Jazz musicians use a very sophisticated approach to harmony. Instead of thinking in terms of simple major, minor, and dominant seventh chords as Mozart, Beethoven, and the Beatles did, they first think of a "modal" key center like Lydian or Dorian, and create chord "voicings" that are built up from all the available intervallic relationships of that mode. Armed with this point of view, jazz musicians' aesthetic goal then is to control the "tension" in the voicing. They do this by grouping the intervals into roughly three classes: (1) the major and minor seconds combined with the major and minor sevenths create "dissonance" and attack our ears; (2) the thirds and sixths are "consonant" and sound sweet; and (3) the perfect fourths, fifths, and octaves are "neutral" and sound somewhat hollow. Make note of the voicings that intrigue you. Just like cooking, there is no right or wrong use of these aural spices!!! Press the "create random jazz voicing" button to create a jazz C major seventh chord. Change to C minor seventh chords with the scale setter. The bullseye chart on the right shows you the compositional makeup of the various chord voicings. With time and practice, your ears will tell you the same thing, and you will be on your way to taking Giant Steps as a jazz musician!
A common and powerful technique used to build good voicings is to choose notes that combine to form a major or minor triad different from the root of the chord. These triads are called "upper structure triads". In Snapshot 1, a D major triad plays over the C root. The three notes of the D major triad, D-F#-A, when heard in the C major context, are the ninth, sharp eleventh, and thirteenth of the C major chord. Similarly, in Snapshot 2 the notes of a G major triad are heard as the ninth, fifth, and major seventh of the C major chord. In Snapshot 3 the Bb major triad achieves the same result in C minor where the notes are heard as the ninth, eleventh, and seventh of C minor. Snapshot 4 is an example of a "fourth voicing" wherein all the intervals are a perfect fourth. Snapshot 5 simply hints at the great variety available.