DE2 Music Synthesizer

Can you guys give me tips on how they've implemented the demo_sound module on the starter code available for the DE2 board Music Synthesizer Project

The notes were created as states, i was wondering if anyone knows how to implement one?

I wanted to know how to read the notes from hexadecimal (i know they are in frequency) so i can customize my own demo songs using the starter code they have! Thanks in advance!