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From: jstein@sun.uucp (Jay Stein)
Newsgroups: net.video,net.audio,net.movies
Subject: Re: Movie sound formats
Message-ID: <5191@sun.uucp>
Date: Thu, 17-Jul-86 16:24:36 EDT
Article-I.D.: sun.5191
Posted: Thu Jul 17 16:24:36 1986
Date-Received: Fri, 18-Jul-86 19:03:45 EDT
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> I've been wondering about this for a long time. What are the characteristics
> of: 6 track dolby stereo, 4 track dolby stereo, THX sound, and dolby surround
> sound? Is 6 track dolby stereo 6 distinct tracks? What about 4 track stereo?
> Is "surround sound" an artifact of home video; I mean is this one of the other
> formats adapted for home video? I hear that surround sound is stereo in front
> and one mono track in the rear. This would make it 3 track stereo, right? And
> I know nothing about THX. Are there others I've left out? And does anyone know
> the history of multitrack film audio?
> 
> 				Anthony Albert
> 				..!ucbvax!kim!albert
> 				albert@kim.Berkeley.EDU

Well...  I know something about a few of those formats... I'll give it a
shot:
   There are several ways of getting Dolby surround sound.  The only method
with which I am familiar involves the recording of Left+Right on one track,
Left-Right (that's left minus right) on another track, and the surround track
is encoded with a low volume carrier on top of both of them.  The cinema
processor decodes these low-volume signals and amplifies them for surround.
This has the serious disadvantage of amplifying background noise in some
cases, which is why it's a good idea to turn the surround systems off for
films that aren't in stereo.  As far as the actual tracks, it is 4, not 3,
tracks- surround, left, center, and right.  The Center track is usually
left+right, I believe.  
    I don't know exactly how 6-track differs from 4-track or surround,
but I would guess that the methods are similar.

If there is interest, I can look up more information in the Dolby system
manuals lying around in a dusty projection booth of a theatre I used to
work at :-)


-- 
============================================
Jay T Stein
           		  	  "Analysis, Spock?"

Go ahead- send me your worst!:	  "I would say that the program is at too early
jstein%hyatt@sun.COM		   a stage to permit solving any serious 
				   difficulties, Jim."

				  "Recommendation?"

				  "Suggest you wait for further plot complica-
				   tion before undertaking corrective measures."