Update the output limiter/compressor

This provides better characteristics for an amplitude limiter. In particular,
it utilizes the peak amplitude instead of the RMS, and the used parameters
basically guarantee no output samples exceed the given threshold... almost, due
to floating-point errors as the threshold is converted from dB to log-e for the
envelope, then is negated and converted to linear amplitude to apply to the
signal. It's quite possible for some rounding errors to creep in and not
perfectly saturate the result.

1 files changed, 80 insertions, 31 deletions

diff --git a/Alc/mastering.h b/Alc/mastering.h
index 0a7b4901..206a6c91 100644
--- a/Alc/mastering.h
+++ b/Alc/mastering.h
@@ -6,51 +6,100 @@
 /* For BUFFERSIZE. */
 #include "alMain.h"
 
+/* These structures assume BUFFERSIZE is a power of 2.
+ */
+typedef struct SlidingHold
+{
+    ALfloat Values[BUFFERSIZE];
+    ALsizei Expiries[BUFFERSIZE];
+    ALsizei LowerIndex;
+    ALsizei UpperIndex;
+    ALsizei Length;
+} SlidingHold;
+
+/* General topology and basic automation was based on the following paper:
+ *
+ *   D. Giannoulis, M. Massberg and J. D. Reiss,
+ *   "Parameter Automation in a Dynamic Range Compressor,"
+ *   Journal of the Audio Engineering Society, v61 (10), Oct. 2013
+ *
+ * Available (along with supplemental reading) at:
+ *
+ *   http://c4dm.eecs.qmul.ac.uk/audioengineering/compressors/
+ */
 typedef struct Compressor {
+    ALsizei NumChans;
+    ALuint SampleRate;
+    struct {
+        ALuint Knee:1;
+        ALuint Attack:1;
+        ALuint Release:1;
+        ALuint PostGain:1;
+        ALuint Declip:1;
+    } Auto;
+    ALsizei LookAhead;
     ALfloat PreGain;
     ALfloat PostGain;
-    ALboolean SummedLink;
-    ALfloat AttackMin;
-    ALfloat AttackMax;
-    ALfloat ReleaseMin;
-    ALfloat ReleaseMax;
-    ALfloat Ratio;
     ALfloat Threshold;
+    ALfloat Slope;
     ALfloat Knee;
-    ALuint SampleRate;
-
-    ALuint RmsSum;
-    ALuint *RmsWindow;
-    ALsizei RmsIndex;
-    ALfloat Envelope[BUFFERSIZE];
-    ALfloat EnvLast;
+    ALfloat Attack;
+    ALfloat Release;
+    ALfloat SideChain[2*BUFFERSIZE];
+    ALsizei SideChainIndex;
+    ALfloat CrestFactor[BUFFERSIZE];
+    SlidingHold *Hold;
+    ALfloat (*Delay)[BUFFERSIZE];
+    ALsizei DelayIndex;
+    ALfloat CrestCoeff;
+    ALfloat GainEstimate;
+    ALfloat AdaptCoeff;
+    ALfloat LastPeakSq;
+    ALfloat LastRmsSq;
+    ALfloat LastRelease;
+    ALfloat LastAttack;
+    ALfloat LastGainDev;
 } Compressor;
 
-/* The compressor requires the following information for proper
- * initialization:
+/* The compressor is initialized with the following settings:
  *
+ *   NumChans       - Number of channels to process.
+ *   SampleRate     - Sample rate to process.
+ *   AutoKnee       - Whether to automate the knee width parameter.
+ *   AutoAttack     - Whether to automate the attack time parameter.
+ *   AutoRelease    - Whether to automate the release time parameter.
+ *   AutoPostGain   - Whether to automate the make-up (post) gain parameter.
+ *   AutoDeclip     - Whether to automate clipping reduction.  Ignored when
+ *                    not automating make-up gain.
+ *   LookAheadTime  - Look-ahead time (in seconds).
+ *   HoldTime       - Peak hold-time (in seconds).
  *   PreGainDb      - Gain applied before detection (in dB).
- *   PostGainDb     - Gain applied after compression (in dB).
- *   SummedLink     - Whether to use summed (true) or maxed (false) linking.
- *   RmsSensing     - Whether to use RMS (true) or Peak (false) sensing.
- *   AttackTimeMin  - Minimum attack time (in seconds).
- *   AttackTimeMax  - Maximum attack time.  Automates when min != max.
- *   ReleaseTimeMin - Minimum release time (in seconds).
- *   ReleaseTimeMax - Maximum release time.  Automates when min != max.
- *   Ratio          - Compression ratio (x:1).  Set to 0 for true limiter.
+ *   PostGainDb     - Make-up gain applied after compression (in dB).
  *   ThresholdDb    - Triggering threshold (in dB).
- *   KneeDb         - Knee width (below threshold; in dB).
- *   SampleRate     - Sample rate to process.
+ *   Ratio          - Compression ratio (x:1).  Set to INFINIFTY for true
+ *                    limiting.  Ignored when automating knee width.
+ *   KneeDb         - Knee width (in dB).  Ignored when automating knee
+ *                    width.
+ *   AttackTimeMin  - Attack time (in seconds).  Acts as a maximum when
+ *                    automating attack time.
+ *   ReleaseTimeMin - Release time (in seconds).  Acts as a maximum when
+ *                    automating release time.
  */
-Compressor *CompressorInit(const ALfloat PreGainDb, const ALfloat PostGainDb,
-    const ALboolean SummedLink, const ALboolean RmsSensing, const ALfloat AttackTimeMin,
-    const ALfloat AttackTimeMax, const ALfloat ReleaseTimeMin, const ALfloat ReleaseTimeMax,
-    const ALfloat Ratio, const ALfloat ThresholdDb, const ALfloat KneeDb,
-    const ALuint SampleRate);
+Compressor* CompressorInit(const ALuint NumChans, const ALuint SampleRate,
+    const ALboolean AutoKnee, const ALboolean AutoAttack,
+    const ALboolean AutoRelease, const ALboolean AutoPostGain,
+    const ALboolean AutoDeclip, const ALfloat LookAheadTime,
+    const ALfloat HoldTime, const ALfloat PreGainDb,
+    const ALfloat PostGainDb, const ALfloat ThresholdDb,
+    const ALfloat Ratio, const ALfloat KneeDb,
+    const ALfloat AttackTime, const ALfloat ReleaseTime);
 
-void ApplyCompression(struct Compressor *Comp, const ALsizei NumChans, const ALsizei SamplesToDo,
+void ApplyCompression(struct Compressor *Comp, const ALsizei SamplesToDo,
                       ALfloat (*restrict OutBuffer)[BUFFERSIZE]);
 
+inline ALsizei GetCompressorChannelCount(const Compressor *Comp)
+{ return Comp->NumChans; }
+
 inline ALuint GetCompressorSampleRate(const Compressor *Comp)
 { return Comp->SampleRate; }