Question

我使用此功能在php中生成wav摇摆音：

$samples = array();
$amplitude = 8192;
$sampleRate = 8000;
$samplesCount = 300000;


for ($n = 0; $n < $samplesCount; $n++) {


    $freqOfTone= 4*sin($n*0.00628)+440;

    $w = 2 * pi() * $freqOfTone / $sampleRate;
    $samples[$n] = (int)($amplitude *  sin($n * $w));



}

但是生成的声音并不是一个持续不断的晃动而是上升......（你可以在那里听到：Sound Link

有谁知道为什么？

谢谢

Answer 1

并没有以同样的方式解决问题，但我花了一些时间与互联网上奇怪的数学角落一起玩，以帮助消除三角关闭。 This帮助我了解它。

无论如何，这就是我正在玩的东西（无论是放大器还是fm mod，我都可以使用它几个小时）：

<?php   

$bps = 16; // bits/s
$Bps = $bps / 8; // byte/s
$duration = 30; // Seconds
$frequency = 440; // Hz
$amplitude = 8192;  

$samples = array();
$sampleRate = 44100;
$samplesCount = $sampleRate * $duration;    

for ($n = 0; $n <= $samplesCount; $n++)
{
    // Time
    $t = $n / $sampleRate;  

    // Freq Mod
    $mod = 0.1 * sin(2 * M_PI * $frequency * $t * 0.00628); 

    // Wave
    $w = $amplitude * sin(2 * M_PI * $frequency * ($t + $mod)); 

    // Amplitude Mod
    ($n / ($sampleRate / 10) % 2 == 0) ? $amplitude-- : $amplitude++;   

    $samples[] = (int)$w;
}   

$str = call_user_func_array("pack",
    array_merge(array("VVVVVvvVVvvVVv*"),
        array(// header
            0x46464952, // RIFF
            ($samplesCount * 2) + 44 - 8, // Filesize
            0x45564157, // WAVE
            0x20746d66, // "fmt " (chunk)
            16, // chunk size
            1, // compression (2 byte iteger)
            1, // nchannels
            $sampleRate, // sample rate
            $sampleRate * $Bps, //bytes/second
            $Bps, //block align
            $bps, //bits/sample
            0x61746164, //"data"
            $samplesCount * 2 // samples * compressed int
        ),
        $samples //data
    )
);  

// echo print_r($samples) . PHP_EOL;
$myfile = fopen("/tmp/sine.wav", "wb") or die("Unable to open file!");
fwrite($myfile, $str);
fclose($myfile);

PHP罪恶功能上升

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