Altered scales are most often played over dominant seventh chords. They introduce flattened fifths, sharpened fifths, flattened ninths and sharpened ninths, giving the full range of altered notes beloved of jazz improvisers.
Altered Scales and Jazz Minor Scales
Altered scales use the same notes as jazz minor scales a semitone higher. Therefore, if you know the jazz minor scale, and encounter a dominant seven chord, play the jazz minor scale a semitone higher than the root note of the dominant chord, and you will be playing an altered scale.
For example, in a song in the key of C major, a jazz guitarist encounters a G7 chord which resolves to a C major chord. He could play an A flat jazz minor scale that started on the G – a G altered scale – to create some very jazzy sounding tensions. For a fuller explanation of this relationship, and to see various altered scale diagrams, visit this page: Altered Scale
Altered Scales In Use
Here is an example of a guitar solo which uses an altered scale over an altered dominant seventh chord. In the first three bars, an F major scale is used, and in the fourth bar the altered scale is used for the C7#5 chord.Example Guitar Solo Improvisation With Altered Scale
For guitarists, here are the relevant scale diagrams:
Improvisation With Altered Scale Backing Track
The altered scale may sound quite strange at first, but if you persevere you will begin to create some very jazzy sounds – and you’ll also hear it being played by many contemporary jazz musicians.