The Omnibus Progression
The omnibus progression is a special type of chromatic sequence in which the bass and another voice in the texture move in contrary motion. Most commonly, the omnibus progression is used to prolong dominant harmony, but it can also be used as a means of modulating into distant keys.
shows the prolongation of a dominant-seventh chord via a voice-exchange between the leading tone (in the soprano) and the root of the chord (in the bass).
Notice that the voice leading in this progression is as smooth as possible: The only voices that are moving are the ones involved in the voice exchange. The other voices remain static as common tones.
The harmony throughout the
There are two ways of writing an omnibus progression: with the bass and upper voices converging, or with the bass and upper voices diverging.
The converging omnibus progression begins on a root-position dominant-seventh chord. The bass moves up- ward by semitone, while the voice with the leading tone moves downward by semitone, creating a voice ex- change. The remaining two upper voices maintain common tones.
Moving three semitones in this fashion brings you to another root-position dominant-seventh chord. Moving four semitones in this fashion brings you to the same dominant-seventh chord on which you began the progression, but this time, in first inversion.
The omnibus progression can be used to move into distant keys (and eventually traverse the octave) if, once you reach the new root-position dominant-seventh chord (that you arrived at after three semitones), you find the new leading tone and begin the process again.
The diverging omnibus progression works almost identically, but instead of moving the leading tone in contrary motion to the bass, you move the seventh. To move into distant keys, find the new seventh in the root-position dominant-seventh chord and repeat the process.
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