|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.
This is written below in musical notation with the essential chord tones coloured black and the non-essential altered chord tones coloured red.
The altered scale is made by the sequence:
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 C altered scale is also enharmonically equivalent to the C Locrian mode with F changed to F♭. For this reason, the altered scale is sometimes called the super-Locrian scale or the Locrian flat four scale (Service 1993, 28).
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).
The super-Locrian scale (enharmonically identical to the altered scale) is obtained by flattening the fourth note of the diatonic Locrian mode:
Another way to obtain the altered scale is by raising the tonic of a major scale by a half step, for example by raising the tonic of the B major scale by a half step: