Lake Tahoe | Blue Note

In jazz and blues, a blue note (also "worried" note) is a note sung or played at a slightly lower pitch than that of the major scale for expressive purposes. Typically the alteration is a semitone or less, but this varies among performers and genres. Country blues, in particular, features wide variations from the diatonic pitches with emotive blue-notes. Blue notes are often seen as akin to relative pitches found in traditional African work songs.

Blue notes (*): ♭3, (♯4)/♭5, ♭7

Like the blues in general, the blue notes can mean many things. One quality that they all have in common, however, is that they are flatter than one would expect, classically speaking. But this flatness may take several forms. On the one hand, it may be a microtonal affair of a quarter-tone or so. Here one may speak of neutral intervals, neither major nor minor. On the other hand, the flattening may be by a full semitone--as it must be, of course, on keyboard instruments. It may involve a glide, either upward or downward. Again, this may be a microtonal, almost imperceptible affair, or it may be a slur between notes a semitone apart, so that there is actually not one blue note but two. A blue note may even be marked by a microtonal shake of a kind common in Oriental music.
The degrees of the mode treated in this way are, in order of frequency, the third, seventh, fifth, and sixth.

—Peter van der Merwe (1989).

The blue notes are usually said to be the flattened third, flattened fifth, and flattened seventh scale degrees. Though the blues scale has "an inherent minor tonality, it is commonly 'forced' over major-key chord changes, resulting in a distinctively dissonant conflict of tonalities". A similar conflict occurs between the notes of the minor scale and the minor blues scale, as heard in songs such as "Why Don't You Do Right?."

• In the case of the flattened third over the root (or the flattened seventh over the dominant), the resulting chord is a neutral mixed third chord.

Blue notes are used in many blues songs, in jazz, and in conventional popular songs with a "blue" feeling, such as Harold Arlen's "Stormy Weather." Blue notes are also prevalent in English folk music. Bent or "blue notes", called in Ireland "long notes", play a vital part in Irish music.

Fuente: Wikipedia