A local luthier told me that he has successfully taught a number of 'tone deaf' people how to do it. He begins with a single note that he has them match. They are invariably, he says, aware of when they've gone too far. He says that a few times of correcting it themselves is often all it takes.

He thinks the reason that some people can't carry a tune is that they haven't learned to 'listen', that they're not aware that there is a physical note to match. He says that the people who don't have a problem simply instinctively listened. Other people have to learn it consciously.

Don't know if this helps?

Ebbie