WavFile.php

<?php

// error_reporting(E_ALL); ini_set('display_errors', 1); // uncomment this line for debugging

/**
* Project: PHPWavUtils: Classes for creating, reading, and manipulating WAV files in PHP<br />
* File: WavFile.php<br />
*
* Copyright (c) 2012, Drew Phillips
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* - Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* - 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.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* Any modifications to the library should be indicated clearly in the source code
* to inform users that the changes are not a part of the original software.<br /><br />
*
* @copyright 2012 Drew Phillips
* @author Drew Phillips <drew@drew-phillips.com>
* @author Paul Voegler <http://www.voegler.eu/>
* @version 1.0 (October 2012)
* @package PHPWavUtils
* @license BSD License
*
* Changelog:
* 
*   1.0 (10/2/2012)
*     - Fix insertSilence() creating invalid block size
*
*   1.0 RC1 (4/20/2012)
*     - Initial release candidate
*     - Supports 8, 16, 24, 32 bit PCM, 32-bit IEEE FLOAT, Extensible Format
*     - Support for 18 channels of audio
*     - Ability to read an offset from a file to reduce memory footprint with large files
*     - Single-pass audio filter processing
*     - Highly accurate and efficient mix and normalization filters (http://www.voegler.eu/pub/audio/)
*     - Utility filters for degrading audio, and inserting silence
*
*   0.6 (4/12/2012)
*     - Support 8, 16, 24, 32 bit and PCM float (Paul Voegler)
*     - Add normalize filter, misc improvements and fixes (Paul Voegler)
*     - Normalize parameters to filter() to use filter constants as array indices
*     - Add option to mix filter to loop the target file if the source is longer
*
*   0.5 (4/3/2012)
*     - Fix binary pack routine (Paul Voegler)
*     - Add improved mixing function (Paul Voegler)
*
*/

class WavFile
{
    /*%******************************************************************************************%*/
    // Class constants

    /** @var int Filter flag for mixing two files */
    const FILTER_MIX       = 0x01;

    /** @var int Filter flag for normalizing audio data */
    const FILTER_NORMALIZE = 0x02;

    /** @var int Filter flag for degrading audio data */
    const FILTER_DEGRADE   = 0x04;

    /** @var int Maximum number of channels */
    const MAX_CHANNEL = 18;

    /** @var int Maximum sample rate */
    const MAX_SAMPLERATE = 192000;

    /** Channel Locations for ChannelMask */
    const SPEAKER_DEFAULT               = 0x000000;
    const SPEAKER_FRONT_LEFT            = 0x000001;
    const SPEAKER_FRONT_RIGHT           = 0x000002;
    const SPEAKER_FRONT_CENTER          = 0x000004;
    const SPEAKER_LOW_FREQUENCY         = 0x000008;
    const SPEAKER_BACK_LEFT             = 0x000010;
    const SPEAKER_BACK_RIGHT            = 0x000020;
    const SPEAKER_FRONT_LEFT_OF_CENTER  = 0x000040;
    const SPEAKER_FRONT_RIGHT_OF_CENTER = 0x000080;
    const SPEAKER_BACK_CENTER           = 0x000100;
    const SPEAKER_SIDE_LEFT             = 0x000200;
    const SPEAKER_SIDE_RIGHT            = 0x000400;
    const SPEAKER_TOP_CENTER            = 0x000800;
    const SPEAKER_TOP_FRONT_LEFT        = 0x001000;
    const SPEAKER_TOP_FRONT_CENTER      = 0x002000;
    const SPEAKER_TOP_FRONT_RIGHT       = 0x004000;
    const SPEAKER_TOP_BACK_LEFT         = 0x008000;
    const SPEAKER_TOP_BACK_CENTER       = 0x010000;
    const SPEAKER_TOP_BACK_RIGHT        = 0x020000;
    const SPEAKER_ALL                   = 0x03FFFF;

    /** @var int PCM Audio Format */
    const WAVE_FORMAT_PCM           = 0x0001;

    /** @var int IEEE FLOAT Audio Format */
    const WAVE_FORMAT_IEEE_FLOAT    = 0x0003;

    /** @var int EXTENSIBLE Audio Format - actual audio format defined by SubFormat */
    const WAVE_FORMAT_EXTENSIBLE    = 0xFFFE;

    /** @var string PCM Audio Format SubType - LE hex representation of GUID {00000001-0000-0010-8000-00AA00389B71} */
    const WAVE_SUBFORMAT_PCM        = "0100000000001000800000aa00389b71";

    /** @var string IEEE FLOAT Audio Format SubType - LE hex representation of GUID {00000003-0000-0010-8000-00AA00389B71} */
    const WAVE_SUBFORMAT_IEEE_FLOAT = "0300000000001000800000aa00389b71";


    /*%******************************************************************************************%*/
    // Properties

    /** @var array Log base modifier lookup table for a given threshold (in 0.05 steps) used by normalizeSample.
     * Adjusts the slope (1st derivative) of the log function at the threshold to 1 for a smooth transition
     * from linear to logarithmic amplitude output. */
    protected static $LOOKUP_LOGBASE = array(
        2.513, 2.667, 2.841, 3.038, 3.262,
        3.520, 3.819, 4.171, 4.589, 5.093,
        5.711, 6.487, 7.483, 8.806, 10.634,
        13.302, 17.510, 24.970, 41.155, 96.088
    );

    /** @var int The actual physical file size */
    protected $_actualSize;

    /** @var int The size of the file in RIFF header */
    protected $_chunkSize;

    /** @var int The size of the "fmt " chunk */
    protected $_fmtChunkSize;

    /** @var int The size of the extended "fmt " data */
    protected $_fmtExtendedSize;

    /** @var int The size of the "fact" chunk */
    protected $_factChunkSize;

    /** @var int Size of the data chunk */
    protected $_dataSize;

    /** @var int Size of the data chunk in the opened wav file */
    protected $_dataSize_fp;

    /** @var int Does _dataSize really reflect strlen($_samples)? Case when a wav file is read with readData = false */
    protected $_dataSize_valid;

    /** @var int Starting offset of data chunk */
    protected $_dataOffset;

    /** @var int The audio format - WavFile::WAVE_FORMAT_* */
    protected $_audioFormat;

    /** @var int The audio subformat - WavFile::WAVE_SUBFORMAT_* */
    protected $_audioSubFormat;

    /** @var int Number of channels in the audio file */
    protected $_numChannels;

    /** @var int The channel mask */
    protected $_channelMask;

    /** @var int Samples per second */
    protected $_sampleRate;

    /** @var int Number of bits per sample */
    protected $_bitsPerSample;

    /** @var int Number of valid bits per sample */
    protected $_validBitsPerSample;

    /** @var int NumChannels * BitsPerSample/8 */
    protected $_blockAlign;

    /** @var int Number of sample blocks */
    protected $_numBlocks;

    /** @var int Bytes per second */
    protected $_byteRate;

    /** @var string Binary string of samples */
    protected $_samples;

    /** @var resource The file pointer used for reading wavs from file or memory */
    protected $_fp;


    /*%******************************************************************************************%*/
    // Special methods

    /**
     * WavFile Constructor.
     *
     * <code>
     * $wav1 = new WavFile(2, 44100, 16);         // new wav with 2 channels, at 44100 samples/sec and 16 bits per sample
     * $wav2 = new WavFile('./audio/sound.wav');  // open and read wav file
     * </code>
     *
     * @param string|int $numChannelsOrFileName  (Optional) If string, the filename of the wav file to open. The number of channels otherwise. Defaults to 1.
     * @param int|bool $sampleRateOrReadData  (Optional) If opening a file and boolean, decides whether to read the data chunk or not. Defaults to true. The sample rate in samples per second otherwise. 8000 = standard telephone, 16000 = wideband telephone, 32000 = FM radio and 44100 = CD quality. Defaults to 8000.
     * @param int $bitsPerSample  (Optional) The number of bits per sample. Has to be 8, 16 or 24 for PCM audio or 32 for IEEE FLOAT audio. 8 = telephone, 16 = CD and 24 or 32 = studio quality. Defaults to 8.
     * @throws WavFormatException
     * @throws WavFileException
     */
    public function __construct($numChannelsOrFileName = null, $sampleRateOrReadData = null, $bitsPerSample = null)
    {
        $this->_actualSize         = 44;
        $this->_chunkSize          = 36;
        $this->_fmtChunkSize       = 16;
        $this->_fmtExtendedSize    = 0;
        $this->_factChunkSize      = 0;
        $this->_dataSize           = 0;
        $this->_dataSize_fp        = 0;
        $this->_dataSize_valid     = true;
        $this->_dataOffset         = 44;
        $this->_audioFormat        = self::WAVE_FORMAT_PCM;
        $this->_audioSubFormat     = null;
        $this->_numChannels        = 1;
        $this->_channelMask        = self::SPEAKER_DEFAULT;
        $this->_sampleRate         = 8000;
        $this->_bitsPerSample      = 8;
        $this->_validBitsPerSample = 8;
        $this->_blockAlign         = 1;
        $this->_numBlocks          = 0;
        $this->_byteRate           = 8000;
        $this->_samples            = '';
        $this->_fp                 = null;


        if (is_string($numChannelsOrFileName)) {
            $this->openWav($numChannelsOrFileName, is_bool($sampleRateOrReadData) ? $sampleRateOrReadData : true);

