Film-Tech Forum ARCHIVE: Dolby digital reader needing adjustment?

This is topic Dolby digital reader needing adjustment? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Garry Knapp (Member # 9697) on 03-11-2018, 03:00 AM:

Hi Guys. My dolby audio sounds great. I run a DA20. One problem i'm having is, the output signal strength is sometimes not very good. I really notice this when running reels of trailers. My signal strength number is usually around 6-7. Some get really good, around 4-5. Apart from cleanliness, Are there any simple things I should look at to enhance the strength?

Posted by Marco Giustini (Member # 4544) on 03-11-2018, 04:56 AM:

Hi,

The number is called the error rate. If some of your content reads 4, then your head is probably ok. There is nothing you can do without using an oscilloscope and test loops.

Unless you have a CP650 sound processor? You can check the video amplitude with that and adjust the voltage.

Posted by Randy Stankey (Member # 64) on 03-11-2018, 06:08 AM:

The error rate display on a Dolby Digital is a golf score. The lower the better.

6 or 7 is bad. If it goes any higher than 7, the display will read "F" and your Dolby Digital processor will revert back to analog sound.

4 or 5 is decent but, if you have somebody who knows how to tune a Dolby reader, you should be able to get it lower than that.

With a good, clean print and a well tuned reader you should be able to get 3 or better.

A couple of tricks you can do to make sure that your error number is as low as it can go without the need for a tune-up is to make sure the reader is threaded with the right amount of tension.

Set the tension arms so that they just line up with the white marks on the back wall/plate of the reader.

Also, you can apply just a smidgeon of back tension on the film.

Once you've done the basics... keep it clean and in proper working order... you've done just about all that you can do without an oscilloscope and/or special tools and software.

However, I might suggest that you have somebody check the LED in your reader. As they age they tend to get weak. Replacing a weak LED will help you get that error number down as low as possible.

Posted by Mark J. Marshall (Member # 1409) on 03-11-2018, 07:18 AM:

I haven't touched a Dolby reader in years, but for what it's worth it was not uncommon for ours to run 0s and 1s.

Make sure your film is clean too, not just the reader. Use Film Guard if you're not already. It helps.

Posted by Carsten Kurz (Member # 5396) on 03-11-2018, 08:13 AM:

Most private users will not have access to lab-fresh prints, so it is pretty common to not have low numbers with the typical privately owned feature and trailer prints.

If you have used prints that reach 3-4, I guess everything is okay. Dig up the reader installation manual from the warehouse and read through it. What type of reader is it? Some use LEDs, the older ones tungsten lamps.

- Carsten

Posted by Gordon McLeod (Member # 33) on 03-11-2018, 11:23 AM:

Is yours a basement vic 5 reader as i find them the hardest to get good results with

Posted by Randy Stankey (Member # 64) on 03-11-2018, 11:27 AM:

quote: Mark J. Marshall
I haven't touched a Dolby reader in years, but for what it's worth it was not uncommon for ours to run 0s and 1s.

Yeah, I would start getting phone calls and e-mails when the Dolbys at my theaters (that I was responsible for) started getting in the 5/6 range.

Posted by Victor Liorentas (Member # 5272) on 03-11-2018, 12:55 PM:

On a cat700 white light reader,after a few years of not being used much,I believe the lamps reflective coating can deteriorate causing 6 7 f. That's what I'm getting lately. I've bought some new lamps but not had a chance to install one and compare the error rate.
I hope that's all it is. Any advice on carefully cleaning the light pipe surface? Without damaging it?

Posted by Mark Gulbrandsen (Member # 72) on 03-11-2018, 01:07 PM:

quote: Victor Liorentas
On a cat700 white light reader,after a few years of not being used much,I believe the lamps reflective coating can deteriorate

The coating typically just clouds up and it is easily cleaned with a cotton swab and lens cleaner. I have never seen a lamp of that type in a Cat 700 or other piece of equipment where the coating is damaged. In my experience the two best penthouse readers are the Cat 700 and the BACP.

If you have a Cat 701/702 then the video level may be low and in need of adjustment from the normal fade rate of the Red LED. Also check the lateral guide roller to see how worn it is. It's the upper roller (I believe) of the two tight loop rollers. They do not last for ever and sometimes are so worn they have to be replaced.Lateral drift of the film in bad cases can really raise the error rate, some times to the point that tracks can no longer be read.

Mark

Posted by Sam D. Chavez (Member # 1841) on 03-11-2018, 03:52 PM:

I wonder if someone can comment on the base error rate these days, now that films are not made as often and by only one lab in the USA, anyway? It could be that the error rate has started to go back up.

I do stock the last of the Dolby LEDs, if anybody needs them. I don't have the Dolby LED in a heat sink, somebody would need to solder it in to the heatsink.I do have stock of the LED/heatsinks for BACP analog and digital reader though. I also have stock of the bulb for the Cat. 700 as well.

Posted by Julian Antos (Member # 5497) on 03-12-2018, 01:51 PM:

The last few NEW prints I've run have gotten 0s and 1s no problem.

Posted by Louis Bornwasser (Member # 3063) on 03-12-2018, 09:29 PM:

I also have hundreds of Dolby LEDS. Also a few of the ones in the heat sink.

Posted by Sam D. Chavez (Member # 1841) on 03-13-2018, 12:26 AM:

So, sell them already. You are very hard to catch.

How many new 650's you have in stock?

