Etymology: Originally, this character meant speak, but with the addition of tongue in the character for mouth 口, it came to mean greater vocalisation (i.e. shouting, or singing). This lead to simply sound.
Hint: Use stand/rise and sun.
Mnemonic: Sound of the rising sun.
音楽 (ongaku) music
発音 (hatsuon) pronunciation
(Based upon Henshall, 1998)