DTS/DD/THX 35mm preservations

[zoidberg]

DTS and THX trailer audio can be had from DTS CD-ROMs (in the trailers folder), obviously different discs will hold different versions.

Unless Tom goes down the grabbing the bits from the film print route, then probably the best source for the Dolby logos would be one of their demo discs, failing that laserdiscs (only 384kbs but possibly beefier tracks, couldn't say without comparing).

With regards to Tom's comments on SR-D Dolby Digital, separate prints would still have been struck for Type-A and SR noise reduction (as the two are not 100% mutually compatible) although I believe that eventually all analogue tracks were SR. Initially the logo would say 'Verify Theater Format' to cover every possible iteration. I get the impression that SR-D was Dolby's initial name for AC-3 as the tracks were of similar bandwidth to analogue SR. Eventually prints were just labelled Dolby Digital. 

There was also 70mm Mag SR which was the king of them all but came at a time when 6-track mag was being phased out completely, eventually being replaced with DTS. However the 6-track SR was still used in the studios for the print masters.

[MrBrown]

... .



So, the overall dimensions in terms of bits are 76 * 76. That's 5776 bits.
The DD logo in the middle always stays the same and has dimensions of 12 * 12 bits, which is of course 144 bits.
...

Do not forget the four corners, that seem to stay and be the same pattern on the Wikipedia image ND the YouTube clip.
Altho there seem to be a kind of steady part in the YouTube clip, that might contain additional steady info , maybe something that the decoding device need to know? Like the number of channels... Or some other Metadata...

[deleted user]

... .



So, the overall dimensions in terms of bits are 76 * 76. That's 5776 bits.
The DD logo in the middle always stays the same and has dimensions of 12 * 12 bits, which is of course 144 bits.
...

Do not forget the four corners, that seem to stay and be the same pattern on the Wikipedia image ND the YouTube clip.
Altho there seem to be a kind of steady part in the YouTube clip, that might contain additional steady info , maybe something that the decoding device need to know? Like the number of channels... Or some other Metadata...

Great catch! I think that could definitely be useful at some point for figuring this out in some way. He replied to me and said he would send me the jpegs of this data, so with a bit of luck we will have a nice sample to work with soon.

[MrBrown]

What if the hole thing is just a "normal" ac-3 Bitstream, that would be the same as a bit perfect ac-3 stream rip from LaserDisc? Maybe the system is that simple...

[spoRv]

Most probably the four corners must be the same for every track, to let the picture be aligned.

[deleted user]

What if the hole thing is just a "normal" ac-3 Bitstream, that would be the same as a bit perfect ac-3 stream rip from LaserDisc? Maybe the system is that simple...

It's possible, but unlikely in my opinion, unless I'm misunderstanding the format. 35mm ac-3 has 320kbps of data, but there's many more bits on those data blocks, as my earlier calculations have shown. Even if you subtract the four corners, that doesn't get you as low as 320 kbps. Also, it's possible (though I can't be sure) that during a bit-perfect capture, error correction is already being automatically applied by whatever capturing hardware you use.

Most probably the four corners must be the same for every track, to let the picture be aligned.

Yep, I'm pretty sure of this and that's also what that PDF I linked described. First the track is captured with a CCD sensor (it says it has 512x512 resolution in the Dolby Decoder), then the corners are found and used to apply a kind of "window" which helps find the positioning of all the individual bits, then a thresholding process is applied (which determines how bright a pixel has to be in order to be considered a 1 instead of a 0) and then some further adjustments that aren't further described. And once all the bits are read, error correction is applied and from that results the actual stream that gets read and processed.

[MrBrown]

Most probably the four corners must be the same for every track, to let the picture be aligned.

Why not use the DD logo for that? But maybe you are right... It gives the image deciding a frame... And as every system is kind of dumb.. It is not a optical alignment, but a serial reading.. And thus the starting and end points make senses... Like giving the reader Infos of the image... No matter how it is zoomed... It may define such things as bit point size in optic... And such...

[spoRv]

I guess the Dolby logo in the center is useful as well for alignment, but also to point out that it's a Dolby track for the ones who does not know it!

[deleted user]

Most probably the four corners must be the same for every track, to let the picture be aligned.

Why not use the DD logo for that? But maybe you are right... It gives the image deciding a frame... And as every system is kind of dumb.. It is not a optical alignment, but a serial reading.. And thus the starting and end points make senses... Like giving the reader Infos of the image... No matter how it is zoomed... It may define such things as bit point size in optic... And such...

The DD logo is likely used as a help to find the center. Using it for alignment may not work perfectly if the scaling is off for some reason, because it's a small part of the image and unless you capture it at an incredibly high resolution, it won't be a reliable measure of the scale of the code that can be extrapolated to the whole width and height. Similar to how QR codes have those static 3 corners that always show the same thing instead of having something in the middle for this purpose.

[MrBrown]

BTW. The Theatrical SR.D Dolby system seems to be invented 1992, while QR codes were official invented 1995...
So, sadly these SR.D do not follow the rules of qr codes..