Jethro Bithell 
German Pronunciation and Phonology [PDF ebook] 

First published in 1952. This book does not confine itself to German phonetics; it aims rather at showing by what processes and tricks of sound words have been shaped in the course of years; it is therefore a book on phonology as well. It should have a wide appeal to students of German. Moreover, since the treatment of laws and sound processes is comparative, it will be useful to students of other languages, particularly of the Scandinavian group and Dutch.