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      1 /*
      2  * Copyright (C) 2011 Google Inc. All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions
      6  * are met:
      7  *
      8  * 1.  Redistributions of source code must retain the above copyright
      9  *     notice, this list of conditions and the following disclaimer.
     10  * 2.  Redistributions in binary form must reproduce the above copyright
     11  *     notice, this list of conditions and the following disclaimer in the
     12  *     documentation and/or other materials provided with the distribution.
     13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
     14  *     its contributors may be used to endorse or promote products derived
     15  *     from this software without specific prior written permission.
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
     18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
     21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #ifndef DynamicsCompressorKernel_h
     30 #define DynamicsCompressorKernel_h
     31 
     32 #include "core/platform/audio/AudioArray.h"
     33 
     34 #include "wtf/OwnPtr.h"
     35 #include "wtf/PassOwnPtr.h"
     36 
     37 namespace WebCore {
     38 
     39 class DynamicsCompressorKernel {
     40 public:
     41     DynamicsCompressorKernel(float sampleRate, unsigned numberOfChannels);
     42 
     43     void setNumberOfChannels(unsigned);
     44 
     45     // Performs stereo-linked compression.
     46     void process(float* sourceChannels[],
     47                  float* destinationChannels[],
     48                  unsigned numberOfChannels,
     49                  unsigned framesToProcess,
     50 
     51                  float dbThreshold,
     52                  float dbKnee,
     53                  float ratio,
     54                  float attackTime,
     55                  float releaseTime,
     56                  float preDelayTime,
     57                  float dbPostGain,
     58                  float effectBlend,
     59 
     60                  float releaseZone1,
     61                  float releaseZone2,
     62                  float releaseZone3,
     63                  float releaseZone4
     64                  );
     65 
     66     void reset();
     67 
     68     unsigned latencyFrames() const { return m_lastPreDelayFrames; }
     69 
     70     float sampleRate() const { return m_sampleRate; }
     71 
     72     float meteringGain() const { return m_meteringGain; }
     73 
     74 protected:
     75     float m_sampleRate;
     76 
     77     float m_detectorAverage;
     78     float m_compressorGain;
     79 
     80     // Metering
     81     float m_meteringReleaseK;
     82     float m_meteringGain;
     83 
     84     // Lookahead section.
     85     enum { MaxPreDelayFrames = 1024 };
     86     enum { MaxPreDelayFramesMask = MaxPreDelayFrames - 1 };
     87     enum { DefaultPreDelayFrames = 256 }; // setPreDelayTime() will override this initial value
     88     unsigned m_lastPreDelayFrames;
     89     void setPreDelayTime(float);
     90 
     91     Vector<OwnPtr<AudioFloatArray> > m_preDelayBuffers;
     92     int m_preDelayReadIndex;
     93     int m_preDelayWriteIndex;
     94 
     95     float m_maxAttackCompressionDiffDb;
     96 
     97     // Static compression curve.
     98     float kneeCurve(float x, float k);
     99     float saturate(float x, float k);
    100     float slopeAt(float x, float k);
    101     float kAtSlope(float desiredSlope);
    102 
    103     float updateStaticCurveParameters(float dbThreshold, float dbKnee, float ratio);
    104 
    105     // Amount of input change in dB required for 1 dB of output change.
    106     // This applies to the portion of the curve above m_kneeThresholdDb (see below).
    107     float m_ratio;
    108     float m_slope; // Inverse ratio.
    109 
    110     // The input to output change below the threshold is linear 1:1.
    111     float m_linearThreshold;
    112     float m_dbThreshold;
    113 
    114     // m_dbKnee is the number of dB above the threshold before we enter the "ratio" portion of the curve.
    115     // m_kneeThresholdDb = m_dbThreshold + m_dbKnee
    116     // The portion between m_dbThreshold and m_kneeThresholdDb is the "soft knee" portion of the curve
    117     // which transitions smoothly from the linear portion to the ratio portion.
    118     float m_dbKnee;
    119     float m_kneeThreshold;
    120     float m_kneeThresholdDb;
    121     float m_ykneeThresholdDb;
    122 
    123     // Internal parameter for the knee portion of the curve.
    124     float m_K;
    125 };
    126 
    127 } // namespace WebCore
    128 
    129 #endif // DynamicsCompressorKernel_h
    130