3.4 Voice Exchange

In the above excerpt of the French lullaby, "Dodo, l'enfant do," the initial tonic is expanded twice by consonant skips in the oboe from scale degree 3 to 1. In the above arrangement, in addition to the consonant skip in the oboe, the bassoon skips in the opposite direction to create a first inversion triad--see the 6's below the staff. Notice the relationship between the notes in these two instruments: As the oboe leaves the third (D) and goes to the root (B-flat), the bassoon leaves the root (B-flat) and goes to the note just "vacated" by the oboe (D). This "swapping" of notes by the bass and another voice is called voice exchange.

The video to the right shows two fundamental harmonic progressions which have been expanded by voice exchange. The first phrase shows that the skip of a third may be filled in with a passing tone. The second phrase shows that it is not necessarily the highest voice which is involved with voice exchange. In this case it is the tenor. In both examples the remaining two voices remain stationary. This is a common and simple voice leading possibility which keeps the root as the doubled note.
In the video below, from Bach's harmonization of "Lobt Gott, ihr Christen, allzugleich" (No. 54 of 371 Harmonized Chorales), there are more variations on voice exchange. In this phrase:
  • The dominant is expanded rather than the tonic.
  • The inverted triad precedes the root position triad rather than following it.
  • The other voices do not remain stationary. On beat 2 Bach chose to have the tenor leap to a tripled root.
In this chapter voice exchange will not expand the dominant of the fundamental harmonic progression. Its root, scale degree 5, would be involved in voice exchange but does not move smoothly to tonic in the soprano.
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