It is not uncommon for someone to not be able to distinguish the pitch difference from two sound sources, especially being able to tell if they're singing in tu

It is not uncommon for someone to not be able to distinguish the pitch difference from two sound sources, especially being able to tell if they're singing in tune or not. That's not at all the same thing as not being able to distinguish the two pitches from each other coming from the same source. I can tune a guitar relatively (ie. start with one string "in tune") by ear very easily. I can't for the life of me tune a guitar to a pitchfork or someone else in the band playing a tone that I need to match. And I can't produce a specific tone with my vocal chords or play along a melody by ear.