Film-Tech Forum ARCHIVE: Trailers causing a BUZZ in Sound System

This is topic Trailers causing a BUZZ in Sound System in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Ian Bailey (Member # 1752) on 04-14-2005, 04:06 AM:

Seem to be having a problem with a couple of trailers.They are causing a Buzz in the sound system but only in one auditorium.Most trailers and all features do not cause any problems on this screen.
Move the trailers to another screen and the problem does not happen.
Equipment: SH-7300 (first 5 star) sound head
Component Engineering reader
Ultra Stereo processor

Posted by Brad Miller (Member # 2) on 04-14-2005, 04:08 AM:

A-chain in the soundhead is off in the auditorium with the buzz. Have your tech realign it and you will be fine. [Wink]

Posted by Ian Bailey (Member # 1752) on 04-14-2005, 06:36 AM:

Thanks Brad but why is it only a couple of trailers causing the Buzz and not everything we run on this machine? In fact I just ran the trailer and feature again and the buzz in the trailer was not there.It appears to be intermittent only on a couple of the trailers we are running.Haven't had the Buzz on any features we have run on this machine as I'm sure we would have got complaints.I am sure you are right about the A-chain as I can't get the full Dolby level.
Would a quick fix be to run the offending trailer and if it does cause the Buzz to adjust the horizontal position of the lay-back roller on the sound drum until the Buzz dissappears?

Posted by Scott Norwood (Member # 30) on 04-14-2005, 07:35 AM:

I'm betting that your A-chain is sufficiently bad that a slightly misprinted DTS timecode track is getting scanned and picked up by the solar cell. I suspect that you will find that the trailers that buzz have DTS tracks.

If you have a white-light exciter, you could try replacing the bulb and try to set Dolby levels again. If the bulb is old, the filament might be sagging.

Posted by Ian Bailey (Member # 1752) on 04-14-2005, 07:59 AM:

Scott it is a Red light(Component Eng,) reader and I think you are right.I just need to maybe try a quick fix untill i can get a Tech to do a proper alignment.
Actually it was "aligned" by a tech not that long ago.
I only get techs passing my way on rare occassions.

Posted by Darryl Spicer (Member # 711) on 04-14-2005, 09:47 AM:

if you have a buzz track loop run it and adjust your lateral in just slightly. Run dolby tone, if you have it, to check levels. If you don't have a buzz track use a piece of green band trailer that has nothing on the sound track audible. That way you can hear if you adjusted to much. You shouldn't have to adjust it very much. If possable use the green band from the trailer that is giving the problems. I have had to do this before as a temporary adjustment until our tech could get in to do the probper A-chain.

Posted by Dominic Espinosa (Member # 2122) on 04-14-2005, 11:39 AM:

Agree with Daryl. I used the green band technique several times on an old R3 that had a faulty latteral guide and the owner was too cheap to fix it.

Posted by Monte L Fullmer (Member # 2797) on 04-14-2005, 02:39 PM:

Course, we know that we hate the 5-star heads due to them using that solid flywheel instead of the dampened flywheel that the 4 star (SH-1000) had.

We also notice when the machine is ramping up to speed, the scanner drum isn't catching up speed due to that solid flywheel. Thus, we see the film, as it leaves the middle constant speed sprocket loop forward due to the idler damper roller moving forward because of the turning resistance of the scanner drum with that solid flywheel. The film actually is travelling all over that scanner/lateral roller assembly until the flywheel catches up to speed. If the sound/dowser opens up while this film wander is happening, then that buzz can be apparent with the film not being completely settled over the scanner drum.

I found out this the hard way with customers complaining of a buzz at the start of the show. I was having my threading leads way too early when dowser/sound opened and picking up the DTS track through the optical before the wander had settled.

Course, this example above was just during startup. Ian's problem was with machine already fully running in which the answers to his problem from other members are valid suggestions.

Wonder if Ian's problem is bearing related? Would he have bad scanner bearings causing the scanner drum shaft to not rotate smoothly?

thx-Monte

Posted by Stephen Frazza (Member # 2320) on 04-14-2005, 02:46 PM:

Just want to ask while we're on this subject -

Dolby tone cat 69T should be run in mono,is that correct?
Also should you run buzz track in format 03 stereo without surrounds or in 04 stereo with surrounds.

