Playing/hearing the progression is perhaps the best way to understand the "how" of it.
In addition to key (C minor, as others have explained), it can be helpful to understand the chords in terms of voice-leading; that is, how one chord voicing proceeds to the next and leads the ear through the progression.
For example:
Cm9
contains G;
Ab9
contains Gb;
Cm11
contains F;
C7(#9b13)
contains E.
A couple points of interest:
- Aside from the initial G, each of the tones proceeding chromatically downward is unique to its chord within the progression.
- Note also how Bb and Eb(D#) are maintained across the progression, lending stability to the sound.
X:1
T:Cm9 => Ab9 => Cm11 => C7(#9b13)
T:G - Gb - F - E chromatic descent
K:none
M:none
L:1/1
[V:V1] "_G""^Eb/Bb"[G_B_e] "_Gb""^Eb/Bb"[_G_B_e] "_F""^Eb/Bb"[F_B_e] "_E""^'Eb'/Bb"[E_A_B^d] |
[V:V2 clef=bass] "_Cm9"[C,C] "_Ab9"[_A,,C] "_Cm11"[C,D] "_C7(#9b13)"[C,C] |
To emphasize the "key of C-ness" of the progression, you could re-voice/reinterpret the chords to produce a C pedal tone. In this case Ab9 becomes Cm7b5b13.
Two more points of interest:
- Notice here that the upper voices from the previous example are preserved.
- Also notice the alternating Bb/Ab in the tenor voice.
X:1
T:Cm9 => Cm7b5b13 => Cm11 => C7(#9b13)
T:C pedal tone
K:none
M:none
L:1/1
[V:V1] [G_B_e] [_G_B_e] [F_B_e] [E_B^d] |
[V:V2 clef=bass] "_Cm9""^Bb"[C,_B,] "_Cm7b5b13""^Ab"[C,_A,] "_Cm11""^Bb"[C,_B,] "_C7(#9b13)""^Ab"[C,_A,] |
There are quite a few voice-leading patterns embedded in this chord sequence, especially when you allow for re-voicing/reinterpreting the chords. Another option emphasizes the alternation between G and Ab. In fact, not just G and Ab, but the G/Bb => Ab/C dyad alternation, again while preserving the voice-leading in the upper part.
X:1
T:Cm9 => Ab9 => Cm11 => C7#9/Ab
T:G/Ab bass alternation
K:none
M:none
L:1/1
[V:V1] [G_B_e] [_G_B_e] [F_B_e] [E_B^d] |
[V:V2 clef=bass] "_Cm9""^Bb"[G,_B,C] "_Ab9""^C"[_A,C] "_Cm11""^Bb"[G,_B,C] "_C7#9/Ab""^C"[_A,C] |