|Modes||I, II, III, IV, V, VI, VII|
|C, D?, D?, E, F?, A?, B?|
|Number of pitch classes||7|
In jazz, the altered scale or altered dominant scale is a seven-note scale that is a dominant scale where all non-essential tones have been altered. This means that it comprises the three irreducibly essential tones that define a dominant seventh chord, which are root, major third, and minor seventh and that all other chord tones have been altered. These are:
The altered forms of some of the non-essential tones coincide (augmented eleventh with diminished fifth and augmented fifth with minor thirteenth) meaning those scale degrees are enharmonically identical and have multiple potential spellings. The natural forms of the non-essential tones are not present in the scale. This means it contains no major ninth, no perfect eleventh, no perfect fifth, and no major thirteenth. An altered scale on C contains the notes:
This is written below in musical notation with the essential chordtones coloured black and the non-essential altered chordtones coloured red.
The altered scale is made by the sequence: semitone - tone - semitone - tone - tone - tone - tone.
The abbreviation "alt" (for "altered") used in chord symbols enhances readability by reducing the number of characters otherwise needed to define the chord and avoids the confusion of multiple equivalent complex names. For example, "C7alt" supplants "C7?5?9?9?11", "C7-5+5-9+9", "Caug7-9+9+11", etc.
The altered scale is also enharmonically the C Locrian mode, C-D?-E?-F-G?-A?-B?, with F changed to F?. For this reason, the altered scale is sometimes called the "super-Locrian mode". It is also enharmonically the seventh mode of the ascending melodic minor scale. The altered scale is also known as the Pomeroy scale after Herb Pomeroy (Bahha and Rawlins 2005, 33; Miller 1996, 35), the Ravel scale (after Maurice Ravel), and the diminished whole-tone scale due to its resemblance to the lower part of the diminished scale and the upper part of the whole-tone scale (Haerle 1975, 15), as well as the dominant whole-tone scale[clarification needed] and Locrian flat four (Service 1993, 28).
The super-Locrian scale (enharmonically identical to the altered scale) is obtained by flattening the fourth note of the diatonic Locrian mode. With a tonic of C, it is spelt: C-D?-E?-F?-G?-A?-B?-C:
Another way to obtain the altered scale is by raising the tonic of a major scale by a half step; for example, taking the tonic of the B-major scale, B-C?-D?-E-F?-G?-A?-B,
and raising the tonic by a half step produces the scale B?-C?-D?-E-F?-G?-A?-B?,
Like the other modes of the melodic minor ascending or jazz minor scale, the altered scale shares six of its seven notes with an octatonic (or "diminished") scale, and five of the six notes of a whole-tone scale, and thus is occasionally referred to as the "diminished whole tone scale". For example, the altered scale C-D?-D?-E-G?-A?-B? shares all but its A? with the octatonic scale C-D?-D?-E-F?-G-A-B?; while sharing five of the six notes in the whole-tone scale C-D-E-G?-A?-B?. This accounts for some of its popularity in both the classical and jazz traditions (Callender 1998,[page needed]; Tymoczko 2004[page needed]).
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