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ISDCF Forum • View topic - naming convention - 20-LtRt audio type
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naming convention - 20-LtRt audio type

PostPosted: Thu Jan 22, 2015 6:53 am
by Carsten
Hi all,

the Digital Cinema Naming Convention still depicts Audio type '20= LtRt Stereo'. However, 'LtRt' is common technical term for matrix encoded audio. Now we have seen a few classic titles using matrix encoded audio in DCPs. While some few cinema audio processors offer the ability to apply matrix decoding to incoming AES audio, there have been earlier discussions on the ISDCF mailing list with the outcome that matrix encoded audio should not be used in DCPs.

Even those cinema processors with support for matrix decoding need special setup or wiring to do it - which usually is beyond staff scope in daily operations, even for those cinemas dedicated to 'classic titles'. And even those cinemas with capable processors may not have the necessary means to switch between 5.1/7.1 to matrix decoding automatically within playlists.

At the same time, those titles using matrix encoded audio so far did not use any special marking to indicate this. Or they were simply assuming the DCN to be formally correct with the 20=LtRt audio type.
Sometimes it looks as if the distributor didn't even know about this aspect of the DCP: 'It's an old movie - it's plain stereo!'.

So, the question is: Should the DCN exclude LtRt explicitly, or should a special audio designator be introduced, separating 20-Stereo from 20-LtRt? I think excluding LtRt from the DCN won't stop studios issuing such DCPs.

While we probably all agree that stereo mixes are not suitable for cinema presentation, they do exist and will exist in the future, and there may well be suitable situations to use them - e.g. music only audiotracks. Most surround soundtracks will contain stereo-only passages to a certain extent anyway ;-)

What do you think? I contacted Jerry about a year ago already, and he said he would correct the issue for the next DCN version review. Unfortunately, the version number didn't change since then ;-)

Jerry, is this still on your To-Do for 9.x?

Regards - Carsten

Re: naming convention - 20-LtRt audio type

PostPosted: Fri Feb 06, 2015 4:56 pm
by jhurst
It is understood that there are stereo programs (and let's not forget mono). The correct way to package these materials is as 5.1 tracks (properly labeled, of course) with silence in the unused channels. While this may require some mental energy on the part of the mastering house, it will play correctly in every theater. One may consider including projection notes such as "Tracks C, LS, RS and LFE are silent".

LtRt programs are another topic altogether. The correct way to package these materials is to first decode to discrete LCRS and then wrap as 5.1 tracks. A well-trained mastering engineer should also be able to "bass manage" the resulting tracks to create an LFE channel.

Re: naming convention - 20-LtRt audio type

PostPosted: Tue Feb 17, 2015 4:03 pm
by jamiegau
John, I agree and recommend that 20/stereo is placed in a 5.1 with silent channels for those unused (mainly use to historical bugs in some SMS's when switching between ads 20->51->20 had caused issues) Its a good idea to standardise on 51, however, I find this is confusing in relation to digitalcinemanamingconvention and channels as reported in the SMS. if the naming convention specifies 20, but the DCP has 6ch, this could be considered confusing.

What I am getting to, if this is a recommended practice, shouldn't the digitalcinemanamingconvention website state this use model and that even tho a DCP may be marked as _20_, it still may have 5.1 channels of audio and that the extra ones are silent..

Re: naming convention - 20-LtRt audio type

PostPosted: Fri Feb 20, 2015 5:03 am
by Carsten
Could someone with access to the SMPTE/DCP documents comment on the allowed format/channel numbers for SMPTE DCPs?

While 5.1 is probably the 'best' pragmatic choice even for stereo programs, I guess all even number channel assignments up to 16 are allowed per spec? Any known issues with specific servers with 2 or 4 channel DCPs?

- Carsten