Posted by Garry Knapp (Member # 9697) on 03-13-2018, 05:22 PM:

WOW...thank you guys for all the great input...I don't know where to start. I can't figure out how to reply individually, so i'll just reply to everyone.
Marco: I have a CP65...
Randy: most of my prints read pretty high...6-7 range. I do get a few times where it falls off and reverts back...
I've been trying to get a hold of someone up here, but the person is very busy it seems...
I run a vic5...theres not much tension adjustment options that I know of...
It's not terribly old either. It only ran in for 7 years before it was pulled out.
Mark J.: Cleanliness helps, this I found out...I will add the film guard to my cleaning unit (kelmar) Haven't been...
Carsten/Gord: Yes, its a basement reader...not much to play with as far as adjustments...It runs LEDs

Thanks everyone...this will help things quite a bit.

Posted by Max Hayman (Member # 8726) on 03-13-2018, 05:23 PM:

hmmmm I always thought a higher number was better...thats not good...our SR-D head seems to stop working every now and again.

Posted by Monte L Fullmer (Member # 2797) on 03-13-2018, 05:36 PM:

CAT701 units has that self contained power supply were we had to tweak up the current on the LED to get the error count down.

I've used exciter power supplies to replace the ones for the CAT699 and 700 units being we're just dealing with a small projector lamp.

But, using WinDRAS, it helped also to get the alignment checked, if one doesn't have an "O-scope" to really fine tune in the camera.

Posted by Sean McKinnon (Member # 612) on 03-16-2018, 07:53 AM:

quote: Sam D. Chavez
How many new 650's you have in stock?

Sam, We have a few here NOS in the original boxes. [Big Grin]

Never opened [Eek!]

Posted by Louis Bornwasser (Member # 3063) on 03-16-2018, 09:20 AM:

WIN DRAS is only for final tweaking. Oscope is the only way. Frankly, we had a technique for just doing it the old fashioned by-eye way that always resulted in audio; a great place to start.

Posted by Sam D. Chavez (Member # 1841) on 03-16-2018, 10:14 AM:

Hi Sean,

You do know where those 650's came from? [beer]

Posted by Sean McKinnon (Member # 612) on 03-16-2018, 12:01 PM:

I do that's why I added the [Big Grin]

Posted by Randy Stankey (Member # 64) on 03-16-2018, 02:45 PM:

quote: Louis Bornwasser
WIN DRAS is only for final tweaking. Oscope is the only way.

AFAIAC, WIN DRAS is nothing more than a display or an indicator.

I would often have the computer and the oscilloscope connected at the same time and bounce back and forth between looking at DRAS and the scope, making adjustments until I got things running just the way I wanted them to.

The nice thing about DRAS is that it has the bar graph that shows the history of how well it has been operating over the last several minutes.

I would often turn on DRAS and leave it running during a whole movie then come back later to see how well (or badly) the unit behaved in a real-world test.

So, yes, DRAS is a tool you can use to tune up your Dolby Digital unit but it is not the only tool in your tool box, nor should you treat it as such.

Posted by Sam D. Chavez (Member # 1841) on 03-16-2018, 05:26 PM:

DRAS only works when the reader is actually working more or less normally. If you are trying to adjust things and it goes too far off it will quit displaying and then you're in the dark and time for the scope.

Posted by Garry Knapp (Member # 9697) on 03-25-2018, 06:50 AM:

Anyone have a any LEDs for sale for the Vic5 basement readers?
Thinking its a good idea to have set...

Posted by Louis Bornwasser (Member # 3063) on 03-26-2018, 10:11 AM:

Low numbers are good/high are bad. That said, stability is even more important. I have seen steady 4-5-6 for years with no problems. Lots depends upon the mechanical integrity of the driving projector as well as optimal set up. Is there any bearing oiling on the V5?

Posted by Gordon McLeod (Member # 33) on 03-27-2018, 09:21 AM:

some versions of the cinemecanica did have a oil hole in the centre of the shaft bracket located between the inner bell and the flywheel

Posted by Mark Gulbrandsen (Member # 72) on 03-27-2018, 11:29 AM:

Perfect for getting oil all over the stereo pickups...

Mark

Posted by Garry Knapp (Member # 9697) on 03-27-2018, 07:36 PM:

This one doesn't.
One more question then, along this same thread..
How many channels does an oscilloscope need to read the audio output? I've heard this from day-one, that a scope was needed. I'm not afraid of going this route as I could surely use the scope for other purposes...

Posted by Sam D. Chavez (Member # 1841) on 03-27-2018, 10:53 PM:

2 channel with X/Y capability. You need fairly high res as solid state screens are relatively slow compared to CRT phosphor displays.

Posted by Sean McKinnon (Member # 612) on 03-28-2018, 05:20 PM:

Your actually not reading an audio output its a video output from a CCD. The DD reader takes a picture of the area between the sprocket holes and sends that picture to the DA-20/Cp500 DA 20 subsection or CP-650 which decodes the clear and black squares from the picture into digital data (ones and zeros).

I prefer an analog CRT for this and it needs to be at least a 20 Mhz scope. (I think its 20 but I have to double check)

Posted by Gordon McLeod (Member # 33) on 03-29-2018, 09:46 AM:

You need a dual channel 20Mhz scope that does X/Y mode
If the drum doesnt have the oil hole then the unit has sealed ball bearings (one of the later)
Mark pray tell me how oil will find its way to the cell or lens it isn't possible

Posted by Mark Gulbrandsen (Member # 72) on 03-29-2018, 11:24 AM:

quote: Gordon McLeod
Mark pray tell me how oil will find its way to the cell or lens it isn't possible

Had it happen on one of the VIC-8's at the Twin Ten in Twin Falls, ID about 15 years ago! I can't explain how it got there either. But I had to take it all apart and clean it.