my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » What causes DTS to drop out at reel splices? (Page 1)

This topic comprises 2 pages: 1  2

Author Topic: What causes DTS to drop out at reel splices? Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 12-18-2002 12:56 PM                    OK, as I understand it, the DTS should keep playing for a number of seconds if it looses track of where it is. Which means it should continue through a splice with no problems because presumably, even if the spliced frame is somewhat screwed up, the very next one should be fine, and things should continue normally. However, every once in a while, our DTS drops on certain reel splices. What would make the DTS just STOP playing sound immediately on a splice? I have a theory of what might be happening, but I wanted to throw it out to the group first. Thanks! Mark  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-18-2002 12:58 PM                        Does the LED on the timecode reader stay lit when the sound drops out? Do you have SRD in the same house? Is this a platter or changeover setup?  |  IP: Logged Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 12-18-2002 01:15 PM                    I'm 99% sure the LED stays on. I'll verify that tonight. I'm not sure which LED you mean though, although I assume you mean the green one and not the red one. There is no SRD in this house, although I'm not sure why that would matter. Platter/change over is irrelevant. The issue is when a --> reel splice <-- goes through. Thanks! Mark  |  IP: Logged Ken McFall Jedi Master Film Handler Posts: 615 From: Haringey, London. Registered: Apr 2001 posted 12-18-2002 03:51 PM                     Hi Mark... in a situation like this everything is relevant.... until it is removed by elimination. In a change over show the DTS player will always play the audio associated with the later Timecode. There is no actual projector selection taking place. The later Timecode will play and discard the earlier. If you had SRD installed it could be that it's not been installed correctly and when it reverts its killing the DTS..... so it is very important to know exactly what systems you have installed. There are a number of things that can cause DTS to drop out.... but you seem to suggest it just stops playing, rather than reverting to SR? You are correct in that DTS will continue to play if the Timecode is damaged, some 5 seconds I think. As the Timecode is very robust and difficult to damage in normal use this does not cause a problem as it is usually restored well within that time. What may be happening here is that there is a fault with the Timecode itself which is effectivley saying that there is no more sound so stop! As it only happens at a reel change I'm think this is what's happening. I've seen it before on a couple of trailers where the Timecode stops before the actual end of the trailer. So, is this a recent problem or long standing. Has any work been done recently to your automation system that may have changed something, maybe a plug on the back of the DTS has worked its way out slightly. Does the DTS revert correctly to SR when you test it by blocking the reders LED for a few seconds? If you are multi screen do you have the same problem if you play the film in another DTS screen? One other point.... have you personally experienced this problem or are you relying on the information of others? Regards.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 12-18-2002 04:01 PM                     I don't have the solution, but I have had what I think he is describing. As the reel change goes through, the dts unit STAYS in digital, timecode never blips, yet it drops out for a split second. It's very annoying and I've never found a fix, but only affects certain movies (fortunately rare).  |  IP: Logged Karen Hultgren Master Film Handler Posts: 492 From: Agoura Hills, CA, USA Registered: Mar 2000 posted 12-18-2002 04:04 PM                        Mark, If the timecode is good at the end of the out-going reel and is good at the beginning of the in-coming reel, there should be no problem with splices. It should not cause a drop-out. The DTS player will keep going for up to 4 seconds without seeing timecode before it drops out to analog. When the drop-out occurs, does the DIGITAL light go out? What is the green TIMECODE light doing? The green TIMECODE light should be on steady (you will see a quick blink when the splice goes through). The red light on the reader's lens should always be on - no matter if film is running or not. It glows whenever the DTS player is powered and means that the reader is powered (besides reading the timecode off the print). BTW - NEVER EVER adjust the reader's lens!!! You may want to try disconnecting automation so that the DTS and CP work together w/o automation. See if the problem goes away. If it does, then autoamtion is interferring. The other possibility is your OFFSET setting. If it is over '70', it may cause a momentary drop-out to analog between reels. If your OFFSET is over '70', you may want to move the reader closer to the projector so that the OFFSET is decreased. Be sure to remember to recalculate and reset the OFFSET setting on the player if you move the reader. I hope this helps. Feel free to send me an email if you'd like to discuss this further. Karen at DTS khultgren@dtsonline.com  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 12-18-2002 05:51 PM                     I have the reverse question; what causes SRD and SDDS to drop out at reel splices? They both have enough redundancy to carry through what should at most be two frames of a really jumpy splice, right? So why do they drop out? Is it a deliberate decision not to "free-wheel" in the absence of evidence that the film hasn't broken? Thanks. --jhawk (who watched the Two Towers last night [at someone else's theatre], and was a bit grumpy about digital sound dropouts at every reel splice, even those though the splices were perfectly steady on-screen...)  |  IP: Logged Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 12-18-2002 06:30 PM                    It is best to have the DTS reader the last thing on top of the projector head. All other readers for SDDS and SRD and the film cleaner mount should be befor it. With the film cleaner mount being either mounted to the platter tree or the very first thing befor all the other readers.