Srotrakasayoh sambandha-samyamad divyam srotram.
= (of) ear; Akasayoh = and space or ether; Sambandha
= (on) relation; Samyamad = by performing Samyama; Divyam
= 'divine', superphysical; Srotram = hearing.
Samyama on the relation between Akasa and the ear superphysical hearing. (III/42)
We perceive an object through our senses. According to yogic science each sense has its corresponding principle (tattawa). For hearing (ear) it is Akasha Tattwa. There is a subtle relation between the sense organs and there corresponding principles. By understanding this relation and performing samyama on the same a yogi can have the knowledge of subtle, superphysical, divine sounds.
It is all question of attunement. Sound is basically, a vibration. When sound vibrations strike our ears, through a fine mechanism, the hearing takes place. Ear is just an instrument. A refined mind can transcend the usual mechanism to pick up subtle, celestial vibrations.
Not long ago there has been a case of a gentleman around the jungle where Prashanti stands now. Suffering from leprosy he wanted to give up his life when he was picked up by some sages. With their divine grace not only was he rid of his dreaded disease but got the capacity to listen to verses belonging to celestial scriptures. Here it was an accidental brush with higher consciousness but a yogi, with systematic discipline, can acquire the art of attuning to subtle sounds.