[Help] Help regarding identifying Up-mix/Down-mix if the original is present

[GjRedo]

Hello folks! 1st time posting & English isn't my native language. So please excuse any mistake.

Suppose there is a 2.0 & a 5.1 track present in a BD. The 5.1 is actually the Upmix of the 2.0 track. The BD publisher didn't specify the upmix. Now even if you downmix the 5.1 upmix using eac3to, it's identical to the original 2.0 track. Since it's identical how do you determine that the 5.1 is actually the Upmix not 2.0 is actually the downmix?

Is there anything unique in Pure 5.1, that by examining the upmixed 5.1 one, you can tell that's it's upmix? Or there are other factor? or There is nothing to do except guess?

[CSchmidlapp]

The big identifier for me is the Center channel, does the Dialogue bleed into the Left & Right Channels. A proper multichannel mix will be discreet, so no sign of it in other channels.
There are obviously exceptions to this rule, but it's a good starting point.

[GjRedo]

The big identifier for me is the Center channel, does the Dialogue bleed into the Left & Right Channels. A proper multichannel mix will be discreet, so no sign of it in other channels.

Are you saying in a proper mutlichannel mix (genreally) Dialouge/Music etc are separted by Channels & don't mix into each other? Can you explain this a bit more? 

I am new in these so not really familiar with audio terms.

[Turisu]

If the 5.1 has split surrounds then the identical 2.0 is a downmix. Dolby 4-track Stereo only allowed for a single mono surround channel which would have to be duplicated if upmixing for 5.1.

[GjRedo]

If the 5.1 has split surrounds then the identical 2.0 is a downmix. Dolby 4-track Stereo only allowed for a single mono surround channel which would have to be duplicated if upmixing for 5.1.

1. By Split Surrounds do you mean LS & RS channel will be kinda different? 

2. If Upmixed from a Stereo/Stereo Surround track the LS & RS channel in 5.1 will be same/indetical?

[CSchmidlapp]

The big identifier for me is the Center channel, does the Dialogue bleed into the Left & Right Channels. A proper multichannel mix will be discreet, so no sign of it in other channels.

Are you saying in a proper mutlichannel mix (genreally) Dialouge/Music etc are separted by Channels & don't mix into each other? Can you explain this a bit more? 

I am new in these so not really familiar with audio terms.

Yes.
Although Music and Effects audio will normally be mixed in 5.1 and be apparent in the Center as well, it really depends on the mix.
But generally the dialogue will just come through on the Centre (unless it pans ect as part of the mix)

It's worth looking through the Technical Discussions on this thread
https://fanrestore.com/forum-19.html
It's full off amazing information.

[zoidberg]

A true multi-channel mix will have a dedicated LFE channel. This information is not included in a 2.0 downmix, only the bass from the main channels