Source/platform/audio/DynamicsCompressor.h

/*
 * Copyright (C) 2011 Google Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
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 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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#ifndef DynamicsCompressor_h
#define DynamicsCompressor_h

#include "platform/audio/AudioArray.h"
#include "platform/audio/DynamicsCompressorKernel.h"
#include "platform/audio/ZeroPole.h"
#include "wtf/Noncopyable.h"
#include "wtf/OwnPtr.h"

namespace blink {

class AudioBus;

// DynamicsCompressor implements a flexible audio dynamics compression effect such as
// is commonly used in musical production and game audio. It lowers the volume
// of the loudest parts of the signal and raises the volume of the softest parts,
// making the sound richer, fuller, and more controlled.

class PLATFORM_EXPORT DynamicsCompressor {
    WTF_MAKE_NONCOPYABLE(DynamicsCompressor);
public:
    enum {
        ParamThreshold,
        ParamKnee,
        ParamRatio,
        ParamAttack,
        ParamRelease,
        ParamPreDelay,
        ParamReleaseZone1,
        ParamReleaseZone2,
        ParamReleaseZone3,
        ParamReleaseZone4,
        ParamPostGain,
        ParamFilterStageGain,
        ParamFilterStageRatio,
        ParamFilterAnchor,
        ParamEffectBlend,
        ParamReduction,
        ParamLast
    };

    DynamicsCompressor(float sampleRate, unsigned numberOfChannels);

    void process(const AudioBus* sourceBus, AudioBus* destinationBus, unsigned framesToProcess);
    void reset();
    void setNumberOfChannels(unsigned);

    void setParameterValue(unsigned parameterID, float value);
    float parameterValue(unsigned parameterID);

    float sampleRate() const { return m_sampleRate; }
    float nyquist() const { return m_sampleRate / 2; }

    double tailTime() const { return 0; }
    double latencyTime() const { return m_compressor.latencyFrames() / static_cast<double>(sampleRate()); }

protected:
    unsigned m_numberOfChannels;

    // m_parameters holds the tweakable compressor parameters.
    float m_parameters[ParamLast];
    void initializeParameters();

    float m_sampleRate;

    // Emphasis filter controls.
    float m_lastFilterStageRatio;
    float m_lastAnchor;
    float m_lastFilterStageGain;

    OwnPtr<const float*[]> m_sourceChannels;
    OwnPtr<float*[]> m_destinationChannels;

    // The core compressor.
    DynamicsCompressorKernel m_compressor;
};

} // namespace blink

#endif // DynamicsCompressor_h