Book is 3rd edition by Andi Vonlanthen and Horst Arndt.

From the Delmar/Cengage Web site:

"Hearing Instrument Technology for the Hearing Healthcare Professional is designed to provide the reader with technical information about hearing aids and related technology in a simple and approachable manner. Written by hearing aid product researchers with over 40 years of combined experience, the text successfully covers the history and contemporary developments of hearing technology without overwhelming the reader. This new edition reflects the rapid increase in the application of digital technology and discusses the corresponding impact on the field whereby the operation of most hearing instruments are now dependent upon digital signal processing. The text is logically organized and features clear illustrations and numerous clinical examples to explain complicated concepts in a way that is easy to understand."