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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » Refersher on A-Chain (Page 1)

 
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Author Topic: Refersher on A-Chain
Randy Stankey
Film God

Posts: 6426
From: Erie, Pennsylvania
Registered: Jun 99


 - posted 01-26-2011 05:35 PM      Profile for Randy Stankey   Email Randy Stankey   Send New Private Message       Edit/Delete Post 
Making tweaks to the A-chain after installing a new processor.
(Finally got rid of that Smart and put in a CP-650.)

I've got a question about how to get it right.

When running a movie, some scenes have poor dialog.
The level of the dialog gets very low, very hard to hear and there is some distortion that sounds kind of like bees buzzing.
(e.g. Like the sound you hear when you tune an AM radio partly off the station.)

This does not happen during the whole movie. Only certain parts with lots of effects in the sound track. Specifically outdoor, street scenes or driving in a car.

You can still hear effects, music and background sounds fairly well.

We do not have surround speakers. Only L/C/R+Sub.

If I could hear dialog in the surrounds, I'd know that my azimuth/focus are off. (Azimuth, primarily.) But, since I don't have surrounds, I can't really tell.

Is this effect what you would expect if the azimuth is off or is there something else I need to check?

T.I.A. [Smile]

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Sean McKinnon
Phenomenal Film Handler

Posts: 1574
From: Peabody Massachusetts
Registered: Sep 2000


 - posted 01-26-2011 09:32 PM      Profile for Sean McKinnon   Email Sean McKinnon   Send New Private Message       Edit/Delete Post 
If you think your that far off in your alignment you could try swapping the Lt Rt inputs from the reader at the processor and see if you dialog comes back.

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Bill Duelly
Film Handler

Posts: 90
From: Roselle Park, NJ
Registered: Feb 2006


 - posted 01-26-2011 10:16 PM      Profile for Bill Duelly   Email Bill Duelly   Send New Private Message       Edit/Delete Post 
The buzzing sound I found out to be one of 2 things: 1) the soundtrack itself is scratchy (which I would doubt since you said the other channels seem fine) 2) the other which I just found when doing an A-Chain with an LED reader, is that the High Frequency compensation level is set too high for the analogs to really handle (even though it may seem fine on the scopes). I just brought that level down and it solved the problem.

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Monte L Fullmer
Film God

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From: Nampa, Idaho, USA
Registered: Nov 2004


 - posted 01-27-2011 03:31 AM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
Ya, sounds like the slit loss adjustment need a bit of tweaking...

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Darryl Spicer
Film God

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From: Lexington, KY, USA
Registered: Dec 2000


 - posted 01-27-2011 01:06 PM      Profile for Darryl Spicer     Send New Private Message       Edit/Delete Post 
If you have a tight XY response on your scope...be sure to run the signal through the analyzer with a loop of pink noise to verify the high frequencies are not over peaking. Back them down a bit if they are high. The less you have to use the slit loss adjustment the better. Make sure the optics are clean before making the adjustments.

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Randy Stankey
Film God

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From: Erie, Pennsylvania
Registered: Jun 99


 - posted 01-27-2011 01:18 PM      Profile for Randy Stankey   Email Randy Stankey   Send New Private Message       Edit/Delete Post 
I will need to redo the A-chain and make the azimuth and focus adjustments better. I checked them with the scope and they are close but not quite there.

It's one of those things I don't do very often, anymore. Although it's not hard to do, it takes practice to get it just perfect and I am out of practice. I just need to put my mind to it and take my time.

Now, with the slit loss correction, the CP-650 does that automatically.
Are you saying that the thing sets itself too high? When I used to do this for Cinemark, the procedure was to find the "high point," if you will, then to back off just a hair. So, I assume you're telling me that I should let the processor find home then manually back it off a couple-few clicks. Right?

How far do you think I should back it off?

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Scott Norwood
Film God

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From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 01-27-2011 01:28 PM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
I assume that you have tried multiple prints to rule out printing issues or a bad mix, correct?

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000


 - posted 01-27-2011 01:42 PM      Profile for Darryl Spicer     Send New Private Message       Edit/Delete Post 
quote: Randy Stankey
Now, with the slit loss correction, the CP-650 does that automatically.
Are you saying that the thing sets itself too high? When I used to do this for Cinemark, the procedure was to find the "high point," if you will, then to back off just a hair. So, I assume you're telling me that I should let the processor find home then manually back it off a couple-few clicks. Right?


Make your adjustments at the sound head and get the highest highs you can get on your anylizer and maintain a tight XY combination on your scope. Make sure the slit loss compensator is turned all the way down. Then make adjustments as needed on the compensator. You don't want the highs to peak above the other frequencies.

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Randy Stankey
Film God

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From: Erie, Pennsylvania
Registered: Jun 99


 - posted 01-27-2011 03:16 PM      Profile for Randy Stankey   Email Randy Stankey   Send New Private Message       Edit/Delete Post 
quote: Scott Norwood
I assume that you have tried multiple prints to rule out printing issues or a bad mix, correct?
The print in question was "Chairo Time." I have not ruled out the fact that there was a problem with the soundtrack on the print but I am not 100% satisfied with my A-chain, either.

