Watch the Phrygian: Dominant Sound online guitar lesson by Kenny Wessel from Shades of Jazz
In this segment we're going to explore using the Phrygian mode (that we've just discussed) as an altered dominant scale. The Phrygian mode is normally used over minor seventh chords, primarily because the chord tones and tensions generate a minor sound: 1, b3, 5, b7, w/ the upper extensions being b9, 11, b13. This fits into the minor family group (as we said before - minor scales and chords have a b3). If we play this mode over a dominant seventh chord (1, 3, 5, b7), something else happens now. We get the same notes/tensions over the dominant chord, but the b3 can be thought of and heard now as a #9, which is an altered tension. It is the same note as a b3 of course, but it is now functioning as an altered tension, because the dominant 7th chord is supplying the major third, which allows us to hear the scale in a different light. For instance, a D Phrygian mode, which normally is a minor scale option over a D min7 chord, can be used over a D7 altered chord (with a b9, #9, 11 and b13) to get an altered dominant sound/function. The cool thing is, we already know this scale and have it under our fingers, up and down the fretboard, as its one of the major modes!