Here is the full list of all 19 Sonority achievements.
Collect all Music Symbols
Unlock the fourth note
Unlock the Panflute
Unlock the fifth note
Unlock the Kalimba
Find the melody
Unlock the fourth Instrument
Open all music chests
Unlock the Bandura
Open the big gate
Unlock the seventh note
Unlock the sixth note
Collect 5 Music Symbols
Collect 15 Music Symbols
Collect 30 Music Symbols
Open the first music chest
Open 3 music chests
Unlock the second note
Unlock the third note