        } else {
            $this->setNumChannels(is_null($numChannelsOrFileName) ? 1 : $numChannelsOrFileName)
                 ->setSampleRate(is_null($sampleRateOrReadData) ? 8000 : $sampleRateOrReadData)
                 ->setBitsPerSample(is_null($bitsPerSample) ? 8 : $bitsPerSample);
        }
    }

    public function __destruct() {
        if (is_resource($this->_fp)) $this->closeWav();
    }

    public function __clone() {
        $this->_fp = null;
    }

    /**
     * Output the wav file headers and data.
     *
     * @return string  The encoded file.
     */
    public function __toString()
    {
        return $this->makeHeader() .
               $this->getDataSubchunk();
    }


    /*%******************************************************************************************%*/
    // Static methods

    /**
     * Unpacks a single binary sample to numeric value.
     *
     * @param string $sampleBinary  (Required) The sample to decode.
     * @param int $bitDepth  (Optional) The bits per sample to decode. If omitted, derives it from the length of $sampleBinary.
     * @return int|float  The numeric sample value. Float for 32-bit samples. Returns null for unsupported bit depths.
     */
    public static function unpackSample($sampleBinary, $bitDepth = null)
    {
        if ($bitDepth === null) {
            $bitDepth = strlen($sampleBinary) * 8;
        }

        switch ($bitDepth) {
            case 8:
                // unsigned char
                return ord($sampleBinary);

            case 16:
                // signed short, little endian
                $data = unpack('v', $sampleBinary);
                $sample = $data[1];
                if ($sample >= 0x8000) {
                    $sample -= 0x10000;
                }
                return $sample;

            case 24:
                // 3 byte packed signed integer, little endian
                $data = unpack('C3', $sampleBinary);
                $sample = $data[1] | ($data[2] << 8) | ($data[3] << 16);
                if ($sample >= 0x800000) {
                    $sample -= 0x1000000;
                }
                return $sample;

            case 32:
                // 32-bit float
                $data = unpack('f', $sampleBinary);
                return $data[1];

            default:
                return null;
        }
    }

    /**
     * Packs a single numeric sample to binary.
     *
     * @param int|float $sample  (Required) The sample to encode. Has to be within valid range for $bitDepth. Float values only for 32 bits.
     * @param int $bitDepth  (Required) The bits per sample to encode with.
     * @return string  The encoded binary sample. Returns null for unsupported bit depths.
     */
    public static function packSample($sample, $bitDepth)
    {
        switch ($bitDepth) {
            case 8:
                // unsigned char
                return chr($sample);

            case 16:
                // signed short, little endian
                if ($sample < 0) {
                    $sample += 0x10000;
                }
                return pack('v', $sample);

            case 24:
                // 3 byte packed signed integer, little endian
                if ($sample < 0) {
                    $sample += 0x1000000;
                }
                return pack('C3', $sample & 0xff, ($sample >>  8) & 0xff, ($sample >> 16) & 0xff);

            case 32:
                // 32-bit float
                return pack('f', $sample);

            default:
                return null;
        }
    }

    /**
     * Unpacks a binary sample block to numeric values.
     *
     * @param string $sampleBlock  (Required) The binary sample block (all channels).
     * @param int $bitDepth  (Required) The bits per sample to decode.
     * @param int $numChannels  (Optional) The number of channels to decode. If omitted, derives it from the length of $sampleBlock and $bitDepth.
     * @return array  The sample values as an array of integers of floats for 32 bits. First channel is array index 1.
     */
    public static function unpackSampleBlock($sampleBlock, $bitDepth, $numChannels = null) {
        $sampleBytes = $bitDepth / 8;
        if ($numChannels === null) {
            $numChannels = strlen($sampleBlock) / $sampleBytes;
        }

        $samples = array();
        for ($i = 0; $i < $numChannels; $i++) {
            $sampleBinary = substr($sampleBlock, $i * $sampleBytes, $sampleBytes);
            $samples[$i + 1] = self::unpackSample($sampleBinary, $bitDepth);
        }

        return $samples;
    }

    /**
     * Packs an array of numeric channel samples to a binary sample block.
     *
     * @param array $samples  (Required) The array of channel sample values. Expects float values for 32 bits and integer otherwise.
     * @param int $bitDepth  (Required) The bits per sample to encode with.
     * @return string  The encoded binary sample block.
     */
    public static function packSampleBlock($samples, $bitDepth) {
        $sampleBlock = '';
        foreach($samples as $sample) {
            $sampleBlock .= self::packSample($sample, $bitDepth);
        }

        return $sampleBlock;
    }

    /**
     * Normalizes a float audio sample. Maximum input range assumed for compression is [-2, 2].
     * See http://www.voegler.eu/pub/audio/ for more information.
     *
     * @param float $sampleFloat  (Required) The float sample to normalize.
     * @param float $threshold  (Required) The threshold or gain factor for normalizing the amplitude. <ul>
     *     <li> >= 1 - Normalize by multiplying by the threshold (boost - positive gain). <br />
     *            A value of 1 in effect means no normalization (and results in clipping). </li>
     *     <li> <= -1 - Normalize by dividing by the the absolute value of threshold (attenuate - negative gain). <br />
     *            A factor of 2 (-2) is about 6dB reduction in volume.</li>
     *     <li> [0, 1) - (open inverval - not including 1) - The threshold
     *            above which amplitudes are comressed logarithmically. <br />
     *            e.g. 0.6 to leave amplitudes up to 60% "as is" and compress above. </li>
     *     <li> (-1, 0) - (open inverval - not including -1 and 0) - The threshold
     *            above which amplitudes are comressed linearly. <br />
     *            e.g. -0.6 to leave amplitudes up to 60% "as is" and compress above. </li></ul>
     * @return float  The normalized sample.
     **/
    public static function normalizeSample($sampleFloat, $threshold) {
        // apply positive gain
        if ($threshold >= 1) {
            return $sampleFloat * $threshold;
        }

        // apply negative gain
        if ($threshold <= -1) {
            return $sampleFloat / -$threshold;
        }

        $sign = $sampleFloat < 0 ? -1 : 1;
        $sampleAbs = abs($sampleFloat);

        // logarithmic compression
        if ($threshold >= 0 && $threshold < 1 && $sampleAbs > $threshold) {
            $loga = self::$LOOKUP_LOGBASE[(int)($threshold * 20)]; // log base modifier
            return $sign * ($threshold + (1 - $threshold) * log(1 + $loga * ($sampleAbs - $threshold) / (2 - $threshold)) / log(1 + $loga));
        }

        // linear compression
        $thresholdAbs = abs($threshold);
        if ($threshold > -1 && $threshold < 0 && $sampleAbs > $thresholdAbs) {
            return $sign * ($thresholdAbs + (1 - $thresholdAbs) / (2 - $thresholdAbs) * ($sampleAbs - $thresholdAbs));
        }

        // else ?
        return $sampleFloat;
    }


    /*%******************************************************************************************%*/
    // Getter and Setter methods for properties

    public function getActualSize() {
        return $this->_actualSize;
    }

    protected function setActualSize($actualSize = null) {
        if (is_null($actualSize)) {
            $this->_actualSize = 8 + $this->_chunkSize;  // + "RIFF" header (ID + size)
        } else {
            $this->_actualSize = $actualSize;
        }

        return $this;
    }

    public function getChunkSize() {
        return $this->_chunkSize;
    }

    protected function setChunkSize($chunkSize = null) {
        if (is_null($chunkSize)) {
            $this->_chunkSize = 4 +                                                            // "WAVE" chunk
                                8 + $this->_fmtChunkSize +                                     // "fmt " subchunk
                                ($this->_factChunkSize > 0 ? 8 + $this->_factChunkSize : 0) +  // "fact" subchunk
                                8 + $this->_dataSize +                                         // "data" subchunk
                                ($this->_dataSize & 1);                                        // padding byte
        } else {
            $this->_chunkSize = $chunkSize;
        }