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 12-18-2002 06:40 PM                    Jhawk, how could SR-D freewheel without audio data? DTS can because it can keep cranking out the track from the disk at the same rate it had been running at. SR-D does use a technique of using their background data to send audio data to cover a bit around the reel change on some films (perhaps it is standard procedure now) but if it's dropping out then it must not have the data and if it can't read at the splice there's not much else they can do.  |  IP: Logged Mike Blakesley Film God Posts: 12767 From: Forsyth, Montana Registered: Jun 99 posted 12-18-2002 06:45 PM                        quote: As the reel change goes through, the dts unit STAYS in digital, timecode never blips, yet it drops out for a split second. I think this is caused by the DTS unit switching from disk A to disk B. On my system at least, the sound will go back to analog for about .5 to 2 seconds, then switch back to DTS. (I'm running one of the older 2-drawer machines.)  |  IP: Logged Karen Hultgren Master Film Handler Posts: 492 From: Agoura Hills, CA, USA Registered: Mar 2000 posted 12-18-2002 08:11 PM                        Mike, You DTS-6 (2-drive) unit should stay in digital when it goes from one drive to the next. Please make sure that your OFFSET is not more than '70'. Karen at DTS khultgren@dtsonline.com  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 12-18-2002 08:58 PM                     Steve, I thought that SRD had sufficient redundancy to freewheel in the absence of 2 frames. I'm not sure how I reached that conclusion, though, so perhaps it is inaccurate (it would explain a lot; see below, looks like it is inaccurate). Certainly there should be some distance it should have sufficient redundancy to freewheel in the presence of (perhaps it's only a few perfs?). I had forgotten about the technique of sending the reel change data in the background earlier; indeed, if it's done on all prints, that should also elminate the problem (yet the problem is still noticable). Since SRD is 6 frames ahead of the analog soundtrack, it seems like maximal redundancy could be acheived by interleaving/spreading a given frame's sound data across up to 6 frames (and if you were going to ignore basement readers, which you can't, you could spread it a lot further). I know that SRD does some interleaving, though I'm not clear on whether that is interleaving between perfs, or interleaving of "fixels" within a perf, or both. In any case, the input to the Error Correction stage is 722 8-bit words (76^2 fixels or bits) in 10.4ms (24fps*4), and the output (input to AC3) is 256 8-bit words in 10ms. Naively, I would think that would mean you could lose 1/3 of your frames (256/722 is .35) and still survive, and 1/3rd of 6 frames is 2, i.e. what you might expect around a reel splice. Thinking about it some more, two other issues come to mind: a) SRD could crossfade/interpolate between the last data before the gap and the first data after the gap, for sufficiently small gaps. This would seem comparable to what DTS does across changeovers. I guess this could sound really bad if it happened a lot, or if the gaps were too large, but presumably there would be hysteresis in the process. b) There's going to be some loss of the redundancy from the missing 2 ID frames, so if the 2 frames around the splice are obscured/shifted or otherwise unreadable, then SRD will see 1 good frame followed by 2 unreadable frames with 2 frames not there, and then another good frame. I guess that means 2 in 6, which is not so good. Digging around in the DA20 manual, I finally came across, "Should the digital data be corrupted through through perforation damge, concealment techniques will be applied for up to 4 perforations (40ms), after which time the DA20 will revert to passing analog audio. Corrected digital data mus tremain valid for a period of time before switching back to the digital track." I guess this leads to the question, "how much SRD data is usually lost on a splice, and why?" Is it due to the splice being jumpy or the film being offset from the true position, such that the CCD can't read the SRD track? Or is it because the SRD track is out of focus due to the splicing tape? I suppose the latter argues for 4-perf (or less) splicing tape... --jhawk  |  IP: Logged David Stambaugh Film God Posts: 4021 From: Eugene, Oregon Registered: Jan 2002 posted 12-18-2002 09:57 PM                        FWIW (which may not be much), I always noticed SR-D dropouts at reel change splices during the first few years of its implementation around here. The sound ALWAYS dropped out at those splices. Then a couple (maybe three) years ago, the problem "went away". I never notice SR-D dropouts now at reel changes. I just sat through 3 hours of Two Towers in SDDS, and it performed flawlessly too. Seems like something has changed for the better since digital first rolled out.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-18-2002 10:21 PM                        SRD dropouts at splices are pretty rare, unless the track itself and/or reader alignment are marginal to begin with. The cat. 700 reader (haven't dealt with the cat. 699 or 701) is much, much better than the LED basement readers from Component Engineering (for Simplex projectors) or Cinemeccanica. (Note that I am assuming the use of clear splicing tape. I don't use zebra or opaque tape, so I don't know how they perform.) DTS almost never drops out. For over a year, we ran DTS prints in a house where the CP200 would fault to silence rather than optical (I don't know exactly why; Tim Reed can explain better than I can, since he was the one who fixed it), and we never had a problem. SDDS (at least the 2000-series units) will fault if you look at it funny. I don't believe I've ever heard an SDDS presentation that didn't involve optical faulting (even with lab-new prints and clear splicing tape). Supposedly, the newer 3000-series readers are better, though.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 12-19-2002 02:56 AM                        Maybe (just a thought) the problems described here are more likely to appear with systems which are run at 25 fps.  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1  2

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.