The song Spaced by Beaver & Krause made this sound before THX, in 1970 on the album Wild Sanctuary
3:10 at http://www.youtube.com/watch?v=2xKO3KAtDZ0
Edit: additional wikipedia searching reveals this unsourced fact
"A variation of the end of their track "Spaced" from the Wild Sanctuary album became the inspiration for dual gliding synthesizer soundtrack for the copied THX Sound Logo in movie theaters, also for which neither Beaver or Krause were compensated."