The First Fade-Out
The Neptune movement from Gustav Holst's The Planets is generally considered the first piece of music to use the fade-out. The soundbite here is an excerpt from the middle of the movement, but later, a female choir enters and slowly fades out into space. As Holst wrote the choir is "to be placed in an adjoining room, the door of which is to be left open until the last bar of the piece, when it is to be slowly and silently closed..." The last bar of the piece is "to be repeated until the sound is lost in the distance."
Now this may not be too innovative by our way of thinking, but you have to remember this was before most people had access to recorded sound, when fade-outs became much more common place. Holst's fade-out might have been the influence for "Hey Jude," which takes more than 2 minutes to fully fade out. I've never been a big fan of the fade-out; to me, it's sort of a cop-out - something for a songwriter who can't think of a good ending. I do, however, like the fade-in - like you hear in "Bittersweet Symphony" by The Verve or Zeppelin's "Misty Mountain Hop."
What's your favorite fade-out? Or Fade-in?