6 channels vs. 2 channels: Best results?

[sandchar99]

I've always used the 6 channel AC3 audiotrack and it is the default when the IFO is selected. But recently I'm beginning to question that when there are two identical soudtracks, 6 channel and 2 channel.

I backed-up a concert DVD with both tracks being muxed with with the video. Settings: 224 bitrate, no downsampling, stereo mode. The resulting MP2 files are identical size (same length and bitrate).

But...the 2 channel sounds noticeably fuller, more robust.

So, I searched the Audio Forum FAQ, question number 3 (DSPGuru)
3) AC3->MP3. which AC3 stream should i decode ? 5.1 or 2.0 ?
the 2.0 stream has a better mix for 2 channels (stereo), than the 5.1 to 2.0 downmix features offered by AC3 decoding tools. therefore, it should be the best to work with the 2.0 stream.
there is only one case when transcoding the 5.1 stream is better :
if your computer has connection to a dolby pro-logic decoder, you could use a surround downmix, and then your dolby pro-logic decoder would reconstruct the multichannel audio.

Anyone else with this result?

If others are getting this result and since we are ending up with two channels anyway, maybe this point could be incorporated into the FAQ or Doom9 guides.

[markrb]

I asked this very question a few months back and I got two standard responses. Here they are.

1. Try it yourself and see what you think.
2. Since the two channel is normally an alternate track (language, commentary etc..) most times it doesn't matter.

I tended to find that #2 was usually right and thus it wasn't worth my time to do #1.

I will look into this further now that someone else has actually done a test. It seems to me the fewer changes to the files we make the better it should be. However my logic doesn't always hold up over time.

As for putting in the FAQ #2 is very often the case. So even though it might be better it could end up causing more problems then it's worth. Let's just let the people that are smart enough to actually read the forum a bit find this nugget for now. :devil:

Mark

[DDogg]

There has always been a feeling that the 2 channel track available sometimes on a dvd might be better due to the fact that pros mixed it on very expensive equipment and may have in fact tweaked & sweetened it slightly.

[DSPguru]

if your computer has connection to a dolby pro-logic decoder, you could use a surround downmix, and then your dolby pro-logic decoder would reconstruct the multichannel audio. don't you think it's a good reason to stick with 5.1 ?

downmix of 5.1 into MP3 isn't a good idea, but putting a dolby surround track on svcd should be better than a simple stereo. (imho).

[DDogg]

DspGuru:

Aren't we talking about a DD 2/0 and a DD 3/2? Isn't the DD 2/0 a professional Dolby surround downmix of the DD 3/2(5.1)?

I always assumed azid was doing the same thing as the studios did when they supplied a DD 2/0

[DSPguru]

@DDogg
i won't count on it. if the 2.0 track is DD track, it's surely better than 5.1 downmix. but it could be plain stereo. couldn't it ?

[markrb]

Actually it should be Dobly Stereo Digital 2/0 (3/1) or (3/2 with DP2) and I would think that converting from Dolby Stereo Digital to Dolby Stereo would be a simpler change over since all the channel information is already encoded into two channel. I am not completely sure, but it sounds good.

I don't think it is plain stereo. I think it is the same track they put on the Video Tape. Why create a new track when you could simply re-use the already created track and it is Dolby Stereo multichannel?

Mark

[DDogg]

i won't count on it. if the 2.0 track is DD track, it's surely better than 5.1 downmix. but it could be plain stereo. couldn't it ?

Well I am speaking specifically of a DD surround downmix that is available on many Hollywood release type DVDs. I am looking at the DVD "What Dreams may come" at the moment with DVD2AVI.

Track 1 is Dolby surround (D2A shows as DD 2/0 192)
Track 2 is Dolby 5.1 (D2A shows as 3/2 384)

So your comment above, "if the 2.0 track is DD track, it's surely better than 5.1 downmix." sounds like you feel pretty clear on this, but I remember endless debates.

As Mark said I think this is the same track used on the tapes.

[sandchar99]

Thanks for weighing in on the subject. A truly heavyweight response.

I agree with markrb
2. Since the two channel is normally an alternate track (language, commentary etc..) most times it doesn't matter.
But there are many instances when the same soundtrack is available in both 6ch and 2ch (especially Concert videos).

This is more of a "heads up" for forum readers. For those of us who are interested in the best possible result it always pays to rip a sample chapter and see the what it looks (and sounds) like before proceeding with the whole backup.

[DSPguru]

Originally posted by DDogg
your comment above, "if the 2.0 track is DD track, it's surely better than 5.1 downmix." sounds like you feel pretty clear on this, but I remember endless debates.i'm 1000% sure.
and it's simply because i count on the studio's engineers, having the most updated HQ sound mixers, and all information needed regarding the very specifiec soundtrack they're editing, that they would provide the beSt Dolby Surround soundtrack.
we can't compare their work to a robustic, straight-forward, dpl downmix.

imho.

[DDogg]

Yeah, I have always thought this also for the same reasons you mentioned. It just makes sense.



we can't compare their work to a robustic, straight-forward, dpl downmix.

Is that sorta like a robot with boobs? :) or "Damn, look at that babe, she's very robustic" :)