A lot of old time CDs tell you hoe the instruments are tuned and what key the tunes are in. Try and find the key by listening with a tuned up instrument in your hands - then look up the answer. You'll soon learn how it's done.
This does NOT apply to tunes recorded in the old days, where they seemed to tune their instruments up to a random pitch, or the recording process took a good pitch and turned it into something slightly different. In these circumstances, it's every man for himself (or the PC equivalent)
Cheers
Ray