Traditionally, the voice is most often accompanied by instruments. But this post is inspired by instances in which the voice has been made equal or subordinate to instruments.
One early example that comes to my mind is the first polyphonic pieces from the Notre Dame school. The melismas in some of these pieces are so long that, contrary to a clear hearing of the text, the listener has little choice but to hear the voices in a similar way one would hear an instrument. One vocal syllable is held for so long that the words are difficult to track. In such cases, vocal parts with fewer long melismas take the role of soloist and those with more drawn-out syllables that of accompanist.
More recently, and in a very different cultural sphere, the bassist and guitarist of Red Hot Chili Peppers, Flea and John Frusciante, at times provide backup vocals in falsetto. Granted, they are supporting a lead vocalist as opposed to lead instrumentalist. In the following audio clip, I support my own guitar solo with discant-like falsetto vocals.
If you have any questions or comments on this topic, I would be glad to read and respond to them! Please be in touch. Thanks.