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This topic comprises 2 pages: 1 2
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Author
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Topic: NEC NC800 digital projector.
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 02-13-2007 05:45 PM
I got the date wrong on my last post; it was 12th of February, not the 15th, so it's now there. The server is not the model which was previously stated in the paperwork, but I can't remember what it is, I intended to make a note of it, and forgot. The 'alternative content' interface is by Christie, and will take composite, Y, Pr,Pb component and RGB (with sync on green, or separate composite sync, or separate H and V syncs. All of these are on BNCs, but it will also take S-Video. There's a DVI input for digital signals, and it's a DVI-I, so it can also be used with VGA, via an adapter. That should cover most things. I think at least in the short to medium term it's likely to be used more for this than for actual digital cinema content. The Clocktower runs digital film making courses, and the College where I work also hires the cinema for end of year shows etc. for media students. The cinema has DVD and DVCAM players installed almost permanently (they are occasionally removed for use elsewhere). It will be interesting to see how this looks on the DC projector, rather than the LCD video one which has been used in the past. I've hot a few Hi-Def digital video clips from the BBC on a computer at home; I'll copy them onto my laptop, and take them in one day, to see how they look. They're big files, maybe I should think about upgrading the home network to Gigabit. ![[Smile]](smile.gif)
I'm not allowed to touch the new digital gear myself, but when I arrived this evening the projectionist that I was relieving was running a few trailers on it between shows. It can't actually be used yet, as the digital interface to the sound system, I'm not sure which of the options available they chose, has not been installed yet. Also, the ADSL line isn't connected yet, and the connection to the fire alarm doesn't seem to be either.
They've made a very neat job of the new port, though it had to be placed even further off-axis than the position specified in the site survey report. Considering how far off it is, the keystoning isn't at all bad; you really don't notice it unless you're looking for it.
First digital show is scheduled for later this month, and in March there are three screenings of 'Wizard of Oz'; I'm going to try to get to one of them.
I've been given permission to take a few photographs, I'll take some on Thursday, and post a couple. I might have to use a very wide angle lens!
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 02-24-2007 04:11 AM
Well, it's two weeks on Monday since the projector went in, and it still can't be used, but the final piece of equipment, a Dolby DMA8 Plus, arrived yesterday, and is due to be installed on Monday, so it shouldn't be long now.
I've not seen the 'Plus' before; it's only one 'U' high, but seems to do just about the same as the original DMA8. I don't like the way that the only thing you can select from the front panel seems to be input to be used; to select the format of that input seems to need a PC connected to it.
The AES inputs are 75 Ohm unbalanced on BNCs, rather than 110 Ohm balanced on XLRs; I think they called it AES-3id, as opposed to the AES/EBU of the balanced version. I've heard of this interface before, but never actually seen it; did the original DMA8 use the same, I never looked at the back of one. The spec. gives a much greater maximum cable length for the unbalanced version, which seems odd; why is this. The other advantage seems to be that while there are differences in Voltage level, and some of the metadata, it's claimed to be cose enough that you can feed a domestic SP/DIF signal from something like a DVD player directly into it.
The first true digital cinema screening will be 'Wizard of Oz' on 3rd of March at 12:15; I'm due to be at work then, but if I can manage to swap a shift at work I'm going to try to be there to see it. If I can't make it I'll go to the second screening on the 7th, at 20:15. Anybody else living anywhere near Croydon going to come?
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 02-24-2007 06:23 AM
quote: Stephen Furley
The AES inputs are 75 Ohm unbalanced on BNCs, rather than 110 Ohm balanced on XLRs; I think they called it AES-3id, as opposed to the AES/EBU of the balanced version.
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By far, the most popular use of copper for moving digital audio is the AES3-id or the unbalanced BNC version. That is because the broadcast industry and all of their players use 75-Ohm BNC type cables for everything. The Consumer S/PDIF signal is also 75-Ohm. The DMA8 Plus has enough range in its input to handle either consumer or pro level (consumer runs at .5V, pro runs at 1V)
Have no fear though...the "4xAES" input (25 pin DSub) is an AES/EBU balanced input so the DMA8 Plus can go both ways.
quote: Stephen Furley
I've heard of this interface before, but never actually seen it; did the original DMA8 use the same
The original DMA8 had pretty much the same inputs though the DMA8 had a S/DIF specific input (RCA input) and I don't recall the DMA8 having a TOSLINK input.