I did a "good" A-chain but, when I had problems, I rechecked it and found that my azimuth was just a hair bit off. I tweaked it and the problem got better but it didn't go away completely.

Here's how I understand the process:

On the Dolby CP-650 processor, you set Dolby levels with the green Dolby Tone film then switch to the pink film. At that point, you adjust azimuth using the scope. Then you switch over to the internal RTA of the CP-650 and adjust focus until the curve is as flat as possible on both channels. Bounce back and forth between focus and azimuth once or twice to be sure that you haven't knocked one out of line while setting the other.

After that point, you tell the CP-650 to auto-adjust for slit loss correction.

I did it all up to this point as well as I could. When I had trouble with the print, I rechecked it and found that I was just a tiny bit off. I retuned and it got better but not all the way gone.

I ran a bunch of trailers and didn't notice any problem. It only occurred on that one print of "Cairo Time."

I am going to retune the A-chain one more time and I'm going to be sure that I make it as good as possible.

In the last 10 years, I have only done A-chains a few times. It's not hard to do but takes a certain touch to get really good results. You guys do this kind of thing all the time. If I give myself some time, I'll get it right. I'm just rusty, that's all.

When I first did it, I'd score myself as 8 out of 10. I retuned it and got it up to 9. Now I want to go for 10.

quote: Darryl Spicer
Make your adjustments at the sound head and get the highest highs you can get on your anylizer and maintain a tight XY combination on your scope. Make sure the slit loss compensator is turned all the way down. Then make adjustments as needed on the compensator. You don't want the highs to peak above the other frequencies.
Are you saying to just screw the automatic setting and do it the old fashioned way? I don't have a problem with that, really. I somewhat prefer to do it that way but I wanted to do it by the book the first time. Then, once I learn the process, I'll go off-script.

So, set the slit loss at zero, tune the azimuth and focus then adjust the slit loss for "flat" and back off a click or two? Is that right?

That's pretty much the way I learned it before.

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Louis Bornwasser
Film God

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From: prospect ky usa
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 - posted 01-27-2011 06:03 PM      Profile for Louis Bornwasser   Author's Homepage   Email Louis Bornwasser   Send New Private Message       Edit/Delete Post 
Stick with the Dolby instructions. You will need to be able to see the "x/y" and the response at the same time. Use a scope and an external analyzer for this. Louis Bornwasser

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Darryl Spicer
Film God

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From: Lexington, KY, USA
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 - posted 01-28-2011 03:00 AM      Profile for Darryl Spicer     Send New Private Message       Edit/Delete Post 
quote: Randy Stankey
So, set the slit loss at zero, tune the azimuth and focus then adjust the slit loss for "flat" and back off a click or two? Is that right?


Yes it is best to get all you can out of the sound head adjustments and then tweak it in the processor.

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Kenneth Wuepper
Jedi Master Film Handler

Posts: 996
From: Saginaw, MI, USA
Registered: Feb 2002


 - posted 01-28-2011 09:09 AM      Profile for Kenneth Wuepper   Email Kenneth Wuepper   Send New Private Message       Edit/Delete Post 
It is wise to insert short pieces of "buzz" and "Left Right crosstalk" in the Pink focus and phase loop to be certain that everything stays centered.

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Randy Stankey
Film God

Posts: 6426
From: Erie, Pennsylvania
Registered: Jun 99


 - posted 02-02-2011 01:51 AM      Profile for Randy Stankey   Email Randy Stankey   Send New Private Message       Edit/Delete Post 
I made some headway tonight.

I retuned the A-chain and I got it down real good. I basically took it all apart and started from scratch. It's the best job I've done in a long time.

However, the problem was still there! This was with a different print, too.
Checked the output of the processor with scope and meter. All channels were operating as they should. That puts it down to the amps and speakers.
I swapped out the amp for the center channel and the problem disappeared.

That problem is solved, I guess! [Smile]

Tomorrow, the Dolby Digital reader is due to arrive. Once I get that installed, I can go through the whole B-Chain procedure and make final adjustments on that and I should be good to go.

It's already sounding good with the EQ set to the curve. Once I get it EQed for the room the should should really pop!

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System Notices
Forum Watchdog / Soup Nazi

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 - posted 07-09-2012 04:17 PM      Profile for System Notices         Edit/Delete Post 

It has been 523 days since the last post.


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Victor Liorentas
Jedi Master Film Handler

Posts: 797
From: london ontario canada
Registered: May 2009


 - posted 07-09-2012 04:17 PM      Profile for Victor Liorentas   Email Victor Liorentas   Send New Private Message       Edit/Delete Post 
If I were to swap an OLD xl head with a 97 era PR 1014, will I need the a chain alignment redone? Is it possible to do this without messing it up?
I use SH1000 sound heads.

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