DTS playback with non-DTS hardware

[David Ferguson]

This is an offshoot of the discussion on the thread about Liquorice Pizza, where the topic of playing back 70mm film with a DTS track on non-DTS hardware was discussed, initially from the comment that the hardware currently being used for 70mm DTS playback is ageing (and could be 28 years old now!) and although Datasat still have a page on their site about it, I would imagine the servicing and replacement options are limited these days. And then I was wondering if anyone's ever played Atmos alongside 70mm (which if so I'd love to see!), and how that might be technically possible.

---

Continuing on from the thread...

Using SMPTE or MIDI time code would only work for NEW film prints. What about all the existing 35mm and 70mm prints with DTS time code? You can't convert time code that has already been written onto film prints. It should be just as easy to update the firmware in a d-cinema processor to be able to understand DTS time code data when it is read off a film print. On release prints DTS time code is the most common kind of time code data out there. There is no good reason to replace it with another standard such as SMPTE or MIDI. The DTS stuff can pretty much be open-sourced at this point.

Apologies, I may have not been clear enough in what I was trying to say. I'm not proposing replacing the timecode on the print - as you say there is no reason to do that. I'm saying you want to convert the signal/data coming out of the DTS timecode reader into a modern and well used timecode format, like SMPTE or MIDI (probably using USB). So it goes DTS Reader ---> Converter Box ---> Computer, and then the computer can read the modern timecode easily, and play back audio to it (using software that's already available). That way you can continue using the existing timecode readers (which are really just an LED and a sensor built round some rollers, so I don't anticipate any hard to fix failures).

As I said, this isn't theoretical, before I got my XD10 I used my computer to play back the audio according to the timecode from the print. It wasn't perfect (only two channels, and occasional audio jitters), but for an afternoon's trial and error, and only using free software, I was pretty pleased.

Now the real trick would be getting a digital projector to sync a DCP to the timecode, which would allow Atmos to be played for a 70mm print. I seem to recall that some of the early 3d systems involved two projectors - I assume that was timecode based?

[Bobby Henderson]

Apologies, I may have not been clear enough in what I was trying to say. I'm not proposing replacing the timecode on the print - as you say there is no reason to do that. I'm saying you want to convert the signal/data coming out of the DTS timecode reader into a modern and well used timecode format, like SMPTE or MIDI (probably using USB). So it goes DTS Reader ---> Converter Box ---> Computer, and then the computer can read the modern timecode easily, and play back audio to it (using software that's already available). That way you can continue using the existing timecode readers (which are really just an LED and a sensor built round some rollers, so I don't anticipate any hard to fix failures).

I'm thinking there needs to be some kind of plan to make new time code readers if necessary. If an existing DTS time code reader still works properly then it works. But there needs to be a plan otherwise. The reader isn't doing too awful much other than seeing the dots on the film strip and converting them into digital data.

Converting that data from DTS time code and making it look like SMPTE or MIDI time code is a potential point of problems. Such a conversion process takes time. Even a few milliseconds can be enough to cause issues with audio sync. That could either mean audio drop outs with the film print or lip sync being thrown off. Would SMPTE or MIDI time code be able to contain all the relevant data from the DTS code? I'm just thinking it would be much more straight forward to update a d-cinema processor's firmware to be able to directly understand that DTS time code rather than going thru some real time conversion step in the chain. The end result would be faster and more reliable. There would be less chance of sync issues. It's pretty common for many computer applications and pieces of computer hardware to be able to read many different kinds of the same type of file. I use a variety of computer graphics applications, some of which do the same basic thing but have their own strengths and weaknesses. They all know how to import and export a wide variety of file formats (to a varying degree of "success" in some cases). DTS time code is not some lesser time code format. In all likelihood DTS time code has been used on extremely many times more feet of film than SMPTE and MIDI put together. And that is especially true for motion picture release prints. IIRC the short-lived LC Digital format from France used SMPTE time code to sync a magneto optical disc drive with audio compressed in Philips Musicam format. That format didn't last. Meanwhile DTS had a run that lasted roughly 20 years. DTS time code is THE standard time code for film now.

[Carsten Kurz]

David - your GitHub page suggests that DTS timecode was 30frames per second - how does that line up with films 24fps?

Also, as far as I know, some of the older DTS units can be configured to output SMPTE timecode from DTS TC.


It IS actually possible to sync ATMOS playout to SMPTE LTC. I remember when the local multiplex installed one of the first BARCO 6p lasers in their premium ATMOS auditorium, the projector absolutely needed BARCOs then brand new ICMP to project images. However, the ICMP could not yet play ATMOS. So they synced it to a DSS200 for the audio part, with some special help from Barco (but no external equipment was used). The ICMP offers both timecode input and output. Also, every ATMOS DCP has a standard LTC track in DCP audio channel 14.
The question is, are DCPs and film version 100% identically cut to the frame level. Very often the 70mm versions have some extra features (e.g. an intermission).


