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This topic comprises 3 pages: 1 2 3
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Author
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Topic: New noise when reverse scans were installed
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Tim Sherman
Expert Film Handler
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Posts: 125
From: North Ridgeville, OH, USA
Registered: Aug 2000
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posted 08-19-2002 03:17 PM
First off this is a drive-in, we just changed over to the component engineering reverse scans, and since we did i have noticed a couple of things i really don't like in the quality of the sound. Anytime someone talks on the sound track that contains the letter "S" it becomes elongated and sounds kinda distorted. (kind of like what people would say a snake sounded like SSSSSSSSS) But it only happens on the "S". They were set up with a scope and an RTA and all of the levels check out. I even turned down the high frequency trimpod alittle to see if that would help. but still no luck. i never had this problem before when we used the exciters. On the one screen i also seem to have a low freq. hum, sounds to me like it would be right around 60hz. Bad ground or ground loop maybe? We run Simplex XL & 35 projectors, XL soundheads (SH-1007 i think) component engineering analog ony reverse scans, Smart Mod2 B-Dit, Beheringer Compressor/Limitors and then a FM modulator. Any Ideas? ------------------ http://www.autoramadrivein.com come on out to the drive-in and spend a night out with the stars"
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John Pytlak
Film God
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Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 08-19-2002 03:47 PM
That's sibilent distortion. Laboratories use a special test known as "cross-mod" to measure and control distortion caused by non-linearities in the printing process: http://www.kodak.com/US/en/motion/support/h44/h442.shtml#123404 With traditional cyan+magenta+silver analog soundtracks, the optimum printing point is slightly different for red LED and "white light" readers, so one may hear slightly more distortion on the reader that the lab did not optimize for. "High Magenta" (magenta+silver) tracks are more compatible with both readers. http://www.kodak.com/US/en/motion/support/dyetrack.shtml Current surveys show that a majority of theatres now use red LED readers, but there is still a high percentage of "white light" readers. "High Magenta" tracks are an interim step until enough theatres use red LED readers to allow the use of cyan dye tracks. ------------------ John P. Pytlak, Senior Technical Specialist Worldwide Technical Services, Entertainment Imaging Research Labs, Building 69, Room 7525A Rochester, New York, 14650-1922 USA Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243 e-mail: john.pytlak@kodak.com Web site: http://www.kodak.com/go/motion
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Manny Knowles
"What are these things and WHY are they BLUE???"
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Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002
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posted 08-19-2002 05:46 PM
We experieced this too with both the Dolby CP-45 and also the Smart MOD IIB. I don't recall what, if anything, was done to cope with this for the Smart processors. It's been ages since I serviced the MOD IIB's. We turned the HF Gain all the way down for the Dolby units. Is there such a thing on the Smarts? ~Manny (ready when you are.)
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Jim Alexander
Film Handler
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Posts: 71
From: Greenwood, Nova Scotia, Canada
Registered: Nov 1999
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posted 08-19-2002 08:04 PM
We ran into the same problem when we installed the ASR-40C reverse LED reader by Component Engineering. What we found was two part. First the shields for the signal line must be complete from one end only (Grounded at one end only) also, even doing this the sound head audio line must be clear of any power lines (12" clearance should be good). The second part dealt with the LED intensity. With the setting of the LED according to Component Engineering, I noticed a faint 60Hz background hum. What I found, through experiment, was the intensity set the signal to noise ratio of the reader. I found that increasing the intensity slightly would increase the signal to noise sufficient enough to reduce the 60hz backgound hum to the point where it was imperceptable. Although the LED runs slightly warmer, I feel the trade off was worth it. In the end, I found that the ASR-40 (which is based on the design of your unit), not only increased the frequency response, from that of our exciter lamp reader, but also resulted in a higher dynamic range. On the whole, I am very pleased with the results.
------------------ Jim Alexander Owner/Manager Zedex Theatre Greenwood, Nova Scotia, Canada
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Steve Guttag
We forgot the crackers Gromit!!!
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Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 08-19-2002 08:32 PM
Nope, a Jaxlight is not the solution. First off, is the film you are listenting to a high-magenta or conventional track? If the color fringe around the track edges (between the soundtrack and picture) is magenta or pink, it is high-magenta. If it is violet, then it is conventional. My guess is you have a conventional track.Then there is the SMART NR circuit that is most likely mistracking to show off the problem (you will have the same problem with the Dolby CAT 222SR/A which is used in the CP-45 and lesser CP-65s). As to the hums...that is poor grounding issues, pure and simple. I've installed CE's 20, 30 and 40 series units and you could put your head in a speaker with wide open gain and not get a hum out of it. Steve ------------------ "Old projectionists never die, they just changeover!"