Thanks

Posted by Gordon McLeod (Member # 33) on 04-14-2005, 02:58 PM:

69T should be run in mono (01) on all processors except the CP45
The Buzz track or cat 97 doesn't matter since one is looking at the signal on your scope on the preamp out point
If a buzz track is being used by the "by the ear"method then mono is also fine since one wants no tones present idealy when listening on the monitor

Posted by Louis Bornwasser (Member # 3063) on 04-14-2005, 03:44 PM:

Special mention must be made: "first 5 star" These did not have the usual lateral guide assembly. Some had a "slider" instead. These were impossible to align (or install) Dolby in due to unusual mounts and extreme weave. (We did it anyway, however, at a theatre near D.C. in Georgetown.)

In addition, now that we have to dance around the dts time code, I find that Buzz track is just not accurate enough. Try Dolby c/n 566 instead if you have access to an analyzer.

Posted by Joop de Gruiter (Member # 84) on 04-14-2005, 04:29 PM:

Gordon,

In the users manual for the cp45 it says to adjust dolby levels with the cp45 set to mono. Why should the cp45 differ from the cp55? I've been taught to do it in mono but if it works better in an other sound format i would like to know. On an Ultra Stereo i've been taught to do it set to stereo...

Joop

Posted by Gordon McLeod (Member # 33) on 04-14-2005, 04:43 PM:

On some versions of the mother board mono summed the preamp output before the meters and the two trim pots will interact

Posted by Ian Bailey (Member # 1752) on 04-15-2005, 02:28 AM:

Thanks for the tips guys.
Monte-the first thing I checked was the bearings and they feel fine.
Louis was correct in saying we have the POS lateral guide assembly which does have way too much weave.
The other thing that I have just learnt is to run the Dolby test loop in MONO-I've always done it in stereo.
So am I correct in saying that a quick fix is to run the Buzz track in MONO and adjust the lateral guide until NO TONES are heard? Then do a Dolby level check-in MONO!!
The other thing I don't understand is why the BUZZ is not apparent when I run a DTS feature on this machine!!

Posted by Monte L Fullmer (Member # 2797) on 04-15-2005, 02:58 AM:

quote:
The other thing I don't understand is why the BUZZ is not apparent when I run a DTS feature on this machine!!

..when DTS is engaged, the processor have switched over to the digital information coming from the DTS player and not needing the optical pickup-if that helps any....

I had to service a theatre of our with the same sort of problem-buzz in the trailers, but when feature kicked in playing DTS, all was good. Turned out that a loose wire was apparent in the camera connections down in the optical section of the 5-star...that was an easy fix. So, maybe check line connections coming from your camera to the preamp section of the processor. Might have an open ground or something.

Yes, buzz track and the dolby tone play in mono. Buzz track is where you don't want to hear anything. Dolby tone sets the output levels.

-thx Monte

Posted by Darryl Spicer (Member # 711) on 04-15-2005, 03:30 AM:

quote: Joop de Gruiter
On an Ultra Stereo i've been taught to do it set to stereo

Actually it doesn't matter when setting the tone levels on an ultra-stereo. I have set the levels with it in nsync. pushed it in stereo and mono and there are no defferences in the levels.

Posted by Ian Bailey (Member # 1752) on 04-15-2005, 05:44 AM:

Monte
the wierd thing is that this is an "analogue only" auditorium,so I don't understand why I'm getting the BUZZ on a couple of DTS trailers and not getting the BUZZ on DTS features that I run in analogue.And the fault is intermittent and when it happens it's from the very start of the trailer to the exact end of the trailer!!WIERD SHIT!!
Anyway the knowledge I have got from you guys today I will put into practise late tonight with the Buzz track and Dolby level track.

Posted by Brad Miller (Member # 2) on 04-15-2005, 05:48 AM:

It's very simple. Your optical soundhead is slightly off alignment to one side and those particular trailers are printed off alignment slightly to the other side (but not enough to produce a buzz on a properly aligned reader). You need to have your soundhead re-aligned...but then I said that yesterday. [Razz]

Posted by Ian Bailey (Member # 1752) on 04-15-2005, 07:23 AM:

Thanks Brad-old barstards like me need to be told a couple of times for it to sink in!! [beer]