Backup only files with a particular file extension

Hi,

It's late.. and it may just be that my (admittedly limited) brain is not functioning as it should.. but I just can't see how to do this:

Source = An external disk (Z:)

Destination = Some folder on my D: drive

I want to backup all .mp3 files on the source (whatever folders they're in), to the destination.

So I thought I could just have "*\*.mp3" in the "Files/folders to copy" side of the filters window (and remove everything from the "Files/Folders not to copy" side). But that only appears to work on the root directory, not the whole disk.

Any help greatly appreciated!

Cheers
Darren