(The melody of the linked song is also mirrored. The original starts with an ascending line; the mirror descends by the same intervals.) At first I was going to link this 18-minute discussion, but it's not exactly clear or all that helpful. Just a starting point. But I figured the song was a better choice. Essentially you end up with major chords becoming minor, minor chords becoming major, and scale positions being offset so that X ==> 7 - X. In other words, the normal diatonic chords built off a major scale: I ii iii IV V vi vii (dim) becomes vi V IV iii ii I "vii (dim)" (it doesn't exactly stay the same, but I doubt if anyone here would know the difference)