he tune originally known as "Dreamy Blues", has now become a jazz standard. What makes the original recording(s) so interesting is the fact that Ellington has taken the traditional front-line of trumpet, trombone and clarinet, and turned them "upside down". At the time of the recording (1930) the usual voicing of the horns would be clarinet at the top (highest pitch), trumpet in the middle, and the trombone at the bottom (lowest pitch). In "Mood Indigo", Ellington voices the trombone right at the top of the instrument's register, and the clarinet at the very lowest. This was unheard of at the time, and also created (in the studio) a so-called "mike-tone" - an effect generated by the overtones of the clarinet and trombone (which was tightly muted as well). The "mike-tone" gives the audio-illusion of the presence of a fourth "voice", or instrument. Ellington was to re-employ this effect in "Solitude"(1932), "Dusk" (1940) and many other pieces throughout his career. The composition, however, is rarely performed in its original conception, no doubt largely due to the difficulty of the very high and sustained muted trombone part (originally recorded and performed by Joe Nanton).
"Mood Indigo" is at least as often performed as an instrumental as a song, and is often also done mostly featuring the instruments with a short vocal chorus (such as Nina Simone's rendition of the song on her debut album Little Girl Blue (1958) and Let It All Out (1966)). The number has enjoyed substantial success in all arrangements, as well as countless interpretations by a countless number of artists, ranging from Paul Robeson to Ella Fitzgerald to Nat King Cole.