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