This book DOES NOT teach you audio basics such as audio theory. Nor is it aimed at "seasoned" audiophiles with an interest in recording or "Live" sound. None of that is in this book. "Well, what's it good for"? you may ask. While this book is not intended to be a Reference book this book is great if you're a service technician that works on consumer audio equipment. It does a GREAT JOB on giving you troubleshhoting tips and procedures and a little bit of theory on the operation and servicing of CD players, DATs, AM/FM receivers(the audio sections only,not RF) and VHS HI-FI VCR's (Remember those?).
Beyond that, that's about it. If you're into recording or want a more "advanced" book on audio theory such as the basics of microphone operation, different types of connectors, mixers, or any other "professional", look for "Understanding Audio" by Daniel M. Thompson or any other book that concentrates on that subject.
That said I must also point out that John D.Lenk IS a foremost authority when it comes to troubleshooting and repair and I would advise anyone in the electronics service field to read as many of his books that you can get your hands on. I personally own most of them and I love them.