AC3 myth...? Well at least for me...

[DaMan]

I've heard of Dolby Surround 5.1, 6.1, 7.1 etc...imbedded within VOB streams. My question is,
when you extract via DVD2AVI as a .wav file, does it still retains 5.1, 6.1 or 7.1 channels information?
Also, when making attempts to reencode it to AC3 prior to mux with .m2v, the default option in BeSweet
to encode to AC3 is only 2 channels, CBR; so what happens to the resulting mpeg2 file, does it retain the integrity
of Dolby Surround of 5.1 or 6.1 or 7.1? Does 5.1/6.1/7.1 designate channels?

Mystified...Sorry I am a newbie

[hakko504]

If you extract to WAV in DVD2AVI it will only be a 2 channel WAV. If you want to keep the integrity of 5.1 you need to use besweet for the whole conversion, and use demux rather than decode in DVD2AVI. If you check the besweet gui you will find options for both azid and ac3 encoding that will let you do most anything with the AC3 file, downmix, lower bitrate, etc. Oh, and as far as I can tell, 6.1/7.1 is encoded as differences, much like Dolby surround can be encoded in 2 channel stereo, which means that you might run into trouble keeping those extra channels if you lower the bitrate.

[DaMan]

Thanks hakko504 for the info. but 2 questions...You said
"...If you want to keep the integrity of 5.1 you need to use besweet for the whole conversion, and use demux rather than decode in DVD2AVI..."

If I want to use BeSweet for the whole conversion (VOBs to AC3?) why would I demux in DVD2AVI? And if
I use BeSweet for the whole conversion to retain 5.1 authenticity, how many files do I end up with, an AC3 file for @ channels?

Please excuse my ignorance on this matter...I am learning.

TIA...

[DJ Bobo]

you don't need besweet at all if you want to keep the original ac3, just load the VOB files in DVD2AVI, check you have dolby digital -> demux (or demux all tracks if you want all of them) and save the project

[hakko504]

Sorry, I wasn't clear. I meant that if you wanted to lower bitrate by reencoding to AC3 you would need besweet. If you don't want to lower bitrate the is of course no need to use besweet at all.

[rmatei]

There's no such thing as a 7.1 soundtrack. However, more and more DVDs (LOTR EE, Gladiator, SW I&II, Fight Club) have 6.1 sountracks, which add a center rear channel to regular 5.1. 7.1 is just a way of playing back 6.1 soundtracks, with 2 center rear channels playing back the same thing. This avoids the effect of sometimes hearing something from straight behing as coming from straight in front.

Both DTS and DD have 6.1 formats (DTS ES and DD EX). There are two ways to add a center right channel: matrixed and discrete. Matrixed, what hakko's talking about, is the most common; it mixes the info into the rear left and rear right channels. Discrete actually has a separate center rear track.

But anyway, this shouldn't matter here, as only high-end receivers can decode 6.1.

[DJ Bobo]

If you ask me, all those super-high-number-of-channels tracks are a waste of bitrate and make our living rooms only smaller if you understand what I mean ;)

IMHO 4.0 is completely sufficient: 2 front + 2 rear. You can matrix whatever you want in a 4.0 track, up to 8.1:
the LFE channel is matrixed in FR & FL
the center channel is matrixed between FR & FL
the rear center channel is matrixed between SR & SL
the left center channel between FL & SL
the right center channel between FR & SR

Too bad that there is too much audio freaks out there :D