Quite a few DCI servers support LTC based chase sync play between two or more units - e.g. Doremis classic servers. Doremi/Dolby has a few papers about it.

[David Ferguson]

David - your GitHub page suggests that DTS timecode was 30frames per second - how does that line up with films 24fps?

While the film does play at 24fps, the DTS audio is split into "frames" that play at 30fps, and the DTS timecode reflects this and gives a timecode frame 30 times a second. If you look at the timecode on the film you'll see there isn't one timecode frame for every picture frame, the timecode frame is smaller.

Also, as far as I know, some of the older DTS units can be configured to output SMPTE timecode from DTS TC.

Do you mean the readers could output SMPTE? Or the players could accept SMPTE input? I know the XD10 can be modified to accept SMPTE input, and this was used in many special venue installations. And DTS also had their "Timecode generator" which could output DTS timecode from SMPTE timecode in, or tach in.

It IS actually possible to sync ATMOS playout to SMPTE LTC. I remember when the local multiplex installed one of the first BARCO 6p lasers in their premium ATMOS auditorium, the projector absolutely needed BARCOs then brand new ICMP to project images. However, the ICMP could not yet play ATMOS. So they synced it to a DSS200 for the audio part, with some special help from Barco (but no external equipment was used). The ICMP offers both timecode input and output. Also, every ATMOS DCP has a standard LTC track in DCP audio channel 14.
The question is, are DCPs and film version 100% identically cut to the frame level. Very often the 70mm versions have some extra features (e.g. an intermission).


Quite a few DCI servers support LTC based chase sync play between two or more units - e.g. Doremis classic servers. Doremi/Dolby has a few papers about it.

That's very interesting to know, although you're right about the caveat that often the 70mm version may be different. I'd love to try this out at some point - any cinema willing?

[Carsten Kurz]

I have to look the SMPTE option up from my quite comprehensive DTS document collection. The TC-board in our DTS-6D unit spots an OTARI SMPTE-LTC integrated circuit. The DTS reader, as you probably know, just outputs a biphase representation of the morse code that makes up the DTS TC track, so, aside from their mechanical and LED/spot reading features, they are pretty dumb. The SMPTE LTC conversion would happen in the DTS player unit.
Interesting that they chose 30fps as the time base for audio and TC, didn't know that. Back when I had to troubleshoot playout issues with our DTS unit, I recorded the DTS TC tapped from the TC cable through a resistor network to a simple rec-able MP3 player so that I could check DTS disc playout easily without running our film projector. But it's 30fps nature escaped me. I guess nowadays one could easily build a new DTS player from a Raspberry PI. That would also offer an easy transition to lossless/PCM.

[Scott Norwood]

I don't have the knowledge to do this, but, if I did, I wouldn't worry about trying to sync to a DCP. Not every DTS film has a DCP available, the timecode may not match, and the mix may be different. Also, not every film venue has DCP capability (even in 2021).

I would probably try to build an input board (to accept the reader timecode) and an output board (to output audio--probably in AES format, but maybe analog) that could fit into a normal desktop computer (via PCI express or maybe USB). At that point, we just need hardware drivers and decoding software. The latter of which might present some problems, since DTS changed to a different format (AUE vs AUD) around 2005-2006 or so. None of this should be terribly difficult or expensive in 2022. Real DTS units do the decoding in hardware, but processing power is now sufficiently advanced that a software decoder should be easily possible.

I'm not too worried about the readers because a) as noted above, they're really just rollers, an LED, and a solar cell and b) there is a good supply of existing ones (maybe not for 70mm, but certainly for 35mm).

[Jack Ondracek]

Converting that data from DTS time code and making it look like SMPTE or MIDI time code is a potential point of problems. Such a conversion process takes time. Even a few milliseconds can be enough to cause issues with audio sync. That could either mean audio drop outs with the film print or lip sync being thrown off.

Delete, Please

[Paul H. Rayton]

Some discussions along this line were held (although, to my knowledge, nothing ever came of them) back in late 2018 when Alfonso Cuaron's movie "Roma" came out. It had a splendid Atmos mix -- which could be heard with the DCP. Cuaron also prevailed on the production company to have a number of 70mm prints made ... but which could, of course, only be presented in DTS standard 5.1 playback. I saw the movie in both versions, and the Atmos mix was quite effective.

