Custom configuration

[locojohn]

Adnan, if it doesn't set the "Content-Disposition" header as per my
example, then it doesn't match the location in which this header is set.
  It is likely that some other location has preference and so the code I
provided will never be triggered.   Look into your nginx config more
closely.   Also, check the error log, do you get any warnings?  
Sometimes, PCRE library may throw a warning, maybe you can use
alternative location syntax compatible with an older version of PCRE:

...
 location ~ /(?P<filename>(?!/).+\.mp3)$ {
...

Are your mp3 links static at all?  

Andrejs

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,224499,224584#msg-224584