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Author Topic: Dolby CP500 RTA Paul Stevens Film Handler Posts: 42 From: Galena, Ohio, USA Registered: Oct 2006 posted 01-25-2007 10:21 PM                     I am thinking of actually using this feature on the 30 plus units in service. The manual calls for Cat 580 microphone multiplexer and mikes to be used. I don't have the Cat 580 on hand and don't have a clue where to look for one. Any experiences with this stuff, I would appreciate your sharing it with me. Thanks  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 01-26-2007 05:45 AM                     You don't need the Dolby multiplexer if your plexer's manufacturer makes a cable for the CP500. I use the USL MMP-10, and USL does make such an adapter. However, I would question the accuracy of the CP500's RTA. I have never used it for a B-chain, but when I adjust focus and slit loss during A-chains, the CP500's on-screen RTA does not agree with my external RTA. For example, if my RTA is flat out to 12K, the on-screen display has major peaking at the high end, and if I adjust the slit loss so that the on-screen display is flat, my RTA rolls off at 4K. I've used a couple different RTA's over the years and this has always happend. I tend to trust my RTA. Now that this is brought up, can anyone shed some light on why this happens?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-26-2007 08:22 AM                     Although I always use my IVIE RTA seperately for all adjustments I always compare it with built in RTA's. Never found one in a Dolby that was very far off yet.... Mark  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 01-26-2007 10:22 AM                       The 500 picks of the preamp signal for the internal RTA display ahead of the slit loss which is a digital function downstream, hence the difference. A minor mistake but annoying.  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 01-26-2007 01:56 PM                     So it basically digitally corrects the display based on the slit loss setting? Anoying, indeed. If I were in a pinch and didn't have my RTA with me, would it be best to set the slit loss so that the on-screen RTA is flat, or should I allow for the peaking since I know that corresponds to flat on my RTA?  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 01-26-2007 09:27 PM                       If you are using modern red readers, mine and others, you're flat to 14kHZ with no slit loss. There is no useful audio above 12 kHZ anyhow so most leave slit loss off these days.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 01-27-2007 03:53 AM                        quote: Ken Lackner If I were in a pinch and didn't have my RTA with me That's why you need to have an Ivie IE-33 or IE-35. Then you always have your RTA with you.  |  IP: Logged Paul Stevens Film Handler Posts: 42 From: Galena, Ohio, USA Registered: Oct 2006 posted 01-27-2007 11:46 AM                     Has anyone used a wireless system to interconnect the multiplexer with the RTA? None of my auditoriums have cable in place that can be used. Is there any RF system clean and flat enough in frequency response out to the bandwidth needed?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 01-27-2007 09:11 PM                        Yes, we are testing a digital, non-compressed wireless system. It's about $1500. Will let you know. Significant audio occurs above 12k up to about 15k. I won't leave an "A" chain until I am flat or 1 db down at 16k. Does anyone else here test/verify the L-R channel? Not many analyzer can do this. Louis  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-27-2007 09:26 PM                     The Sony techs used a wieless system on their rta when they came out to theaters to do software upgrades and attempt to make SDDS actually work but I don't remember any specifics about it. For any wireless system to work well it can't have any phase shift across the audio bandwidth or between channels at same frequencies, etc for it to be accurate, especially on multi mic RTA systems. Indeed a digital based FM system might be the best for this purpose. A simple FM system with phase shift held to a minimum would work ok on a single mic system but hopefully none of us here are going that dinosaur route. In reality a needless lazy mans(or handicapped persons) toy. Mark  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 01-28-2007 07:45 AM                     Um...who leaves slit loss off?? quote: Louis Bornwasser Does anyone else here test/verify the L-R channel? Not many analyzer can do this. What exactly do you mean?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 01-28-2007 09:35 AM                        If you don't compare the left total versus the right total, then you could have phase & level changes between them. If the DIFFERENCE is wide band and flat, then surround crosstalk cannot occur. The issue is important for SR tracking and 4 channel decoding. You can certainly see level and eq on the 2 channels directly. You can not see phase errors which, because of encoding, are particularly important. louis  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 01-28-2007 12:33 PM                       Regarding slit loss, with the original B&W Cat. 69, I would have confidence to tweak the slit loss to flat, but with the color test film produced the last few years, it's not worth the trouble due to the variance in the film,batch to batch. Don't forget the original reason for the slit loss was back in the day when the front scan lens would go only to 2Khz before the rolloff began. Louis, when was the last time you did a serious PM service call?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 01-28-2007 01:53 PM                        Friday!  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 01-28-2007 03:58 PM                        quote: Louis Bornwasser If you don't compare the left total versus the right total, then you could have phase & level changes between them. If the DIFFERENCE is wide band and flat, then surround crosstalk cannot occur. The issue is important for SR tracking and 4 channel decoding. You can certainly see level and eq on the 2 channels directly. You can not see phase errors which, because of encoding, are particularly important. louis On the IE-33/35, you can compare, add and subtract channels. But I think it's still easier and more accurate to simply look at the XY display of the two channels for optimimum phase. The length and symmetry of the "spiral galaxy" also tells you about frequency response and level. If the frequency responses of the two channels don't agree, you can't get a straight flat line either.  |  IP: Logged

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