Film-Tech Forum ARCHIVE: Dolby CP500 RTA

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Posted by Paul Stevens (Member # 4016) on 01-25-2007, 10:21 PM:

I am thinking of actually using this feature on the 30 plus units in service. The manual calls for Cat 580 microphone multiplexer and mikes to be used. I don't have the Cat 580 on hand and don't have a clue where to look for one. Any experiences with this stuff, I would appreciate your sharing it with me.

Thanks

Posted by Ken Lackner (Member # 1002) on 01-26-2007, 05:45 AM:

You don't need the Dolby multiplexer if your plexer's manufacturer makes a cable for the CP500. I use the USL MMP-10, and USL does make such an adapter. However, I would question the accuracy of the CP500's RTA. I have never used it for a B-chain, but when I adjust focus and slit loss during A-chains, the CP500's on-screen RTA does not agree with my external RTA. For example, if my RTA is flat out to 12K, the on-screen display has major peaking at the high end, and if I adjust the slit loss so that the on-screen display is flat, my RTA rolls off at 4K. I've used a couple different RTA's over the years and this has always happend. I tend to trust my RTA.

Now that this is brought up, can anyone shed some light on why this happens?

Posted by Mark Gulbrandsen (Member # 72) on 01-26-2007, 08:22 AM:

Although I always use my IVIE RTA seperately for all adjustments I always compare it with built in RTA's. Never found one in a Dolby that was very far off yet....

Mark

Posted by Sam D. Chavez (Member # 1841) on 01-26-2007, 10:22 AM:

The 500 picks of the preamp signal for the internal RTA display ahead of the slit loss which is a digital function downstream, hence the difference.

A minor mistake but annoying.

Posted by Ken Lackner (Member # 1002) on 01-26-2007, 01:56 PM:

So it basically digitally corrects the display based on the slit loss setting?

Anoying, indeed. If I were in a pinch and didn't have my RTA with me, would it be best to set the slit loss so that the on-screen RTA is flat, or should I allow for the peaking since I know that corresponds to flat on my RTA?

Posted by Sam D. Chavez (Member # 1841) on 01-26-2007, 09:27 PM:

If you are using modern red readers, mine and others, you're flat to 14kHZ with no slit loss. There is no useful audio above 12 kHZ anyhow so most leave slit loss off these days.

Posted by Michael Schaffer (Member # 1204) on 01-27-2007, 03:53 AM:

quote: Ken Lackner
If I were in a pinch and didn't have my RTA with me

That's why you need to have an Ivie IE-33 or IE-35. Then you always have your RTA with you.

Posted by Paul Stevens (Member # 4016) on 01-27-2007, 11:46 AM:

Has anyone used a wireless system to interconnect the multiplexer with the RTA? None of my auditoriums have cable in place that can be used. Is there any RF system clean and flat enough in frequency response out to the bandwidth needed?

Posted by Louis Bornwasser (Member # 3063) on 01-27-2007, 09:11 PM:

Yes, we are testing a digital, non-compressed wireless system. It's about $1500. Will let you know.

Significant audio occurs above 12k up to about 15k. I won't leave an "A" chain until I am flat or 1 db down at 16k.

Does anyone else here test/verify the L-R channel? Not many analyzer can do this. Louis

Posted by Mark Gulbrandsen (Member # 72) on 01-27-2007, 09:26 PM:

The Sony techs used a wieless system on their rta when they came out to theaters to do software upgrades and attempt to make SDDS actually work but I don't remember any specifics about it. For any wireless system to work well it can't have any phase shift across the audio bandwidth or between channels at same frequencies, etc for it to be accurate, especially on multi mic RTA systems. Indeed a digital based FM system might be the best for this purpose. A simple FM system with phase shift held to a minimum would work ok on a single mic system but hopefully none of us here are going that dinosaur route. In reality a needless lazy mans(or handicapped persons) toy.

Mark

Posted by Ken Lackner (Member # 1002) on 01-28-2007, 07:45 AM:

Um...who leaves slit loss off??

quote: Louis Bornwasser
Does anyone else here test/verify the L-R channel? Not many analyzer can do this.

What exactly do you mean?

Posted by Louis Bornwasser (Member # 3063) on 01-28-2007, 09:35 AM:

If you don't compare the left total versus the right total, then you could have phase & level changes between them. If the DIFFERENCE is wide band and flat, then surround crosstalk cannot occur. The issue is important for SR tracking and 4 channel decoding. You can certainly see level and eq on the 2 channels directly. You can not see phase errors which, because of encoding, are particularly important. louis

Posted by Sam D. Chavez (Member # 1841) on 01-28-2007, 12:33 PM:

Regarding slit loss, with the original B&W Cat. 69, I would have confidence to tweak the slit loss to flat, but with the color test film produced the last few years, it's not worth the trouble due to the variance in the film,batch to batch.

