Not the skill
I was best at, when I was a student. But as a teacher, I have come to realize, and explain to the parents of my students, that it's one, out of a tool-box
, that all musicians should have some proficiency at.
Some students--one out of a million, or more--have absolute pitch. A bit like photograhic memory, they can tell the name of a note after hearing it once. Not just the interval of distance between two notes, after hearing them twice (the usual standard). In my years of teaching, I have taught one such. It is as if they are hard wired to know this. She could tell me the name of any note I played.
I could play any group of notes, or chord and she could tell me all the notes. She might not know the name, or kind of chord, but the notes, sure. This I thought kind of curious, until I realized these must be two different parts of the brain. The second, knowing what name, or kind, as a kind of processing, or reflection upon the actual hearing.
For the ear training part of the examinations of the Royal Conservatory of Music of Toronto, for the few more advanced students I teach--I teach more beginners, and general students--I use a technique one of my teachers used with me.
The trick--for the playback of melodies--is finding the first note, the next tend to be easier. So, to teach the position of the notes with respect to the common chord, the 4-note version of the major chord or minor chord.
Using do re mi fa so la ti do, I have my students sing re-do, fa-mi, la-so, ti-do, in all keys, these being the natural resolutions of these notes.
This seems to work because music is built upon tension-resolution, or more specifically, dissonance-consonance. I don't pretend this explains the more esoteric music, say stochastic, or atonal, or other music that is a little bit away from songs that send shivers down your spine, but the kind of music that moves most people most of the time.
I've never seem this idea anywhere, but I don't think it too original--anyone who listens to music knows this.
When one listens to music, the ear become trained.