        $this->setActualSize();

        return $this;
    }

    public function getFmtChunkSize() {
        return $this->_fmtChunkSize;
    }

    protected function setFmtChunkSize($fmtChunkSize = null) {
        if (is_null($fmtChunkSize)) {
            $this->_fmtChunkSize = 16 + $this->_fmtExtendedSize;
        } else {
            $this->_fmtChunkSize = $fmtChunkSize;
        }

        $this->setChunkSize()    // implicit setActualSize()
             ->setDataOffset();

        return $this;
    }

    public function getFmtExtendedSize() {
        return $this->_fmtExtendedSize;
    }

    protected function setFmtExtendedSize($fmtExtendedSize = null) {
        if (is_null($fmtExtendedSize)) {
            if ($this->_audioFormat == self::WAVE_FORMAT_EXTENSIBLE) {
                $this->_fmtExtendedSize = 2 + 22;                          // extension size for WAVE_FORMAT_EXTENSIBLE
            } elseif ($this->_audioFormat != self::WAVE_FORMAT_PCM) {
                $this->_fmtExtendedSize = 2 + 0;                           // empty extension
            } else {
                $this->_fmtExtendedSize = 0;                               // no extension, only for WAVE_FORMAT_PCM
            }
        } else {
            $this->_fmtExtendedSize = $fmtExtendedSize;
        }

        $this->setFmtChunkSize();  // implicit setSize(), setActualSize(), setDataOffset()

        return $this;
    }

    public function getFactChunkSize() {
        return $this->_factChunkSize;
    }

    protected function setFactChunkSize($factChunkSize = null) {
        if (is_null($factChunkSize)) {
            if ($this->_audioFormat != self::WAVE_FORMAT_PCM) {
                $this->_factChunkSize = 4;
            } else {
                $this->_factChunkSize = 0;
            }
        } else {
            $this->_factChunkSize = $factChunkSize;
        }

        $this->setChunkSize()    // implicit setActualSize()
             ->setDataOffset();

        return $this;
    }

    public function getDataSize() {
        return $this->_dataSize;
    }

    protected function setDataSize($dataSize = null) {
        if (is_null($dataSize)) {
            $this->_dataSize = strlen($this->_samples);
        } else {
            $this->_dataSize = $dataSize;
        }

        $this->setChunkSize()   // implicit setActualSize()
             ->setNumBlocks();
        $this->_dataSize_valid = true;

        return $this;
    }

    public function getDataOffset() {
        return $this->_dataOffset;
    }

    protected function setDataOffset($dataOffset = null) {
        if (is_null($dataOffset)) {
            $this->_dataOffset = 8 +                                                            // "RIFF" header (ID + size)
                                 4 +                                                            // "WAVE" chunk
                                 8 + $this->_fmtChunkSize +                                     // "fmt " subchunk
                                 ($this->_factChunkSize > 0 ? 8 + $this->_factChunkSize : 0) +  // "fact" subchunk
                                 8;                                                             // "data" subchunk
        } else {
            $this->_dataOffset = $dataOffset;
        }

        return $this;
    }

    public function getAudioFormat() {
        return $this->_audioFormat;
    }

    protected function setAudioFormat($audioFormat = null) {
        if (is_null($audioFormat)) {
            if (($this->_bitsPerSample <= 16 || $this->_bitsPerSample == 32)
              && $this->_validBitsPerSample == $this->_bitsPerSample
              && $this->_channelMask == self::SPEAKER_DEFAULT
              && $this->_numChannels <= 2) {
                if ($this->_bitsPerSample <= 16) {
                    $this->_audioFormat = self::WAVE_FORMAT_PCM;
                } else {
                    $this->_audioFormat = self::WAVE_FORMAT_IEEE_FLOAT;
                }
            } else {
                $this->_audioFormat = self::WAVE_FORMAT_EXTENSIBLE;
            }
        } else {
            $this->_audioFormat = $audioFormat;
        }

        $this->setAudioSubFormat()
             ->setFactChunkSize()     // implicit setSize(), setActualSize(), setDataOffset()
             ->setFmtExtendedSize();  // implicit setFmtChunkSize(), setSize(), setActualSize(), setDataOffset()

        return $this;
    }

    public function getAudioSubFormat() {
        return $this->_audioSubFormat;
    }

    protected function setAudioSubFormat($audioSubFormat = null) {
        if (is_null($audioSubFormat)) {
            if ($this->_bitsPerSample == 32) {
                $this->_audioSubFormat = self::WAVE_SUBFORMAT_IEEE_FLOAT;  // 32 bits are IEEE FLOAT in this class
            } else {
                $this->_audioSubFormat = self::WAVE_SUBFORMAT_PCM;         // 8, 16 and 24 bits are PCM in this class
            }
        } else {
            $this->_audioSubFormat = $audioSubFormat;
        }

        return $this;
    }

    public function getNumChannels() {
        return $this->_numChannels;
    }

    public function setNumChannels($numChannels) {
        if ($numChannels < 1 || $numChannels > self::MAX_CHANNEL) {
            throw new WavFileException('Unsupported number of channels. Only up to ' . self::MAX_CHANNEL . ' channels are supported.');
        } elseif ($this->_samples !== '') {
            trigger_error('Wav already has sample data. Changing the number of channels does not convert and may corrupt the data.', E_USER_NOTICE);
        }

        $this->_numChannels = (int)$numChannels;

        $this->setAudioFormat()  // implicit setAudioSubFormat(), setFactChunkSize(), setFmtExtendedSize(), setFmtChunkSize(), setSize(), setActualSize(), setDataOffset()
             ->setByteRate()
             ->setBlockAlign();  // implicit setNumBlocks()

        return $this;
    }

    public function getChannelMask() {
        return $this->_channelMask;
    }

    public function setChannelMask($channelMask = self::SPEAKER_DEFAULT) {
        if ($channelMask != 0) {
            // count number of set bits - Hamming weight
            $c = (int)$channelMask;
            $n = 0;
            while ($c > 0) {
                $n += $c & 1;
                $c >>= 1;
            }
            if ($n != $this->_numChannels || (((int)$channelMask | self::SPEAKER_ALL) != self::SPEAKER_ALL)) {
                throw new WavFileException('Invalid channel mask. The number of channels does not match the number of locations in the mask.');
            }
        }

        $this->_channelMask = (int)$channelMask;

        $this->setAudioFormat();  // implicit setAudioSubFormat(), setFactChunkSize(), setFmtExtendedSize(), setFmtChunkSize(), setSize(), setActualSize(), setDataOffset()

        return $this;
    }

    public function getSampleRate() {
        return $this->_sampleRate;
    }

    public function setSampleRate($sampleRate) {
        if ($sampleRate < 1 || $sampleRate > self::MAX_SAMPLERATE) {
            throw new WavFileException('Invalid sample rate.');
        } elseif ($this->_samples !== '') {
            trigger_error('Wav already has sample data. Changing the sample rate does not convert the data and may yield undesired results.', E_USER_NOTICE);
        }

        $this->_sampleRate = (int)$sampleRate;

        $this->setByteRate();

        return $this;
    }

    public function getBitsPerSample() {
        return $this->_bitsPerSample;
    }

    public function setBitsPerSample($bitsPerSample) {
        if (!in_array($bitsPerSample, array(8, 16, 24, 32))) {
            throw new WavFileException('Unsupported bits per sample. Only 8, 16, 24 and 32 bits are supported.');
        } elseif ($this->_samples !== '') {
            trigger_error('Wav already has sample data. Changing the bits per sample does not convert and may corrupt the data.', E_USER_NOTICE);
        }

        $this->_bitsPerSample = (int)$bitsPerSample;

        $this->setValidBitsPerSample()  // implicit setAudioFormat(), setAudioSubFormat(), setFmtChunkSize(), setFactChunkSize(), setSize(), setActualSize(), setDataOffset()
             ->setByteRate()
             ->setBlockAlign();         // implicit setNumBlocks()

        return $this;
    }

    public function getValidBitsPerSample() {
        return $this->_validBitsPerSample;
    }

    protected function setValidBitsPerSample($validBitsPerSample = null) {
        if (is_null($validBitsPerSample)) {
            $this->_validBitsPerSample = $this->_bitsPerSample;
        } else {
            if ($validBitsPerSample < 1 || $validBitsPerSample > $this->_bitsPerSample) {
                throw new WavFileException('ValidBitsPerSample cannot be greater than BitsPerSample.');
            }
            $this->_validBitsPerSample = (int)$validBitsPerSample;
        }

