Try cleaning out your ears with a cotton swab and listening to her again. Could be a wax buildup problem.
Whitney Houston - Star Spangled Banner
http://www.youtube.com/watch?v=1h9NN5FhJ7I&feature=related
Whitney Houston - Greatest Love Of All:
http://www.youtube.com/watch?v=IYzlVDlE72w
Whitney Houston - All the Man That I Need:
http://www.youtube.com/watch?v=3WH1Ma50QUk
more...
http://www.youtube.com/artist?a=GxdCwVVULXe_vW4e3LAP7XRSDMhxC2FS&feature=artistob
Listen up, jackass. I was a voice major in college and have been a professional singer for 40 years. I know more about singing than you know about anything.
Whitney yells from her throat and her chest. Her switch to her head voice, when she uses it, is the most obvious in the history of the pop charts. She yells so forcefully that her pitch suffers. It's all over the place.
She has been singing incorrectly for so long that she can no longer sing. Great singers can cut it into their sixties and seventies. Whitney hasn't even turned 50!
Her ruined instrument isn't the function of substance abuse. Pavarotti and Sinatra smoked...the worst thing you can do for your voice outside of gargling with acid...and held their own for decades past Miss Houston.
If you think this woman is a great singer, you're stone-cold deaf...and an idiot.