Minor Sixth

Eight semitones, a ratio of eight to five. Turn a major third upside down and you get a minor sixth, which is the quickest way to find one: if you can hear a major third, you can find its inversion.

Wide and slightly aching, sitting between the settled fifth and the bright major sixth. It sounds like a leap that costs something.

The reliable way to learn an interval is to hear it against a drone on the root, not to hunt for a song that starts with it. A song hook fixes the interval in one direction, one register and one rhythm, and the moment it turns up somewhere else you are back to guessing.

In minor chords in first inversion, between the bass and the top note. In the harmonic minor scale, where the gap between the sixth and seventh degrees gives the scale its Spanish edge. In augmented triads, where the interval from the root up to the raised fifth is written differently but sounds the same.

With the perfect fifth, one semitone narrower, and with the major sixth, one semitone wider. It sits between two much more common intervals, which is exactly why it is hard.