Hexatonica

Harmonizing the Blues

I was writing out the melody to “Bags’ Groove” for a class the other day and noticed something interesting about how the melody is harmonized on the original recording.

The primary melody phrase (or riff), initially played by the trumpet, outlines the minor pentatonic scale.

The primary phrase is harmonized by the vibraphone like this:

Notice that the phrase is harmonized in 3rds, except for below the note F, where it’s harmonized in 2nds.

If you take all of the notes of the main phrase (F minor pentatonic scale) and add any additional notes from the harmonization, you end up with a 6 note scale, which we might call a F minor hexatonic (6 note) scale.

It’s like F minor pentatonic with the 2nd degree added, or an F minor scale with the 6th removed.

These hexatonic (6 note) scales, can be grouped into a pair of triads.

F minor and Eb major.

On the repeat of the melody, Milt Jackson makes use of this technique in harmonizing the melody.

This time the vibraphone is playing the lead line above the trumpet. The melody starts on a different pitch, but still traces the minor pentatonic scale.

The trumpet plays the line previously played by the vibraphone:

A middle line is filled in by the vibraphone, so now there’s a 3-part harmonization:

With that middle voice added, it becomes clear that Jackson is harmonizing the melody with either of the two triads derived from the F minor hexatonic scale.

If the melody note is a chord tone of the F minor triad he harmonizes it with that chord, and if the melody note is a chord tone of the Eb major triad he harmonizes it with that chord.

Sounds good!

The moral of the story?

Try using triad pairs to harmonize pentatonic melodies!