOPE_MIN, 1.0f/attackCount);
+    state->ReleaseMult = powf(AMP_ENVELOPE_MIN/AMP_ENVELOPE_MAX, 1.0f/releaseCount);
 
     return AL_TRUE;
 }
@@ -97,71 +110,52 @@ static ALvoid ALcompressorState_process(ALcompressorState *state, ALsizei Sample
 
     for(base = 0;base < SamplesToDo;)
     {
-        ALfloat temps[64][4];
-        ALsizei td = mini(64, SamplesToDo-base);
-
-        /* Load samples into the temp buffer first. */
-        for(j = 0;j < 4;j++)
-        {
-            for(i = 0;i < td;i++)
-                temps[i][j] = SamplesIn[j][i+base];
-        }
+        ALfloat gains[256];
+        ALsizei td = mini(256, SamplesToDo-base);
+        ALfloat env = state->EnvFollower;
 
+        /* Generate the per-sample gains from the signal envelope. */
         if(state->Enabled)
         {
-            ALfloat gain = state->GainCtrl;
-            ALfloat output, amplitude;
-
-            for(i = 0;i < td;i++)
+            for(i = 0;i < td;++i)
             {
-                /* Roughly calculate the maximum amplitude from the 4-channel
-                 * signal, and attack or release the gain control to reach it.
+                /* Clamp the absolute amplitude to the defined envelope limits,
+                 * then attack or release the envelope to reach it.
+                 */
+                ALfloat amplitude = clampf(fabsf(SamplesIn[0][base+i]),
+                                           AMP_ENVELOPE_MIN, AMP_ENVELOPE_MAX);
+                if(amplitude > env)
+                    env = minf(env*state->AttackMult, amplitude);
+                else if(amplitude < env)
+                    env = maxf(env*state->ReleaseMult, amplitude);
+
+                /* Apply the reciprocal of the envelope to normalize the volume
+                 * (compress the dynamic range).
                  */
-                amplitude = fabsf(temps[i][0]);
-                amplitude = maxf(amplitude + fabsf(temps[i][1]),
-                                 maxf(amplitude + fabsf(temps[i][2]),
-                                      amplitude + fabsf(temps[i][3])));
-                if(amplitude > gain)
-                    gain = minf(gain+state->AttackRate, amplitude);
-                else if(amplitude < gain)
-                    gain = maxf(gain-state->ReleaseRate, amplitude);
-
-                /* Apply the inverse of the gain control to normalize/compress
-                 * the volume. */
-                output = 1.0f / clampf(gain, 0.5f, 2.0f);
-                for(j = 0;j < 4;j++)
-                    temps[i][j] *= output;
+                gains[i] = 1.0f / env;
             }
-
-            state->GainCtrl = gain;
         }
         else
         {
-            ALfloat gain = state->GainCtrl;
-            ALfloat output, amplitude;
-
-            for(i = 0;i < td;i++)
+            /* Same as above, except the amplitude is forced to 1. This helps
+             * ensure smooth gain changes when the compressor is turned on and
+             * off.
+             */
+            for(i = 0;i < td;++i)
             {
-                /* Same as above, except the amplitude is forced to 1. This
-                 * helps ensure smooth gain changes when the compressor is
-                 * turned on and off.
-                 */
-                amplitude = 1.0f;
-                if(amplitude > gain)
-                    gain = minf(gain+state->AttackRate, amplitude);
-                else if(amplitude < gain)
-                    gain = maxf(gain-state->ReleaseRate, amplitude);
-
-                output = 1.0f / clampf(gain, 0.5f, 2.0f);
-                for(j = 0;j < 4;j++)
-                    temps[i][j] *= output;
-            }
+                ALfloat amplitude = 1.0f;
+                if(amplitude > env)
+                    env = minf(env*state->AttackMult, amplitude);
+                else if(amplitude < env)
+                    env = maxf(env*state->ReleaseMult, amplitude);
 
-            state->GainCtrl = gain;
+                gains[i] = 1.0f / env;
+            }
         }
+        state->EnvFollower = env;
 
-        /* Now mix to the output. */
-        for(j = 0;j < 4;j++)
+        /* Now compress the signal amplitude to output. */
+        for(j = 0;j < MAX_EFFECT_CHANNELS;j++)
         {
             for(k = 0;k < NumChannels;k++)
             {
@@ -170,7 +164,7 @@ static ALvoid ALcompressorState_process(ALcompressorState *state, ALsizei Sample
                     continue;
 
                 for(i = 0;i < td;i++)
-                    SamplesOut[k][base+i] += gain * temps[i][j];
+                    SamplesOut[k][base+i] += SamplesIn[k][base+i] * gains[i] * gain;
             }
         }