Don't forget the original reason for the slit loss was back in the day when the front scan lens would go only to 2Khz before the rolloff began.

Louis, when was the last time you did a serious PM service call?

Posted by Louis Bornwasser (Member # 3063) on 01-28-2007, 01:53 PM:

Friday!

Posted by Michael Schaffer (Member # 1204) on 01-28-2007, 03:58 PM:

quote: Louis Bornwasser
If you don't compare the left total versus the right total, then you could have phase & level changes between them. If the DIFFERENCE is wide band and flat, then surround crosstalk cannot occur. The issue is important for SR tracking and 4 channel decoding. You can certainly see level and eq on the 2 channels directly. You can not see phase errors which, because of encoding, are particularly important. louis

On the IE-33/35, you can compare, add and subtract channels. But I think it's still easier and more accurate to simply look at the XY display of the two channels for optimimum phase. The length and symmetry of the "spiral galaxy" also tells you about frequency response and level. If the frequency responses of the two channels don't agree, you can't get a straight flat line either.

Posted by Pete Naples (Member # 761) on 01-28-2007, 04:16 PM:

Louis, yes, I and I believe our other engineers do that procedure. We are all using Abacus ARTA 80 analysers which have the facility to look at Sum and Difference of the two channels at the push of a button. The Cat 566 function is very handy too.

Posted by Louis Bornwasser (Member # 3063) on 01-29-2007, 01:30 PM:

Alas; they are no longer made! Really great box! (Bought a spare which is still wrapped.) Louis

Posted by Richard Fowler (Member # 893) on 01-29-2007, 06:28 PM:

The 80, my favorite box [Cool]

Posted by Steve Guttag (Member # 268) on 01-29-2007, 06:32 PM:

80 schmatey....the ARTA-600 was the real deal. [thumbsup]

Posted by Ian Bailey (Member # 1752) on 01-30-2007, 07:06 AM:

Hi guys
I'm at the point with my business that i need to buy the equipment and learn how to do these sound adjustments.
Our sites are all some distance from major cities and it is very costly to get equipment repair in a hurry.I'm doing 95% of our breakdown work but I am still getting all the projection equipment serviced regularly as I just don't have the time.The only part of the equipment service that I haven't bothered to get my head around is the sound alignment with the CRO and RTA.
I've been a sound freak for years(hence the 1/2 deaf in one ear!)I understand the concepts in what you are doing i just need to buy the gear and put it into practise.I am an old electronics tech and the last time i used a CRO I had a school uniform on as I have had no need for one in my work but i can still remember how they work!
What gear do you recommend that I get and where can I find all the information I need to be able to do this?
Cheers Ian

Posted by Pete Naples (Member # 761) on 01-30-2007, 01:27 PM:

Too true! Mine got badly bashed about by airline baggage handlers last year, fortunately Mr Plunkett was able to revive the innards, and some superglue was able to revive the casing. You should have seen the state of the Peli case! God knows what they'd done to it, towed a 747 over it I suspect!

Ian, as the Arta 80 is no more, I don't know what RTAs are available. I had a look at the Ivie website and the PDA based one looks interesting, especially as it can behave as a scope, although I suspect it's way not fast enough for looking at SR.D readers, probably suitable for checking cell alignment and the like.

I've got a LG Goldstar CRA which goes everywhere in the car, cheap as chips and works superbly, howver it's a built bulky. If I'm flying I've got a PicoScope box which basically uses the laptop as a display, perfect for A chain, and just fast enough to checking SR.D reader video voltage and LED alignment, NOT suitable for aligning an SR.D reader from scratch, you can't see the 'grass' in the middle clearly enough. For that application you can't beat a good CRO.
I carry the Arta80 as mentioned above, Cat85 pink noise card, eq extender card and my laptop. Sorted!

Posted by Paul Stevens (Member # 4016) on 01-30-2007, 09:55 PM:

Thanks to everyone for the posts on this subject. With your combined experience and my knack for finding things that need solutions, this group has been invaluable to me.

I look forward to hearing more on the wireless digital interface.

Paul Stevens

Posted by Ian Bailey (Member # 1752) on 01-31-2007, 05:23 AM:

Thanks Pete-that sounds like the way to go for me.
Cheers Ian

Posted by Gordon McLeod (Member # 33) on 01-31-2007, 07:02 AM:

Goldline makes a good rta and the D2 is an excellent unit as well
older Ivies often show up on ebay

[ 01-31-2007, 10:30 AM: Message edited by: Gordon McLeod ]

Posted by John Hawkinson (Member # 1135) on 01-31-2007, 12:33 PM:

We have a Goldline 30M8RM that we are not entirely pleased with (UI is clunky, time averaging is awkward, etc.). Gordon, what do you like about Goldline?

