I needed this book. I just experienced sudden total deafness in my left ear. What the heck?? So I'm going to rely on hearing alternative technology for the rest of my days. This book is the best text I found discussing hearing aid technology as the other texts were actually physics texts about the science of sound. This book is a near perfect blend of the biology of the auditory system and the physical science of sound that only the human ear can process for the brain. Then it must approach all the difficulties that sensory electronics face by today's technological boundaries and recognize that we cannot reproduce the perfection of the human ear. Sadly, the greatest boundary is posed by the economics of greed by the producers of modern hearing aids. Or, the sadly insufficient "low cost" items selling only promises that don't yield performance.