I'm in the school of "there is tone deaf, and then there's TONE DEAF!"

I do accept that a good many folks who think they are tone deaf simply have untrained muscles -- both those needed for listening and those needed for vocal reproduction. But not all!

I had a dulcimer and singing student once, years ago, who was honestly unable to tell me, when I played her two notes about 5 whole notes apart, which was the higher of the two. We worked together on some simple American folk material -- Liza Jane, I wish I was a Single Girl Again, that sort of thing -- with really straightforward, simple melodies, and while she could play them by memorizing where her fingers went on the fretboard, she absolutely could not produce with her voice a tune that had remotely the right shape (ups and downs), never mind the right notes. I tried and tried, but nothing helped. I was very relieved when she moved away and I couldn't give her lessons anymore.