Audio systems in the theatre?

Barmack

Barmack

Member
I'm a complete Noob:cheesy: so I'm not sure if this is in the proper section. but I'm curious as to what ways the theaters manage the audio for the 35mm film. and how all of that works..... is the sound on the 35mm film? and how does the surround sound work?

I checked wikipedia but it talks about projectors in general. well there is info on how there is sound on 35mm film but is this 35mm film a standard for all theaters?

again sorry i just want to learn. even though my questions may be dumb.:lipsrseal
 
Not so dumb.
35mm is THE standard theatrical playback format. Sound on 35 comes in a number of flavors. The most basic is a mono optical track, but the most common is a LtRt optical track. You can also just have stereo optical but for a film with even a modest budget you will have a LtRt. LtRt stands for Left Total and Right Total, it's what you get when you matrix encode a 4.0 surround mix. Dolby is the main maker of "matrix" boxes but there are others such as SRS. It is the theatrical equivalent of ProLogic on home video. Anyway that is what 99% of theatrical 35mm prints have. It decodes to Left Center Right and mono Surround (and the matrix decoder box takes all the lows and sends them to the sub woofer so you get a sort of 4.1 on playback). Most films also come out these days with some form of digital surround. Dolby digital is printed like a barcode between frames. SDDS uses a separate CD that locks to time code that gets printed on the film (I think to the side of the frame). Both can have problems on playback and the decoder boxes automatically detect the bad info and switch to the optical track. In the theatre if you ever heard this happen the sound feels like it all just jumped back to the screen, a very interesting sensation.
Dolby Digital is a 5.1 L, C, R, Left Surround, Right Surround, and LFE (subwoofer). As a historical note part of why it's 5.1 is that 5.1 uses 6 tracks and 6 tracks is the number of tracks on a 35mm analog dubber (big ass tape recorder that records on to 35mm magnetic film).
SDDS is 7.1 L, Left Center, C, Right Center, R, Ls, Rs, LFE.
Second historical note, SDDS came out after DA-88 and other digital eight track recorders came in to popular use in film post (7.1 = 8 tracks).

Dolby Digital is encoded as an AC3 stream, basically an MP3 file. SDDS uses something else I believe but certainly something similar. They are after all fitting a films worth of sound (~90-120 min) at 8 tracks onto a CD that normally holds 80 min of 2 track 44.1/16 audio.

So there you go.
 
I should add that I suspect that some time in the next 5-10 years digital playback will take over as the main theatrical playback, at lest in the US and Europe.
 
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