Generate WAV and add a second (stereo) channel

Question

I found the following incedibly code on stackoverflow. Please can anybody help me adding a second channel (stereo)

There will be nchannels = 2 The file size must (somehow) be increased and the 2. array (i.e. samples2) must be added.

When I try I only achieve a higher frequency.

Thanks alot from germany : Martin

$freqOfTone = 440;
$sampleRate = 44100;
$samplesCount = 80000;

$amplitude = 0.25 * 32768;
$w = 2 * pi() * $freqOfTone / $sampleRate;

$samples = array();
for ($n = 0; $n < $samplesCount; $n++) {
$samples[] = (int)($amplitude *  sin($n * $w));
}

$srate = 44100; //sample rate
$bps = 16; //bits per sample
$Bps = $bps/8; //bytes per sample /// I EDITED

$str = call_user_func_array("pack",
array_merge(array("VVVVVvvVVvvVVv*"),
    array(//header
        0x46464952, //RIFF
        160038,      //File size
        0x45564157, //WAVE
        0x20746d66, //"fmt " (chunk)
        16, //chunk size
        1, //compression
        1, //nchannels
        $srate, //sample rate
        $Bps*$srate, //bytes/second
        $Bps, //block align
        $bps, //bits/sample
        0x61746164, //"data"
        160000 //chunk size
    ),
    $samples //data
)
);
$myfile = fopen("sine.wav", "wb") or die("Unable to open file!");
fwrite($myfile, $str);

Don't worry :D takes time and I remember starting out myself. Enjoy! — Bugs, Jun 30 '17 at 19:21

score 0 · Answer 1 · answered Jun 30 '17 at 19:06

Moved solution from question to answer:

SELF SOLUTION: I checked the recorder.js Web Worker, found the SPEC and how to use it. Here is a slightly modified code for a tone going from the right speaker to the left in 1 sec. Maybe it helps somebody.

$freqOfTone = 440;
$sampleRate = 44100;
$samplesCount = 80000;

$amplitude = 0.25 * 32768;
$w = 2 * pi() * $freqOfTone / $sampleRate;

$samples = array();
$samples2 = array();
for ($n = 0; $n < $samplesCount; $n++) {
    $samples[] = (int)($amplitude*($n/$samplesCount) *  sin($n * $w));
    $samples2[] = (int)($amplitude*(1-$n/$samplesCount) *  sin($n * $w ));
}

function interleave($l,$r){
 $data=array();
$ix=0;
for($i=0;$i<count($l);$i++){
   $data[$ix++]=$l[$i];
   $data[$ix++]=$r[$i];
 }
 return $data;
}

$stereo=interleave($samples,$samples2);


echo(count($samples));
echo(count($stereo));

$srate = 44100; //sample rate
$bps = 16; //bits per sample
$Bps = $bps/8; //bytes per sample /// I EDITED


$samples_merge=array_merge($samples,$samples2);

$str = call_user_func_array("pack",
    array_merge(array("VVVVVvvVVvvVVv*"),
       array(//header
          0x46464952, //RIFF
           80000*2*2+36,      //File size  *2*Channels +36
        0x45564157, //WAVE
        0x20746d66, //"fmt " (chunk)
        16, //chunk size
        1, //compression
        2, //nchannels
        $srate, //sample rate
        $Bps*$srate, //bytes/second
        $Bps, //block align
        $bps, //bits/sample
        0x61746164, //"data"
        80000 * 2 *2 //chunk size (filesize * 2 *Channels)
    ),
    $stereo // Stereo tone left[0], right[0], left[1], right[1], ...
)
);
$myfile = fopen("sine.wav", "wb") or die("Unable to open file!");
fwrite($myfile, $str);
fclose($myfile);

Generate WAV and add a second (stereo) channel

1 Answers1