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Author Topic: Surround Output from CP750 using analog?
Mark Vernon
Film Handler

Posts: 2
From: Ulverstone Tasmania Australia
Registered: Jan 2014


 - posted 01-16-2014 05:58 PM      Profile for Mark Vernon   Author's Homepage   Email Mark Vernon   Send New Private Message       Edit/Delete Post 
Hi Guys
I am hoping someone can offer some advice. We are producing some work for a local cinema and are looking to actually do a sound mixing session in the cinema itself. Our editing system is a blackmagic decklink Extreme 3D, and there Cinema Processor is a Dolby CP750. What is need to know, first is it possible, and secondly how, for us to be able to plug into their processor and be able to have it process in surround so we can get an accurate mix so once we have the DCP and playing through there server we are getting the same (or very close) to what we heard in the mixing session. Processor info and connections can be found here

http://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/cp750_specifications.pdf

Our blackmagic connections can be found here (Page 7)
http://www.blackmagicdesign.com/media/1034544/decklinkconnectionsapril2011.pdf

Any help or suggestions appreciated.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12205
From: Annapolis, MD
Registered: Dec 1999


 - posted 01-16-2014 07:37 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
For DCPs...one normally does NOT decode. It is expected to be in discrete channel form as you intend for it to be heard.

It IS possible to have the CP750 take a 2-channel source and perform a "Pro-Logic" decode (via either the dedicated control program...look under the "inputs" tab) or via a serial/Ethernet command one can have it switch to something like Pro Logic II.

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Marcel Birgelen
Film God

Posts: 2610
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012


 - posted 01-17-2014 01:45 AM      Profile for Marcel Birgelen   Email Marcel Birgelen   Send New Private Message       Edit/Delete Post 
It doesn't look like this "DeckLink HD Extreme 3D+" card offers more than just two discrete audio output channels, either via AES/EBU or Analog.

If you want to have discrete access to all 8 channels on the CP750, you can either use Digital 1 (4x AES/EBU, most probably already occupied) or the multi-channel analog input.

If you're stuck with two discrete channels, you could indeed try something like Dolby ProLogic II, if your mixing system actually supports encoding to that format in real time.

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Carsten Kurz
Film God

Posts: 3774
From: Cologne, NRW, Germany
Registered: Aug 2009


 - posted 01-17-2014 05:00 AM      Profile for Carsten Kurz   Email Carsten Kurz   Send New Private Message       Edit/Delete Post 
Your best option is to to use the Decklink HDMI output for 8ch LPCM audio output. There are cheap converters available to transform this to discrete analog 5.1 audio which can be fed to the CP750 analog multichannel input. Find out wether they have a 5.1 or 7.1 audio installation.

Maybe you can find out the exact equipment list for this screen - projector, server/IMB type. There is a chance they might use a Doremi ShowVault/IMB combo - then you could feed HDMI video and 8ch LPCM audio directly to the projector, and it goes to the CP750 via AES from there. That would be the best solution, and it would interfere the least with their cinema operations.

Another option would be to use BMDs SDI->AES multichannel digital audio converter 'Mini Converter SDI to Audio'.

Would probably again depend on the projector/server in use there, wether you connect video through HD-SDI or HDMI.

These solutions vary a bit on the amount of interference with the existing equipment, e.g. how many cables need to be unplugged from the existing installation, how long you will need to be there, how competent local staff is to reestablish cinema operations when you're done.

- Carsten

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Mark Vernon
Film Handler

Posts: 2
From: Ulverstone Tasmania Australia
Registered: Jan 2014


 - posted 01-17-2014 06:29 AM      Profile for Mark Vernon   Author's Homepage   Email Mark Vernon   Send New Private Message       Edit/Delete Post 
Thanks for all the advice guys. This area is getting a little over my head, but trying to keep up! I think a HDMI > 25 Pin Analogue converter would be the go. I can't seem to find a one though, any links?

I did ask if we could run through the HDMI inputs on the projector, but apparently there projectors do not feed audio to the processors, the audio is feed from the server direct to the processor. The blackmagic SDI>AES would would work ok but would blow the budget when I don't know if I'll ever use it again. We use audition for the surround mix, so can't encode the signal... were working in discreet channels. Would there be any way to plug into the server rather than direct to the processor? I am not familiar with them so not sure if that is at all possible?

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Marcel Birgelen
Film God

Posts: 2610
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012


 - posted 01-17-2014 08:00 AM      Profile for Marcel Birgelen   Email Marcel Birgelen   Send New Private Message       Edit/Delete Post 
I don't think there will be any easy way to hookup an alternative sound source to the server. Some more recent installs have an additional card (a so called IMB) in the projector, that allows access to "alternative content" via e.g. HDMI. In that case, the audio is being fed from this IMB card to the audio processor and not directly from the server.

If the HDMI-out of the Decklink actually supports 6/8 channel LPCM, you could indeed convert those to 6 or 8 analog channels using something like this, just like Carsten already mentioned.

Maybe, another alternative is to install an additional sound card into the PC that's doing the mixing, you might even opt for an "USB sound card".

Then you need to feed those analog channels into the CP750, using the correct pin-out. If the venue doesn't have something compatible lying around (to hook up a DVD or Blu-Ray player for example), you could try to make your own cable, which is probably much cheaper and easier than trying to order something that fits. Something that needs to be considered is that, as far as I know, the CP750 has balanced analog inputs, whereas your analog outputs will most likely be unbalanced.

Obviously, you're stuck with the probably somewhat limited quality of the DA converters of either the HDMI converter or sound card if you go this route, but it would probably be the cheapest route to multi-channel discrete audio at an acceptable quality level.

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Steve Moore
Expert Film Handler

Posts: 198
From: Leeds, West Yorks, UK
Registered: Apr 2008


 - posted 01-17-2014 11:49 AM      Profile for Steve Moore   Email Steve Moore   Send New Private Message       Edit/Delete Post 
I have run this soundcard into the multi-in on a CP750 before. It has 6 analogue outputs, so I made a 1/4" jack to 25way D plug lead connecting to the correct pins will give you 6 channels of discreet outputs from your computer (5.1)

http://www.soundonsound.com/sos/may08/articles/fasttrackultra.htm.

That card is just over £100 here in UK. Would cost about £10 to make a custom lead.
You would have to mix in your software, then bounce down to 6 separate wav files and then use something to encode those to DCP

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