Being a projectionist by trade here goes.
3 digital formats exist in movie theatres today.
DTS -
Has time code embedded between the image and analog soundtrack. It syncs with 2 compact discs which has the soundtrack on them. The information is decoded and converted to an analog signal and passed to the cinema processor. It is routed through the equalization cards and passed on to the amps.
Dolby Digital -
Uses the area between the sprockets for its soundtrack. The DD reader which is a good bit larger than the DTS timecode reader uses a video camera to read the information on the film. There is a LED or Halogen lamp on one side of the film which projects this information onto the DD camera/reader. The information is decoded and converted to an analog siganl and passed to the cinema processor as DTS does. However being Dolby is the leading provider of cinema processors it now incorporates the DD unit into its newer processors. DD does not use DVD or CD's of any kind. It's soundtrack is on the film.
SDDS - (Sony Dynamic Digital Sound) -
Uses the area on the edge of the film to encode its information. It uses both edges of the film and a video based camera system similar to the DD method. SDDS also does a couple things different. It EQ's in the digital domain instead letting the processor do this in the analog stage. It is also capable of having 8 discreet channels of information encoded. (left - left center - center - right center - left surround - right surround - subwoofer ) You would then have five main speakers behind the screen instead of 3. Never really used any more. Starship Troopers, Matrix and Godzilla where 3 films with this ST. But over 90% of theatres dont have these extra channels. Plus it did not make that big of a difference. Especially if the auditorium already had a good system in the first place.
DD and DTS both offer the EX/ES configuration in movie theatres but is RARELY used. It is also a matrixed channel and not discreet. Most of the sutdios seem pleased with 5.1 and alot of theatres have not added the decoder to decode this anyways. The improvement is not that noticeable in theatres like it is at home.
Cinema Processor - - Dolby Stereo
These are basically a receiver just setup differently. They use a series of cards that are removeable for repairs and such. They have a pre amp stage to boost the voltage from the analog reader at the base of the projector. They have a noise reduction card to reduce the inherint noise with optical based soundtracks. The signal then passes through a matrix decoder card/circuit just like a reciever does.The Matrixing Card (or 2:4 channel decoder) constantly compares the Left and Right analog signal. Any information that is identical in both amplitude (volume) and phase (time) is re-routed to the Center speaker. Information encoded with a distinct phase shift is sent to the Surround speakers.There are now four channels: Left, Right, Center, and Surround. The signal is then passed through the EQ cards then through the crossover stage depending on how the theatre is set up. Then on to the speakers in the auditorium.
Speaker Configurations -
Most auditoriums have 6 channels of sound. You have three main screen channels behind the screen. Consisting of a large horn and bass bin. Very large auditoriums will double stack the bass bins. You typically have 2 to 4 subs on a shelf or on the floor behind the screen. Depending on the size of the auditorium. Some auditoriums such as Mann's Chinese use 8 subs. The Arclight in Hollwood uses 8 to 10 subs if im not mistaken. But these are huge auditoriums.
The surround channels work as such. They are typically run in a series configuration. All the speakers on the left wall and half of the speakers on the left side of the back wall will be the left surround channel. The same goes for the right surround channel. All the speakers on the back wall are in even numbers. So split the number in half and the ones on left side are part of the left surround, and the ones on the right side are part of the right surround.
The number of speakers on wall does not indicate how many channels of sound there are. Despite what alot of people think.
I hope this helps explain some things.
