A social choir that I belong to is predominantly female with only two of us males regularly in the tenor section. The leader and other members say that we both sing in tune but the other always sounds "off" to me. I can usually match a note with the others with no difficulty but not with him. Similarly at the folk club I can make a fair attempt at singing a harmony with most other singers but not, unfortunately, with the woman that I most often sing with although she is in the alto range.

Is there some particular quality in a voice, that make some difficult to follow, or some kind of "blind spot" in good hearing that doesn't show any signs of deafness in any frequency ranges?