Hirajōshi scale, or hira-choshi (Japanese 平調子: chōshi = tuning and hira = even, level, tranquil, standard or regular) is a tuning scale adapted from shamisen music by Yatsuhashi Kengyō for tuning of the koto.[5] "The hirajoshi, kumoijoshi, and kokinjoshi 'scales' are Western derivations of the koto tunings of the same names. These scales have been used by rock and jazz guitarists in search of 'new' sounds."[3]
This scale is similar to a minor triad with an added major 2nd and minor 6th degrees. It has a root, major 2nd, minor 3rd, perfect 5th, minor 6th, and an octave.
Following the formula to produce a modal pentatonic scale, the 1st, 3rd, 4th, 5th and 7th scale degrees of a mode are borrowed. This is most commonly practied over the dorian, phrygian, and aeolian modes, resulting in a "minor" pentatonic scale. The pentatonic formula can also be used over the lydian mode to produce the hirajoshi scale, the mixolydian mode to produce a dominant pentatonic scale, and the locrian mode to produce the kumoi scale. Although following this formula over the lydian and locrian modes produces the two scales (hirajoshi, and kumoi) in there 5th modes, it is a logical reference point in creating pentatonic scales based on the major modes.
It is essentially a pentatonic subset of the Lydian mode (i.e. the fourth degree of the major scale).
It can also be derived in its inversions (the 5 modes of hirajoshi) from the root notes of the locrian, ionian, phrygian, and lydian modes.
This scale is most commonly practiced over the phrygian mode using its scale degrees: root, minor 2nd, perfect 4th, perfect 5th, and minor 6th. This is due to the harmonic tensions between the root and the minor 2nd.
In its 3rd mode starting from D, it consists of: D-Eb-G-A-Bb.[6]
Other scales include the insen, iwato and kumoi-choshi scales.