When I'm doing a routine check of the Dolby Levels using the test loop in the projectior. What formatt should the CP-55 be in.

Newer runs of the Dolby Tone film have Mono clearly marked on them to avoid confusion.
 

See also "Hum in CP-45" for a Film-Tech discussion where this came up.

if you look at page 2.3 of the CP45 users manual it clearly states select format 01 Mono!!

All Dolby processors require you to setup with format 01 Mono as that's how the test films are calibrated.

There is a copy in the manuals section if anyone want's to check it out online.

Steve

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"Old projectionists never die, they just changeover!"
 

(Having said that, I've always used format 01, since that's what the manual says.)
 

Note: I am using fabulous CP50's

If you set it in 01, then leave the tone running and press 04 you probably won't see any difference on the Cat222 meters, if however you had an SRA5 or a Cat222 SR/A, and pressed 05 after setting level in 01, you would see a level increase.
 

Our CP 45's have given faultless service for over five years. I'm sure if there was a problem it would have reared it's head by now. Our boards are the first issue from what I can see. Is it possible that a later issue had a design change relating to this.

Peter Hall would also have found fault if this was an issue as he installed quite a number of them for City Screen, all running faultlessly as far as I know.

Steve

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"Old projectionists never die, they just changeover!"
 

There's no outcry about poor reproduction as a result... so is it that much of a concern. Provided the levels are indeed matched is it noticable.... we're not talking into the red just level.

I follow the manual and use Mono as with all processors and the labeling on the tone film itself. I make sure I'm the only one who does Dolby tone so there is consistency and no chance of any other trims being changed by mistake.

I've never had to check Dolby tone because of a sound problem, its checked as a matter of routine. Sometimes the levels have dropped and I've not been aware of it until I did a check.

People will continue to do it the way they have become familier with until they can have it demonstrated that there is a difference. So does it make a noticable difference within the auditorium?
 

Steve

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"Old projectionists never die, they just changeover!"
 

I recall you mentioning Cat 222SR/A with some distain a few times before -- are they really that bad? The museum is about to install in their CP55. Should I be expecting something less in audio quality from them?

And while we are on CP55's, can anyone tell me if the Subbass channel output is active in all formats or just the stereo formats? We just purchased a BGW Powered Subbass bin but unfortunately it does not fit behind the screen so it must be setup for each show. I don't want to have to schedule an extra crew person in to do this every time we run a mono print (quite often) if there is no output in 01 format.

Frank

 

Unless, of course, there is a difference between the US and UK boards. I have some UK models so I may check it next time I'm near one of them.

If you use Dolby A to set the level (following the installation manual) you will get a different result than if you used SR -- I forget which, but one of them will be louder -- so there is apparently a difference between the formats.

Steve G: What exactly do you mean when you say that the 222 will "mistrack" ?

Sorry to hear you're under the weather. Hope you feel better soon.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
 

Josh

Anyone have an SRA-5 they want to trade for a 222SR/A
 

Cat 222 A Two channels of 'A'
Cat 222 B Two channels of 'SR'
Cat 222 SR/A Two channels of each type.

Have I understood this much correctly?

The Cat. 222 B is described as: "Two-channel IC based SR upgrade module" Does this mean that it is a card which could replace a Cat. 222 A, or that it is just some chips which can be added to some existing card? If it is a card, and you have to remove the Cat. 222A to fit it then how do you play 'A' type films? Dou you have to swap cards to do it? Why would you want to fit a Cat. 222B anyway, if the CP-65 already has SR playback via the two Cat. 350s? Were some CP 65s made without the SR capability?

If the Cat. 222 SR/A provides inferior quality SR, why would you want to do it that way? The Cat. 222 SR/A is an expensive card, 1315 pounds in the list I have, the Cat. 222A is listed at 565 pounds, and the Cat. 350 at 595 pounds, so two Cat 350s plus a Cat 222A would cost 1755 pounds, not a great deal more than one Cat. 222 SR/A.

To confuse things even further, not only can a two channel 222 now do SR, as well as A but it seems there is a CP65 300, were the Cat. 350s are replaced by Cat. 300s, which can do 'A' as well as 'SR'. This is said to be for format 42, what is this? Is it one of the magnetic formats? I didn't think the CP 65 could handle Dolby encoded magnetic.

I assumed that when you selected A type playback then the card in the Cat. 222 slot would be used, and when you selected SR that the cards in the Cat. 350 slots would be used. If a single card in the Cat. 222 slot can be used for SR, and two cards in the Cat. 350 slots can be used for A type, how does the processor know which cards it should be using? What would happen if you fitted a Cat. 222 SR/A, plus two Cat. 300s, you would seem to have two of everything?

What is a DPN 98500 Mag./Optical signal routing card.

Finally, why do Dolby still produce the CP65, which I think is one of the best processors they have made, but will only supply them to studios and dubbing theatres, and why does their web site seem to be so lacking in technical information?

I think that's enough questions for today, thanks for any answers you can give.

 

As for how often do you check Dolby levels... how long is a length of string? I normally make it a routine to check it once a month, unless I have reason to suspect there is a problem.

A 1dB error might not seem like much but it can be enough to cause slight audible mistracking, particularly with A-type, which is less tolerant of errors than SR.

(Note that with Panastereo processors the LED meter is independent of the NR subtraction so any format can be selected when setting Dolby tone. A more sensible approach wouldn't you agree?)

