DTS sync issue? Sound going in and out of sync several times within a feature.

[Jerry G. Axelsson]

Hello colleagues,

I had a talk today with a senior cinema technician.
We got into the discussion about Dolby Digital vs DTS when running 35mm film.

He was preferrable to Dolby Digital for mainly practical reasons. (no need to mess with discs etc.)
How also suggested that he had seen a general issue with DTS that it ususally went in and out of sync during a typical feature quite a few times. Not in a big way, but just slightly so he was disturbed by not seeing lip-sync 100% throughout a feature. He also pointed out that he never had seen a sync-testfilm from DTS.

After giving it some thought, I found it odd if that was indeed the case that DTS did not offer sync-testfilm.

I must admit that I have not seen or been bothered with DTS going in and out of sync on a 35mm feature. I have been running DTS for over 20 years...

What are your views on this topic? Have you noticed these issues on a correct and healthy installation?

[Leo Enticknap]

DTS did publish what they call a "Demo Reel" (The Buzz and Bill Show) that enables you to check the sync. I used it once, when installing an XD-20.

I've never noticed any drifting sync issues with DTS. The only possibility that springs to mind is that if the player loses the timecode, it will run the audio wild (unsynchronized) for a few seconds before sending the cue to the main cinema processor to revert to SR (or in the case of DTS 70mm, going silent). I couldn't tell you precisely how long, but it's a significant time. Maybe your co-worker had a system with perennial loss of timecode issues (e.g. the LED in the reader was starting to fade), never long enough for the DTS player to drop out completely, but long enough for it to be running wild for a while, with consequent sync drift?

[Brad Miller]

The DTS will run wild (without timecode) for a maximum of 8 seconds with their later firmware. And it takes quite a lot to get the dts timecode to mistrack.

I'm going to have to call bs on that senior cinema technician Jerry was speaking with. I have never heard of nor experienced out of sync DTS.

[Leo Enticknap]

Unless something is seriously screwed up with the projector's motor (running at an erratic speed), I wouldn't have thought that eight seconds would be long enough to cause clearly visible loss of lip sync.

[Brad Miller]

8 seconds definitely is not enough time for sync drift, but what likely happened was the install tech likely was using some content to check for lip sync and he did it from the booth (and later viewed in the auditorium where there is a slight delay).

Alternatively his initial setup adjustment may have been a tad bit early and a later reel of film he was watching had dubbing not quite perfect which was out of sync a tad bit late. That would make for lip sync that is noticeably off.

Also if the sound isn't spot on, it's always better to have the sound lag by a frame. Something about hearing sound before you see the lips move is more jarring than hearing the sound after you see the lips move.

[Jerry G. Axelsson]

Thank you for your comments guys.

Well, the techncian is no stranger to install dozens of screens with SRD. No problems with getting that in sync.

Back in the 1990:s Sweden has a lot of older projectors in use. Quite a few of them had asynchronous motors.
I wonder if slight differences in the power grid could affect the speed of the projector and the present slight sync issues througout a film?
If that was the case, that should not be unique to our territory of course...

[Carsten Kurz]

We never had sync issues with DTS.

DTS as well als SRD will follow typical speed variations of projectors just fine.

[Steve Guttag]

There was some versions of the firmware were DTS sync could drift, notably at changeovers but it was quickly addressed. And by drift I mean back and forth...not just get further and further apart. It WILL sync up. Part of the nuance of dealing with various projector speeds is having a system to "slew" the lip sync so it always matches but one can't move it instantly or you get a bit of a robo sound and if you go to slow you can drift out of sync and then take too long to recover. Again, changeovers (or splices) can exasperate this as there will be a sudden timecode shift at changeover. I'm unaware of any of the later firmware revisions that had lip sync issues.

[Jerry G. Axelsson]

Thanks Steve. What you describe sounds like the issue/irritation at hand. A slight drift in sync that synced up after a shorter period of time.

I think I have a DTS player with the 1.37 firmware (not the last version). Steve, do you remember which firmware/period in time when the issues you mention took place?

[Mark Gulbrandsen]

I never had issues with the 1.37 version, but we also never ran change over in the theaters I services. All platters. When I was cleaning out my stuff after retirement I even found a couple still new 1.37 ROM chips.

[Steve Guttag]

I don't have any documents handy that indicate the various revisions. I just know that 1.46 is where they ended up and can be required to run later discs. Also, even in a platter theatre, you'll get a timecode jump at reel changes (or splices for repair)...all of which could cause lip sync to drift if it doesn't slew correctly.

[Jim Cassedy]

I never had a DTS disk go "in-and-out of sync". I do recall one feature from an independent Asian distributor where the DTS sound for the entire movie was obviously out-of-sync by a couple of frames. (It had an Asian language sound track, with English subtitles, so even though you might not understand Mandarin or Cantonese, you could still tell the dialogue was outta sync. - It was also obvious during certain percussive sound efx, such as doors slamming or gunshots, etc) I simply readjusted the DTS delay setting to compensate for the error and correct the sync. I had all the trailers running Dolby analog, and when the feature came on the DTS digitaldiskthingy automatically kicked in for the feature. When we changed shows the following week, I just restored the DTS delay back to normal.

[Emiel de Jong]

Hello colleagues,

I had a talk today with a senior cinema technician.
We got into the discussion about Dolby Digital vs DTS when running 35mm film.

Sorry, but I can't resist the little red devil sitting on my shoulder who wants me to ask: is that senior cinema technician by any chance the same person as the former main technician you mentioned in the other thread who experienced so much flutter with the old DP70 optical soundheads?

[Jerry G. Axelsson]

No Emiel. I know quite a few technicians...

[Mark Gulbrandsen]

Sorry, but I can't resist the little red devil sitting on my shoulder who wants me to ask: is that senior cinema technician by any chance the same person as the former main technician you mentioned in the other thread who experienced so much flutter with the old DP70 optical soundheads?

Emiel, Yes... the DP-70 sound reproducer had it's problems. No bearing preload and the bearing lube evaporating after a couple years. Also the lateral guide roller was not split as it should have been. Anyway, we took care of all that when we rebuilt DP-70's. Splitting the lateral guide is not all that difficult either.