David tweeted this on 30 Aug, saying that he was going to record a scratch vocal on a new song:

Some fans asked Sunny Hilden, one of David’s songwriter, what a scratch vocal is, and she was nice enough to reply via her Twitter:
A scratch vocal is temporary, to test tempo, key, structure, build of a new song, before committing to more instruments.
During Monday’s scratch vocal, we changed the order of the verses, the key, the tempo & experimented with the time signature.
During Tuesday’s scratch vocal, on a different song, we added time after the 1st chorus & altered the piano part…it’s fun…
For those of you asking what “comping vocals” is, one song had 40 takes – comping is figuring out which line to use from which take. Some takes have melody experiments, a “v” that sounds too much like “d,” magic moments, “p’s” that “pop,” fun puzzle:)
All sounds pretty complicated to me. haha…