Force file download with Nginx

server {
    listen 80;
    server_name my.domain.com;
    location ~ ^.*/(?P<request_basename>[^/]+\.(mp3))$ {
        root /path/to/mp3/
        add_header Content-Disposition 'attachment; filename="$request_basename"';
    }
}

{
    listen 80;
    server_name  backup.baifu-tech.net;
    root /data/backup/rechargecent-mago;
    location / {
        auth_basic   "baifu backup center";
        auth_basic_user_file /etc/nginx/ssl/htpasswd;
        autoindex on;
        autoindex_exact_size off;
        autoindex_localtime on;
    }
}