        $this->setAudioFormat();  // implicit setAudioSubFormat(), setFactChunkSize(), setFmtExtendedSize(), setFmtChunkSize(), setSize(), setActualSize(), setDataOffset()

        return $this;
    }

    public function getBlockAlign() {
        return $this->_blockAlign;
    }

    protected function setBlockAlign($blockAlign = null) {
        if (is_null($blockAlign)) {
            $this->_blockAlign = $this->_numChannels * $this->_bitsPerSample / 8;
        } else {
            $this->_blockAlign = $blockAlign;
        }

        $this->setNumBlocks();

        return $this;
    }

    public function getNumBlocks()
    {
        return $this->_numBlocks;
    }

    protected function setNumBlocks($numBlocks = null) {
        if (is_null($numBlocks)) {
            $this->_numBlocks = (int)($this->_dataSize / $this->_blockAlign);  // do not count incomplete sample blocks
        } else {
            $this->_numBlocks = $numBlocks;
        }

        return $this;
    }

    public function getByteRate() {
        return $this->_byteRate;
    }

    protected function setByteRate($byteRate = null) {
        if (is_null($byteRate)) {
            $this->_byteRate = $this->_sampleRate * $this->_numChannels * $this->_bitsPerSample / 8;
        } else {
            $this->_byteRate = $byteRate;
        }

        return $this;
    }

    public function getSamples() {
        return $this->_samples;
    }

    public function setSamples(&$samples = '') {
        if (strlen($samples) % $this->_blockAlign != 0) {
            throw new WavFileException('Incorrect samples size. Has to be a multiple of BlockAlign.');
        }

        $this->_samples = $samples;

        $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()

        return $this;
    }


    /*%******************************************************************************************%*/
    // Getters

    public function getMinAmplitude()
    {
        if ($this->_bitsPerSample == 8) {
            return 0;
        } elseif ($this->_bitsPerSample == 32) {
            return -1.0;
        } else {
            return -(1 << ($this->_bitsPerSample - 1));
        }
    }

    public function getZeroAmplitude()
    {
        if ($this->_bitsPerSample == 8) {
            return 0x80;
        } elseif ($this->_bitsPerSample == 32) {
            return 0.0;
        } else {
            return 0;
        }
    }

    public function getMaxAmplitude()
    {
        if($this->_bitsPerSample == 8) {
            return 0xFF;
        } elseif($this->_bitsPerSample == 32) {
            return 1.0;
        } else {
            return (1 << ($this->_bitsPerSample - 1)) - 1;
        }
    }


    /*%******************************************************************************************%*/
    // Wave file methods

    /**
     * Construct a wav header from this object. Includes "fact" chunk in necessary.
     * http://www-mmsp.ece.mcgill.ca/documents/audioformats/wave/wave.html
     *
     * @return string  The RIFF header data.
     */
    public function makeHeader()
    {
        // reset and recalculate
        $this->setAudioFormat();                                    // implicit setAudioSubFormat(), setFactChunkSize(), setFmtExtendedSize(), setFmtChunkSize(), setSize(), setActualSize(), setDataOffset()
        $this->setNumBlocks();

        // RIFF header
        $header = pack('N', 0x52494646);                            // ChunkID - "RIFF"
        $header .= pack('V', $this->getChunkSize());                // ChunkSize
        $header .= pack('N', 0x57415645);                           // Format - "WAVE"

        // "fmt " subchunk
        $header .= pack('N', 0x666d7420);                           // SubchunkID - "fmt "
        $header .= pack('V', $this->getFmtChunkSize());             // SubchunkSize
        $header .= pack('v', $this->getAudioFormat());              // AudioFormat
        $header .= pack('v', $this->getNumChannels());              // NumChannels
        $header .= pack('V', $this->getSampleRate());               // SampleRate
        $header .= pack('V', $this->getByteRate());                 // ByteRate
        $header .= pack('v', $this->getBlockAlign());               // BlockAlign
        $header .= pack('v', $this->getBitsPerSample());            // BitsPerSample
        if($this->getFmtExtendedSize() == 24) {
            $header .= pack('v', 22);                               // extension size = 24 bytes, cbSize: 24 - 2 = 22 bytes
            $header .= pack('v', $this->getValidBitsPerSample());   // ValidBitsPerSample
            $header .= pack('V', $this->getChannelMask());          // ChannelMask
            $header .= pack('H32', $this->getAudioSubFormat());     // SubFormat
        } elseif ($this->getFmtExtendedSize() == 2) {
            $header .= pack('v', 0);                                // extension size = 2 bytes, cbSize: 2 - 2 = 0 bytes
        }

        // "fact" subchunk
        if ($this->getFactChunkSize() == 4) {
            $header .= pack('N', 0x66616374);                       // SubchunkID - "fact"
            $header .= pack('V', 4);                                // SubchunkSize
            $header .= pack('V', $this->getNumBlocks());            // SampleLength (per channel)
        }

        return $header;
    }

    /**
     * Construct wav DATA chunk.
     *
     * @return string  The DATA header and chunk.
     */
    public function getDataSubchunk()
    {
        // check preconditions
        if (!$this->_dataSize_valid) {
            $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()
        }


        // create subchunk
        return pack('N', 0x64617461) .                    // SubchunkID - "data"
               pack('V', $this->getDataSize()) .          // SubchunkSize
               $this->_samples .                          // Subchunk data
               ($this->getDataSize() & 1 ? chr(0) : '');  // padding byte
    }

    /**
     * Save the wav data to a file.
     *
     * @param string $filename  (Required) The file path to save the wav to.
     * @throws WavFileException
     */
    public function save($filename)
    {
        $fp = @fopen($filename, 'w+b');
        if (!is_resource($fp)) {
            throw new WavFileException('Failed to open "' . $filename . '" for writing.');
        }

        fwrite($fp, $this->makeHeader());
        fwrite($fp, $this->getDataSubchunk());
        fclose($fp);

        return $this;
    }

    /**
     * Reads a wav header and data from a file.
     *
     * @param string $filename  (Required) The path to the wav file to read.
     * @param bool $readData  (Optional) If true, also read the data chunk.
     * @throws WavFormatException
     * @throws WavFileException
     */
    public function openWav($filename, $readData = true)
    {
        // check preconditions
        if (!file_exists($filename)) {
            throw new WavFileException('Failed to open "' . $filename . '". File not found.');
        } elseif (!is_readable($filename)) {
            throw new WavFileException('Failed to open "' . $filename . '". File is not readable.');
        } elseif (is_resource($this->_fp)) {
            $this->closeWav();
        }


        // open the file
        $this->_fp = @fopen($filename, 'rb');
        if (!is_resource($this->_fp)) {
            throw new WavFileException('Failed to open "' . $filename . '".');
        }

        // read the file
        return $this->readWav($readData);
    }

    /**
     * Close a with openWav() previously opened wav file or free the buffer of setWavData().
     * Not necessary if the data has been read (readData = true) already.
     */
    public function closeWav() {
        if (is_resource($this->_fp)) fclose($this->_fp);

        return $this;
    }

    /**
     * Set the wav file data and properties from a wav file in a string.
     *
     * @param string $data  (Required) The wav file data. Passed by reference.
     * @param bool $free  (Optional) True to free the passed $data after copying.
     * @throws WavFormatException
     * @throws WavFileException
     */
    public function setWavData(&$data, $free = true)
    {
        // check preconditions
        if (is_resource($this->_fp)) $this->closeWav();


        // open temporary stream in memory
        $this->_fp = @fopen('php://memory', 'w+b');
        if (!is_resource($this->_fp)) {
            throw new WavFileException('Failed to open memory stream to write wav data. Use openWav() instead.');
        }

        // prepare stream
        fwrite($this->_fp, $data);
        rewind($this->_fp);

        // free the passed data
        if ($free) $data = null;

        // read the stream like a file
        return $this->readWav(true);
    }

    /**
     * Read wav file from a stream.
     *
     * @param $readData  (Optional) If true, also read the data chunk.
     * @throws WavFormatException
     * @throws WavFileException
     */
    protected function readWav($readData = true)
    {
        if (!is_resource($this->_fp)) {
            throw new WavFileException('No wav file open. Use openWav() first.');
        }

        try {
            $this->readWavHeader();
        } catch (WavFileException $ex) {
            $this->closeWav();
            throw $ex;
        }

        if ($readData) return $this->readWavData();

        return $this;
    }

    /**
     * Parse a wav header.
     * http://www-mmsp.ece.mcgill.ca/documents/audioformats/wave/wave.html
     *
     * @throws WavFormatException
     * @throws WavFileException
     */
    protected function readWavHeader()
    {
        if (!is_resource($this->_fp)) {
            throw new WavFileException('No wav file open. Use openWav() first.');
        }

