Peculiar Cache

From: Mr. Black
Description: We've collected all the keys to help us open Sophia's cache and discover what kind of gift is more precious to her than her own life or the citizens' safety. Strange, we did everything right, but the lock won't open. Bring your tools, let's try to turn it!
Completed: I get it - each key plays a piece of a melody if you turn them in the correct sequence. Do you have a good ear? Tell me which key to turn! It worked, the door has opened. Look, there's a tuba inside containing Sophia's diary!