DTS-HD 6.1 channel layout

[BartasBoy]

Hello everyone,

I'm creating a DCP from a ripped bluray .mkv, but I cannot figure out how to map the audio channels - the source is a DTS-HD in 6.1 format, which I'm trying to map to "classic" SMPTE cinema 5.1 / 7.1 (therefore either leave out the Cb channel altogether or put it in both BsL / BsR), however I'm unable to find the channel layout for this particular format

The default 5.1 channel mapping matrix in DCP-o-matic after opening the .mkv looks like this ...



... however when I play the DCP in our cinema, I can hear that something is definitely wrong with the surround speakers (like the sound is not always where I think it should be), but I'm unable to tell exactly just by listening.

What is the channel order in DTS-HD 6.1 ? Is there a way to find out ? The only thing that I tried is analyze the .mkv file with MediaInfo, which gave this result:



I'm almost sure that the layout showed in the table is not true, since that would mean the front speakers would be messed up too, which is almost definitely not the case (i think I would be abe to tell).

Does anyone have any experience with this ? Any help would be most appreciated.

[Carsten]

Wow, that C/L/R/Ls/Rs/LFE/Cb channel sequence from MediaInfo looks weird, but, if it is right, your channel map in DCP-o-matic should probably look like this:

Bildschirmfoto 2019-11-24 um 22.44.03.png

You need a 7.1 setup to play a 6.1 mix properly, with the Cb channel mapped to both BsL and BsR, thus creating a mono back surround.

In order to activate the BsL and BsR channels in the matrix, you have to select a 7.1/12ch layout under DCP->Audio.

As there are still very many 5.1 screens, the proper way to do this would be to create a 5.1 OV (Ls, Rs and Cb mapped to Ls/Rs), and create a 7.1 CPL as a VF to this. The 6.1->5.1 mapping for the OV should probably look like this:

Bildschirmfoto 2019-11-24 um 23.01.41.png

I reduced the level of the surround channels by -6dB to avoid clipping, because two channels are mixed into one.This is a safety measure and may actually not be necessary, as typically, surround signals are not going full scale. You may try leaving them at full level and check with the audio level graph wether clipping occurs. There will also be hints given if this occurs.

In general, it is not easy to verify a channel mapping by listening to a sound track. However, typical 5.1/6.1 and 7.1 mixes can be identified by their typical patterns when you open them in an audio editor. Audacity, with the FFMPEG plugin enabled, can usually open typical video/audio interleaved media types and display a track overview. With some experience, you can pinpoint the channel sequence graphically. It is impossible to identify L vs. R or Ls vs. Rs. visually, but in general, Left comes first, and, again, with some experience, the proper L/R order can be identified by listening to a stereo pair through headphones.

This is a typical timeline view of a 5.1 mix with a standard DCI channel layout. Easy to spot the stereo grouped L/R (1&2) and Ls/Rs (5&6) pairs, as well as the mono center (3) and LFE (4) channel.

Bildschirmfoto 2019-11-24 um 22.55.18.png

- Carsten

[Carsten]

This is a 7.1/12ch layout:

Bildschirmfoto 2019-11-24 um 23.22.43.png

Very often, you can tell the BsL/BsR from the Lss/Rss pair by their lower level and distribution.

[Carsten]

I noticed I do have a DTS 6.1 ES disc here. MediaInfo reports a similar channel order as your's - but when I look at the file in audacity, it looks like a standard L/R/C/LFE/Ls/Rs/Cb pattern. I don't think that Audacity changes the channel order. DCP-o-matic recognizes 7 channels, and the channel order after DCP creation is the same as the one shown in Audacity, so no codec/file specific channel reordering.

If you want to be sure, open the audio part of your source in an audio editor.

- Carsten

Bildschirmfoto 2019-11-25 um 14.41.02.png

[BartasBoy]

Thank you very much for a really exhaustive reply, I will try the ffmpeg plugin for Audacity once I have the chance.

Also I will try to make a 7.1 DCP and listen if there's any change in the audio perception, maybe it's all just a feeling I have (about the messed up surround sound I mean).

However I still get the feeling that the Cb channel is not the last one in the order, since that would mean it would just be missing in the 5.1 layout, therefore not that big of a deal I would think, I will have to make some "test" clips ...

Thanks again for your help !

[Carsten]

I think the best is to judge from the visual representation in Audacity, and for L/R and Ls/Rs, assume Left first.

- Carsten