We can use udev tool to detect Audio CD, likes:
/lib/udev/cdrom_id --debug /dev/sr0 |grep ID_CDROM_MEDIA
If the audio cd in your odd, the output likes:
ID_CDROM_MEDIA=1
ID_CDROM_MEDIA_CD=1
ID_CDROM_MEDIA_DVD_RW=1
ID_CDROM_MEDIA_TRACK_COUNT_AUDIO=1
anymore? you can find that the /lib/udev/* have a lots of Test Tool, usb_id/path_id/edd_id and so on~!