In jazz music, altered chords and scales are often used to create a sense of tension and release. They are usually used in the context of dominant chords, which are chords that are built on the fifth degree of a diatonic scale.
An altered chord is a dominant chord in which one or more of the chord tones have been raised or lowered by a half step. The most common alterations are b9 (flat nine), #9 (sharp nine), b5 (flat five), and #5 (sharp five). These alterations create dissonance, which can be resolved by resolving the chord to a consonant chord.
An altered scale is a scale that is used to improvise over an altered chord. It is a scale that contains all the altered chord tones, as well as the root, third, fifth, and seventh. The most common altered scale is the seventh mode of the melodic minor scale, also known as the altered scale.
Altered chords and scales are typically used in situations where there is a dominant chord that resolves to a major or minor chord. The dissonance created by the altered chord creates tension, which is then resolved by resolving the chord to a consonant chord.
Altered chords and scales are also commonly used in situations where there is a chord progression that contains several dominant chords. In this case, the altered chords and scales are used to create a sense of tension and release throughout the progression.
In conclusion, altered chords and scales are an important tool in the jazz musician's arsenal. They are used to create tension and release, and are typically used in the context of dominant chords. While they can be used in other genres of music, they are most commonly associated with jazz.