        // get actual file size
        $stat = fstat($this->_fp);
        $actualSize = $stat['size'];

        $this->_actualSize = $actualSize;


        // read the common header
        $header = fread($this->_fp, 36);  // minimum size of the wav header
        if (strlen($header) < 36) {
            throw new WavFormatException('Not wav format. Header too short.', 1);
        }


        // check "RIFF" header
        $RIFF = unpack('NChunkID/VChunkSize/NFormat', $header);

        if ($RIFF['ChunkID'] != 0x52494646) {  // "RIFF"
            throw new WavFormatException('Not wav format. "RIFF" signature missing.', 2);
        }

        if ($actualSize - 8 < $RIFF['ChunkSize']) {
            trigger_error('"RIFF" chunk size does not match actual file size. Found ' . $RIFF['ChunkSize'] . ', expected ' . ($actualSize - 8) . '.', E_USER_NOTICE);
            $RIFF['ChunkSize'] = $actualSize - 8;
            //throw new WavFormatException('"RIFF" chunk size does not match actual file size. Found ' . $RIFF['ChunkSize'] . ', expected ' . ($actualSize - 8) . '.', 3);
        }

        if ($RIFF['Format'] != 0x57415645) {  // "WAVE"
            throw new WavFormatException('Not wav format. "RIFF" chunk format is not "WAVE".', 4);
        }

        $this->_chunkSize = $RIFF['ChunkSize'];


        // check common "fmt " subchunk
        $fmt = unpack('NSubchunkID/VSubchunkSize/vAudioFormat/vNumChannels/'
                     .'VSampleRate/VByteRate/vBlockAlign/vBitsPerSample',
                     substr($header, 12));

        if ($fmt['SubchunkID'] != 0x666d7420) {  // "fmt "
            throw new WavFormatException('Bad wav header. Expected "fmt " subchunk.', 11);
        }

        if ($fmt['SubchunkSize'] < 16) {
            throw new WavFormatException('Bad "fmt " subchunk size.', 12);
        }

        if (   $fmt['AudioFormat'] != self::WAVE_FORMAT_PCM
            && $fmt['AudioFormat'] != self::WAVE_FORMAT_IEEE_FLOAT
            && $fmt['AudioFormat'] != self::WAVE_FORMAT_EXTENSIBLE)
        {
            throw new WavFormatException('Unsupported audio format. Only PCM or IEEE FLOAT (EXTENSIBLE) audio is supported.', 13);
        }

        if ($fmt['NumChannels'] < 1 || $fmt['NumChannels'] > self::MAX_CHANNEL) {
            throw new WavFormatException('Invalid number of channels in "fmt " subchunk.', 14);
        }

        if ($fmt['SampleRate'] < 1 || $fmt['SampleRate'] > self::MAX_SAMPLERATE) {
            throw new WavFormatException('Invalid sample rate in "fmt " subchunk.', 15);
        }

        if (   ($fmt['AudioFormat'] == self::WAVE_FORMAT_PCM && !in_array($fmt['BitsPerSample'], array(8, 16, 24)))
            || ($fmt['AudioFormat'] == self::WAVE_FORMAT_IEEE_FLOAT && $fmt['BitsPerSample'] != 32)
            || ($fmt['AudioFormat'] == self::WAVE_FORMAT_EXTENSIBLE && !in_array($fmt['BitsPerSample'], array(8, 16, 24, 32))))
        {
            throw new WavFormatException('Only 8, 16 and 24-bit PCM and 32-bit IEEE FLOAT (EXTENSIBLE) audio is supported.', 16);
        }

        $blockAlign = $fmt['NumChannels'] * $fmt['BitsPerSample'] / 8;
        if ($blockAlign != $fmt['BlockAlign']) {
            trigger_error('Invalid block align in "fmt " subchunk. Found ' . $fmt['BlockAlign'] . ', expected ' . $blockAlign . '.', E_USER_NOTICE);
            $fmt['BlockAlign'] = $blockAlign;
            //throw new WavFormatException('Invalid block align in "fmt " subchunk. Found ' . $fmt['BlockAlign'] . ', expected ' . $blockAlign . '.', 17);
        }

        $byteRate = $fmt['SampleRate'] * $blockAlign;
        if ($byteRate != $fmt['ByteRate']) {
            trigger_error('Invalid average byte rate in "fmt " subchunk. Found ' . $fmt['ByteRate'] . ', expected ' . $byteRate . '.', E_USER_NOTICE);
            $fmt['ByteRate'] = $byteRate;
            //throw new WavFormatException('Invalid average byte rate in "fmt " subchunk. Found ' . $fmt['ByteRate'] . ', expected ' . $byteRate . '.', 18);
        }

        $this->_fmtChunkSize  = $fmt['SubchunkSize'];
        $this->_audioFormat   = $fmt['AudioFormat'];
        $this->_numChannels   = $fmt['NumChannels'];
        $this->_sampleRate    = $fmt['SampleRate'];
        $this->_byteRate      = $fmt['ByteRate'];
        $this->_blockAlign    = $fmt['BlockAlign'];
        $this->_bitsPerSample = $fmt['BitsPerSample'];


        // read extended "fmt " subchunk data
        $extendedFmt = '';
        if ($fmt['SubchunkSize'] > 16) {
            // possibly handle malformed subchunk without a padding byte
            $extendedFmt = fread($this->_fp, $fmt['SubchunkSize'] - 16 + ($fmt['SubchunkSize'] & 1));  // also read padding byte
            if (strlen($extendedFmt) < $fmt['SubchunkSize'] - 16) {
                throw new WavFormatException('Not wav format. Header too short.', 1);
            }
        }


        // check extended "fmt " for EXTENSIBLE Audio Format
        if ($fmt['AudioFormat'] == self::WAVE_FORMAT_EXTENSIBLE) {
            if (strlen($extendedFmt) < 24) {
                throw new WavFormatException('Invalid EXTENSIBLE "fmt " subchunk size. Found ' . $fmt['SubchunkSize'] . ', expected at least 40.', 19);
            }

            $extensibleFmt = unpack('vSize/vValidBitsPerSample/VChannelMask/H32SubFormat', substr($extendedFmt, 0, 24));

            if (   $extensibleFmt['SubFormat'] != self::WAVE_SUBFORMAT_PCM
                && $extensibleFmt['SubFormat'] != self::WAVE_SUBFORMAT_IEEE_FLOAT)
            {
                throw new WavFormatException('Unsupported audio format. Only PCM or IEEE FLOAT (EXTENSIBLE) audio is supported.', 13);
            }

            if (   ($extensibleFmt['SubFormat'] == self::WAVE_SUBFORMAT_PCM && !in_array($fmt['BitsPerSample'], array(8, 16, 24)))
                || ($extensibleFmt['SubFormat'] == self::WAVE_SUBFORMAT_IEEE_FLOAT && $fmt['BitsPerSample'] != 32))
            {
                throw new WavFormatException('Only 8, 16 and 24-bit PCM and 32-bit IEEE FLOAT (EXTENSIBLE) audio is supported.', 16);
            }

            if ($extensibleFmt['Size'] != 22) {
                trigger_error('Invaid extension size in EXTENSIBLE "fmt " subchunk.', E_USER_NOTICE);
                $extensibleFmt['Size'] = 22;
                //throw new WavFormatException('Invaid extension size in EXTENSIBLE "fmt " subchunk.', 20);
            }

            if ($extensibleFmt['ValidBitsPerSample'] != $fmt['BitsPerSample']) {
                trigger_error('Invaid or unsupported valid bits per sample in EXTENSIBLE "fmt " subchunk.', E_USER_NOTICE);
                $extensibleFmt['ValidBitsPerSample'] = $fmt['BitsPerSample'];
                //throw new WavFormatException('Invaid or unsupported valid bits per sample in EXTENSIBLE "fmt " subchunk.', 21);
            }

            if ($extensibleFmt['ChannelMask'] != 0) {
                // count number of set bits - Hamming weight
                $c = (int)$extensibleFmt['ChannelMask'];
                $n = 0;
                while ($c > 0) {
                    $n += $c & 1;
                    $c >>= 1;
                }
                if ($n != $fmt['NumChannels'] || (((int)$extensibleFmt['ChannelMask'] | self::SPEAKER_ALL) != self::SPEAKER_ALL)) {
                    trigger_error('Invalid channel mask in EXTENSIBLE "fmt " subchunk. The number of channels does not match the number of locations in the mask.', E_USER_NOTICE);
                    $extensibleFmt['ChannelMask'] = 0;
                    //throw new WavFormatException('Invalid channel mask in EXTENSIBLE "fmt " subchunk. The number of channels does not match the number of locations in the mask.', 22);
                }
            }

