Behind the perception of intervals we will find mathematical relationships.
Each
interval has its fraction or deviation from such fraction.
When
two tones in the main diagram is horizontal in relation to each
other, they form a precise fraction and its inversion (eg major
third/ minor sixth)
We
will now find all known relationships (unrelated to the 7th and 11th
overtones)
Vector
tip would have been on the top tone if the diagram had focused on the
inverted interval.
I
have prioritized 3/2, 5/4 and 6/5. If Ihad chosen the fourth, 4/3
instead of 3/2 (forth instead of fifth) then the tip of the
vector would always point the opposite way.
Pictures:
.
I
want to focus at the relationship between 256/243 (also called
Pythagorean Limma) and 16/15 .
The
Pythagorean Limma we get after five pure fifths in succession.
But
also of course in a chain like this :
A
pure 16/15 semitone is 660 TU wider than 256/243 (Limma :horizontal
dotted line)
Sometimes
I also get a little confused and mix together deviation of an
interval and the interval itself. Besides, it can be difficult to get
hold of which direction of the vector would have been in these more
distant intervals.
If
we take a look at F# 7 in the previous diagram we see that B / A # is
the interval pyth.limma, the dotted horizontal line through five
fifths. It gives a deviation of 660 TU from the interval 16/15 (the
oblique dotted line) It can look like the size of half tone (16/15)
increases when the tone A# rises, but it shrink to be smaller than
the 16/15 ratio, ie A# ladders, lead tone becomes higher, and we get
an interval smaller than 16/15
If
I have a vector to 16/15 interval, then should the arrow here
been turned down! Which in turn would have meant that this interval
is less than 16/15.
This
can be good to have consciously done before we look at some simple
dominant-tonic progressions. And even more importantly it will be in
our next diagram called «do-re-mi-fa-so».
A
Pythagorean major third (660 TU) is no interval to rest in , but it
gives a high leading-tone and works extra good in such a function.
We
will now see (hear) some simple chord progressions
Here
we are hearing a pythagorean third, B/A # has the pythagorean limma
interval.
The
minor triad Bm is nice.
B-D
= - 300 TU
D-F
# = 300 TU
B-F
# = 0 TU
The
major triad is worse.
B-D
# = 660 TU
D
# -F # = - 660 TU
B-F
# = 0 TU
So
we take an example where the interval-quality of minor and major has
swapped.
Here
we see that the leading-tone has a longer way (low lead tone) up to
the high lead tone (Limma) (dotted line)
A
minor triad with large deviations from pure minor third
Bb
Db = - 660 TU
Db-F
= 660 TU
Bb
F = 0 TU
However,
the major third are here quite good
Bb-D
= 300 TU
D-
F = -300 TU
Bb
F = 0 TU
Major
thirds are even better here:
Major
third is
F
A = 180 TU
A-C
= -300
The
fifth is not pure here
F-C
= -120 TU
Finally
This
allows you to analyze yourself. :)
I
have left out the numbers for seventh chords, but I think that the
reader now manages this.
Here
I will mention that seventh position is quite different in the
examples.
We
see here that the seventh is much higher in A7 than F7.
--------------------------------------------------
--------------------------
TETRA
chords (do-re-mi-fa-so)
These
things I have made to get an overview of the size of the whole tones
and semitone steps.
I
focused on pyth.limma largely due to this diagram, where I do a
twist. I place the upper graph (constantly based on fifth-chains) so
that having five pure fifths in succession (here
Db-Ab-Eb-Bb-F-C), the first five notes of the scale from Ab
will get in line.
The
C-Db will be a pyth.limma (no violet vector)
If
the first two whole tones are small ((and if the forth between do and
fa is quite pure) then the half tone between the 3rd and 4th
(the semitone)will be correspondingly larger as it is reflected in
the violet vector. It shows the deviation from pyth. Limma (256/243).
A long arrow upward reflects that the interval is a good amount
larger than limma.
256/243
which is the ratio between the upper and lower graph shown in purple
vector is not a consonant interval but I have chosen it to more
easily assess half and whole-tone step relatively. By studying the
pattern on the first five tones we get a sense of (or using exact
numbers) the relationship between the notes of the scale.
(The
major third in the highlighted notes relate to 81/64 and not 5/4 (the
minor third 32/27))
Here
comes a Kirnberger III variation.
And
here comes the scales in different keys:
Additionally,
we can see visualized that 10/9 whole tone is not included in
particularly useful tunings.
And
again the syntonic comma . A pure 9/8 (whole tone) is 660 TU greater
than 10/9.
To
obtain a whole tone at 10/9 the 2 fifths must take -330 TU
each(average), and that is a very impure fifths.
It's
Kirnberger II
And
here we see a whole tone (D-E) as a 10/9
Here
we see the impossibility of 10/9 whole tone without highly impure
fifths.
10/9
is found more frequently in "just intonation".
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