Co.Design:

Something between a black MIDI glissando and a brown note, the THX “Deep Note” is one of the world’s most recognizable audio logos, signaling the highest quality audio standard in films. Yet despite its distinctive crescendo, the THX Deep Note wasn’t actually composed so much as it was programmed, which makes it a fascinating success story of early computer audio design.

I remember the first time I heard that sound. It gave me chills.