i been looking and i could not find a way to force to save a mp3 file ( from link )
i found this that works with the files on same host Like
$file = $_GET['file'];
header("Content-disposition: attachment; filename=".$file.";");
In HTML use:
<a download href="file.mp3">
In modern browsers it forces download.
This also allows you to avoid using PHP to serve that particular file. By default PHP prevents download resumption and makes serving relatively expensive for your server.