Strange and confusing channel mapping for 7.1 audio.

[dcpforever]

According to the PDF with the audio standards for DCP RDD52 (Bv2.1), 7.1 audio carries the Lrs and Rrs tracks on channels 11-12. However, in DoM, these channels do not appear in the audio map panel, but rather others (DBP and DBS). Where are the Lrs and Rrs channels?

Are they perhaps the channels marked as BsL and BsR? These are channels 9-11 and should be empty, correct?

Can anyone help me?

[carl]

BsL and BsR are the "extra" 7.1 surrounds, yes. Channels 9 and 10 are hidden in the DCP-o-matic interface as they are not used for anything, so it may look in the matrix like the BsL and BsR are shifted over two places... but they map to 11 and 12 in the DCP.

[dcpforever]

Okay, but that confuses the user. First, they are not named Lrs and Rrs, which are the correct names (or so I believe). Please, what do BsL and BsR mean, so that I can understand why they are equivalent...
And secondly, shouldn't the channels be numbered so that it's easy to see that 9 and 10 are not present, making the mapping less confusing?

In short, something more user-friendly
Thank you.

[carl]

BsL/BsR is "back surround left" and "back surround right". It's what Dolby calls them, at least. It's true that SMPTE seems to mostly use Lrs/Rrs. I'll think about how to clarify this (maybe a tooltip would help).

I'm not convinced that numbering the channels would make things any less confusing. Then I'd have some numbers, which don't mean anything unless you've memorised the DCP channel mappings, and two mapping boxes for 9/10 that the UI would somehow have to tell you not to use. Surely what I care about here is knowing which channel is which?

[dcpforever]

Well, if the channels are named using their correct nomenclature, according to SMPTE, there would be less confusion.
And yes, I think the numbering helps. For me, as a non-English speaker, it is easier to memorise a number (which is the same in most languages) and, furthermore, in the SMPTE document (D-Cinema Packaging_SMPTE DCP Bv2. 1_rdd52-2020.pdf), the 16 channels are numbered, with 11 being Lrs and 12 being Rrs (page 16).
Why reinvent the wheel?

[dcpforever]

Before I started generating the DCP, with the issue of channel mapping confusion, I asked Gemini to clarify things a bit for me. And I told him I was going to ask in the forum.
Now he has given me this answer, which I found amusing :
My advice for your forum post:
Remind them that, even though it may be obvious to them that ‘no one uses’ certain channels, DCP-o-Matic is a technical tool. Technical tools should not assume what the user uses; they should be a faithful reflection of standards (like the PDF you have) or, at least, document their deviations.