Does Ajax need to read from a physical file in order to refresh the details?
It could be a PHP page that fetchs the song data and hands it off to the AJAX request or a simple txt file which is updated by a server side script.
How are you getting the radio server data?
If you set up a PHP file to fetch the song data you can pass the data directly to the request. If that is the case the url in the AJAX script would point to the PHP file.
Edit: Uncomment the alert for the error handling to see if an error is returned
alert('A ' + err.status + ' Error Occurred.\nError Message: ' + err.statusText);