The wedgie: Difference between revisions
m →Basics |
|||
| Line 3: | Line 3: | ||
The ''[[Wedgies_and_Multivals|wedgie]]'' is a way of defining and working with an [[Abstract_regular_temperament|abstract regular temperament]]. If one takes r independent [[Vals|vals]] in a p-limit group of n primes, then the wedgie is defined by taking the [[Wedgies_and_Multivals|wedge product]] of the vals, and dividing out the greatest common divisior of the coefficients, to produce an r-multival. If the first non-zero coefficient of this multival is negative, it is then scalar multiplied by -1, changing the sign of the first non-zero coefficient to be positive. The result is the wedgie. Wedgies are in a one-to-one relationship with abstract regular temperaments; that is, regular temperaments where no tuning has been decided on. | The ''[[Wedgies_and_Multivals|wedgie]]'' is a way of defining and working with an [[Abstract_regular_temperament|abstract regular temperament]]. If one takes r independent [[Vals|vals]] in a p-limit group of n primes, then the wedgie is defined by taking the [[Wedgies_and_Multivals|wedge product]] of the vals, and dividing out the greatest common divisior of the coefficients, to produce an r-multival. If the first non-zero coefficient of this multival is negative, it is then scalar multiplied by -1, changing the sign of the first non-zero coefficient to be positive. The result is the wedgie. Wedgies are in a one-to-one relationship with abstract regular temperaments; that is, regular temperaments where no tuning has been decided on. | ||
===How the period and generator falls out of a rank-2 wedgie=== | ===How the period and generator falls out of a rank-2 wedgie=== | ||
The following is both a procedure for finding a period and a generator for a rank-2 regular temperament given the temperament's wedgie, and a (hopefully convincing and enlightening) proof | The following is both a procedure for finding a period and a generator for a rank-2 regular temperament given the temperament's wedgie, and a (hopefully convincing and enlightening) proof of why the procedure always works. We'll assume that the [[interval of equivalence|equave]] is the octave, but non-octave equaves can be substituted for the octave if needed. | ||
The following assumes that: | The following assumes that: | ||
| Line 22: | Line 22: | ||
We already have W(2,3) = 1, so we can use 3/1 as our generator. Alternatively, W(2, 3/2) = W(2,3) - W(2, 2) = W(2, 3) = 1, so 3/2 is a valid generator for meantone as well. | We already have W(2,3) = 1, so we can use 3/1 as our generator. Alternatively, W(2, 3/2) = W(2,3) - W(2, 2) = W(2, 3) = 1, so 3/2 is a valid generator for meantone as well. | ||
'''Proof | '''Proof:''' | ||
The period ''p'' (fraction of octave) and generator ''g'' form a basis for all the intervals of a rank-2 temperament. For example, p = 2/1 and g = 3/2 form a basis for meantone. But from a linear algebra perspective, there's nothing special about the basis {p, g}; I could have chosen the basis p' = 3/1 and g' = 2/1. What makes the wedgie a unique identifier for a temperament is that rather than specify a basis directly, the wedgie acts more like a set of constraints that any basis for the temperament must satisfy. | The period ''p'' (fraction of octave) and generator ''g'' form a basis for all the intervals of a rank-2 temperament. For example, p = 2/1 and g = 3/2 form a basis for meantone. But from a linear algebra perspective, there's nothing special about the basis {p, g}; I could have chosen the basis p' = 3/1 and g' = 2/1. What makes the wedgie a unique identifier for a temperament is that rather than specify a basis directly, the wedgie acts more like a set of constraints that any basis for the temperament must satisfy. | ||