A very interesting book which attempts to explore the nature of oral culture and the effects of literacy on such a culture is David Buchan's 'The Ballad and the Folk' (first pub. 1972 by Routledge & Kegan Paul; repub. by Tuckwell Press, 1997).

The book takes for its example the ballad tradition of North East Scotland. Certain aspects of its thesis are necessarily speculative and controversial but it provides plenty of food for thought all the same.

I wonder if there's an equivalent (American?) book which looks at the effects of commercial recording technology on a 'traditional' culture (in the rural South of mid-twentieth century North America perhaps?).