It was a damn shame that the visual quality of the 70mm prints sacrificed the superior Atmos audio, but there was no readily-workable solution. Ironically, then, the definitive performance(s) of that movie would have been in the VERY few DCP houses equipped with both Atmos and HDR/Dolby Vision. Here in L.A., at the time, there were only one or two that I know of so equipped: the El Capitan, and (I think) one in the AMC Burbank 18 complex. So, really, it was virtually impossible to see that show in the ultimate presentation: the El Capitan (which definitely had Dolby Vision by that time) runs almost exclusively Disney product, and all the other major exhibition companies with the expensive extra equipment were boycotting the movie, since it was from the hated arch-enemy, Netflix. That was one big no-win situation for Cuaron, and theatrical audiences everywhere. Maybe the home Atmos presentation was almost an equivalent, but that's not going to help cinemas ...

(And which reminds me -- Christopher Nolan told us all that the ultimate & superior way to see "Dunkirk" was to see the film version in an Imax film presentation. Maybe so, but by that point in time, virtually all Imax screens were silver-surfaced for 3D. The Imax normal 2D presentation was compromised by the hot-spotting of the image caused by the silver screen, so ... many of the advantages of a film presentation were completely wasted. Sigh...)

[Sean McKinnon]

This would be very easy to do and could in fact be done for any movie brand new or old without altering the DTS time code on the print at all. All it takes is someone willing to pay to do it and get the players involved to play nice with each other.

[Marcel Birgelen]

I guess even I could come up with a 3D printed contraption to read DTS timecode from film. If it can be converted to SMPTE timecode with open software, I guess you can take it from there. But without the magnetic sound track being present, shouldn't there be sufficient room on there to print an SMTP timestamp right on there? How difficult would it be for the labs to print a simple binary SMTPE timecode track on there? Maybe even put in a little extra error correction?

[Sean McKinnon]

At that point you could just use a bi-phase rotary encoder to drive the smpte time-code generator. The scheme that I have in mind uses all existing equipment, standard off the shelf DTS players and readers, standard DTS timecode on the prints.

[Carsten Kurz]

The DTS timecode is a standard feature now for all film releases. Why bother creating another addition to labworks that is already struggling with their economics and quality management? Converting DTS timecode to SMPTE timecode is trivial (even converting from 30fps to 24fps is simple, based on it's absolute timestamp nature), and keeping the DTS timecode will stay compatible with the existing DTS players.

That said, they should have used SMPTE timecode on film prints right from the start back in the nineties.

[Marcel Birgelen]

The DTS timecode is a standard feature now for all film releases. Why bother creating another addition to labworks that is already struggling with their economics and quality management? Converting DTS timecode to SMPTE timecode is trivial (even converting from 30fps to 24fps is simple, based on it's absolute timestamp nature), and keeping the DTS timecode will stay compatible with the existing DTS players.

That said, they should have used SMPTE timecode on film prints right from the start back in the nineties.

Because it's an open standard, nobody can claim license fees for that and it would be pretty trivial to read it from the prints and sync it up with existing audio standards. DTS players and readers will eventually vanish and with no real support from DTS, it remains to be seen how this format can be supported in the future. I'm trying to look a bit ahead.

I have no clue how much work it would be for labs to put it on there, but I guess a similar process to encoding the DTS timecode on there can easily be repurposed.

[David Ferguson]

Because it's an open standard, nobody can claim license fees for that and it would be pretty trivial to read it from the prints and sync it up with existing audio standards. DTS players and readers will eventually vanish and with no real support from DTS, it remains to be seen how this format can be supported in the future. I'm trying to look a bit ahead.

Note: I'm not a lawyer, this is just me thinking aloud.

As far as I can see, the US patent for the DTS timecode, which was filed in 1992, has expired, so there shouldn't be any license fees to use it. There probably are license fees to call it "DTS" or "Datasat Digital Sound", though one could just call it "Timecode Digital Sound" and I think you'd be fine. I can also see patents for the apt-x100 encoder/decoder that look like they've expired - this EU one, and this US one. And there's already software out there that can decode and encode DTS audio files (I've used it to play back DTS discs, and also encode my own for movies where I couldn't get the disk).

I have no clue how much work it would be for labs to put it on there, but I guess a similar process to encoding the DTS timecode on there can easily be repurposed.

In theory you could put any linear timecode in place of the DTS code on the film. As far as I'm aware, the code is printed onto negatives (or positives in the case of the Cinevator) using an LED that's driven by a DTS timecode generator, so replace that with a different timecode generator and you get a different timecode on the film. And the reader will read out the new one no problem, you'd just need to feed that into your own decoder. However as Carsten says, imo it's better to keep using the DTS timecode to keep compatibility with the current hardware, and I can't see a downside to doing this either.

[David Ferguson]

I guess nowadays one could easily build a new DTS player from a Raspberry PI. That would also offer an easy transition to lossless/PCM.

Should be very possible, I may have a play with this actually. There is already software that can play back audio to a timecode, so the hard part is done and all that's needed is for the Pi to read the timecode from the reader which should be trivial. How well it all works in practice, I'll have to see (if I end up trying it out, that is!).