Yes, it's a digital file flag just like 4:3 vs 16:9 (as in if it's incorrectly flagged, a 16:9 video will play back squished or a 4:3 stretched). Whether it sounds natural is not really relevant (I mean in the technical sense of whether the file is flagged or not, rather than what the original mix was or if it was perhaps a mono track remixed to stereo or stereo surround). It's a 2.0 surround track if the flag is there. It could be a 2-channel source with the surround flag activated or it could be the pre-matrixed Dolby Stereo stems mixed down to 2.0 and flagged, or a 5.1 mix folded down to 2.0 with surround activated (there are just as many DVDs where the 2.0 downmix of the 5.1 is not flagged). It could be the matrixed 2.0 channel source run through a Dolby Stereo decoder with the results recorded and then folded down back to 2.0. It could be a dual mono or stereo mix with the flag activated during the encoding.Jari_Kovalainen wrote:2.0 stereo vs surround can be a bit tricky since, like I said, I believe all stereo tracks add some surround activity with Pro Logic. But are they technically really 100% 2.0 surround? Is there a surround "flag" or something? And is this stereo vs 2.0 surround even that important issue?
I guess people should test the disc and watch&listen. If the dialogue is coming nicely (and sounds natural) from the front center and there's some nice (and natural) surround activity, I would say that 2.0 surround works. Then again if you're a purist and stick to the stereo option, that's probably alright too (audio wise).
Whether it was a surround mix originally or not, if it's flagged and your receiver is set to automatic then prologic will be engaged when the 2.0 source is flagged. If it was a folded down 5.1 mix or a Dolby Stereo mix, the surround content is there whether it's flagged or not (in which case you'd have to just turn on pro-logic yourself). If it was a surround mix or left-right stereo mix, Pro-logic to synthesize a mix (Pro Logic I with dual mono or stereo to four channels, or Pro Logic II with one channel up to 5.1) using its own algorithms and what it recognizes from the two channel mix as being mixed like Dolby Stereo (the sound meant for the surround channels would have had its phase shifted and mixed at 3db lower than the left and right channels while the centered dialogue would have also been set at -3db).
VLC (with Dolby Surround set to "Auto" in preferences) with a DVD featuring a surround-flagged track;