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

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Why does the CP650 warble at all?

Author Topic: Why does the CP650 warble at all? Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 12-17-2005 04:54 PM                    This seems to be a real design flaw in my opinion, but I wanted to see what others thought. I really can't think of any application where allowing the CP650 to vary the PITCH based on how fast the data is coming in would make sense, but maybe I'm missing something. This should at least be something that could be turned OFF in the software (maybe it is, but I don't see it). In this thread, I'm not really interested in how to mechanically fix the warbling, I'm looking for people's opinions on why the software was designed that way to begin with, and if you think it's a good idea or not. Thoughts?  |  IP: Logged Carl Martin Phenomenal Film Handler Posts: 1424 From: Oakland, CA, USA Registered: Feb 2002 posted 12-18-2005 12:38 AM                        never worked with a cp650, but i'll speculate. could it be so that it will match the pitch of the analog track in case of a dropout?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 12-18-2005 09:11 AM                     You may actually have the unit toggling at a high rate back and forth between analogue and digital that did happen with the odd DA20  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 12-18-2005 09:47 AM                        I concur with Gordon. To test this theory, either turn off the analog light source or temporarily block the analog LED. Reversions to analog will then show up as missing audio. You will then know if a well qualified Dolby tech should be called to repair the Digital. Louis  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 12-18-2005 10:16 AM                     This happens on the DTS too. I remember when we installed some units we checked the film path while the film was running and we were "forcing" the film to go faster than it should. It was speeding up the pitch on the DTS discs. But a properly alinged soundhead and a proper projector should not do such warbling. Maybe you should check your film path if you have a problem like this. D  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 12-18-2005 10:18 AM                     I've seen projectors not running exactly at 24FPS exhibit the complaint he has. I've also seen this from platters with a bouncy payout, particularly with dts.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 12-18-2005 08:17 PM                     quote: Brad Miller I've seen projectors not running exactly at 24FPS exhibit the complaint he has. I've seen this happen with Sony's but not with Dolbys. Dolby has a pretty wide tolerance for speed as does DTS.... something like +/- 5% or thereabouts. The Sony 2000's seem a but more touchy as regards speed accuracy. Mark  |  IP: Logged Ken Jacquart Film Handler Posts: 82 From: San Francisco, CA, USA Registered: Mar 2000 posted 12-18-2005 08:40 PM                        The CP650 (and DA20 and CP500D) has a Dolby Digital decoder speed tolerance of +7% to -11%. This is a wide latitude. This allows for variances in AC voltage, projector / motor gearing, and it's simply good practice. If you are actually hearing warbling on a regular basis, then there is probably something wrong... check to see if you hear it in analog playback (Dolby SR... Format 05). If you do, then something is wrong with your projector drive train. If it's okay in SR, then you may have a problem with your Cat. No. 773 (Dolby Digital film decoder) card. -ken  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 12-18-2005 09:51 PM                     quote: +7% to -11% Ken, I knew it had wide speed lattitude but thats practically good enough to be able to hand crank in an emergency and still maintain SRD playback! Mark  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 12-18-2005 10:10 PM                     I am confused by the focus of recent responses. Why does the digital decoder's speed tolerance have anything to do with warble? Of course digital needs to track speed changes in the film, otherwise the sound would be out of sync. And if the speed of the film rapidly changes, producing a warble in analog, you'd see the same warble in digital. But it wouldn't be digital's fault. If you exceeded the decoder's speed tolerance, then presumably you'd have dropouts, which are completly unrelated. --jhawk  |  IP: Logged Ken Jacquart Film Handler Posts: 82 From: San Francisco, CA, USA Registered: Mar 2000 posted 12-21-2005 04:41 PM                        John, There were some "early" Cat. No. 773 cards (Dolby Digital film decoder) in CP650s that exhibited undue pitch changes because of some capacitor problems. If someone were to experience a described "warble", the first thing I ask them to do is switch to SR and see if it's still there. If it is not, then yes, it could be "digital's" fault (at least in this case).  |  IP: Logged Robb Johnston Expert Film Handler Posts: 147 From: St. Louis Suburbs Registered: Nov 1999 posted 12-21-2005 11:29 PM                        are the tension arms bouncing? if so, you might find that the airpot is busted in the reader Perhps the bounce is enough of a spee dup/slow down over and over again to cause it to cut in and out. If that is the case call Dave H. for replacement  |  IP: Logged

All times are Central (GMT -6:00)

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.