Anyone interested in this period of history might want to find out more and I'll suggest two books.
'Hitler's Airwaves', by Bergmeier and Lotz, Yale University Press, 1997. ISBN 0300067097. Comes with a CD some of which is probably on the Proper Box set.
'Different Drummers', by Michael H.Kater, Oxford University Press, 1992. ISBN 0195050096.
There's also a third, briefer, book by Mike Zwerin. Title escapes me at the moment but it's published by Quartet, London.
John Delaney