This methods is rather simple and doesn’t involve much theory. All we are simply doing is shifting half a step down (or whole step depending on position) and playing the 7th of the chord from that root. Just by simply doing that, we get a very soul sounding chord progression.
E.g. let start with Abmaj 7th, then shift half a step down to G. Now you just do trial and error and use your ears Gmaj 7th doesn’t sound right, so play Gmin 7th and you can already hear the soulful sound.
Next shift 1/2 a step again to the left and you get Gb. And trail and error but Gb maj 8th sounds best here. You can even shift again to Fmin 7th.
Check out the video below to see how I am playing it. I will be posting some other too, using different scales.