David-Jubal: Difference between revisions
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== Theory == | == Theory == | ||
=== Interval strength === | === Interval strength === | ||
'''Interval strength''' is a term invented by O'Sullivan to describe a measure of the strength of a just interval. It equals | '''Interval strength''' is a term invented by O'Sullivan to describe a measure of the strength of a just interval. It equals ''2/n + 2/d (where n/d is the simplified interval [[ratio]])''. | ||
Any just interval n/d is acceptable in a melodic context (notes or chords played sequentially, not simultaneously) if its interval strength is greater than 0.25 | ; Melodic contexts | ||
Any just interval n/d is acceptable in a melodic context (notes or chords played sequentially, not simultaneously) if its interval strength is greater than 0.25: | |||
* An interval with a strength value between 0.25 and 0.4999 is a '''neutral interval'''. | |||
* An interval with a strength value between 0.5 and 0.9999 is a '''strong interval'''. | |||
* An interval with a strength value greater than 1.0 is a '''very strong interval'''. | |||
Over a one octave range the very strong intervals are [[4/3]], [[3/2]] and [[5/3]]; these have a value greater than 1.0 using O'Sullivan's formula. | |||
; Harmonic contexts | |||
As regards chord construction, every interval in a chord must have a strength value greater than 0.5. | As regards chord construction, every interval in a chord must have a strength value greater than 0.5. | ||
O'Sullivan allows a tempering of just intervals by up to plus or minus 6.7758 cents ([[256/255]]). | ; Tempering | ||
O'Sullivan allows a [[temperament|tempering]] of just intervals by up to plus or minus 6.7758 [[cents]] ([[256/255]]). | |||
=== David's chord === | === David's chord === | ||