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Martin Dean
Film Handler
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Posts: 11
From: Duluth, MN, USA
Registered: Aug 2002
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posted 08-20-2002 12:43 PM
My first encounter with the problem of higher end sibilance was at a preview theatre. They rand me to complain that the clients (from the advertising) industry were very unhappy with the analogue sound they were hearing in the prints. They found the digital track to be fine and so initially I believed it was the new projectors the theatre had just had installed (Sondor's with Basement readers). After fine tuning the optics several times the problem did was not resolved, so as a compromise I even tried rolling off the slit loss as far as I could and still keep it within Dolby spec. But this was still not satisfactory so I reverted back to a flat response.So I am left scratching my head as to what the problem is. But several things began to point me in the right direction. 1) A feature reel used as a test seemed to play fine in analogue without the noticeably sibilance. 2) The clients where reporting that the same advert played at another preview house sounded fine. So we duly took the advert to this preview house, where we did indeed find the problem was not noticeable, we also took it to a third theatre, equipped with Sondor's also, and lo and behold the problem was there. The second preview house was a very dry room and for a while I thought this could be a factor, but then this would not explain why Digital was fine in the theatre I was investigating. Eventually the pieces began to fall into place. After a few discussions with the Chief Engineer and a phone call to Dolby we discovered the problem mentioned in previous posts about the cross-mod effects of silver sound tracks on red light readers. The adverts were being printed at one of the smaller processing houses near London and despite a lot of pressure from Dolby had not yet converted over to High Magenta, something all of the major film printers had done, which is why the feature test reel sounded fine, but the advert was sibilant. And, of course, the second preview theatre was still running with tungsten lamps, so no problem with silver prints. So at the end of the day both the production company that owned the preview theatre and their clients discovered that they should be insisting on magenta prints in order for the products to sound as good as possible in cinemas. Since then we have discovered that problem is more noticeable eon the latter processors (i.e. the CP500, CP45 and CP650), but does not seem to be a problem on CP-65’s a lower. This may have something to do with sound processing in the digital rather than analogue domain. So what is the remedy for running older prints (all new prints should be hi-magenta), well the only one I have heard suggested so far would be to mount an older Dolby analogue pre-amp in an interface box so that it could be switched into the system to run older prints. I don’t believe this has been tested yet so I have no idea if would actually work. Of course it would require using non-sync input or the like to work, and switches in the cell lines (not a good option), but it may be an option where places run older prints. The fact that the problem had not been widely publicized is interesting. A compromise was obviously decided upon in favor of newer prints and of course it is now too late to go back.
------------------ Martin Dean martinidean@charter.net
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Martin Dean
Film Handler
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Posts: 11
From: Duluth, MN, USA
Registered: Aug 2002
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posted 08-20-2002 12:58 PM
No disrespect to JAX lights, but there pre-amps are known to be sensitive to electrical noise. Not a problem in a good clean system, but in a lot of systems (especially where ancient wiring or micro-invertors are involved) lots of extra noise can appear.The only other alternatives to the JAX light I know of are using reverse scan units, which give great results, have space for the digital reverse scan, but cost more, or use a laser replacement. Lasers are a pig to line up (for the engineer) but work well with existing cells with no need of any extra pre-amps, can often use the existing exciter supply (if it is regulated), give good results and cost less than reverse scan. The only caveat with lasers is that the optic assembly has to be in good condition. But even the cost of a new optic is factored in it is still cheaper than reverse scan. Interestingly the response from the lasers can in fact be too good. I have installed several on systems consisting of Westar 2001’s with CP-45’s, along with new optics and discovered even when the slit loss is fully rolled off that there was still a light peak at the HF end (only 1dB or so, so not critical). The theatre did complain of the occasional sibilant film, but I latter put this down to the cross-mod distortion effects of red-light readers with silver soundtracks.
------------------ Martin Dean martinidean@charter.net
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Tim Sherman
Expert Film Handler
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Posts: 125
From: North Ridgeville, OH, USA
Registered: Aug 2000
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posted 08-20-2002 03:18 PM
Ok thanks for the help so far. I have narrowed down the hum to the lamphouse. If the Lamp is lit there is a hum. I checked the ground at the rectifier and all is good their. No matter what i seem to do at the lamphouse nothing helps get rid of the ground loop. Any other Ideas?And you were also asking weather it was conventional film or the high-megenta. I havn't checked yet but i would asume high-magenta. The films playing right now are "xXx" "spy kids 2" "Blue Crush" so they are all new releases if that helps. I'll be sure to check tonight though ------------------ http://www.autoramadrivein.com come on out to the drive-in and spend a night out with the stars"
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