Interval of the Moment

Diminished octave. In particular, in Villa-Lobos's Suite Popular Brasileira, V - Chorinho, where there's a held low E in the bass, struck D G# B in the middle, and struck G natural in the melody. It's obviously a dominant 7th chord to A minor, even though it doesn't actually resolve that way; the G natural goes down to F then E. It's the clash of the two natures of "traditional" melodic minor that sounds so great.

Another great interval is the diminished third, especially between the raised 7th and lowered 2nd, as used melodically in Tarrega's Recuerdos de Alhambra (which, unlike the Villa-Lobos, I have not yet attempted to play; the right hand figuration is HARD). One phrase ends on the G#, the 3rd of the dominant 7th of A minor, and the next one begins on Bb, the b9th of the secondary dominant to D minor. The melody: C B A B A G#; Bb A G A G F... The first few times I heard it, I couldn't identify the interval. It's just so remote -- a diminished 3rd -- and it was THAT interval that led me to realize that a diminished 3rd is NOT the same as a major 2nd. Ah, context.