            $this->_fmtExtendedSize    = strlen($extendedFmt);
            $this->_validBitsPerSample = $extensibleFmt['ValidBitsPerSample'];
            $this->_channelMask        = $extensibleFmt['ChannelMask'];
            $this->_audioSubFormat     = $extensibleFmt['SubFormat'];

        } else {
            $this->_fmtExtendedSize    = strlen($extendedFmt);
            $this->_validBitsPerSample = $fmt['BitsPerSample'];
            $this->_channelMask        = 0;
            $this->_audioSubFormat     = null;
        }


        // read additional subchunks until "data" subchunk is found
        $factSubchunk = array();
        $dataSubchunk = array();

        while (!feof($this->_fp)) {
            $subchunkHeader = fread($this->_fp, 8);
            if (strlen($subchunkHeader) < 8) {
                throw new WavFormatException('Missing "data" subchunk.', 101);
            }

            $subchunk = unpack('NSubchunkID/VSubchunkSize', $subchunkHeader);

            if ($subchunk['SubchunkID'] == 0x66616374) {        // "fact"
                // possibly handle malformed subchunk without a padding byte
                $subchunkData = fread($this->_fp, $subchunk['SubchunkSize'] + ($subchunk['SubchunkSize'] & 1));  // also read padding byte
                if (strlen($subchunkData) < 4) {
                    throw new WavFormatException('Invalid "fact" subchunk.', 102);
                }

                $factParams = unpack('VSampleLength', substr($subchunkData, 0, 4));
                $factSubchunk = array_merge($subchunk, $factParams);

            } elseif ($subchunk['SubchunkID'] == 0x64617461) {  // "data"
                $dataSubchunk = $subchunk;

                break;

            } elseif ($subchunk['SubchunkID'] == 0x7761766C) {  // "wavl"
                throw new WavFormatException('Wave List Chunk ("wavl" subchunk) is not supported.', 106);
            } else {
                // skip all other (unknown) subchunks
                // possibly handle malformed subchunk without a padding byte
                if ( $subchunk['SubchunkSize'] < 0
                  || fseek($this->_fp, $subchunk['SubchunkSize'] + ($subchunk['SubchunkSize'] & 1), SEEK_CUR) !== 0) {  // also skip padding byte
                    throw new WavFormatException('Invalid subchunk (0x' . dechex($subchunk['SubchunkID']) . ') encountered.', 103);
                }
            }
        }

        if (empty($dataSubchunk)) {
            throw new WavFormatException('Missing "data" subchunk.', 101);
        }


        // check "data" subchunk
        $dataOffset = ftell($this->_fp);
        if ($dataSubchunk['SubchunkSize'] < 0 || $actualSize - $dataOffset < $dataSubchunk['SubchunkSize']) {
            trigger_error('Invalid "data" subchunk size.', E_USER_NOTICE);
            $dataSubchunk['SubchunkSize'] = $actualSize - $dataOffset;
            //throw new WavFormatException('Invalid "data" subchunk size.', 104);
        }

        $this->_dataOffset     = $dataOffset;
        $this->_dataSize       = $dataSubchunk['SubchunkSize'];
        $this->_dataSize_fp    = $dataSubchunk['SubchunkSize'];
        $this->_dataSize_valid = false;
        $this->_samples        = '';


        // check "fact" subchunk
        $numBlocks = (int)($dataSubchunk['SubchunkSize'] / $fmt['BlockAlign']);

        if (empty($factSubchunk)) {  // construct fake "fact" subchunk
            $factSubchunk = array('SubchunkSize' => 0, 'SampleLength' => $numBlocks);
        }

        if ($factSubchunk['SampleLength'] != $numBlocks) {
            trigger_error('Invalid sample length in "fact" subchunk.', E_USER_NOTICE);
            $factSubchunk['SampleLength'] = $numBlocks;
            //throw new WavFormatException('Invalid sample length in "fact" subchunk.', 105);
        }

        $this->_factChunkSize = $factSubchunk['SubchunkSize'];
        $this->_numBlocks     = $factSubchunk['SampleLength'];


        return $this;

    }

    /**
     * Read the wav data from the file into the buffer.
     *
     * @param $dataOffset  (Optional) The byte offset to skip before starting to read. Must be a multiple of BlockAlign.
     * @param $dataSize  (Optional) The size of the data to read in bytes. Must be a multiple of BlockAlign. Defaults to all data.
     * @throws WavFileException
     */
    public function readWavData($dataOffset = 0, $dataSize = null)
    {
        // check preconditions
        if (!is_resource($this->_fp)) {
            throw new WavFileException('No wav file open. Use openWav() first.');
        }

        if ($dataOffset < 0 || $dataOffset % $this->getBlockAlign() > 0) {
            throw new WavFileException('Invalid data offset. Has to be a multiple of BlockAlign.');
        }

        if (is_null($dataSize)) {
            $dataSize = $this->_dataSize_fp - ($this->_dataSize_fp % $this->getBlockAlign());  // only read complete blocks
        } elseif ($dataSize < 0 || $dataSize % $this->getBlockAlign() > 0) {
            throw new WavFileException('Invalid data size to read. Has to be a multiple of BlockAlign.');
        }


        // skip offset
        if ($dataOffset > 0 && fseek($this->_fp, $dataOffset, SEEK_CUR) !== 0) {
            throw new WavFileException('Seeking to data offset failed.');
        }

        // read data
        $this->_samples .= fread($this->_fp, $dataSize);  // allow appending
        $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()

        // close file or memory stream
        return $this->closeWav();
    }


    /*%******************************************************************************************%*/
    // Sample manipulation methods

    /**
     * Return a single sample block from the file.
     *
     * @param int $blockNum  (Required) The sample block number. Zero based.
     * @return string  The binary sample block (all channels). Returns null if the sample block number was out of range.
     */
    public function getSampleBlock($blockNum)
    {
        // check preconditions
        if (!$this->_dataSize_valid) {
            $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()
        }

        $offset = $blockNum * $this->_blockAlign;
        if ($offset + $this->_blockAlign > $this->_dataSize || $offset < 0) {
            return null;
        }


        // read data
        return substr($this->_samples, $offset, $this->_blockAlign);
    }

    /**
     * Set a single sample block. <br />
     * Allows to append a sample block.
     *
     * @param string $sampleBlock  (Required) The binary sample block (all channels).
     * @param int $blockNum  (Required) The sample block number. Zero based.
     * @throws WavFileException
     */
    public function setSampleBlock($sampleBlock, $blockNum)
    {
        // check preconditions
        $blockAlign = $this->_blockAlign;
        if (!isset($sampleBlock[$blockAlign - 1]) || isset($sampleBlock[$blockAlign])) {  // faster than: if (strlen($sampleBlock) != $blockAlign)
            throw new WavFileException('Incorrect sample block size. Got ' . strlen($sampleBlock) . ', expected ' . $blockAlign . '.');
        }

        if (!$this->_dataSize_valid) {
            $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()
        }

        $numBlocks = (int)($this->_dataSize / $blockAlign);
        $offset = $blockNum * $blockAlign;
        if ($blockNum > $numBlocks || $blockNum < 0) {  // allow appending
            throw new WavFileException('Sample block number is out of range.');
        }


        // replace or append data
        if ($blockNum == $numBlocks) {
            // append
            $this->_samples    .= $sampleBlock;
            $this->_dataSize   += $blockAlign;
            $this->_chunkSize  += $blockAlign;
            $this->_actualSize += $blockAlign;
            $this->_numBlocks++;
        } else {
            // replace
            for ($i = 0; $i < $blockAlign; ++$i) {
                $this->_samples[$offset + $i] = $sampleBlock[$i];
            }
        }

        return $this;
    }

    /**
     * Get a float sample value for a specific sample block and channel number.
     *
     * @param int $blockNum  (Required) The sample block number to fetch. Zero based.
     * @param int $channelNum  (Required) The channel number within the sample block to fetch. First channel is 1.
     * @return float  The float sample value. Returns null if the sample block number was out of range.
     * @throws WavFileException
     */
    public function getSampleValue($blockNum, $channelNum)
    {
        // check preconditions
        if ($channelNum < 1 || $channelNum > $this->_numChannels) {
            throw new WavFileException('Channel number is out of range.');
        }

        if (!$this->_dataSize_valid) {
            $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()
        }

