Film-Tech Forum ARCHIVE: Audio Description channel question

This is topic Audio Description channel question in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Matthew Philp (Member # 7132) on 06-17-2013, 10:02 AM:

Hello All,

We are currently showing the feature "Summer in February", and last night a customer requested to use the audio description facility (which the film data says it supports) only to find there was no audio described track coming through the headphones. Ive investigated this morning to find that the AD track is actually coming out of BSR (which in this auditorium is not actually connected to an amp as it is an 5.1 auditorium) Ive spoken to Arts Alliance who supplied the drive, and they insist that their AD is coming out on channel "7 or 8" and that it must be our equipment that is at fault. Ive never had another problem with any other feature, and tested it again this morning with Fast 6 which works just as it should.

Firstly, just to put my mind at rest, what is the channel number for BSR? and is there anything i can do short term for this feature should I get another patron asking for AD?

Thanks

Matthew

Posted by Jim Cassedy (Member # 4115) on 06-17-2013, 01:19 PM:

According to a DCP inter-op chart I have (which may or may not be the latest version)

>Hearing impaired audio should be on Channel 7
>Visually impaired (descriptive audio track) should be Channel 8.

However, a disclaimer on the chart says:
"Interop DCP does not have a standardized way of sending multichannel packages.
The attached document describes the most common way of transporting multi-channel audio"

If you have access to the Dolby Extranet website, they have downloadable 5.1 & 7.1 channel
ID DCP's which contain valid Hearing & Visually impaired tracks
- - or you might possibly already have these loaded on your server.

Posted by Harold Hallikainen (Member # 5405) on 06-17-2013, 02:22 PM:

I agree.http://isdcf.com/papers/ISDCF-Doc4-Interop-audio-channel-recommendations.pdf says VI-N should be on track 8 of Interop DCPs, which USUALLY puts it on AES/EBU channel 8.

Harold

Posted by Carsten Kurz (Member # 5396) on 06-17-2013, 04:03 PM:

Matthew - which server and audio processor are you using? Some servers and processors have channel mapping capabilities, so you can route an audio descriptive track from any DCP channel to the right HI/VI channels on your processor.

Some projectionists also have patchbays or breakout-boards which will allow them to change the channel routing between server and processor in hardware.

- Carsten

Posted by Dave Macaulay (Member # 813) on 06-18-2013, 10:56 AM:

If you connect a server's 16 channel digital audio output directly to a digital input cinema processor (ie CP750), the processor only has 8 digital input channels (4x AES/EBU stereo digital signal) and expects the BSL and BSR channels to be on channels 7 and 8 (AES/EBU #4). However, the channel assignemnts were developed before 7.1 was dreamed up, and DCP soundtracks have HI and DV audio on channels 7 and 8.
(technically SMPTE DCPs have flexible channel assignment but most DCPs are still Interop, and as far as I know no SMPTE DCP has dared to differ from the Interop layout)
To actually get 7.1 sound you have to swap the digital channels somehow, and present soundtrack channels 11 and 12 to processor inputs 7 and 8. Doremi servers, and maybe others, have a built-in channel swapping capability to accomplish this.
Presumably you have not done that if you get the DV audio on your BSR channel.
If you by some odd chance have a 16 channel (8x AES/EBU) digital input on your processor (as on the CP850 for example) then there's some configuration issue overlooked.
Odyssey makes cards that do the channel correction for 7.1 and include a HI/DV digital output, you would need an extra D/A converter (also available from Odyssey if you don't want to find something else that works) to get a usable analog signal for your headphone system.

Posted by Matthew Philp (Member # 7132) on 06-18-2013, 12:10 PM:

Thanks all,

Im using Doremi 2k4 servers to Dolby CP750's and in this screen a CM8 Crossover/Monitor unit.

What strikes me odd about this, is this is the first feature we have had this problem with, so I think our channel mapping is correct. All of our other features play the AD channel as they should.

when i'm next back on site, i'm going to try to test it in one of our 7.1 screens to see if that makes any difference, and just to eliminate any problem that may be specific to that auditorium.

Matthew

Posted by Carsten Kurz (Member # 5396) on 06-18-2013, 04:43 PM:

Maybe the DCP is just bad. May happen. The Doremi has a simple channel mapping option to correct it.

- Carsten