Howevever if you dislike just the 4 input selection buttons you would have HATED the DMA8...only two buttons (film or digital) and you couldn't select which digital input from the front! They eventually did allow for pressing the digital button to cycle through the inputs though you had no idea of which input it was on or how it was being decoded since it had only two LEDs..."Film" and "Digital".
[quoteThe spec. gives a much greater maximum cable length for the unbalanced version, which seems odd; why is this.[/quote]
The unbalanced version has a greater transmission length due to a larger potential copper cable (less resistive losses) and due to it being a matched impedance (75-Ohm). That is one of the keys of coax...if the cable is made well and has a 75-Ohm intrinsic impedance and the receiving device has a 75-Ohm input impedance, you can get VERY long transmission legths before either resistive losses or the errors in the actual impedance of the cable add up to no longer being true 75-Ohms. But consider that with say Belden 1694A cable (typical for HD-SDI type video signals) you have an 18awg center conductor that isn't going to attenuate the signal the way a 22awg cable would.
What AES/EBU or balanced cable brings is noise immunity. However, to get the maximum length out of it, it must be 110-Ohm cable which typically has extra thick insulation so it is harder to work with. A 4-cable snake of AES/EBU cable takes up as much room as an 8-cable of mere analog audio cable (diameter of the outer jacket).
While the DMA8 Plus does have presets that can be done via computer, very little need be done by the operator on the front panel other than choosing the source. The DMA8 Plus will let you see what decode it is doing (PCM, Dolby Digital, Dolby-E...etc).
Personally I too would like more accessability from the front panel too but I can also appreciate limiting that in some installations. Overall the DMA8 PLUS hit much closer to the mark than the original DMA8.
Steve
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 02-25-2007 03:30 PM
quote: Steve Guttag
Have no fear though...the "4xAES" input (25 pin DSub) is an AES/EBU balanced input so the DMA8 Plus can go both ways.
I'm not quite clear about this "4xAES" thing. is this 4x2 channels of PCM, for 8 channels in total, with just the first one of the four being used to carry multi-channel audio if it is in AC-3 or Dolby E format?
quote: Steve Guttag
Howevever if you dislike just the 4 input selection buttons you would have HATED the DMA8...only two buttons (film or digital) and you couldn't select which digital input from the front! They eventually did allow for pressing the digital button to cycle through the inputs though you had no idea of which input it was on or how it was being decoded since it had only two LEDs..."Film" and "Digital".
I've used an original DMA8 just once, but I didn't set it up, and I don't remember much about it.
quote: Steve Guttag
While the DMA8 Plus does have presets that can be done via computer, very little need be done by the operator on the front panel other than choosing the source. The DMA8 Plus will let you see what decode it is doing (PCM, Dolby Digital, Dolby-E...etc).
I like the LEDs which that you've got a valid clock on each of the inputs, whether it's active or not, and the ones that indicate PCM, AC-3, Dolby E etc.
Let's consider an example of something that I actually want to try: On my laptop I have a couple of Hi-Def video clips that I'd like to try on the system. The laptop can output digital video on DVI, and digital audio on an optical interface, both via non-standard miniature connectors. By means of passive adapters these can be converted to standard DVI-D and Toslink connectors, The DVI can be fed into the Christie interface unit (I cannot remember the name of it) and from there into the NEC NC800 projector. The audio can be taken by a standard Toslink cable into the Digital 4 input on the DMA8 Plus, and from there to the CP-65. Internally the audio is in MPEG AAC format, which is decoded within the laptop, and output as 2-cnannel PCM with pro-logic type surround encoding. Obviously I would need to press the 'Digital 4' button on the DMA8 Plus, but what about the format of the signals? Will the DMA8 auto detect that they are PCM, rather than Dolby Digital or Dolby E or AUX, whatever that is, or would I have to configure it via a PC? What about the fact that I want Pro-logic decoding on? A two-channel Dolby Digital stream on a DVD can be flagged that the Pro-logic decoder should be turned on, and most 'home cinema' type amps will respond to this, but can this be done with a PCM stream?
quote: Steve Guttag
Personally I too would like more accessability from the front panel too but I can also appreciate limiting that in some installations. Overall the DMA8 PLUS hit much closer to the mark than the original DMA8.
