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Can a 70mm film god please tell me if my list is correct or not? I haven't found a list of track assignments and the little documentation that is out there is contradictory.
Remove Side and Rear designations. Mono surrounds have surrounds on sides and rear. Stereo surrounds wrap around the rear corners like a hockey stick. Only times that the rear surrounds are broken out is if there was an EX mix (none that I'm aware on 70mm but it may exist) and no 7.1 mixes exist on 70mm though it is certainly possible with DTS/Datasat but I presume you are referring to magnetic tracks.
40: Correct
41: Should match 40. Only difference is Dolby NR on all tracks.
42: No surround information on tracks 2 or 4. Just LFE below 250Hz.
43: Track 4 is Right Surround above 500Hz (track 2 is Left surround above 500 Hz).
44-46: not standard format designations and can vary from site-to-site. The only processor that Dolby made that had both A and SR NR built in was the CP650 (and it did it in DSP) but it only emulated SR on 2 (and maybe 4) channels. The manual I have only shows support for format 42 but I was pretty sure it could handle format 43 (the CP500 could but it only had up to 6 channels of A and 2-channels of SR via physical cards (two CAT300s and one CAT 222A.
[Edited to correct the format 43 surround frequencies.]
Last edited by Steve Guttag; 03-29-2023, 08:20 AM.
In format 43, the mono surround information below 500Hz is fed to both left and right surrounds. In this manner the surrounds are all full range but they are only directional above 500Hz.
I worked with the "Apocalypse" team to set up Century 21, San Jose. This and the Northpoint SF were used as local test houses for the ever evolving sound mix. Due to the round dome shape of Century 21 we decided to use channel 6 mono surround for the rear surrounds and 2 and 4 for left and right side surrounds.
Worked spectacularly.
There was no 12Khz trigger tone on 70mm soundtracks, only on 35mm 4 track mag, so I would remove that designation.
The original Century 21 was wired for 8 channels and powered by Ampex 120 Watt tube power amplifiers. They were probably thinking some sort of Cinerama sound format at the time. Only had the one projection room though. Never saw any evidence of dubbers either.
In format 43, the mono surround information below 500Hz is fed to both left and right surrounds. In this manner the surrounds are all full range but they are only directional above 500Hz.
Oh I see so they are overlaid together essentially, giving you directional surround when you want it and mono by default.
No, it is more clever than that. Format 43 is, essentially a backwards compatible format. If you run it in a theatre without the decoder, it will play, without issue in a theatre that can only support format 42. If, on the other hand, one were to play it in a really old theatre with no Dolby processing (so the NR is going to be wrong already), it would still play if you disconnect the HF section of LC and RC because of the crossover points (LFE comes in at 250Hz and most cinema speakers, of the era, like Altec, used a 500Hz crossover.
For those movies mixed in Format 43, they had stereo surrounds at all times...it was just mono below 500Hz.
Think of it as a practical way to provide stereo surrounds while still maintaining compatibility to surrounds mostly wired as mono back then. You could use channel 6 to feed the whole surround string or break out the wiring as left/right and feed them from tracks 2 and 4. Backward compatibility was a big item with Dolby.
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