Surround Sound for Cinema can be quite confusing, considering all of the audio release formats currently in use; not to mention all of the formats used in the recent past. I had set out researching all of this information, with the intention of organizing it all into one concise and easy to understand article -- but I discovered that an anonymous scholar and former projectionist had already done it better than I could!
Like many of you, I hate it when Hollywood remakes a classic film that does not need remaking! So rather than remake an article that is already near perfect, I choose to present the link to it instead.
I have tried to contact the author via his (extremely difficult to track down) Facebook page, but he has not replied to me yet. I hope that he is not offended by our link to his work, but that he feels flattered to be so recognized and his work so sought after. Note that Elmer is the copyright holder of his article, and that the various audio manufacturers referred to in the article are the registered trademarks of those respective companies.
And with that introduction, I present to you:
Elmer's Guide to Motion Picture Sound Formats
http://atomicelmer.topcities.com/sound.html
There are a few minor notes that I would like to add to his article as further explanation.
DTS is now know as DataSat Digital Sound. You may see the credit, DataSat, scrolled at the end of many motion pictures, along with credits for Dolby and Sony SDDS.
Historically, DTS reminds me of one of the very first high fidelity audio formats for movies, known as Vitaphone. According to wikipedia:
Vitaphone was a very early audio system used for movies released by Warner Brothers and its sister studio First National from 1926 to 1931.The audio was not printed on the film itself, but came from a phonograph disc played back in sync with the projector. The discs, recorded at 33 1/3 rpm (a speed first used for this system) and typically 16 inches in diameter, would be played on a direct drive turntable physically interlocked to the projector motor while the film was being projected. Many early talkies, such as The Jazz Singer (1927), used the Vitaphone system. The name "Vitaphone" derived from the Latin and Greek words, respectively, for "living" and "sound".
A Vitaphone-equipped theater had normal projectors which had been furnished with special phonograph turntables and pickups; a fader; an amplifier; and a loudspeaker system. The projectors operated just as motorized silent projectors did, but at a fixed speed of 24 frames per second and mechanically interlocked with the attached turntables. When each projector was threaded, the projectionist would align a start mark on the film with the film gate, then cue up the corresponding soundtrack disc on the turntable, being careful to place the phonograph needle at a point indicated by an arrow scribed on the record's surface. When the projector was started, it rotated the linked turntable and (in theory) automatically kept the record "in sync" (correctly synchronized) with the projected image.
Compare that to today's DataSat system, where audio CD's or DVD's are played back in sync to the picture, via timecode (as opposed to a mechanical shaft). History repeats itself.
Dolby Digital Surround EX adds an additional channel to Dolby 5.1 It offers Left, Center, Right across the screen; Left Rear Surround, Center Rear Surround, and Right Rear Surround behind the audience; and the LFE sub-woofer.
Dolby 7.1 takes it even further, with Left, Center, Right across the screen; Left (flank) Surround, Left Rear Surround, Right (flank) Surround, and Right Rear Surround; and the LFE sub-woofer.
The latest Dolby format is Dolby Atmos, which is an elastic surround format that can encompass up to 128 discreet channels along with up to 64 unique speaker feeds. Atmos takes audio to new heights, literally, by addressing speakers placed overhead the audience as well as surrounding them. The format is elastic in that it can reconfigure itself and scale back, based on the resources of the theater, so that even smaller or less sophisticated venues can still playback the same prints as the best equipped showcase cinemas.
The other new format is Barco Auro 11.1 3D. They use the basic 5.1 surround setup (Left, Center, Right, Left & Rear surround, Right & Rear Surround, plus the LFE (low frequency speaker) somewhere in the front). But they add a second plane of speakers near the ceiling (Left, Center, Right, Left & Rear surround, Right & Rear Surround) and one more monaural track up in the ceiling itself (aka the VOG or "voice of God" track). The Auro system is compatible with DCP 5.1 formats and does not require Dobly licensing nor Dobly mastering, so it has a lot of appeal to independent or small filmmakers.
STUDY GUIDE:
Digital 5.1 Surround consists of actually six soundtracks. The "dot one" refers to the sixth track, which is reserved for low frequency special effects (sub-woofer) and is played out from a speaker placed just to one side of screen center. The main five audio tracks are: Left front, Center front, Right front, Left surround (rear side and rear back, imagine an L shape) and Right surround (rear side and rear back, imagine a J shape).
Digital 7.1 Surround is similar to 5.1, but the side surrounds are separate from the rear surrounds.