Film-Tech Forum ARCHIVE: Dolby Tone problem

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Posted by Paul Vollmers (Member # 927) on 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

Posted by Steve Guttag (Member # 268) on 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.

Posted by Paul Vollmers (Member # 927) on 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.

Posted by Louis Bornwasser (Member # 3063) on 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

Posted by Paul Vollmers (Member # 927) on 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.

Posted by Richard Hamilton (Member # 321) on 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

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Louis Bornwasser (Member # 3063) on 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

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Paul Vollmers (Member # 927) on 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???????

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Paul Vollmers (Member # 927) on 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.

Posted by Louis Bornwasser (Member # 3063) on 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

Posted by Richard May (Member # 2627) on 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?

Posted by Brad Miller (Member # 2) on 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.

Posted by Gordon McLeod (Member # 33) on 09-01-2005, 06:46 PM:

If it was a tone issue the tone would have to been printed to hot cause the preamp to be set low gain and as such the NR would tend to muffle it
Since the track is variable area the exposure will only effect the Cross Mod not the overall level
Is it possible that by accident the level was set with the cat 97 loop instead

Posted by Jack Ondracek (Member # 1466) on 09-01-2005, 08:51 PM:

I think Brad touched on the real issue here.

A Dolby tone loop won't help at all in dealing with muddy sound... as long as it's related to the parts in the sound head. If you're getting proper level indications on your SR cards, you've done about as much as you can with that loop.

You need to get the proper loops, and have someone adjust your a-chain alignment who knows what he/she's doing.

If that doesn't fix it, I'd think your muddy sound problems would be in your equalizers (if someone's messed with them) or maybe your speakers.

How does you non-sync sound?

Posted by Paul Vollmers (Member # 927) on 09-02-2005, 11:13 AM:

Jack,
The EQ's are okay as the DTS sounds great.......all three 64b's were done property with a RTA.
I'm not using non-sync at all.
Speakers were checked for polarity etc.

I'm presently rechecking the lens focus etc.

Posted by Richard Hamilton (Member # 321) on 09-02-2005, 03:50 PM:

Paul,
this just seems a little odd. You have 2 projectors doing the exact same thing with the same Dolby unit? Are both projectors using the same cable, or are they hooked up to proj 1 and proj 2 on the processor?

Posted by Gordon McLeod (Member # 33) on 09-02-2005, 04:16 PM:

What does it sound like in Mono and in bypass?

Posted by Paul Vollmers (Member # 927) on 09-02-2005, 11:12 PM:

Richard,
The two projectors are hooked up to Proj 1 and Proj 2 on the CP65.

Gordon,

Mono and Bypass are pretty much the same.

I have just finished rechecking the lens focus.....and found the lens back a little to far.......the muddy sound has improved the highs are back.......however the volume level just is not where it should be.
The spl's have been rechecked and optical is at 85db across the front.
To listen at a good sound level while running a reel not trailers, the fader has to be at around 7.5 or 8.
When switching between DTS and SR there is a 1.5 fader number differance in level.........and the DTS spl's have been checked at 85db across the front.

Posted by Brad Miller (Member # 2) on 09-03-2005, 12:15 AM:

Paul, it's blatantly apparent now...your ENTIRE A-chain needs to be realined. There is really nothing else to it.

Posted by Louis Bornwasser (Member # 3063) on 09-03-2005, 12:26 PM:

I agree with Brad....now the big question: do you let the same technician come back or do you get another with a fresh view. (It helps not knowing the personalities.)

I am basing this on the fact that you were able to improve things. (Is it possible that the tech had the c/n 69-p with the emulsion toward the screen. It would be "out" by about the amount you are describing.) Louis

Posted by Brad Miller (Member # 2) on 09-03-2005, 12:29 PM:

I can answer that question after Paul answers one.

Scenario 1 - did you pay $$$ for this tech to perform the A-chain? If so, yes you should rehire him to come back and fix the problem, but on his dime.

Scenario 2 - the tech is a friend and it was done for free. Odds are he isn't that great of a tech. Hire someone else.

I agree with Louis the cat69P loop may have been loaded backwards, but even that goof is no excuse because he should have ran some analog content to verify the job was properly done AND ran some digital material to verify the analog was level matched before he left.

Posted by Paul Vollmers (Member # 927) on 09-05-2005, 06:12 AM:

Currently the A chain is being realigned in both projectors........there is a bug some place.

Posted by Paul Vollmers (Member # 927) on 09-16-2005, 07:59 AM:

After a full A chain realignment on both projectors, a lens focus and two bad cards in the CP65 were found.....Cat 240a proj 2 and Cat 242 had issues...........both were replaced and all is well.
I'd like to thank all who offerd help in this sound problem.

Paul

Posted by Andy Summers (Member # 3207) on 09-19-2005, 05:08 PM:

Paul’

I’ve read the problems you have had not sure if you are still having the funny, anyway I’ve been over to the (In-70mm) site to try and find some information, is it a (Phillips DP 70) is that won’t you are running, the dullness in the sound sounds like an Azimuth error, alignment I’m guessing must be 1to1 something like that.

Anyway hears some info, have a look around it may help you out then again it may not good luck….

http://www.dp70.com/library/story/construction.htm

Up-grades to DP 70
http://www.dp70.com/library/modify/

More images close up of DP 70
http://www.dp70.com/library/modify/cinefocus/index.htm

Optical sound Processing
http://www.kodak.com/US/en/motion/support/processing/h249/h2409_05.shtml

http://www.iceco.com/Century/CNTYMR3.pdf

http://www.smpte.org/membership/warner.cfm

Larry Blake sound mix “Swelltone”
http://www.northbeachpost.com/handy_glossary.html

Posted by Sam D. Chavez (Member # 1841) on 09-19-2005, 07:33 PM:

I hope your DP70 "dullnes problems" are solved for good.

Sound techs flip the Dolby tone emulsion inside out on this projector as the exciter is on the base side of the film and some were taught that the emulsion goes next to the exciter rather than look at the projector as an entity.

There were also some DP70's with bad optics right from the factory. These would only go to about 3 Khz but back in the days of tone sweep tone films they were good enough for academy mono.

The reason I believe they were bad from the start is the bad ones i found were in pairs in two projector booths. Having two bad lenses at the same time is statistically very improbable.

Posted by Paul Vollmers (Member # 927) on 09-21-2005, 06:12 AM:

Sam,

Thank you for your responce............should the dolby tone "be flipped on the DP70 ? or run as normal ? I'm using it as normal .
Paul

Posted by Gordon McLeod (Member # 33) on 09-21-2005, 08:24 AM:

since one doesn't flip the release print around it still runs the same way emulsion towards the lamphouse

Posted by John Pytlak (Member # 331) on 09-21-2005, 08:31 AM:

The standard orientation for ALL 35mm release prints is with the emulsion toward the lamphouse, per SMPTE 194-2002:

quote:
2 Position of photographic emulsion and magnetic striping
2.1 The photographic emulsion shall be on the side of the film which faces away from the projector lens. The projectable image area is specified in SMPTE 195.
2.2 The magnetic striping shall be on the side of the film which faces the projector lens.