By studying the bazilian choro songs , and also the songs by Jacob do bandolim, which are consideed of expecially complicated harmony , a frequent pattern appears in the chromatic harmony.
There are 2 ways to perceive the patterns. A simple one which neverthless doe not reveal all the secretes and a more complicated which does.
The simple one is that chords utilized are a connected arc of 7 or 8 consecutive chords in the wheel by 4ths. We have commented in previous posts for such 7 cycles or 8-cycles And for each such chord either the major or the minor or both are ustilized.
A more revealing perceptions is the next : They are utlized 3 diatonic scales consecutive onthe wheel by 4ths. E.g. [G major C major F major] , or [f major , Bb major, Eb major] etc.
And furthermore each of these diatonic scales are in chromatic tomality derived by the harmonic minor version of its aelonian natural mode , or the double harmonic minor of its aelonian natural minor mode.
When the harmonic minor version is utilized the 3m chord becomes 3M, and when the double harmonic minor version is utilized then the 7d becomes 7M chord as well.
We may compare this type of complicated chromatic tonality with that of the post 373 which also utilizes 3 diatonic scales but in melodic not harmonic relation.
As in the case of reharmonization as in the Gypsy jazz,so with choro, a simple chor progression, to reharmonize it within the choro harmony might require rules like
1) When a chord A transitions to a next chord B and this transition is melodic (interval by 3rd) or chromatic (interval by 2nd) we reharmonize it by interpolation a 3rd chord major 7nth that resolves to B. (harmonic relations like G7->C)
2) We substitute a major chord with its relative minor and vice versa if this keeps the local sequence of the chords progression to a connected arc by 4ths in the wheel by 4ths.
With this 2 rules we create a bias and preference to harmonic chord transitions rather than melodic or chromatic chord transitions.
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