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Fractal scale: Difference between revisions

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The ''order'' of a fractal scale is the number of iterations of the division process used to obtain the scale. An order-0 fractal scale contains only the starting interval. An order-1 fractal scale contains the original ratio only once. An order-N scale with M steps in its division contains M<sup>N</sup> steps.
The ''order'' of a fractal scale is the number of iterations of the division process used to obtain the scale. An order-0 fractal scale contains only the starting interval. An order-1 fractal scale contains the original ratio only once. An order-N scale with M steps in its division contains M<sup>N</sup> steps.


A fractal scale can be uniquely identified by its order, its ratio and its type. For example, the order-5 2:3:4 linear fractal scale is a 32-tone octave-repeating scale
A fractal scale can be uniquely identified by its order, its ratio and its type. For example, the order-5 1:2 linear fractal scale is a 32-tone octave-repeating scale


Fractal scales provides a certain form of symmetry which is very different in nature than that of other scale families, such as [[MOS scale]]s or [[Regular temperament theory|regularly tempered scale]]s.
Fractal scales provides a certain form of symmetry which is very different in nature than that of other scale families, such as [[MOS scale]]s or [[Regular temperament theory|regularly tempered scale]]s.
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=== Linear fractal scales ===
=== Linear fractal scales ===
{| class="wikitable"
{| class="wikitable"
|+2:3:4 linear fractal scales
|+1:1 linear fractal scales
|-
|-
! Order
! Order
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{| class="wikitable"
{| class="wikitable"
|+3:4:6 linear fractal scales
|+1:2 linear fractal scales
|-
|-
! Order
! Order
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{| class="wikitable"
{| class="wikitable"
|+ Golden (<math>1:2^{\phi-1}:2</math>) logarithmic fractal scales, as approximated by 55edo
|+ Golden (1:φ) logarithmic fractal scales, as approximated by 55edo
! Order
! Order
! Number of steps
! Number of steps
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|}
|}


The fractal scale of <math>1:\sqrt{2}:2</math> is accurately consistent with edo to the power of 2 (e.g. [[16edo]]).
[[User:R-4981|R-4981]] calls the order-4 <math>1:\frac{1-\sqrt{3}}{\sqrt{3}}</math> fractal scale [[redbull]].
 
[[User:R-4981|R-4981]] calls the order-4 <math>1:2^{1/\sqrt{3}}:2</math> fractal scale [[redbull]].


The initial division may contain more than 2 intervals. Here is a simple example with 3 divisions.
The initial division may contain more than 2 intervals. Here is a simple example with 3 divisions.


{| class="wikitable"
{| class="wikitable"
|+ <math>1:2^{1/4}:2^{3/4}:2</math> logarithmic fractal scales, represented in 64edo
|+ <math>1:2:1</math> logarithmic fractal scales, represented in 64edo
! Order
! Order
! Number of steps
! Number of steps
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=== Truncated fractal scales ===
=== Truncated fractal scales ===
Since the division is applied to every interval in each step, some intervals will become very small compared to others. For example, if we divide the octave logarithmically by the ratio <math>1:2^a:2</math> with <math>1/2 < a < 1</math> (like the golden logarithmic fractal scale above), then after ''N'' steps, the largest scale step will have size <math>2^{aN}</math> and the smallest scale step will have size <math>2^{(1-a)N}</math>. The ratio between the two is <math>2^{(2a-1)N} > 2^N</math> which grows exponentially as ''N'' grows linearly, so the scale will have very uneven steps.
Since the division is applied to every interval in each step, some intervals will become very small compared to others. For example, if we divide the octave logarithmically by the ratio <math>1:a</math> with <math>1 < a</math> (like the golden logarithmic fractal scale above), then after ''N'' steps, the largest scale step will have size <math>2^{aN}</math> and the smallest scale step will have size <math>2^{(1-a)N}</math>. The ratio between the two is <math>2^{(2a-1)N} > 2^N</math> which grows exponentially as ''N'' grows linearly, so the scale will have very uneven steps.


If we wish to make the scale steps more even, then we can choose some smallest '''threshold interval''' ''ε'' in the linear case (or 1+''ε'' in the logarithmic case). Here we consider the linear case. On each step, we divide an interval if it is larger than ''ε'', otherwise we leave it untouched if it is smaller than ''ε''. Since the divided intervals get smaller and smaller, we will eventually reach a point where the intervals become smaller than ''ε'', so this process will terminate after a finite amount of steps (and hence the scale is also finite). Here is an example:
If we wish to make the scale steps more even, then we can choose some smallest '''threshold interval''' ''ε'' in the linear case (or 1+''ε'' in the logarithmic case). Here we consider the linear case. On each step, we divide an interval if it is larger than ''ε'', otherwise we leave it untouched if it is smaller than ''ε''. Since the divided intervals get smaller and smaller, we will eventually reach a point where the intervals become smaller than ''ε'', so this process will terminate after a finite amount of steps (and hence the scale is also finite). Here is an example:


{| class="wikitable"
{| class="wikitable"
|+3:4:6 truncated linear fractal scales, threshold ''ε'' = 1/16
|+1:2 truncated linear fractal scales, threshold ''ε'' = 1/16
!Order
!Order
!Number of steps
!Number of steps
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{| class="wikitable"
{| class="wikitable"
|+ Pre-stopped 3:4:6 truncated linear fractal scales, threshold ''ε'' = 1/16  
|+ Pre-stopped 1:2 truncated linear fractal scales, threshold ''ε'' = 1/16  
!Order
!Order
!Number of steps
!Number of steps
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ratio = [1, 2]  
ratio = [1, 2]  
# the "shape" of the ratio, only input integers please.  
# the "shape" of the ratio, only input integers please.  
# [a, b] corresponds to the ratio 1:2^{a/(a+b)}:2,
# [a, b] corresponds to the ratio a:b,
# [a, b, c] corresponds to the ratio 1:2^{a/(a+b+c)}:2^{(a+b)/(a+b+c)}:2, etc.
# [a, b, c] corresponds to the ratio a:b:c, etc.


c = ratio
c = ratio
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