Thanks for the answer! The music repository will definitely come in handy.
My issue more had to do with inserting custom instruments/voices that I ripped from other games. For instance, if I ripped an instrument from Chrono Trigger’s soundfont and wanted to import that instrument into FE so it could be used as part of a song in-game.
The tutorial here is what I had been reading (scroll down to where it says “Obtaining the Frequency Adjustment Value”).
The Frequency Calculator is no longer available, so I was just wondering what other ways there were to import custom instruments from other games.