--jhawk

Posted by Gordon McLeod (Member # 33) on 01-31-2007, 02:01 PM:

The 30m8rm was a analogue rta that has not been made in a while
I beleive it actually had analogue edge type VU meters when it first surfaced a long long time ago (I also believe if memory serves it is 2.5db per step on the led display)
The DSP30 is a good stable unit and with the winsoftware will do most testing one needs at an affordable price

Posted by Michael Schaffer (Member # 1204) on 01-31-2007, 04:24 PM:

quote: Pete Naples
Ian, as the Arta 80 is no more, I don't know what RTAs are available. I had a look at the Ivie website and the PDA based one looks interesting, especially as it can behave as a scope, although I suspect it's way not fast enough for looking at SR.D readers, probably suitable for checking cell alignment and the like.

I suspect you suspect correctly. I actually never bothered to check what it's doing with SR*D because it is obvious that it's way too slow for that. But for everything else, it works miraculously well. I have had the IE-33 for over 3 years, and it served me extremely well in that time. I will probably get an IE-35 some time soon. The main difference between these two is that the former runs on an iPaq, and that wasn't such a great idea since those sometimes discharge completely, and then you have to reinstall everything. Not such a big deal, though, and they also have a cabinet file that you can store in the iPaq's non-volatile memory, so if it has run completely out of battery, you just hook it up to a power source and reinstall the program from that cab file. Still, a little annoying. Which is why they migrated the whole system to a Dell platform. But the RTA itself is great, small and handy, and it does a lot of extra things as well. The scope function also works great for analog A-chains.

Posted by Mark Gulbrandsen (Member # 72) on 01-31-2007, 07:59 PM:

Does anyone know what the bandwidth and residual noise is on the scope finction? I would say that Ivie has hit closer to the mark this time around. The Dell platform males ALOT more sense to me. Having owned Comnpaq pocket puters in the past I can honeltly say they are junk.

Mark

Posted by Michael Schaffer (Member # 1204) on 02-01-2007, 04:45 AM:

Dunno, but I am sure Ivie can furnish you with that information. They are just around the corner from where you are.
But I have compared it to a 60MHz scope, and it left nothing to be desired in direct comparisons for doing analog A-chains. At first, there was a phase error between the two channels, but they quickly corrected that. I haven't had a chance yet to compare the 33 and 35 models directly, so I don't know what added quality the new platform brings. I guess it will have more brainpower than the old iPaq platform, but I don't know yet how that influences the results you get with the unit. But the old one already worked really well after they ironed the kinks out. I actually just used it to restore an A-chain which had been totally knocked out of alignment.

Posted by Richard May (Member # 2627) on 02-01-2007, 05:08 PM:

The DSP-30 is a very nice unit.

Posted by Michael Schaffer (Member # 1204) on 02-01-2007, 06:21 PM:

But it's not an analyzer.

Posted by Richard May (Member # 2627) on 02-01-2007, 08:54 PM:

The DSP30? Since when?

Posted by Eric Robinson (Member # 2966) on 02-02-2007, 12:26 AM:

Now that we are completely off topic, but on a topic I am very interested in:

I have a Leader 325 scope to do digital A chain, but would prefer to use some device which interfaces to my laptop instead. I need to lighten the load a bit. So far I havn't found any digital scope solutions which compare to the traditional 60Mhz analog scope. Any ideas?

Posted by Tristan Lane (Member # 1169) on 02-02-2007, 12:27 AM:

The problem with a bunch of companies using the same model #'s

What Richard is referring to:

Maybe Michael was thinking of this

I like the Goldline DSP30 analyzer, but I still favor the old Ivie IE-30.

Posted by Michael Schaffer (Member # 1204) on 02-02-2007, 02:31 AM:

You are right, I thought Rich meant the QSC unit of the same name. I have only seen the Goldline RTA once and never played with it myself.
Back in the old world, I worked mostly with the analog Ivie and sometimes the Abacus. Since I came here almost 4 years ago, I have always had the IE-33.

Posted by Richard May (Member # 2627) on 02-02-2007, 08:02 PM:

Ah, I feel better now. Thought I was losing it for a minute. Thanks Tristan. I was definitely talking about the Goldline. Sorry for the confusion Michael. [Smile]

Posted by Michael Schaffer (Member # 1204) on 02-05-2007, 01:17 AM:

No, it was actually me who was confused. That happens more and more, the older you get.