One of the best sources to use when trying to determine what jazz singing really is, is to consider the classic and most famous jazz singers themselves: Carmen McRae, Sarah Vaughan, Anita O’Day, Ella Fitzgerald and Billie Holiday. These individuals were all born in between the years of 1915 and 1924 and their lives are parallel with the history of jazz. These are the women who developed the art that has made it what it is today.
While it has undergone a number of permutations since it was initiated, jazz – vocal or instrumental – is generally characterized by two primary elements: swing and improvisation.
However, the complexity that makes up jazz singing is not able to be defied by these elements only. Classic jazz singers do much more than just swing and improvise. One of the most basic requirements that every jazz vocalist must have is a great sounding vocal instrument. While there have been a number of great jazz singers who did not have a beautiful voice (Billie Holiday and Louis Armstrong come to mind), a more classic singer will have an exceptionally beautiful voice (Sarah Vaughan).
More often than not, the voices of great jazz singers will be in the lower register, which is a range that is much more pleasing to listeners.
Another important attribute for great jazz singers is having a highly developed and accurate sense of time. The driving and complex rhythm is essential for jazz and is generally produced by the piano, drugs and bass, which makes up the standard rhythm section of any jazz group. Keep in mind, though, while the backup group will create the beat, it is the singer that sets the tempo. This is why having an acute sense of time is essential.
Improvisation is also extremely important. Jazz singers must have the ability to approach a song in a creative manner and will be able to express their own personality and musicality by embellishing on the song in a number of different ways. There are a number of singers that actually improvise a large amount, while others only do so subtly.
Sensitivity to lyrics, a highly developed musicality, superior sense of rhythm and a great sounding voice are all essential for any authentic jazz singer. These are mostly skills that a person will have to have, rather than ones that are able to be learned.