Thought Experiments: Modern PCM Audio sync'd to Film

[David Ferguson]

When I saw the title of this thread my first thought was that I was sure this had been discussed many years ago - managed to dig up that thread, it has some interesting bits of info: https://www.film-tech.com/vbb/forum/...n-dts-hardware

As others have said:

• DTS timecode is super simple, and converting that to another timecode format is quite trivial. Before I had a XD10 I converted it to MIDI and played back the soundtracks that way using some free MIDI audio player (it wasn't very good, but it did the job at the time). I've also done the other way - SMPTE to DTS to play back audio using a DTS player.
• DTS does support lossless audio (not uncompressed, it still is compressed, but is lossless) using the coherent acoustics codec. All XD10s (and I assume XD20s) support this, but I have never seen a disc for this. If anyone has one, please let me know as I'd love to see the format.
• XD10s also do support SMPTE timecode - but that's less relevant here as the goal seems to be to play a print with DTS timecode without DTS hardware.
• Yes, SRD also has a "timecode" which outputs block numbers. However, in a huge oversight that I still can't believe Dolby did, they didn't standardise the start block number for a reel. Their guidance to labs was to do "about <num>" (I forget what the number was). I have verified this that reels of different movies have different starting numbers. And in fact, two identical reels of the same movie, but done by different labs, also have different starting numbers! This difference is usually quite small, within a second - which makes it ok for subtitles (this is what Dolby ScreenTalk used), but is very annoying for audio sync as you have to have a map of what the starting reel numbers are for each reel of movies.

As I say in the other thread, I think the most viable option for cinema owners today is to convert the DTS into a timecode format the a digital projector can chase/sync to, and then have that run the DCP. This could potentially let you run an Atmos mix with a 35mm print - if such a mix existed. I have always wanted to try that, but for some reason, no cinema owner with both 35mm and atmos will let me come in and plug my DIY converters into their expensive hardware. I wonder why not? Any volunteers here?

[Ryan Gallagher]

When I saw the title of this thread my first thought was that I was sure this had been discussed many years ago - managed to dig up that thread, it has some interesting bits of info: https://www.film-tech.com/vbb/forum/...n-dts-hardware

Thanks for digging up that thread David, glad to know I wasn't the only one thinking about these things. Definitely a bit of thinking through the topic has been done prior! (Perhaps even a bit of doing it).

One nuance you were driving at in the other thread is looking ahead to a day when these aged DTS processors are no longer viably maintainable. Another perfectly valid reason to do it, and perhaps a larger need than special pairings of prints to modern immersive soundtracks.

I'd happily volunteer if ATMOS made the cut on our renovation plans... but due to historical architecture priorities the rumor is that ATMOS has hit the cutting room floor. Our smaller venue is still in the running but it is digital only. So other than maybe stepping up to DCP 7.1 audio sync (which debatably could be done with existing DTS hardware and coherent acoustics tracking instead), none of this will apply at my venue. Just pondering directions the industry or willing parties could go for special 35/70mm screenings, which are of course the minority now rather than the majority, so it seems unlikely the market would support a commercial hardware approach, and instead most likely approaches would leverage existing standards, booth infrastructure, and a layer of more open approaches.

If server/IMB "chase modes" were not universally a viable solution, but one still wanted DCP deliverables for the audio, maybe some of the more open DCP software players could step in... but as has been done, at that point one might as well skip the DCP container entirely if not tied to any hardware, but for wider releases delivering such a solution like ProTools sync with an ATMOS renderer seems cumbersome, perhaps the IAB standard is more approachable in that special case.

That bit about SRD block numbering not being consistent is interesting (and unfortunate).

[Ryan Gallagher]

Not very necessary, but another side benefit to having the ability to chase with a DCP (completely separate from providing audio via the sync'd DCP) would be for backup management. If chasing supported pause on loss of timecode, and the ability to enter/exit chase modes easily... you'd have a backup that was timecode accurate to the breakdown (ish, the projector/DTS reader might spool forward a bit in the shutdown), but at least the backup would maybe pause on it's own)

I realize not all DCP's are going to be frame accurate to their 35/70 corresponding prints... so backup tracking would always be approximate, hence the silliness of the thought.

I'm not sure whether I was imagining DCPs for film syncing audio deliverables as including the picture or not. Probably not, as they probably would need to be feature specific to the prints, but if everyone runs backups, picture would be great too... just means studios would have to spin all the versions for the different DCI visual systems that might be in play, which seems unlikely. Or maybe you only get the bare minimum, a SDR 4K/2K compatible picture for backup within the file, but can switch to something more venue appropriate if you want to book a better backup too.

