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Author Topic: Dolby Tone problem Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 08-31-2005 03:31 PM                     Has anyone had a problem with a Dolby Tone Film Cat 68T dated 2/98? After having a full stereo cell alignment ........with a osciliscope and rta.......all right on...with a white light. Then running a Dolby Tone film, and ajusting to two green lights on the 222 cat ...left and right....then using a pink noise card to set spl at 85db L,C,R,S. I'm set at 8.0 volts exciter. Running a feature reel the sound has a low muddy sound in Dolby A and SR. DTS is good. If I turn the 222 hi gain pots clockwise 1.5 turns out past the green light setting, the sound level comes up, and the tone has much better highs. The date on the Dolby Tone film is 2/98. Any suggestions  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-31-2005 05:43 PM                     Dolby Tone is nominally 800Hz (it is modulated to give its characteristic tone) and will not provide a suitable method of determining HF response. You would need to ensure your entire A-chain is in correct alignment (best focus and azimuth) and that the HF pots are set correctly, not by ear. You say you set your exciter lamp to 8-volts...any chance you are running a cyan film (blue colored soundtrack) this would also give you a very low level and the NR circuits would tend to make it sound low and muddy.  |  IP: Logged Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 08-31-2005 07:39 PM                     Steve, Thanks for your responce. Presantly I do not have any blue colored sound tracks. I'm a collector, hobbiest, not a theater owner, operator. The complete A chain was aligned per Dolby manual, with the correct equiptment. This was done by a Tech.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 08-31-2005 08:01 PM                        Remember Dolby tone on almost all Dolby processors is to be set in 01 (mono) format. This is not obvious unless you read the manual very closely. Louis  |  IP: Logged Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 08-31-2005 09:11 PM                     Louis, Yes, I used Format 01 Mono........! This is on a Dolby CP65.....with all cards...SR 350 etc. This unit was checked by Dolby recently as well.  |  IP: Logged Richard Hamilton Phenomenal Film Handler Posts: 1341 From: Evansville, Indiana Registered: Jan 2000 posted 09-01-2005 01:17 AM                     Paul, Is this problem the reason you had the tech check the alignment, or did it appear after he did it? It sounds like a problem with the focus and high freq response. This should also be done looking at a scope and RTA using a loop of pink noise. With the Hi Freq pots all the way down you should get the best focus and azimuth adjustment that you can. Then the HF pots are brought up to fine tune the high freq on each channel. Rick  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 09-01-2005 05:28 AM                     I'm surprised that your "tech" didn't run a reel or two of stereo track after he finished. He ought to make a follow up call at N/C if he didn't test run some stereo track of some sort. Thats pretty standard practice when setting up equipment, especially the first time around. If this is your DP-70 that is exhibiting this problem it could be a number of things that are wrong. Bad slit, bad solor cell, or a bad objective lens. Any of these three things, if defective, could lead to murky sound. I doubt that its oil contamination because the optical reproducer is in a compartment of its own away from any "oil". Miswiring may also lead to this problem if there were for instance a bad ground loop. Installation of a Todd-AO slit if you can locate one is a good idea and will extend your hf response another two or three octaves. The original DP slits are pretty inconsistent generally. We gave up on Jax Lights and any type of slit mod when the BACP scanner kit became available and have so far done over 30 of them. No rebuilt DP-70 leaves our shops with out it installed!! Mark  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 09-01-2005 05:31 AM                        Mark: Thank you...a major pet peeve of mine is following techs who do not check their work. (Prob 60% don't even thump the optical.) Naturally call backs are then frequent. Actually running a reel of something is superb. Louis  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 09-01-2005 05:36 AM                     I actually carry a reel of high quality "track" that I am very familiar with in the van. Time spent doing this has paid off in not having to go back for a second visit for the original complaint!! Mark  |  IP: Logged Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 09-01-2005 06:46 AM                     Rick, This CP65 came from Dolby after a general checkup........it was installed in the rack with proper A Chain setup. I use this sound rack with both projectors....a Simplex E7 w/ Sh1000 sound head and a Norelco DP70. Both were tested after words with the muddy sound.....reused the Dolby Tone to check for the two green lights in the 222 card. I was presant and watched all of the steps....scope...RTE...Buzz Track....LF RT......Tone.....cleaned lenses....HF..EQ..SPL.. 85db...(all not in this order) The Tech thought it was possibly one of several cards...240A..242...222..he is going to get back with me.........but will be a while. Just can't figure this one out! Like I mentioned in my first post..........if "I" run Dolby Tone.......and get two green lights.......then continue 2 complete turns clockwise.....the lights go out, but the sound level comes up, and the sound tone is so much brighter when running a feature reel. When switching from DTS to SR on the front pannel there would be a sound level change as well as the muddy sound...but after turning both hi gain pots 2 turns clockwise out the sound tone and level are ok. This is why I'm thinking maybe the Dolby Tone film dated 2/98 may possibly have a problem???????  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 09-01-2005 08:12 AM                     Comming freshly from Dolby means very little to me especially after some transit company has handled it. Does it behave the same way in SR as it does in type A? And have you tried the Projector 2 input on the preamp card? quote: Paul Vollmers This is why I'm thinking maybe the Dolby Tone film dated 2/98 may possibly have a problem??????? Doubtful. Dolbly dud a great job back then QC'ing test films. MArk  |  IP: Logged Paul Vollmers Expert Film Handler Posts: 161 From: Sister Lakes, MI, USA Registered: Jul 2001 posted 09-01-2005 11:57 AM                     Mark, SR and A Type is the same. Both the Simplex E7 and the DP70 have the same sound and level issues. I ran the same reel on both. This is why I'm thinking the Dolby Tone film may be the issue.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 09-01-2005 06:29 PM                        I know for sure that some bad Dolby test films have been circulated at some times in the past. I do not know specifically the exact dates that are bad. Do you have any other D. Tone? If you do, then both should read the same. Is this film actually real Dolby film? There have been times when Dolby did not have any to sell and I have been suspicious of "plentiful supplies" from oportunistic suppliers......if it's too cheap, it's probably not right. Use another date test film! Louis  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 09-01-2005 06:38 PM                     This does not sound like a dolby tone issue. If the dolby tone test film was bad, it would just give a bad reading on the level coming into to processor. It should not give you muddy sound. Was pink noise test film ran and if so was the HF okay on the RTA?  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 09-01-2005 06:45 PM                     There definitely WAS some bad batches of Dolby tone film in the past, but if the levels were set accordingly it would end up making the optical too loud, which isn't your problem. I recall having this problem around 2000, so I was probably using a loop from 97-99. Regardless, you shouldn't have muddy sound, it's something else. Do make sure your output trimpots on the dts unit are set properly before using the dts to compare levels. Remember unlike a DA20, they could've been knocked off.  |  IP: Logged

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