Altered tension

Last night Jazz guitar lesson taught altered tension. The altered feeling is funny. Listed what I understand here for reference. This is pure music theory and could apply to all musical instruments.

II-V-I is a progression which has a relax-tension feeling.

• II – Relaxation chord (minor seventh chord; 1-b3-5-b7)
• V – Tension chord (dominant seventh chord; 1-3-5-b7)
• I – Resolution chord (major seventh chord; 1-3-5-7)

There are two kinds of tension could apply to the V chord.
Nature tension: Adding 9 or 11 note of the V chord to rich the sound
Altered tension: Adding b5, #5, b9 or #9 note of the V chord to make an altered feeling

Play altered tension by chord (key = C major). The G7b9 would make an altered feeling in the chord progression.

Dm7	Dm7	Dm7	Dm7
G7	G7	G7	G7b9
Cmaj7	Cmaj7	Cmaj7	Cmaj7

For scale, we can substitute the V scale by scales which contain those alter notes (b5, #5, b9 and #9). For example, we can replace G scale by Ab major scale or F# major pentatonic scale. Both of them hit the alter notes and chord tones. There are more than two possibility scales for substitution in reality.

Ab major scale	Ab	Bb	C	Db	Eb	F	G
Relevant position of G	b9	#9	4	b5	#5	b7	#7

F# major pentatonic scale	F#	G#	A#	C#	D#
Relevant position of G	7	b9	#9	b5	#5

Note: while substitute the scales, remember to let the solo in tension part walking close to resolution part. Otherwise the sound would be too odd when changing back to the resolution chord. For example, putting C/F/G as the last note in the solo of Ab major scale (C/F/G belongs to C major scale).