Just intonation point: Difference between revisions
Wikispaces>genewardsmith **Imported revision 515964888 - Original comment: ** |
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The '''just intonation point''' ('''JIP'''), also known as '''just tuning map''', is a special [[tuning map]] that maps every [[monzo]] in some [[subgroup]] to its [[span]] in [[cent]]s (or any other logarithmic [[interval size unit]]), relative to the point 1/1 (which maps to 0 cents). | |||
For instance, in 5-limit JI, the JIP is {{val | 1200.000 1901.955 2786.314 }}; if we take the {{w|dot product}} of this tuning map with any monzo, we get its size in cents. Of course, one can always build the JIP using different units than cents. | |||
For prime limits, the JIP has a particularly simple definition in Tenney-weighted coordinates, where it is always the all-ones vector, {{val | 1 1 1 … }}. | |||
< | == Units == | ||
It may be helpful to think of the units of each entry of the JIP—as with a normal (temperament) tuning map—as <math>\mathsf{¢}\small /𝗽</math> (read "cents per prime"), <math>\small \mathsf{oct}/𝗽</math> (read "octaves per prime"), or any other logarithmic pitch unit per prime. For more information, see [[Dave Keenan & Douglas Blumeyer's guide to RTT/Units analysis]]. | |||
< | |||
< | == Mathematical definition == | ||
The JIP, commonly denoted ''J'', is a point in ''p''-limit [[vals and tuning space|tuning space]] which represents untempered ''p''-limit JI. Specifically, it is equal to {{val| log<sub>2</sub>2 log<sub>2</sub>3 log<sub>2</sub>5 … log<sub>2</sub>''p'' }}, meaning that each prime ''q'' in the ''p''-prime limit is tuned to log<sub>2</sub>''q'' octaves (which is exactly the just value of the prime ''q''). | |||
The JIP is the target of optimization in optimized tunings including [[TOP tuning|TOP]] and [[TE tuning]]. If '''m''' is a monzo, then {{vmprod|''J''|'''m'''}} is the untempered JI value of '''m''' measured in octaves. In Tenney-weighted coordinates, where '''m''' = {{monzo|''m''<sub>2</sub> ''m''<sub>3</sub> ''m''<sub>5</sub> … ''m''<sub>''p''</sub>}} is represented by the ket vector {{monzo| ''e''<sub>2</sub>log<sub>2</sub>2 ''e''<sub>3</sub>log<sub>2</sub>3 ''e''<sub>5</sub>log<sub>2</sub>5 … ''e''<sub>''p''</sub>log<sub>2</sub>''p'' }}, then ''J'' becomes correspondingly the covector {{val| 1 1 1 … 1 }}. | |||
As seen in the 5-limit [[projective tuning space]] diagram, it is the red hexagram in the center. Equal-temperament maps which are relatively close to this hexagram, which means low tuning error, such as {{val| 53 84 123 … }}, have integer elements which are in proportions relatively similar to the proportions of the corresponding elements in ''J'' = {{val| log<sub>2</sub>2 log<sub>2</sub>3 log<sub>2</sub>5 … }} ≈ {{val| 1.000 1.585 2.322 … }}, e.g. 84/53 ≈ 1.585/1.000 and 123/53 ≈ 2.322/1.000. | |||
[[Category:Regular temperament theory]] | |||
[[Category:Math]] | |||
[[Category:Terms]] | |||
Latest revision as of 07:39, 4 December 2025
The just intonation point (JIP), also known as just tuning map, is a special tuning map that maps every monzo in some subgroup to its span in cents (or any other logarithmic interval size unit), relative to the point 1/1 (which maps to 0 cents).
For instance, in 5-limit JI, the JIP is ⟨1200.000 1901.955 2786.314]; if we take the dot product of this tuning map with any monzo, we get its size in cents. Of course, one can always build the JIP using different units than cents.
For prime limits, the JIP has a particularly simple definition in Tenney-weighted coordinates, where it is always the all-ones vector, ⟨1 1 1 …].
Units
It may be helpful to think of the units of each entry of the JIP—as with a normal (temperament) tuning map—as [math]\displaystyle{ \mathsf{¢}\small /𝗽 }[/math] (read "cents per prime"), [math]\displaystyle{ \small \mathsf{oct}/𝗽 }[/math] (read "octaves per prime"), or any other logarithmic pitch unit per prime. For more information, see Dave Keenan & Douglas Blumeyer's guide to RTT/Units analysis.
Mathematical definition
The JIP, commonly denoted J, is a point in p-limit tuning space which represents untempered p-limit JI. Specifically, it is equal to ⟨log22 log23 log25 … log2p], meaning that each prime q in the p-prime limit is tuned to log2q octaves (which is exactly the just value of the prime q).
The JIP is the target of optimization in optimized tunings including TOP and TE tuning. If m is a monzo, then ⟨J | m⟩ is the untempered JI value of m measured in octaves. In Tenney-weighted coordinates, where m = [m2 m3 m5 … mp⟩ is represented by the ket vector [e2log22 e3log23 e5log25 … eplog2p⟩, then J becomes correspondingly the covector ⟨1 1 1 … 1].
As seen in the 5-limit projective tuning space diagram, it is the red hexagram in the center. Equal-temperament maps which are relatively close to this hexagram, which means low tuning error, such as ⟨53 84 123 …], have integer elements which are in proportions relatively similar to the proportions of the corresponding elements in J = ⟨log22 log23 log25 …] ≈ ⟨1.000 1.585 2.322 …], e.g. 84/53 ≈ 1.585/1.000 and 123/53 ≈ 2.322/1.000.