FamousTHX Deep NoteTHX Deep Note, 1983 · James A. (Andy) Moorer
The final chord of the THX logo trailer shown before films, first heard at the premiere of Return of the Jedi in 1983
The THX logo sound ends on a huge D major chord. Thirty synthesized voices slide out of a random swarm and settle on stacked Ds and As, from the very bottom of hearing up to D6, with a single F sharp, the major third, on top. Since almost all of it is octaves and fifths, it sounds like an enormous power chord, and that one high third makes it bright instead of hollow.
Also called Deep Note, THX logo theme
Sources: John D. Cook, Mathematics of the THX Deep Note logo sound (2018) · Stoyan Stefanov, WebAudio Deep Note, part 1 · Deep Note, Wikipedia · Nerdist: THX Has Shared The Sheet Music For Their Iconic 'Deep Note' Sound