Interesting article from NPR explaining hearing loss.

http://www.npr.org/blogs/health/2013/04/06/175945670/the-real-sounds-of-hearing-loss#

The Real Sounds Of Hearing Loss

by Audrey Carlsen

April 06, 2013 3:38 PM

It's easy enough to restore 20/20 eyesight with glasses or contacts. But even state-of-the-art can't perfectly restore hearing for people whose inner ears have been damaged by noise exposure, medications or just the wear and tear of aging.

Part of the problem is that this kind of — the result of permanent damage to the sensory cells of the inner ear — does more than just make sounds quieter. It can jumble the sounds, too, in ways that garble speech.
To give people with normal hearing an inkling of how wild these distortions can be, hearing and speech researcher created several audio clips for Shots. Each demo uses the same spoken sentence, but is distorted in a different way. (You can hear the original, undistorted sentence further down in this post. But before you do, take a listen to the demos and try to figure out what's being said.)
First up: Many people, especially those with age-related hearing loss, lose the ability to detect high-frequency sounds. Because consonants are typically higher-pitched than vowels, the loss of high frequencies can make it difficult to tell consonant sounds apart. As a result, speech sounds muddy — in some cases, almost beyond comprehension.  More...