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29 #ifndef DynamicsCompressorKernel_h
30 #define DynamicsCompressorKernel_h
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"
40 class PLATFORM_EXPORT DynamicsCompressorKernel {
41 WTF_MAKE_NONCOPYABLE(DynamicsCompressorKernel);
43 DynamicsCompressorKernel(float sampleRate, unsigned numberOfChannels);
45 void setNumberOfChannels(unsigned);
47 // Performs stereo-linked compression.
48 void process(const float* sourceChannels[],
49 float* destinationChannels[],
50 unsigned numberOfChannels,
51 unsigned framesToProcess,
70 unsigned latencyFrames() const { return m_lastPreDelayFrames; }
72 float sampleRate() const { return m_sampleRate; }
74 float meteringGain() const { return m_meteringGain; }
79 float m_detectorAverage;
80 float m_compressorGain;
83 float m_meteringReleaseK;
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);
93 Vector<OwnPtr<AudioFloatArray> > m_preDelayBuffers;
94 int m_preDelayReadIndex;
95 int m_preDelayWriteIndex;
97 float m_maxAttackCompressionDiffDb;
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);
105 float updateStaticCurveParameters(float dbThreshold, float dbKnee, float ratio);
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).
110 float m_slope; // Inverse ratio.
112 // The input to output change below the threshold is linear 1:1.
113 float m_linearThreshold;
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.
121 float m_kneeThreshold;
122 float m_kneeThresholdDb;
123 float m_ykneeThresholdDb;
125 // Internal parameter for the knee portion of the curve.
129 } // namespace WebCore
131 #endif // DynamicsCompressorKernel_h