$w0 = 2 * M_PI * $f0 / $fs;

$cos0 = cos($w0);

$sin0 = sin($w0);

$alpha = $sin0 / (2 * $q);

$b0 = $alpha;

$b1 = 0;

$b2 = - $alpha;

$a0 = 1 + $alpha;

$a1 = -2 * $cos0;

$a2 = 1 - $alpha;

$c0 = 65536 * 4;

$c = $c0 / $a0;

$b0 = round($b0 * $c);

$b1 = round($b1 * $c);

$b2 = round($b2 * $c);

$a0 = $c0;

$a1 = round($a1 * $c);

$a2 = round($a2 * $c);

return array('a' => array($a0, $a1, $a2), 'b' => array($b0, $b1, $b2));

$res = array();

$amp = 120;

$offs = 128;

$w = 2 * M_PI * $f;

$dt = 1 / $fs;

for ($t = 0; $t < $time; $t += $dt) {

$res[] = floor(sin($t * $w) * $amp + $offs);

}

return $res;

$avg = 0;

$n = count($data);

foreach ($data as $x) {

$avg += $x;

}

$avg /= $n;

$avg2 = 0;

foreach ($data as $x) {

$avg2 += pow($x - $avg, 2);

}

return sqrt($avg2 / $n);

list($a0, $a1, $a2) = $filter['a'];

list($b0, $b1, $b2) = $filter['b'];

$res = array($data[0], $data[1]);

for ($i = 2; $i < count($data); $i++) {

$y = ($b0 * $data[$i] + $b1 * $data[$i - 1] + $b2 * $data[$i - 2]

- $a1 * $res[$i - 1] - $a2 * $res[$i - 2]);

$res[] = floor($y / $a0);

}

return $res;

global $fs, $filter;

$data = generate($freq, 0.1, $fs);

$res = filter($data, $filter);

if ($prn) {

for ($i = 0; $i < count($data); $i++) {

echo "{$data[$i]}\t{$res[$i]}\n";

}

}

$aIn = amplitude($data);

$aOut = amplitude($res);

return $aOut / $aIn;