Decode a String

[hidz_stitch]

Need help..

I'd found an example of using mb_convert_encoding() to encode a string.

<?
   $string = 'Test:!"$%&/()=ÖÄÜöäü<<';  
   echo mb_convert_encoding($string,'ASCII'); 
?>

and the output is :

Test:!"$%&/()=??????<<

Anyone know how to decode it back to string?
Urgently need it..