~ flat Thirteen ~

~ b13 ~ augmented 12th ~

'move minor 6th / augmented 5th up an octave ...'

In a nutshell. We rarely if ever see a 'b13' in the written literature, but in our thoroughness here we're simply exploring the possibilities and their ramifications. If it does ever come along chances are it will be a colortone in dominant harmony and included in a chord that has a b7th in it and possibly an Nine and or Eleven.

So in theory, flat Thirteen is simply our minor 6th / augmented 5th transposed up an octave as part of our extended arpeggio.

As we've been seeing in a few of the last of our numerically sequenced studies, many of the cool things that happen with these upper pitches are based on their octave lower cousins. Examine the 'flat 13' interval, letter name pitches and their sound. Thinking in C major. Example 1.

numerical scale degrees
1
2
3
4
5
6
7
8
9
10
11
12
b13
13
14
15
two octave C major scale
C
D
E
F
G
A
B
C
D
E
F
G
Ab
A
B
C
arpeggio degrees
1
.
3
.
5
.
7
.
9
.
11
.
b13
.
.
15
C major arpeggio
C
.
E
.
G
.
B
.
D
.
F
.
Ab
.
.
C

So where in the music? Again the idea that the symbol 'b13' is very rare. I know I've seen it at some point somewhere but now cannot find a trace of it in any of my jazz guitar theory / method books. Chord Chemistry? No trace. Really? Nope but I might have missed it too. That leaves the possibility of some real book chart or big band chart at college I guess.

Regardless, we theorists tend to be a bit scientist too, leaving no stone unturned. Do re-explore if necessary the core ideas for flat thirteen's cousins down the octave to the intervals of a minor 6th / augmented 5th.

Review and forward. The interval of a flatted or minor Thirteen is created by moving the minor 6th / augmented 5th up one octave. Our next interval in our numerical explorations is the Thirteenth, and for those artists with a blues and jazz direction, new coolness is just a click away.

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