Film-Tech Forum ARCHIVE: Multiple digital audio inputs with CP650

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Posted by James Skinner (Member # 7385) on 01-21-2013, 06:25 PM:

We have a small rural community operated cinema that has recently updated to digital. We have had a Christie CP200-M Digital Cinema Projector for a few years for alternative content but recently added a Doremi DCP-2K4 Digital Cinema Server for movies.

We have been using a Dolby CP650 for audio but are running into some limitations. Essentially we are having a problem due to the lack of extra digital inputs into the CP650. Currently we have the DCP-2K4 connected to the CP650 via an Odyssy 650-OPTIO-ASE Option I/O Board. This uses up the CP650's only digital audio input. The only other audio input are the 6 analog inputs which we currently connect to a PC for preshow, Blu-ray, and other content.

We would like to be able to easily connect other equipment into the system such as stand alone blu-ray palyer, satillite receiver, etc via standard consumer interfaces such as HDMI, RCA S/PDIF, and Tosklink. We are struggling with the best way to do this given the limited budget that a community theatre has.

Some options we have come up with are as follows:

1) The most ideal option might be to replace the CP650 with a CP750 or CP850. This would also upgrade us from 5.1 surround to the more current 7.1 surround. This is cost prohibitive however.

2) A possible 'hack' solution would be to connect a consumer A/V receiver with preamp outputs to the analog CP650 inputs. This would provide multiple input types and allow easy switching. This is probably the cheapest option but I worry about its reliability.

3) If we just wanted to connect a satillite receiver (our current motivation) we could use something like the Doremi StreamIt box. This however doesn't provide much flexibility with regard to connecting multiple devices.

4) Another option is to use a Gefen Pro 2 as a switcher. This seems like the best compromise but is still a bit pricey. Also it means that we still have only 5.1 and I wonder about spending the money on this when moving to 7.1 would be desirable as well.

Does anyone have any other suggestions for possible solutions? What are other theatres doing that are in this situation?

Posted by Carsten Kurz (Member # 5396) on 01-21-2013, 06:59 PM:

Depends on wether you need automatiom features. There are cheap S/P-DIF or TOSLINK Switchers, so you can just put a switch in front of the CP650 digital input.

You could as well use an HDMI->multichannel analog audio converter with HDMI passthrough. Sort of like a stripped down AV receiver. I recently saw HDMI->Toslink converters as well. Although you never know without testing which combinations of input signals and conversions they actually support. Too many option in HDMI audio.

A Datasat AP20 would solve any of these issues much better than any Dolby processor, but it will cost you something like 5000-6000US$.

A home AV receiver is not a bad choice, but you need one with discrete analog preamp outs. These are usually the more expensive ones.

S/P-DIF or TOSLINK is limited to the lossy breed of BluRay codecs, AC-3 and DTS, it doesn't support the higher quality DTS Master audio or Dolby TrueHD lossless codecs (only through AC-3/DTS fallbacks/downconversion). Wether that is a real issue - I doubt it. Most people will not notice the difference. AC-3 and DTS on BluRay is much better than DolbyDigital on film (higher bitrate) anyway.

On satellite broadcasts, only AC-3 is used.

- Carsten

Posted by Bajsic Bojan (Member # 4928) on 01-24-2013, 12:09 PM:

There are some Dolby DMA8plus around the marketplace for 800$ or so. They give you 8ch AES, 2x Aes 3 (can be spdif) and 1 toslink. Can go to the Analog input on the CP650.

Christie has a scaler/audio processor with the new SKA3D, its worth a look at a couple k$.

Using 'home' receivers, people seem to have decent results with some top of the line Yamaha products like Aventage series, but might be more comfortable with just buying an AP20 for the same price.