@tonilope
If you want back all your data, then you'll have to uncompress the whole 750 MB file, yes.
But if you want only parts of the archive, you can access them seperately. But make shure, you have not selected "solid archive" on creation, because then WinRAR has to read the hole file from beginning until it reaches your requested data.

@CrazyJay

In the best case you could have

2352 bytes x 75 f x 60 s x 99 min = 1047816000 bytes = 999.28 MB of data stored as audio.

But forget it to read such a disc to the end without errors ...