Understanding dolby atmos (true hd) with ac3 core

[CapricornX10X]

Hi everyone,
I have to understand something,
I have a movie whose audio format is AC3 core + TRUE HD + ATMOS
Peak speed: 7050kbps (core 640kbps)
Sample Rate: 48Khz Channels: 7.1

For example, when I play the movie through POWERDVD 22 in an iso (full bluray) or mt2s file, the audio selection shows me only one choice of dolby true-hd 7.1.

Alternatively when I convert the same file to an mkv file and I also play it through powerdvd 22, I suddenly see that I have 2 audio choices:
1.dolby true-hd 7.1
2.dolby ac3 5.1

Can anyone explain to me what's going on here?

When I convert to an mkv file do I lose some audio quality that I choose dolby true hd 7.1, because ac3 core is not in the same audio?

[tebasuna51]

For compatibility with old players a track TrueHD in BD (see BD specs) movies must have interleaved another track AC3 in the m2ts container (THD+AC3).
A updated player can play the best of both and only show the THD.

The mkv container can't have both tracks interleaved but can be separated tracks, and offer the two choices. The quality is the same.

EDIT: please read the forum rules, duplicated posts aren't allowed.

[CapricornX10X]

Okay, so if I understand correctly.
There is no quality damage once ac3 core will be separate from true-hd?

if i play true-hd...

[nevcairiel]

No, the AC3 part is not used at all when you decode the TrueHD part.