I have noticed years back that the nitrate elements that exist on Steve Stanchfield's clip reels for 'Mr. and Mrs. is the Name' and 'Viva Buddy', two Warner Bros. shorts, use a variable density soundtrack printed onto the film. 'Hollywood Steps Out' is one of the only other shorts from Warner Bros. on those reels to use a variable area soundtrack.

Note that Western Electric optical recording stations were generally set to record at variable density, and the latter for R.C.A. optical recording stations set to record at their own method: variable area. See my next post below for more.

Previously, I had thought that Warner Bros. and First National had always used R.C.A. Photophone, commonly generalized as variable area, for sound on film alternatives to the Vitaphone sound disc system. However, the presence of variable density tracks on the sole elements of the titles I mentioned above bring suspicion; can anybody give a clue?

https://en.wikipedia.org/wiki/RCA_Photophone 

There is also a correction I want to make somewhere else:

The only time that ever happened was with the opposite case, if memory serves me; for example, 'Steamboat Willie', a Disney title, the Cinephone variable density track was rerecorded on R.C.A. Victor equipment to a variable area track for future elements.

Nevermind that quote; it is possible that every optical Cinephone negative from Disney was rerecorded onto variable area at some point, likely for archival purposes starting with the company's arrangements with R.C.A. Victor. I would need any extra confirmation from anyone who has been with Disney in the past; I am simply just a bystander.

The earliest element I have identified where this process had begun was with a non-theatrical reissue element of 'The Beach Party'; this print looks to be a later generation dual bilateral soundtrack. A later generation Fuji stock element of 'The Skeleton Dance' has shown up recently on eBay, also with a bilateral variable area soundtrack.

Does anyone know or have any Vitaphone or Cinephone track disks of Mickey Mouse or Silly Symphony cartoons that they would like to share? They would serve well for an audio comparison against the Treasures sets.