Voice exchange
A medieval exchange of voices.
What it means
Voice exchange is a compositional technique of medieval polyphony in which two or more voices exchange their material with each other. What one voice sings first, the other takes over in the next section, and vice versa. The combined sound thereby remains largely the same, but the lines change their place.
Musical use
The procedure was widespread in the polyphony of the twelfth and thirteenth centuries, especially in organa and conductus, in which the upper voices exchange their sections over a sustained or slowly moving lower voice. Because the voices sing within the same tonal space, the ear hears the repetition of the combined sound, while the individual singers each perform new material. This creates unity and variety at once.
Voice exchange is an early form of those techniques in which voices are laid out so that they can change their position. Later this became invertible counterpoint, in which two voices can be swapped above and below each other; with this exchange every interval transforms into its complement, which is why the texture must be laid out for this from the outset.
In the music of the canon and of imitation, too, the idea lives on that the same lines appear in different voices.
Voice exchange is to be distinguished from voice crossing, in which a voice briefly moves above or below another without material being exchanged, and from the hocket, in which a melody is distributed between the voices in short pieces.
Voice exchange is found especially in the English rondellus of the thirteenth century: several voices sing the same sections, but staggered in time and in changing distribution, so that every melody wanders through all the voices in turn. In the sound image little changes, because the same combined sounds recur while the individual singers exchange their parts.
Performance practice
If you sing in a voice exchange, listen to the other voice that sings your material before or after — the shared understanding of the line connects both sections. Shape the exchange audibly but not conspicuously; the combined sound is to stay the same. And watch for the same sound and the same articulation in both voices.