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Author Topic: Penthouse digital readers Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-16-2007 04:10 PM                     quote: Sam D. Chavez when it comes to wow caused by the platter jerking on the film ..wouldn't the 'holdback' sprocket in the soundhead prevent the wow caused by the jerking from the platter?  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 11-16-2007 04:36 PM                     Monte, it is the payout side of the platter that affects a penthouse reader, not the takeup side. I've had this same thing happen when using an upper reel arm with a clutch that wasn't quite perfect or a reel that was out of round.  |  IP: Logged Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 11-16-2007 07:45 PM                    The worst part for us is when a piece of cue tape goes through to signify the end of the movie. The music "Taa daa..." cue always sounds like "Taa Daaaaaoowaowaowaaa" causing the audience to laugh. That's probably not what the film makers intended. Music throughout the movie itself can sound anywhere from perfect to an analog cassette tape that's been sitting on your car's dashboard for the whole summer. So we just stick with SDDS in that house. Or if there's no SDDS, plain old SR.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-17-2007 12:08 AM                     Thx Brad for the correction, but an interesting question then, for I know of one cinema that has a BACP penthouse reader and they're complaining on the same "wow" issue ... and they're using STRONG platters. If the head is just picking up data from the film how does it 'wow' if it's just reading data? You would then think that SDDS would have the same problem then we we don't have to worry on DTS being just timecode.. ..guess, I don't fully understand this faulty procedure then and would please ask for a little help on this area .. so that I can tell this cinema on how to curtail their little problem. thx-Monte  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 11-17-2007 07:01 AM                     The problem is pretty simple. Digital sound readers adjust their playback speed based on the speed that film goes through them (because projectors don't run at exactly 24.000Hz and it is important that the sound matches the picture). So when there is insufficient tension on the sound reader and the film wows as it goes through the reader, that's another way of saying that the speed of the film through the digital sound reader is not constant. You hear the corresponding pitch variation. This is all a function of tension and film path, etc. Also length of your tail/drag strip. --jhawk  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-17-2007 07:27 AM                     Brad...all of eggs in one basket? How so? The readers themselves are separate, using separate LEDs and often with separate LED supplies. What is common? The drum? It better be spinning properly or you'll have film damage soon. Better to have digital drop to let you know of a pending failure than to gleefully run in digital and not understand why the film is being damaged or if you have something without digital tell you that your spare tire is flat. The counter arguement is that with a penthouse you have twice as many failure points. Mark's problem is a curious one. Just in case...are you running the latest firmware in the CP650? It is 2.3.5.something now (I forget if it is 2 or 4 on that last digit). I always thought it was unfortunate that the penthouse people eliminated the sprung roller that was present in the Cat 699...it was a nice debouncer that took some of the shock off of the closed loop system. Monte...how the digital decoder deals with speed variations is up to the people that write the code. You need to allow it to deal with speed variations as John noted but how fast is a matter of opinion. My opinion is that it should never be audible. However, that means it can only adjust for speed slowly and that may also mean it will need to use a large enough buffer to deal with catching up to a suddenly faster running machine. But, then again, other than start up or changeover, when is a projector going to suddenly change speed? A clever programmer should have special case algorhythms for those situations as they are known (speeds starting below the minimum are start up...changeovers have motor start signals, changeover signals and such). Once the speed is set for a particular start up...it should be a very slow change if the speed varies to avoid noticable wow/flutter. DTS went through this problem too a while back (one of those dark firmware versions between 1.29 and 1.46). They had to deal with changeovers between dissimilar machines that have different speeds. Unfortunately, they took a special case and tried to apply it as a general fix. Most changeover houses have identical machines for both and even if there are variances between the two (presumming async motors), it shouldn't be real different to need such a drastic speed change instantly. John....CUE MARKERS....some machines are indeed right on 24fps to three decimal places...those with good frequency inverters and good motors. I've stobed machines where they they were spot on. We recently conveted some DP75s to inverter drive using some Bodine motors and Lenze controllers and upon verifying the speed with a strobe using the shutter as the target...it was frozen (also indicating little slop in the gear train too). Now, not all motors/controllers are created equally...in fact, the reason I strobed the unit was to see how off they were...I've found several low-cost inverters that put out "about" 60Hz. The