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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 "platform/PlatformExport.h"
     33 #include "platform/audio/AudioArray.h"
     34 #include "wtf/Noncopyable.h"
     35 #include "wtf/OwnPtr.h"
     36 #include "wtf/PassOwnPtr.h"
     37 
     38 namespace blink {
     39 
     40 class PLATFORM_EXPORT DynamicsCompressorKernel {
     41     WTF_MAKE_NONCOPYABLE(DynamicsCompressorKernel);
     42 public:
     43     DynamicsCompressorKernel(float sampleRate, unsigned numberOfChannels);
     44 
     45     void setNumberOfChannels(unsigned);
     46 
     47     // Performs stereo-linked compression.
     48     void process(const float* sourceChannels[],
     49                  float* destinationChannels[],
     50                  unsigned numberOfChannels,
     51                  unsigned framesToProcess,
     52 
     53                  float dbThreshold,
     54                  float dbKnee,
     55                  float ratio,
     56                  float attackTime,
     57                  float releaseTime,
     58                  float preDelayTime,
     59                  float dbPostGain,
     60                  float effectBlend,
     61 
     62                  float releaseZone1,
     63                  float releaseZone2,
     64                  float releaseZone3,
     65                  float releaseZone4
     66                  );
     67 
     68     void reset();
     69 
     70     unsigned latencyFrames() const { return m_lastPreDelayFrames; }
     71 
     72     float sampleRate() const { return m_sampleRate; }
     73 
     74     float meteringGain() const { return m_meteringGain; }
     75 
     76 protected:
     77     float m_sampleRate;
     78 
     79     float m_detectorAverage;
     80     float m_compressorGain;
     81 
     82     // Metering
     83     float m_meteringReleaseK;
     84     float m_meteringGain;
     85 
     86     // Lookahead section.
     87     enum { MaxPreDelayFrames = 1024 };
     88     enum { MaxPreDelayFramesMask = MaxPreDelayFrames - 1 };
     89     enum { DefaultPreDelayFrames = 256 }; // setPreDelayTime() will override this initial value
     90     unsigned m_lastPreDelayFrames;
     91     void setPreDelayTime(float);
     92 
     93     Vector<OwnPtr<AudioFloatArray> > m_preDelayBuffers;
     94     int m_preDelayReadIndex;
     95     int m_preDelayWriteIndex;
     96 
     97     float m_maxAttackCompressionDiffDb;
     98 
     99     // Static compression curve.
    100     float kneeCurve(float x, float k);
    101     float saturate(float x, float k);
    102     float slopeAt(float x, float k);
    103     float kAtSlope(float desiredSlope);
    104 
    105     float updateStaticCurveParameters(float dbThreshold, float dbKnee, float ratio);
    106 
    107     // Amount of input change in dB required for 1 dB of output change.
    108     // This applies to the portion of the curve above m_kneeThresholdDb (see below).
    109     float m_ratio;
    110     float m_slope; // Inverse ratio.
    111 
    112     // The input to output change below the threshold is linear 1:1.
    113     float m_linearThreshold;
    114     float m_dbThreshold;
    115 
    116     // m_dbKnee is the number of dB above the threshold before we enter the "ratio" portion of the curve.
    117     // m_kneeThresholdDb = m_dbThreshold + m_dbKnee
    118     // The portion between m_dbThreshold and m_kneeThresholdDb is the "soft knee" portion of the curve
    119     // which transitions smoothly from the linear portion to the ratio portion.
    120     float m_dbKnee;
    121     float m_kneeThreshold;
    122     float m_kneeThresholdDb;
    123     float m_ykneeThresholdDb;
    124 
    125     // Internal parameter for the knee portion of the curve.
    126     float m_K;
    127 };
    128 
    129 } // namespace blink
    130 
    131 #endif // DynamicsCompressorKernel_h
    132