Lydian chord
In jazz music, the lydian chord is the maj7♯11 chord,[1] or ♯11 chord, the chord found on the first degree of the lydian mode, the sharp eleventh being a compound augmented fourth. It is described as, "beautiful," and, "modern sounding".[1] The 7#11 chord generally resolves down by half step while the enharmonically equivalent 7(♭5) generally resolves up a fourth to the tonic[2] being a dominant chord (♯11=♯4=♭5, see octave equivalency).
Major 7(♯11) may also refer to the Lydian augmented chord, an augmented seventh chord with augmented fourth appearing in the Lydian augmented scale 
Play (help·info).[3]
In a chord chart the notation "Lydian" indicates a major family chord with an added augmented eleventh, including maj7♯11, add9(♯11), and 6(♯11).[1]
Harmonic function
Lydian chords may function as subdominants or substitutes for the tonic in major keys.[4]
_png/180px-Thirteenth_chord_CMA13(sharp11).png)
Lydian (CΔ♯11):
r 3 5 7 (9) ♯11 (6))
- The Lydian chord has a peculiarity, in that placing the root both above and below the augmented eleventh creates an unpleasant dissonance of a tritone.
- The interval of the sixth is used even though it is described after other compound intervals, and perhaps should also be a compound interval (i.e., 13th). However, convention in Jazz dictates that when describing the major sixth, the simple interval, i.e., 6 is almost invariably used instead of the compound interval, i.e., 13. This helps avoid confusion with the dominant thirteenth.
_png/180px-Thirteenth_chord_C13(sharp11).png)
The dominant 7th ♯11 or Lydian dominant (C7♯11) comprises the notes:
r 3 (5) ♭7 (9) ♯11 (13)
Basing this chord on the pitch C results in the pitches:
C E G B♭ D F♯ A
The same chord type may also be voiced:
C E B♭ F♯ A D F♯
This voicing omits the perfect fifth (G) and raises the major ninth (D) by an octave. The augmented eleventh (F♯) is also played twice in two different registers. This is known as "doubling".
Sources
- ↑ 1.0 1.1 1.2 Juergensen, Chris (2006). The Infinite Guitar, p.50. ISBN 1-4116-9007-9.
- ↑ Juergensen (2006), p.51.
- ↑ Munro, Doug (2002). Jazz Guitar: Bebop and Beyond, p.39. ISBN 978-0-7579-8281-1.
- ↑ Miller, Scott (2002). Mel Bay Getting Into Jazz Fusion Guitar, p.44. ISBN 0-7866-6248-4.
- ↑ Benward & Saker (2009). Music in Theory and Practice: Volume II, p.185. Eighth Edition. ISBN 978-0-07-310188-0.