DTMF-Generator.php

<?php


//samples per second
$sample_rate = isset($sample_rate) ? intval($sample_rate) : 8000; 

//signal length in milliseconds
$signal_length = isset($signal_length) ? intval($signal_length) : 100; 

//break between signals in milliseconds
$break_length = isset($break_length) ? intval($break_length) : 100;

//pause length in milliseconds - pause character is ','
$pause_length = isset($pause_length) ? intval($pause_length) : 500; 

//amplitude of wave file in the range 0-64
$amplitude = isset($amplitude) ? intval($amplitude) : 64;

//$upper_case and $lower_case specifies how letters in upper and 
//lower case are treated. Either should have one of the following
//values: 'abcd', 'spell' or false.
//
//'abcd' means that letters specify the signals A, B, C, D (some phones 
//has special keys for these signals positioned to the right of the keys 
//9, 6, 3, # respectively)
//
//'spell' means that letters spell numbers like in 1-800-CALL-NOW.
//
//false means that letters of the specified case cannot not be used.
$upper_case = isset($upper_case) ? $upper_case : 'abcd'; 
$lower_case = isset($lower_case) ? $lower_case : 'spell'; 



//---end of configuration---


//build frequency tables
$lowfreqs = array(697, 770, 852, 941);
$highfreqs = array(1209, 1336, 1477, 1633);
$signals = array(
    '1', '2', '3', 'A', 
    '4', '5', '6', 'B', 
    '7', '8', '9', 'C', 
    '*', '0', '#', 'D');
$i = 0; foreach ($signals as $signal) {
    $low[$signal] = $lowfreqs[$i / 4] / $sample_rate * 2 * M_PI;
    $high[$signal] = $highfreqs[$i % 4] / $sample_rate * 2 * M_PI;
    $i++;
}

$alphabet    = 'abcdefghijklmnopqrstuvwxyz';
$spelldigits = '22233344455566677778889999';

$n = $HTTP_GET_VARS['n'];
if ($lower_case == 'spell') {
    $n = strtr($n, $alphabet, $spelldigits);
} else if ($lower_case == 'abcd') {
    $n = preg_replace('/[^0-9a-d#*,]/', '', $n);
}
if ($upper_case == 'spell') {
    $n = strtr($n, strtoupper($alphabet), $spelldigits);
} else if ($upper_case == 'abcd') {
    $n = preg_replace('/[^0-9A-D#*,]/', '', $n);
}

//remove frequently used formatting characters 
//that are not part of the actual number
$n = strtr($n, '+-()', 
               '    ');
$n = str_replace(' ', '', $n);

$output = '';

for ($i = 0; $i < strlen($n); $i++) {
    $signal = $n[$i];
    
    if ($signal == ',') {
        $output .= str_repeat("\0", $pause_length / 1000 * $sample_rate);
    } else if ($low[$signal]) {
        for ($j = 0; $j < $signal_length / 1000 * $sample_rate; $j++) {
            $output .= chr(floor($amplitude * (sin($j * $low[$signal]) + 
                                               sin($j * $high[$signal]))));
        }
        $output .= str_repeat("\0", $break_length / 1000 * $sample_rate);
    } else {
        //an invalid character has been encountered - stop
        break;
    }
}

//make sure that all output contains at least 1 byte excl. the header
if (strlen($output) == 0) {
    $output = "\0";
}


function encode_int($n) {
    $s = '';
    for ($i = 3; $i >= 0; $i--) {
        $j = pow(256, $i);
        $s .= chr(floor($n / $j));
        if ($n > $j) $n -= $j;
    }
    return $s;
}


//description of snd/au format available at http://www.wotsit.org/search.asp?s=music
$output = ".snd" .                //"magic number"
    "\0\0\0\x18" .                //data offset
    encode_int(strlen($output)) . //data size (0xffffffff = unknown)
    "\0\0\0\2" .                  //encoding (2 = 8-bit linear PCM, 3 = 16-bit linear PCM)
    encode_int($sample_rate) .    //sample rate
    "\0\0\0\1" .                  //channels
    $output;

header('Content-Length: ' . strlen($output));
header('Content-Type: audio/*');
header('Content-Disposition: filename="dtmf.wav"');
// header('Content-Disposition: filename="' . $HTTP_GET_VARS['n'] . '"');



print $output;
?>