Film-Tech Forum ARCHIVE: Dolby Toning CP45's

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Posted by Oliver Harper (Member # 4245) on 09-08-2009, 04:47 AM:

I run a projection booth for Cineworld in the UK. I have come across a lot projectionists who have been trained at others site to Dolby tone the CP45s in the Dolby SR channel instead of MONO!..

We have had staff transfer over to our booth and i gave them a projector to maintain and was finding every week they had to do major adjustments to the processor to get the sound back to normal. Then i found out what channel they had it set in, but the member of the staff said that was the way he was shown.I grabbed the manual and made him read the Dolby toning section to show how its done.

Has anyone else come across this?

Posted by Gavin Lewarne (Member # 5397) on 09-08-2009, 05:12 AM:

Actually I do thin with our CP45, but for a very good reason.

For ages i could not figure out why most of the dialog was being sent to Centre + left and we had terribly unbalanced sound in the auditorium. dialog leakage into left + surrounds and virtually nothing from right.

I toned and toned my head off in MONO and A-TYPE (my CP45s manual actually says to do it in A-Type), checkd slit azimuth, focus and pink noise response. everything was as good as it could be. We even called in a service engineer from Sound Associates but even then could not figure it out. Everntually i though, Heck with it, and toned it in SR. ever since, now get balanced sound with dialog correctly being decoded and no surround leakage! If i tone in mono and switch to SR with the loop still running, there is actually very very little difference needed between the modes to get the green's lit evenly. for me, it was just half a turn of the right trim pots. but evidently, that was enough to throw off the decode.

Oh, and check that the input type jumper is set correctly. we have jaxlite XLA-650 preamps in our projectors that have an unbalanced output, but for the years prior to my employment the CP45 had been set to Balanced inputs, leading to huger amounts of crosstalk than you can get even with a badly aligned A-Chain. Once i corrected this to Unbalanced and re-toned in SR, decoding is absolutely spot on. We have even had customers commenting on the quality of our sound compared to the all-new multiplex nearby

Posted by Oliver Harper (Member # 4245) on 09-08-2009, 05:31 AM:

Thats strange your manual says A-type. We havent' had issues with leakage, the only complaints we get is that there is hardly any use of the surround channels. usually depends where the customers are sitting or I just crank the volume up.

When i was dolby toning the other day switching between SR and MONO the signals were completely different where as the mono only need a minor adjustment the SR channel was way out!.

We are using the Kelmar pre-amps for our sreens..and they are rubbish, we just recently got some modified ones for the Dolby EX screens and they work a treat.

Where can i check the input jumper?

Posted by Gavin Lewarne (Member # 5397) on 09-08-2009, 05:39 AM:

how weird!

the jumpers for input type are located directly behind the level trimpots. but are swapped, eg:

the jumper for Proj1 input type is behind the trimpots for Proj2 and vice-versa (caused me much confusion in the past!)

if you cant find them i will take a photo later.

thats strange your level dirrerence between mono and SR. can you take a photo of the EQ settings? i found out that setting the treble freq too hgh can have an affect on the sound path (at least on mine).

I think the CP45 is just old and weird, and mine certainly has its quirks

Posted by Oliver Harper (Member # 4245) on 09-08-2009, 06:02 AM:

Yeah sure Gavin, i will take pic and post tomorrow. CP45's are still getting installed in new theaters, its crazy its old technology. Fair enough if the screen is small and a CP45 would be fine but you can better sound from Bluray..Paying like £8 to see a film and you get sound in just SR, we get customers complaining all the time that they can get better sound at home!..

Posted by Jonathan Worthing (Member # 803) on 09-08-2009, 06:16 AM:

[QUOTE] my CP45s manual actually says to do it in A-Type/QUOTE]

Are you sure.

I have looked at my hard copys (Install & User) & the on-line copy on Filmtech & they both say to do tone in MONO Format 01.

This is the way Dolby Teach on there training course.

Jonathan

Posted by Gavin Lewarne (Member # 5397) on 09-08-2009, 06:55 AM:

absolutely sure! if i tone in MONO and switch to A-Type, no adjustments are necessary, they tim to exactly the same level. Only SR is very very slightly different on ours. like i said, only half a turn of the right trims is necessary betweern Mono / A-Type and SR

Posted by Demetris Thoupis (Member # 833) on 09-08-2009, 07:13 AM:

Actually on page 45 of the film-tech install manual it clearly indicates A-Type! In the film-tech user manual in page 17 it says mono. Which to believe?

Posted by Gavin Lewarne (Member # 5397) on 09-08-2009, 07:20 AM:

they are probably both right. as i indicated, on our unit there are no differences in trim levels between mono and a-type when toning.

Posted by John Hawkinson (Member # 1135) on 09-08-2009, 08:23 AM:

There have been several threads on this. Try searching.

It is supposed to be Mono for all Dolby processors. On some processors it makes a difference, on other models it does not matter (depending on how the internal circuitry is set up). I don't recall for the CP45.

I believe a level difference between mono and SR is expected. Generally speaking SR has more dynamic range so more gain is applied, relative to A-type, which should be the same as Mono.

The mystery here is why Gavin's CP45 decodes SR badly when calibrated in mono. The obvious choices are a bad SR decoder card (have you tried swapping?) and a bad batch of Dolby tone (those have happened -- what's your batch date?).

Also, there's quite a lot of variation in the metering sometimes. Try hooking a DMM up to the test points and seeing what voltage you actually hit in both cases. (For most processors it is 300mV nominal, though I don't recall for the CP45...).

--jhawk

Posted by Gordon McLeod (Member # 33) on 09-08-2009, 10:09 AM:

mono enhancement must be disabled for calibration
also check the preamp jumper settings for cell vs reverse scan reader

Posted by Gavin Lewarne (Member # 5397) on 09-08-2009, 01:04 PM:

well, in regard to my cp45 decoding badly, i swapped with a brand new 222sr/a and had exactly the same result, so put the old one back. I am very happy with the sound mine produces when calibrated in SR and i dont see it as a problem for our application. what is interesting is why mine behaves differently to olivers. and why his should have such a massive level difference between mono and SR calibration.

my preamps have no jumnpers, either on the casing and connector or on the circuit itself. its simply signal in and out.

Posted by Gordon McLeod (Member # 33) on 09-08-2009, 01:47 PM:

J1 and J2 seect balanced or unbalanced inputs ie reverse scan or cell
J7 selects mono enhanced and regular mono
calibration must be in regular mono

Posted by Marin Zorica (Member # 1716) on 09-08-2009, 05:06 PM:

You are sure there are no jumpers on preamp? Maybe it's some earlier model without it, and signal path between MONO/A/SR is a bit different? So measuremnts are different? But A/SR path should be same, as same card is used for decoding both, only don't know where LED are measuring, probably on input of cat 222? So levels should be same.....

Posted by Manny Knowles (Member # 1171) on 09-08-2009, 05:19 PM:

After tone, I like to run a loop of 69P (Pink Noise) in SR to verify via signal LED's that the signal is being steered (primarily) to center and also there should be a null in the surrounds. This is to verify the status of the other alignment variables that could affect proper decoding. A certain amount of signal leakage to the other channels is to be expected. It's not a full-on alignment at this stage so I don't bust out the scope; I just do a quick look-n-listen to verify status.

Posted by Gavin Lewarne (Member # 5397) on 09-08-2009, 07:43 PM:

sorry, i thought you were referring to the jaxlite preamps. the preamp board on my cp45 is sert to unbalanced to match the jaxlite inputs. and its always in normal mono mode, never use enhance.