For those of us who play fixed pitched instruments, the chromatic scale is our universal set. The same is true for guitarists who either, never bend notes or always bend in 1/2 step increments.
The White keys form the C major Scale (or any of its modes), the black Keys form the Eb minor or Gb Major Pentatonic.
This can be understood by looking at the Cycle. The notes that are altered in the cycle are spaced in 4ths or fifths depending which direction you go. Since the major Pentatonic starts on the root and add a P5 until you ave 5 notes, you can understand how
the black keys form the Gb Major Pentatonic.
Gb Db Ab Eb Bb In 5ths or Gb Ab Bb Db Eb ascending. The formula is 2,2,3,2,3 in terms of half steps.
The major scale COULD be thought of as the remaining notes left after removing these five notes from one of the modes of the chromatic scale.
The note choices used in minor Pentatonic Based playing frequently include the b5, Major 3rd, Major 6th, Major 2nd, if we build the resultant scale say in A Minor
A B C C# D D# E F# G G#
we are left with the holes
If you ever pass into Aeolian you might use F or into Phrygian you might use A# (Bb)
This is getting more and more like the Chromatic scale.
If you examine the Pentaonic based playing of yourself or somone you admire, you will probably find that all 12 tones are used with differing frequency.
The point here is any note can work depending on the situation and the amonut of tension you are trying to achieve, and RESOVE.
I would venture to guess that a statistical analysis of (name your favorite player here) would yeild some interesting favortism of note choice.
These extra tones are not always used as passing tones.
The sounds I hear most often, in my playing are Major 3rd, Major 6th, b5, Major 2nd, minor 6th in that order.
I have seen Larry Carlton speak of a triad approach where he spells out triads in some pseudo random fashion starting with diatonic traids and moving toward more distantly related triads.
This was all based on a cycle of tones alternating between M3 and m3.
Ab C Eb G Bb D F A C E G B D F# A C# E G# B D# F# A# C# F
His example was improv over a Dm7 Vamp.
He played and example and said it was Dm Am Em
D F A C E G B D
To go further down on the cycle he chose
Bb Eb Ab or Gm Cm Fm
Ab C Eb G Bb D F
This a cool idea and with some practice it could be incorporated into your own style.
This is another method of reduction.
Does anyone have similar ideas to share?