How create .wav file with a custom frequency tone

问题:

I have a problem with my wave generator. I'm trying to create a .wav file with sound of given frequency. The code I use:

$freqOfTone = 21000;
$sampleRate = 44100;
$samplesCount = 80000;

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

for ($n = 0; $n < $samplesCount; $n++)
{
    $data->samples[1][] = 32768 + (int)($amplitude *  sin($n * $w));
}

Unfortunately, the output wave is incorrect, I get few frequencies instead of one: http://i49.tinypic.com/ab1nx0.png

It should look like this: http://i50.tinypic.com/33zbslk.png

Where am I doing something wrong? :(

回答1:

Given that sample rate, the desired frequency is too close to the Nyquist frequency to be sampled properly. I recommend you use a sample rate of 96kHz for this.

回答2:

I have achieved something finaly, but my solution is a little bit different from this which I meant... Anyway, I took the samples and put them through hi-pass frequency filter. Signal is a little bit distorted, but stil good enough for my purpose :)