It would certainly be useful in a festival-type situation, where all sorts of odd things turn up at the last minute, often without warning, but I suppose real, physical switches would take up extra space, something that we're very short of in our rack.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 02-25-2007 03:44 PM
quote: Stephen Furley
I'm not quite clear about this "4xAES" thing. is this 4x2 channels of PCM, for 8 channels in total, with just the first one of the four being used to carry multi-channel audio if it is in AC-3 or Dolby E format?
Yes it handles 4 AES pairs for a total of 8-channels. However, only pair 1/2 can detect AC3 and Dolby-E signals. This is a bit annoying since most of the broadcast quality tapes use channels 3/4 for Dolby-E encoding as per Dolby recommended practice! Thus one may need an AES switcher or be willing to do manual patching.
As for your example...
9 times out of 10 you want to set the unit such that it will decode PCM audio (no Dolby encoding) with a pro-logic decode the same way an analog 2:4 decoder would work. Most 2-channel sources presume a much smaller audio field than is in the cinema (a video suite might have the speakers separated by only 6 or so feet)...when projected on a theatre sized screen, the 2-channel audio really has a noticable hole in the middle. Using the pro-logic decode will eliminate this an also play out of phase information in the surrounds....rarely is this interpreted badly though I have had some tapes that clearly they didn't pay attention to the phase on some elements!
Once the PCM mode is set to pro-logic, then the DMA8 Plus will do the rest for you. If it sees an AC3 encoded stream, it will play it back as it was encoded...likewise for Dolby-E.
On Dolby-E though, you can decide how it should decode and also set that up as a preset...normally you want the first group. This will have the 5.1 mix in a 5.1+2 configuration play.
For those occasions were one does have to do something other than the norm, then I don't think it is bad that one has to have a computer to make the changes since that person will likely understand they need to change it back.
If the facility really does need the flexibility then there are Ethernet and RS232 means to change the DMA8 Plus on the fly. As such, controller like AMX or Crestron can give a lot of user control. In a more simple form, you could use a product like Extron's CTL208CM to program up to 8 RS232 commands (16 if toggle mode is used) so the common changes are a mere pushbutton away.
Steve
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 03-01-2007 07:34 AM
Thanks for the reply Steve. There were some issues with the DMA8 Plus install on Monday, I don't know what they were, but when I went to a show last night I spoke to the projectionist and he said they have now been resolved.
The show I went to yesterday was on Beta SP, and there are still some problems with the Christie interface unit dor getting video into the digital system, again don't know the details, so that show was run on the video projector, not the new digital. The digital 'print' of 'Wizard of Oz' is due to arrive tomorrow morning, so Saturday's first digital screening should be going ahead. There was a possible lack of suitable projectionist problem, but that seems to have been resolved. I'm going to try to get to see that screening. At least we shouldn't have the sort of problems that caused the cancellation of last week's Saturday morning show, as I described in the 'You suck' thread.
It would be interesting to see how black and white looks on the digital system, but I don't think there's anything scheduled at the moment. I assume that the monochrome scenes in 'Oz' will be 'toned' in the digital version, as in the original.
Edit.
Oh dear,we're not having much luck with this. The projectionist problems have not been resolved after all, so I have beed asked to start the show, but will not interfere with the equipment in any other way. The trained projectionist will make up the show tomorrow, and I will have a quick run-through tomorrow evening, between shows. I will be running the rest of the shows that day, on 35mm.
If by any chance there is anybody living near Croydon who comes to see the show, come and say hello. It's on Saturday 3rd March in the David lean Cinema at the Croydon Clocktower. web page It says 'Digitally restored print', but it will be projected digitally. I'm sure the Duty Manager would let any Film-Tech people come up to the box to have a look at the equipment. I've taken some pictures, but I haven't processed the film yet.
[ 03-01-2007, 12:25 PM: Message edited by: Stephen Furley ]
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