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

Whilst we have certainly come up with a method of verifying the lateral position of the soundtrack (we bought an expensive measurement microscope and compare our test films to the relevant SMPTE standards), we have not yet determined a reliable and highly accurate way to verify such things as level and frequency response characteristics. But we are exploring several ways of doing this.

In the meantime I would suggest the following:

For Cat69T Dolby tone if you have several batches of NEW (unworn) stock which disagree with each other, choose the batch with the lowest output level and use it as your reference. It is better to err on the side of setting your preamp gain too high than too low for several reasons. Too low a setting may cause pumping of low level dialogue particularly with Dolby A films, whereas setting the gain too high will make things sound a bit brighter, the latter being less objectionable than the former. Secondly, film prints themselves will vary in calibration from one to the next so once again, erring on the high gain side will give less objectionable errors.

For cat69P we have found that the most recent (pale pink coloured) stock has the flattest response. The dark pink stuff has a severe roll off in the 16kHz - 20kHz region and the old B&W stock is not a whole lot better (at least not using red LED readers).

For cat97 (left/right) the important thing is lateral alignment and you can compare your stock by carefully overlaying it with some BT-35. Cat 97 has two alternate burst sine wave signals printed as a negative soundtrack running down the centre of each track, wheras BT-35 has two square wave signals runing down the outer edges of the soundtrack area. Using a magnifier you can check that the outer edges of the Cat97 waveforms are both exacty the same distance from the inner edges of the BT-35 square waves. Be careful to accurately align the edges of the two films on the soundtrack side.

That is the best I can offer at this stage, but we are working on it. Maybe someone from Dolby can offer something more conclusive as they make the stuff!

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
 

The indecison is driving me to drink!

Where's the Gin

Playing analog A prints also has a horrendous amount of distortion in the audio when the actual Dolby loops are used. The level meters will pin themselves during program material. I am hoping that I just got a bad batch, but even if that is the case that really blows.

Our pal Steve Guttag has devised some way of verifying Dolby tone, but he hasn't shared it yet. Steve?

It is possible to measure the peak to peak excursion of the Dolby tone sine wave with a microscope to verify that it occupies the correct track width for a 50% modulated signal, but this is complicated by the fact that the level of the tone could vary quite significantly along a short section of film and yet still average out to give a correct reading on a meter.

If the Ultra 50% tone is considered to be more accurate, maybe Clint can let us know how they verify that their stock is "on the money".

Of course, any consistant difference between Dolby's and Ultra's 50% levels may come down to one company's definition of 100% modulation vs the other's. The maximum track width "available" per track for SVA prints is set down in the SMPTE standards. However I seem to recall that the standards are not specific on whether you should consider 100% modulation to be the entire available track width, or something a little less to allow say, for sideways weave. I also seem to recall that Dolby uses something less (like maybe 90%), but I do not recall exactly what that something is. Where is Steve Guttag when you need him? This is one of the problems when individual companies are permitted to set their own standards.

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

Also, what is the periodic 'blip-blip-blip' in the Dolby tone sound? Is that what's called "warble tone"? If so, why is it there?
 

Steve, I am not sure how much effect print density will have on level, if any. This is something we are trying to find out. But if there is an effect it will probably be different for red, infrared and "tungsten" light readers. As infrared light is not blocked by the colour or "blackness" of the film, but rather by the silver content, in infra red and tungsten readers presumably variations in the silver content will have more effect than colour density and vice versa in red light readers. Maybe John P can "throw a little light" on this subject (or should I say throw a little LINK at this subject - John is becoming known as The Linkman around here). Keep up the excellent work, John.

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
 

For aligning encoders and studio equipment 1 kHz sinus (100 Hz for LFE) at studio Dolby level is used.

And they chose 850Hz because it only hurts (your ears that is), but 1kHz is a killer AND it hurts.

Yes, I truely dislike the Cat. 222SR/A and would never recommend using it as my front line of analog sound reproduction.

As to the various Dolby levels...Ultra's TT-1 was not perfect either. On much of the batches I have the left and right channels are not properly balanced. The pink noise is pretty good though I heard from some that some batches may be clipped. It is recorded loud unlike Cat. 69.

Both Cat 69 and TT-1 were products of NTAV.

My "method" of determining good test film from the bad is mostly observation when the next batch comes in if it disagrees with the pervious batch. We have also measured and compared using an R2 various batches over the years. When Dolby first went to the color stock test film all hell broke loose!

Back to SR....if you have a CP-55 either obtain an SRA-5 or look into the new Panastereo SR unit...they are your best bets...$1995 (list) for the Cat. 222SR/A just isn't such a good bargain...it isn't real SR.

Steve

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"Old projectionists never die, they just changeover!"
 

When running tone loops with the SRD enabled (such as in a CP-500), one hears two tones (especially with worn loops) , a higher frequency for the digital as opposed to the optical tone. If the optical tone is 850Hz, what is the frequency of the digital tone?
 

When Dolby introduced their digital systems, Dolby tone lost it's relevance because the traditional primary line up tone for pro-audio is 1kHz. You will notice that virtually all audio specifications use 1kHz as the primary reference. 1000 is a nice round number and conveniently located in the "most densely populated" part of the audio spectrum. So 1kHz is used as the standard reference for ALL digital audio.

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935