Lenze AC-Tech inverters we used on this particular project were not very expensive as inverters go so I was curious. With sync motors now the norm in most cinemas/screening rooms, odds are, the speeds are quite close to 24.000fps but more importantly to this topic are not varying around by any signficant amount as that would require the line frequency (not voltage) to be varying. Steve  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-17-2007 06:03 PM                     Thx, John and Steve for this SRD info very much which really clears things up on this one condition that this one cinema has-that I wasn't for sure since I'm justr lightly educated of the full spectrum with SRD playback. For there is an induction motor on their 5-Star head and I have mentioned on changing that motor out for a sync motor to keep speed more constant since they do have voltage fluctuations in that building from time to time. thx-Monte  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 11-17-2007 08:59 PM                     Steve, to pick on you I will give you an example. When using a Kinoton basement reader, if the O'ring breaks during a show...the show is lost because the operator can't switch to SR to finish the show. Hence, all your eggs in one basket. Don't tell me it doesn't happen, because it has happened to me before and the projectors were less than a year old at the time. And that is also why I am a fan of not playing trailers in digital. That alerts you if there is something wrong with your analog backup.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-17-2007 10:09 PM                     No arguement that there was a bad batch of O-rings on Kinoton. However, I never had one break all of the sudden...just puff up and get oversized...that doesn't just happen but over time...however if it happens in the middle of a show...pull the roller off, switch it around and put it back...you are back in business...the outboard O-ring will not be so afflicted as well. Again, one shouldn't be running the film with O-ring missing...the problem needs to be fixed right then and there. The O-rings are indeed a wear item. The current green colored ones last a good long time though. This is a case of good trade off on a wearable...that is, yes they add to the cost of operation but the increased friction the O-rings bring offset the added tension that was required for the non-O-ringed pinch rollers of previous soundhead designs by Kinoton. Steve  |  IP: Logged Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 11-18-2007 12:30 AM                    Jhawk is right. My problem is a simple one to understand. What I don't understand is everyone's lack of interest in fixing it. I can't even get a Dolby tone loop to play without the pitch wowing all over the place. I believe it was a Dolby tech on these forums that told me that when he runs a test loop, he adds a weight of some sort on the loop to hold it steady in the reader. That's great, but it doesn't in any way simulate how film travels to the reader. When I run the same loop on a CP65 / DA20 / CAT 699 setup, I can push the reader's tension rollers up and down all day long and it won't wow at all. Something changed between then and now. And it sucks. Changing the speed of the audio to match the speed of the picture is one thing. Changing the pitch is something else entirely. It should be pretty easy for the processor to be able to tell what the pitch SHOULD be, based on sprocket count. I dunno. I've beaten this horse to death.  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 11-18-2007 04:54 AM                     When using the Dolby Tone loop, you have to thread the whole projector and not just the lower giveaway sprocket and the reader. This applies to all test films! As regarding the Penthouse Readers, I go for BACPs DSTR-20 Reader. We recently retrofited 5 Christie projectors with these and the projectionists were amazed for they have seen for the first time on the Digital Processors error rates of 2!!! I have always thought that putting the DTS reader the highest of the readers is a good case. In this way you can always bypass DTS with no problem and go straight to Digital reader using just an auxiliary roller on the DTS reader. It also "looks" better considering first that there is enough film matched to the delay in the DTS decoder/processor. Demetris  |  IP: Logged Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 11-18-2007 09:08 AM                    quote: When using the Dolby Tone loop, you have to thread the whole projector and not just the lower giveaway sprocket and the reader. This applies to all test films! What does that have to do with the tension of the film coming into the reader?  |  IP: Logged John T. Hendrickson, Jr Jedi Master Film Handler Posts: 889 From: Freehold, NJ, USA Registered: Apr 2001 posted 11-18-2007 11:44 AM                     Thread the whole projector? That's news to me.  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 11-18-2007 12:21 PM                     I've seen someone who used Dolby Tone with threading just the drum and the giveaway sprocket. I am saying that when you use test films, you should thread the whole path (Upper Take In Sprocket, gate, Intermitent, Giveway Sprocket).  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-18-2007 12:21 PM                     FWIW...I've always used 10' loops and threaded the whole film path. I want to simulate the dynamics of the entire film path as much as possible...naturally, the outside forces caused by the reels or film path are much harder to simulate with test film. Steve  |  IP: Logged

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