The word alteration means modify cloth fit to the needs. An Altered Dominant is a dominant chord/scale altered to fit for the needs.
Must understand what is Altered Dominant Chord
I often hear students plays practiced altered dominant scales. I hear some schools teach melodic minor scale starting half step above the root of the dominant chord (theoretically no justification on this explanation). I strongly against students to practice improvisation with scales especially when altered dominant (and diminished chord). I will try to explain why understanding what altered dominant let you blow cool phrases.
Let’s review what is dominant chord
The definition of Dominant Chord
- Dominant means most powerful of all
- Dominant chord contains a tritone
- Tritone is an interval of diminished 5th/augmented 4th between 2 notes
- In the Early Music Era, tritone was called Devil’s Interval because the sound of the interval was too uncomfortable to human ear
- Because of its unstable sound of tritone, tritone makes human ear want to hear resolution to tonic
Dominant chord’s avoid note
As explained in my Jazz Theory Workbook, you find avoid notes by placing scale notes 1 octave above each chord tones (because that’s how it’d sound when the note is played by a different instrument) and examine if the interval is major 9th or minor 9th. If minor 9th, it becomes avoid note since such interval will destroy the identity of the chord.
In case of dominant chord, because its tritone is powerful, minor 9th interval notes will not have the effect of destroying the identity of dominant chord, except 2 notes that destroys tritone itself: these are perfect 4th and major 7th of the chord.
Example: In case of G7, which tritone is between B and F, the note C, which is minor 9th above the bottom tritone B and F# which is minor 9th above the top tritone F. Any notes except these 2 notes cannot destroy the tritone of G7.
Tension ♭9 and ♭13
Tension ♭9 creates minor 9th interval against root, and ♭13 creates minor 9th interval against 5th, but it will not destroy the identity of the dominant chord.
In fact, T♭9 is a tonal note when V of II, V of III and V of VI (Jazz Theory Workbook page 25), and ♭13 is also a tonal note when V of III and V of VI.
The 5th isn’t a tension. The 5th is one of the chord tones. However, 5th is the least important note in the chord. The 3rd determines the major/minor identity. The 7th determines major/dominant identity. The root anchors 3rd and 7th. A chord sounds just fine without 5th most of the times.
In short, the 5th is the least important so you can alter it if and when needed.
Know the difference between ♭5 and T#11
Because ♭5 is the last note to alter, there cannot be a Mixolydian scale with ♮9th, ♭5th, ♮13th. Instead of ♭5th, the same pitch needs to be called #11, which tells the improvisor the scale is Mixo #11 (or some schools call it Lydian ♭7).
This also suggests this dominant chord is functioning as SubV (see Hiro’s Jazz Theory Workbook page 16). On a side note, this is how Altered Scale is born.
Understand where the Altered Dominant came from
The Altered Dominant is derived from SubV (substituted dominant). SubV is a dominant chord that shares the same tritone (see Hiro’s Jazz Theory Workbook page 16).
For example, the tritone of G7 is B (the 3rd) and F (the ♭7th). There is one other dominant chord that has the same tritone, D♭7, which 3rd is F and ♭7th is C♭ (B). Thus D♭7 can substitute G7.
The SubV scale must be Mixo #11 instead of straight Mixo because D♭ Mixo does not have G. Since D♭7 is substituting G7, its scale must contain G, which is #11 to D♭ Mixo. And if you play D♭ Mixo #11 scale over G7, it becomes G Altered Scale, that is G Mixo ♭9, ♭5, ♭13 as shown below.