        $sampleBytes = $this->_bitsPerSample / 8;
        $offset = $blockNum * $this->_blockAlign + ($channelNum - 1) * $sampleBytes;
        if ($offset + $sampleBytes > $this->_dataSize || $offset < 0) {
            return null;
        }

        // read binary value
        $sampleBinary = substr($this->_samples, $offset, $sampleBytes);

        // convert binary to value
        switch ($this->_bitsPerSample) {
            case 8:
                // unsigned char
                return (float)((ord($sampleBinary) - 0x80) / 0x80);

            case 16:
                // signed short, little endian
                $data = unpack('v', $sampleBinary);
                $sample = $data[1];
                if ($sample >= 0x8000) {
                    $sample -= 0x10000;
                }
                return (float)($sample / 0x8000);

            case 24:
                // 3 byte packed signed integer, little endian
                $data = unpack('C3', $sampleBinary);
                $sample = $data[1] | ($data[2] << 8) | ($data[3] << 16);
                if ($sample >= 0x800000) {
                    $sample -= 0x1000000;
                }
                return (float)($sample / 0x800000);

            case 32:
                // 32-bit float
                $data = unpack('f', $sampleBinary);
                return (float)$data[1];

            default:
                return null;
        }
    }

    /**
     * Sets a float sample value for a specific sample block number and channel. <br />
     * Converts float values to appropriate integer values and clips properly. <br />
     * Allows to append samples (in order).
     *
     * @param float $sampleFloat  (Required) The float sample value to set. Converts float values and clips if necessary.
     * @param int $blockNum  (Required) The sample block number to set or append. Zero based.
     * @param int $channelNum  (Required) The channel number within the sample block to set or append. First channel is 1.
     * @throws WavFileException
     */
    public function setSampleValue($sampleFloat, $blockNum, $channelNum)
    {
        // check preconditions
        if ($channelNum < 1 || $channelNum > $this->_numChannels) {
            throw new WavFileException('Channel number is out of range.');
        }

        if (!$this->_dataSize_valid) {
            $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()
        }

        $dataSize = $this->_dataSize;
        $bitsPerSample = $this->_bitsPerSample;
        $sampleBytes = $bitsPerSample / 8;
        $offset = $blockNum * $this->_blockAlign + ($channelNum - 1) * $sampleBytes;
        if (($offset + $sampleBytes > $dataSize && $offset != $dataSize) || $offset < 0) { // allow appending
            throw new WavFileException('Sample block or channel number is out of range.');
        }


        // convert to value, quantize and clip
        if ($bitsPerSample == 32) {
            $sample = $sampleFloat < -1.0 ? -1.0 : ($sampleFloat > 1.0 ? 1.0 : $sampleFloat);
        } else {
            $p = 1 << ($bitsPerSample - 1); // 2 to the power of _bitsPerSample divided by 2

            // project and quantize (round) float to integer values
            $sample = $sampleFloat < 0 ? (int)($sampleFloat * $p - 0.5) : (int)($sampleFloat * $p + 0.5);

            // clip if necessary to [-$p, $p - 1]
            if ($sample < -$p) {
                $sample = -$p;
            } elseif ($sample > $p - 1) {
                $sample = $p - 1;
            }
        }

        // convert to binary
        switch ($bitsPerSample) {
            case 8:
                // unsigned char
                $sampleBinary = chr($sample + 0x80);
                break;

            case 16:
                // signed short, little endian
                if ($sample < 0) {
                    $sample += 0x10000;
                }
                $sampleBinary = pack('v', $sample);
                break;

            case 24:
                // 3 byte packed signed integer, little endian
                if ($sample < 0) {
                    $sample += 0x1000000;
                }
                $sampleBinary = pack('C3', $sample & 0xff, ($sample >>  8) & 0xff, ($sample >> 16) & 0xff);
                break;

            case 32:
                // 32-bit float
                $sampleBinary = pack('f', $sample);
                break;

            default:
                $sampleBinary = null;
                $sampleBytes = 0;
                break;
        }

        // replace or append data
        if ($offset == $dataSize) {
            // append
            $this->_samples    .= $sampleBinary;
            $this->_dataSize   += $sampleBytes;
            $this->_chunkSize  += $sampleBytes;
            $this->_actualSize += $sampleBytes;
            $this->_numBlocks = (int)($this->_dataSize / $this->_blockAlign);
        } else {
            // replace
            for ($i = 0; $i < $sampleBytes; ++$i) {
                $this->_samples{$offset + $i} = $sampleBinary{$i};
            }
        }

        return $this;
    }


    /*%******************************************************************************************%*/
    // Audio processing methods

    /**
     * Run samples through audio processing filters.
     *
     * <code>
     * $wav->filter(
     *      array(
     *          WavFile::FILTER_MIX => array(          // Filter for mixing 2 WavFile instances.
     *              'wav' => $wav2,                    // (Required) The WavFile to mix into this WhavFile. If no optional arguments are given, can be passed without the array.
     *              'loop' => true,                    // (Optional) Loop the selected portion (with warping to the beginning at the end).
     *              'blockOffset' => 0,                // (Optional) Block number to start mixing from.
     *              'numBlocks' => null                // (Optional) Number of blocks to mix in or to select for looping. Defaults to the end or all data for looping.
     *          ),
     *          WavFile::FILTER_NORMALIZE => 0.6,      // (Required) Normalization of (mixed) audio samples - see threshold parameter for normalizeSample().
     *          WavFile::FILTER_DEGRADE => 0.9         // (Required) Introduce random noise. The quality relative to the amplitude. 1 = no noise, 0 = max. noise.
     *      ),
     *      0,                                         // (Optional) The block number of this WavFile to start with.
     *      null                                       // (Optional) The number of blocks to process.
     *  );
     *  </code>
     *
     * @param array $filters  (Required) An array of 1 or more audio processing filters.
     * @param int $blockOffset  (Optional) The block number to start precessing from.
     * @param int $numBlocks  (Optional) The maximum  number of blocks to process.
     * @throws WavFileException
     */
    public function filter($filters, $blockOffset = 0, $numBlocks = null)
    {
        // check preconditions
        $totalBlocks = $this->getNumBlocks();
        $numChannels = $this->getNumChannels();
        if (is_null($numBlocks)) $numBlocks = $totalBlocks - $blockOffset;

        if (!is_array($filters) || empty($filters) || $blockOffset < 0 || $blockOffset > $totalBlocks || $numBlocks <= 0) {
            // nothing to do
            return $this;
        }

        // check filtes
        $filter_mix = false;
        if (array_key_exists(self::FILTER_MIX, $filters)) {
            if (!is_array($filters[self::FILTER_MIX])) {
                // assume the 'wav' parameter
                $filters[self::FILTER_MIX] = array('wav' => $filters[self::FILTER_MIX]);
            }

            $mix_wav = @$filters[self::FILTER_MIX]['wav'];
            if (!($mix_wav instanceof WavFile)) {
                throw new WavFileException("WavFile to mix is missing or invalid.");
            } elseif ($mix_wav->getSampleRate() != $this->getSampleRate()) {
                throw new WavFileException("Sample rate of WavFile to mix does not match.");
            } else if ($mix_wav->getNumChannels() != $this->getNumChannels()) {
                throw new WavFileException("Number of channels of WavFile to mix does not match.");
            }

            $mix_loop = @$filters[self::FILTER_MIX]['loop'];
            if (is_null($mix_loop)) $mix_loop = false;

            $mix_blockOffset = @$filters[self::FILTER_MIX]['blockOffset'];
            if (is_null($mix_blockOffset)) $mix_blockOffset = 0;

            $mix_totalBlocks = $mix_wav->getNumBlocks();
            $mix_numBlocks = @$filters[self::FILTER_MIX]['numBlocks'];
            if (is_null($mix_numBlocks)) $mix_numBlocks = $mix_loop ? $mix_totalBlocks : $mix_totalBlocks - $mix_blockOffset;
            $mix_maxBlock = min($mix_blockOffset + $mix_numBlocks, $mix_totalBlocks);

            $filter_mix = true;
        }

        $filter_normalize = false;
        if (array_key_exists(self::FILTER_NORMALIZE, $filters)) {
            $normalize_threshold = @$filters[self::FILTER_NORMALIZE];

            if (!is_null($normalize_threshold) && abs($normalize_threshold) != 1) $filter_normalize = true;
        }

