Deep Note is the name of THX's audio logo, a distinctive synthesized crescendo sound. It was created by Dr. James A. Moorer, then an employee of the Lucasfilm Computer Division, in 1983. The sound is used on trailers for THX-certified movie theatres and video releases; it debuted in the THX trailer shown before the 1983 premiere of Return of the Jedi in Los Angeles.
The U.S. trademark registration for the sound contains this description of it:
The THX logo theme consists of 30 voices over seven measures, starting in a narrow range, 200 to 400 Hz, and slowly diverting to preselected pitches encompassing three octaves. The 30 voices begin at pitches between 200 Hz and 400 Hz and arrive at pre-selected pitches spanning three octaves by the fourth measure. The highest pitch is slightly detuned while there are double the number of voices of the lowest two pitches.
While the Deep Note had originally been from a soft to loud pitch from its debut in 1983, the Deep Note over the years has been remixed digitally, with then-new technology, which made the Deep Note with a more abridged sound. Beginning notably in 1988 the Deep Note became louder and abridged, and in 1993 the Deep Note was cut short to save time for Laserdisc (1995 for VHS). Most recently, however, the Deep Note has been cut short to the single note (where both sounds stay in one pitch), in favor of other sound effects in certain THX logos.
The sound is perceived as louder than it actually is; sound designer Gary Rydstrom explains that, "from a technical standpoint, 'Deep Note' just feels loud because it has a spectrum of frequencies that grows from small to large."
James A. Moorer has been quoted as saying, "I like to say that the THX sound is the most widely-recognized piece of computer-generated music in the world. This may or may not be true, but it sounds cool!"
The score consists of a C program of about 20,000 lines of code. The output of this program is not the sound itself, but is the sequence of parameters that drives the oscillators on the Audio Signal Processor (ASP). That 20,000 lines of code produce about 250,000 lines of statements of the form "set frequency of oscillator X to Y Hertz".
The sound can be approximated vocally by two (or more) people by both starting on the same note, then each continuously diverging, one up and one down, until the same note is reached two octaves apart and then sustaining for several moments.
Previous works 
Prior to the creation of Deep Note, several other works made use of similar techniques of frequency spread.
In their book Analog Days, Trevor Pinch and Frank Trocco point to the track "Spaced," from the 1970 Beaver & Krause album In a Wild Sanctuary as the source for Deep Note. They quote synthesizer builder Tom Oberheim as saying the original analog form is much richer than the "digital perfection" used in movie theatres.
Popular culture 
The perceived loudness of the Deep Note is frequently depicted as having actual destructive effects:
- The 1992 direct-to-video film Tiny Toon Adventures: How I Spent My Vacation shows a THX Deep Note–like trailer (which features a hand holding a baton) blasting an audience, sending many people flying and wrecking the theater, concluding with the text, "THUD: The Audience Is Now Deaf." This could be based off the cimarron trailer.
- The episode of Bill Nye the Science Guy called "Sound" parodied the logo, replacing "THX" with "SOUND, The Audience is listening". Instead of the Deep Note playing, an orchestra tunes up.
- In a 1994 episode of The Simpsons entitled "Burns' Heir", a THX trailer plays before a film, literally blowing the audience out of their seats, shattering eyeglasses, teeth, and even causing one person's head to explode; the audience whoops in response. Grampa Simpson shouts, "Turn it up! Turn it up!" This segment was later turned into a THX theatrical trailer in widescreen format.
- On Sesame Street, there was a parody of the THX logo and it reads "ABC: The Audience is Learning" before a Letter of the Day segment starts. The Deep Note sounded like kids singing along with the THX theme song and some kids laugh in the background when the logo appeared. Above the logo is "Nucasfilm," another parody of Lucasfilm.
- In the 2006 film Over the Hedge, Deep Note is featured in a scene late in the movie, when the animals enter a house and Penny accidentally switches on the television nearly waking up Gladys Sharp which shows a THX trailer on the screen. The sheer force of the sound blows some of Penny's porcupine quills off. Stella the Skunk tells Gladys' Persian cat guard that the noise is the sound of her heart.
- In the very beginning of the 2006 film Tenacious D and the Pick of Destiny, Deep Note is parodied in the beginning by Jack Black and Kyle Gass with cartoon versions of themselves flying via flatulence propulsion, and the words "THC: The Audience is Baking" appear on the screen.
- The LucasArts adventure game The Curse of Monkey Island opens with a large "CMI" logo with a Deep Note made by the sound of monkeys, accompanied by the caption "The Monkeys Are Listening."
- The promotion for the upcoming Cartoon Network block "Flicks" featured a parody of the Deep Note.
- A documentary on The IT Crowd Series One DVD has various male voices vocalise the Deep Note sound. As they reach the end, some of the voices in the background end up screaming. The first captions state that the video is "shittily mastered for minimal sound and picture quality." This is followed by the logo where "THX" is replaced by "KEN", which when fully read in the context of the captions on the screen reads "Mastered by "KEN using a VCR."
- The New Jersey Nets and other teams use the Deep Note when there is about 10 seconds left in warm-ups. At the end of the Deep Note, the buzzers go off.
- A similar sound can be heard as an easter egg in μTorrent.
- In an episode of Back at the Barnyard, when Otis and Pip watch a DVD, at the beginning there is a parody of the THX logo that reads "BYX," and the Deep Note is sung by a choir.
- When you start the Europe levels in Doritos Crash Course, there is a parody of the deep note.
- The radio station Bob FM sometimes plays the Deep Note before another song is going to play or before commercials play.
- Asia used Deep Note as the opening for the song "Countdown to Zero" from their 1985 album Astra.
- Alice Cooper used the Deep Note at the start of the song "Hell Is living Without You", from the 1989 album Trash.
- The Brown Derbies, a collegiate a cappella group from Brown University, replicated Deep Note using only human male voices. The first track of their 1997 CD "Nightcap" is entitled "THX."
- Rapper Dr. Dre was sued in 2000 by Lucasfilm, then-owner of THX, for using an unauthorized cover of Deep Note on his album 2001.
- Another collegiate a cappella group, Redefined, from UW-Madison, replicated Deep Note with both male and female human voices as the first track on their self-titled 2002 debut album.
- Progressive metal band Dream Theater used a modified version of Deep Note during the 2007-2008 Chaos in Motion tour.
- Timbaland used Deep Note as the opening for the song "Intro with DJ Felli Fel" on their 2009 album Shock Value II.
- Amberian Dawn used the Deep Note in the introduction for their song Incubus on their 2009 album The Clouds of Northland Thunder.
- The "Mega Lo Mania Remix" of Mylène Farmer's song "California" begins with Deep Note.
- Drum and bass artist Delta Heavy used the Deep Note in their song titled "Space Time"
- Moorer, James A. "James A. Moorer Personal Website". Retrieved 2006-12-03.
- THX Ltd. "THX Trailers". Retrieved 2006-12-03.
- "Trademark Applications and Registrations Retrieval (TARR)". United States Patent and Trademark Office. Retrieved 2006-12-03.
- Whitwell, Tom (2005-05-25). "TINY MUSIC MAKERS: Pt 3: The THX Sound". Music Thing. Retrieved 2006-12-03.
- Dansby, Andrew (2000-04-21). "LucasFilm (sic) Taking Dr. Dre to Court". Rolling Stone. Retrieved 2006-12-03.