Would probably have to be an alternate normal DCP as backup, that one could strike lamp and load manually... but having a piece of software that showed you the last timecode before the failure would allow you to jump into it at approximately the right place. Or just run the Blu-Ray as backup and remember to hit pause in the event of a disaster (not possible on new releases of course!)

Postulated from the perspective of a manually operated booth, which I assume all 70mm/35mm venues kinda are these days? If loss of timecode cannot trigger a chasing pause, maybe those lucky enough to have fail-safes could implement an automation based pause of the ST or backup.

[Tony Bandiera Jr]

Not very necessary, but another side benefit to having the ability to chase with a DCP (completely separate from providing audio via the sync'd DCP) would be for backup management. If chasing supported pause on loss of timecode, and the ability to enter/exit chase modes easily... you'd have a backup that was timecode accurate to the breakdown (ish, the projector/DTS reader might spool forward a bit in the shutdown), but at least the backup would maybe pause on it's own)

I realize not all DCP's are going to be frame accurate to their 35/70 corresponding prints... so backup tracking would always be approximate, hence the silliness of the thought.

I'm not sure whether I was imagining DCPs for film syncing audio deliverables as including the picture or not. Probably not, as they probably would need to be feature specific to the prints, but if everyone runs backups, picture would be great too... just means studios would have to spin all the versions for the different DCI visual systems that might be in play, which seems unlikely. Or maybe you only get the bare minimum, a SDR 4K/2K compatible picture for backup within the file, but can switch to something more venue appropriate if you want to book a better backup too.

Would probably have to be an alternate normal DCP as backup, that one could strike lamp and load manually... but having a piece of software that showed you the last timecode before the failure would allow you to jump into it at approximately the right place. Or just run the Blu-Ray as backup and remember to hit pause in the event of a disaster (not possible on new releases of course!)

Postulated from the perspective of a manually operated booth, which I assume all 70mm/35mm venues kinda are these days? If loss of timecode cannot trigger a chasing pause, maybe those lucky enough to have fail-safes could implement an automation based pause of the ST or backup.

On a few of my "critical" screenings at HIB 100, (in reality most every one was as they were all one-offs) I ran the DVD backups with the film feature, by starting the DVD 5 minutes after the film print. That allowed me plenty of time to fire up the video projector, let the lamp get to full brightness, and do a nice switch in under 2 minutes ... which also backed up the program a few minutes before the breakdown which the audiences appreciated. I didn't have to cue up anything, or press play.. just switch the sound over on the CP650. In many cases I was also able to preset the video image to the film masking so it was relatively seamless.

That only came to pass once, on a Korean cinema 35mm print that was very shrunken and brittle, made it all the way to the last reel before disaster struck.

As for most of the others, very careful hand inspections of the prints (with any necessary repairs made) plus the Kinoton projector's gentle film paths, prevented any other breakdowns, even when the print sounded like a chainsaw going through the projector.

[Ryan Gallagher]

On a few of my "critical" screenings at HIB 100, (in reality most every one was as they were all one-offs) I ran the DVD backups with the film feature, by starting the DVD 5 minutes after the film print. That allowed me plenty of time to fire up the video projector, let the lamp get to full brightness, and do a nice switch in under 2 minutes ... which also backed up the program a few minutes before the breakdown which the audiences appreciated. I didn't have to cue up anything, or press play.. just switch the sound over on the CP650. In many cases I was also able to preset the video image to the film masking so it was relatively seamless.

That is our identical approach essentially, but because we roll DCP preshow content I'm also able to have automation fire the Blu-Ray play trigger 5 minutes after we are rolling with no need to remember to do it. We too take the time to size our digital backups to the film masking... our DCI formats and Analog lensing are not quite matchy matchy, so backup can be it's own challenge, but have most formats by now, not all masking is motorized, and neither is our DCI zoom (ILS motor failed)... so most painless just to do the work ahead and make it fit the masking.

Like you, have not needed it yet. But now I've got a pattern where the first film I don't have a backup for will be the one I need it for sure. lol

Chasing for a backup was a silly idea anyway, cause the other approaches works fine for releases that have DCP or Blu-Ray versions. If the DCP was instead delivering special audio only to sync to film, and no blu-ray available, only DCP, then you might need some kind of counter or method know where to load an alternate DCP backup into. But a low-tech stopwatch could do it. ;-)