fsk.pl

use constant BPS   => 300;
use constant SRATE => 44100;

$dur = 0;
for (qx!cat olddata.asc!) {
  chomp($a = $_);
  if ($a * $preva < 0) {
    $nbits = int($dur / (SRATE/BPS) + .5);
    print ((($preva < 0) ? 1 : 0) x $nbits);
    $dur = 0;
  } else {
    $dur++;
  }
  $preva = $a;
}