albert@kim.Berkeley.EDU (Anthony Albert) (07/17/86)
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? I have posted this to net.video, net.audio, and net.movies. I think a discussion about this would be interesting to people in all three groups, however, I usually only read net.video. So, please reply to me directly, or to some combination of the newsgroups which includes net.video. I actually think it is more interesting to have replies to the net for others to react to, but I'll summarize any which are mailed to me directly. Anthony Albert ..!ucbvax!kim!albert albert@kim.Berkeley.EDU
good@pixar (Blink twice, son, if any of this is gettin' through.) (07/17/86)
In article <14889@ucbvax.BERKELEY.EDU> albert@kim.Berkeley.EDU.UUCP (Anthony Albert) writes: >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? Having just finished the final mix of our SIGGRAPH reel, maybe I can shed some light for you. The only "Dolby stereo" formats I know of are the optical one, used on 35mm film, and the mag stripe used on 70mm releases. The latter is the 6 track Dolby you hear about. More tracks are available on mag stripe than an optical sound track which explains that part of the difference. In the case of normal Dolby stereo, a box (called a DS-4 I think) takes the LT + RT (Left Total, Right Total) channels and derives left, center, right, and surround channels. The center channel is easy to get by summing L and R, and completely out of phase information gets sent to the surrounds. When you watch 70mm they can give you left, center, right, a stereo pair of surrounds in the middle of the theatre, and the back surrounds. I'm pretty sure I have that right. Anyway, the far back surrounds in either case would be mono. Most people don't realize that there is a center channel on the screen which is why they get confused counting tracks on their fingers. THX is part of the playback system, and not a format in itself. The heart of it is the crossover designed by Tom Holman. Thus, in addition to the obvious "THX 1138" reference in the name, it stands for the Tom Holman Xover. Tom's system also specifies a set of JBL theatre horns and a subwoofer (yes, it's a two-way system!), the "wall" it is mounted in behind the screen, and the amplifiers (last I heard he was using the Hafler 500). It's really the first time theatre playback has changed since the 1940's. And, as Tom says, with a THX a theatre sounds almost as good as a cheap home stereo... If you've never heard a good sound picture in a THX room you really should. It makes quite a difference. Getting back to 35mm vs 70mm, the biggest difference is often the sound quality. Besides the better channel definition, the mag stripe buys you a much larger bandwidth and better S/N. I *always* opt for the 70mm show when I have a choice, even if I have to drive farther. Hope this answers some of your questions. -- --Craig ...{ucbvax,sun}!pixar!good
jstein@sun.uucp (Jay Stein) (07/17/86)
> 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."
tardis@ihu1n.UUCP (John Golkosky) (07/19/86)
> 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? > There is an interesting article in Modern Electronics Feb '85 regarding the construction of a Delay Enhanced L-R Decoder (not a "true" surround sound decoder). It gives some background on how the surround information is recorded and played back. Also check out Video Review Nov '85. The article talks about Surround Sound and difference between true Dolby Surround decoders and imitations. It also gives some buying tips and sample prices as well as what to look for if you are buying one (i.e. built in amp, number of audio outputs, etc...). John Golkosky ihu1n!tardis AT&T Bell Labs Naperville, ILL "Would you mind being careful where you throw your rocks Mr. Spock!" - Capt. Kirk "The Apple"