        $filter_degrade = false;
        if (array_key_exists(self::FILTER_DEGRADE, $filters)) {
            $degrade_quality = @$filters[self::FILTER_DEGRADE];
            if (is_null($degrade_quality)) $degrade_quality = 1;

            if ($degrade_quality >= 0 && $degrade_quality < 1) $filter_degrade = true;
        }


        // loop through all sample blocks
        for ($block = 0; $block < $numBlocks; ++$block) {
            // loop through all channels
            for ($channel = 1; $channel <= $numChannels; ++$channel) {
                // read current sample
                $currentBlock = $blockOffset + $block;
                $sampleFloat = $this->getSampleValue($currentBlock, $channel);


                /************* MIX FILTER ***********************/
                if ($filter_mix) {
                    if ($mix_loop) {
                        $mixBlock = ($mix_blockOffset + ($block % $mix_numBlocks)) % $mix_totalBlocks;
                    } else {
                        $mixBlock = $mix_blockOffset + $block;
                    }

                    if ($mixBlock < $mix_maxBlock) {
                        $sampleFloat += $mix_wav->getSampleValue($mixBlock, $channel);
                    }
                }

                /************* NORMALIZE FILTER *******************/
                if ($filter_normalize) {
                    $sampleFloat = $this->normalizeSample($sampleFloat, $normalize_threshold);
                }

                /************* DEGRADE FILTER *******************/
                if ($filter_degrade) {
                    $sampleFloat += rand(1000000 * ($degrade_quality - 1), 1000000 * (1 - $degrade_quality)) / 1000000;
                }


                // write current sample
                $this->setSampleValue($sampleFloat, $currentBlock, $channel);
            }
        }

        return $this;
    }

    /**
     * Append a wav file to the current wav. <br />
     * The wav files must have the same sample rate, number of bits per sample, and number of channels.
     *
     * @param WavFile $wav  (Required) The wav file to append.
     * @throws WavFileException
     */
    public function appendWav(WavFile $wav) {
        // basic checks
        if ($wav->getSampleRate() != $this->getSampleRate()) {
            throw new WavFileException("Sample rate for wav files do not match.");
        } else if ($wav->getBitsPerSample() != $this->getBitsPerSample()) {
            throw new WavFileException("Bits per sample for wav files do not match.");
        } else if ($wav->getNumChannels() != $this->getNumChannels()) {
            throw new WavFileException("Number of channels for wav files do not match.");
        }

        $this->_samples .= $wav->_samples;
        $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()

        return $this;
    }

    /**
     * Mix 2 wav files together. <br />
     * Both wavs must have the same sample rate and same number of channels.
     *
     * @param WavFile $wav  (Required) The WavFile to mix.
     * @param float $normalizeThreshold  (Optional) See normalizeSample for an explanation.
     * @throws WavFileException
     */
    public function mergeWav(WavFile $wav, $normalizeThreshold = null) {
        return $this->filter(array(
            WavFile::FILTER_MIX       => $wav,
            WavFile::FILTER_NORMALIZE => $normalizeThreshold
        ));
    }

    /**
     * Add silence to the wav file.
     *
     * @param float $duration  (Optional) How many seconds of silence. If negative, add to the beginning of the file. Defaults to 1s.
     */
    public function insertSilence($duration = 1.0)
    {
        $numSamples  = (int)($this->getSampleRate() * abs($duration));
        $numChannels = $this->getNumChannels();

        $data = str_repeat(self::packSample($this->getZeroAmplitude(), $this->getBitsPerSample()), $numSamples * $numChannels);
        if ($duration >= 0) {
            $this->_samples .= $data;
        } else {
            $this->_samples = $data . $this->_samples;
        }

        $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()

        return $this;
    }

    /**
     * Degrade the quality of the wav file by introducing random noise.
     *
     * @param float quality  (Optional) The quality relative to the amplitude. 1 = no noise, 0 = max. noise.
     */
    public function degrade($quality = 1.0)
    {
        return $this->filter(self::FILTER_DEGRADE, array(
            WavFile::FILTER_DEGRADE => $quality
        ));
    }

    /**
     * Generate noise at the end of the wav for the specified duration and volume.
     *
     * @param float $duration  (Optional) Number of seconds of noise to generate.
     * @param float $percent  (Optional) The percentage of the maximum amplitude to use. 100 = full amplitude.
     */
    public function generateNoise($duration = 1.0, $percent = 100)
    {
        $numChannels = $this->getNumChannels();
        $numSamples  = $this->getSampleRate() * $duration;
        $minAmp      = $this->getMinAmplitude();
        $maxAmp      = $this->getMaxAmplitude();
        $bitDepth    = $this->getBitsPerSample();

        for ($s = 0; $s < $numSamples; ++$s) {
            if ($bitDepth == 32) {
                $val = rand(-$percent * 10000, $percent * 10000) / 1000000;
            } else {
                $val = rand($minAmp, $maxAmp);
                $val = (int)($val * $percent / 100);
            }

            $this->_samples .= str_repeat(self::packSample($val, $bitDepth), $numChannels);
        }

        $this->setDataSize();  // implicit setSize(), setActualSize(), setNumBlocks()

        return $this;
    }

    /**
     * Convert sample data to different bits per sample.
     *
     * @param int $bitsPerSample  (Required) The new number of bits per sample;
     * @throws WavFileException
     */
    public function convertBitsPerSample($bitsPerSample) {
        if ($this->getBitsPerSample() == $bitsPerSample) {
            return $this;
        }

        $tempWav = new WavFile($this->getNumChannels(), $this->getSampleRate(), $bitsPerSample);
        $tempWav->filter(
            array(self::FILTER_MIX => $this),
            0,
            $this->getNumBlocks()
        );

        $this->setSamples()                       // implicit setDataSize(), setSize(), setActualSize(), setNumBlocks()
             ->setBitsPerSample($bitsPerSample);  // implicit setValidBitsPerSample(), setAudioFormat(), setAudioSubFormat(), setFmtChunkSize(), setFactChunkSize(), setSize(), setActualSize(), setDataOffset(), setByteRate(), setBlockAlign(), setNumBlocks()
        $this->_samples = $tempWav->_samples;
        $this->setDataSize();                     // implicit setSize(), setActualSize(), setNumBlocks()

        return $this;
    }


    /*%******************************************************************************************%*/
    // Miscellaneous methods

    /**
     * Output information about the wav object.
     */
    public function displayInfo()
    {
        $s = "File Size: %u\n"
            ."Chunk Size: %u\n"
            ."fmt Subchunk Size: %u\n"
            ."Extended fmt Size: %u\n"
            ."fact Subchunk Size: %u\n"
            ."Data Offset: %u\n"
            ."Data Size: %u\n"
            ."Audio Format: %s\n"
            ."Audio SubFormat: %s\n"
            ."Channels: %u\n"
            ."Channel Mask: 0x%s\n"
            ."Sample Rate: %u\n"
            ."Bits Per Sample: %u\n"
            ."Valid Bits Per Sample: %u\n"
            ."Sample Block Size: %u\n"
            ."Number of Sample Blocks: %u\n"
            ."Byte Rate: %uBps\n";

        $s = sprintf($s, $this->getActualSize(),
                         $this->getChunkSize(),
                         $this->getFmtChunkSize(),
                         $this->getFmtExtendedSize(),
                         $this->getFactChunkSize(),
                         $this->getDataOffset(),
                         $this->getDataSize(),
                         $this->getAudioFormat() == self::WAVE_FORMAT_PCM ? 'PCM' : ($this->getAudioFormat() == self::WAVE_FORMAT_IEEE_FLOAT ? 'IEEE FLOAT' : 'EXTENSIBLE'),
                         $this->getAudioSubFormat() == self::WAVE_SUBFORMAT_PCM ? 'PCM' : 'IEEE FLOAT',
                         $this->getNumChannels(),
                         dechex($this->getChannelMask()),
                         $this->getSampleRate(),
                         $this->getBitsPerSample(),
                         $this->getValidBitsPerSample(),
                         $this->getBlockAlign(),
                         $this->getNumBlocks(),
                         $this->getByteRate());

        if (php_sapi_name() == 'cli') {
            return $s;
        } else {
            return nl2br($s);
        }
    }
}


/*%******************************************************************************************%*/
// Exceptions

/**
 * WavFileException indicates an illegal state or argument in this class.
 */
class WavFileException extends Exception {}

/**
 * WavFormatException indicates a malformed or unsupported wav file header.
 */
class WavFormatException extends WavFileException {}