45 gb unknown audio on mac

Go to the Music folder in your Home folder, open it, there should be one itunes folder, click on it and hit Get Info in Menu Bar or Command-I.

See if it is bigger than what iTunes tells you.
There might also be more iTunes folders although unlikely.

 

You could try a program like Disk Inventory X to see where all the space is.
There are similar programs but right now can't recall their names.

You could also get info on the folders at the root level.
So, get info on:

Applications
Library
System
Users

There are more folders on the root level but many of them are invisible, I think the Library mentioned above is also invisible on your system.
The above process will show you if there is a lot of space taken by that folder, if you find a huge one go inside and get info on each separate folder.
Command-I gives you info on one file/folder, Command-Option-I on multiple files/folders.

If you want an easy small program to make them visible try Show & Hide.