k karaoke: physical.

You've been practicing karaoke, and you're certain you'll be the next American Idol. So why did Simon say: "You're tone deaf"?

"Listening to yourself sing is like crawling into a grand piano, closing the lid, and then hearing the sounds bounce around inside the box," says Ingo Titze, professor of speech science and voice at the University of Iowa.

There are two ways you hear yourself. You're mostly listening to your voice through the bones tissues in your head. And others hear airborne signals that escape from your mouth. But by the time those signals reverberate (bounce back) to your ears, they're only close to what others heard.

So how do you know what sounds good? "Most singers have a teacher point out what's right. Then they register that in the brain and practice coordinating the vocal muscles to get that sound," says Titze.

When you sing, sound waves form from air traveling through the larynx (voice box), vibrating at the vocal cords (small muscular folds), and then resonating (echoing) inside your mouth. The different shapes you make with your lips, tongue, and the back of your throat determine sound quality. "It's really more about learning how a sound feels instead of what you think it sounds like," says Titze.