AC3 5.1ch vs. AC3 2ch

[SEALs1230]

Whats the difference? I'm compressing a movie that has both of these types of audio. If I get rid of the 5.1 ch then it will lessen the compression by 7%. But I dont exactly know what the 5.1 ch is. Will this get rid of my audio all together? or will it not make much difference, meaning the 7% is more important than the 5.1 ch audio?

[guns1inger]

AC3 2 channel has either standard stereo (left and right channels), 2 channel mono (same signal in both channels) or Dolby ProLogic. AC3 5.1 has 6 discrete channels (centre, front left and right, rear left and right, and sub woofer). If you have a surround amp you will get the full effect. If you don't, your DVD player will down-mix 5.1 for stereo output.

Sometimes the 2 channel is audio for the movie, sometimes it is the commentary track.

My advice, future proof your backups and keep the 5.1 audio. You can still play it back now, and if you get a surround amp in the future, you don't have to do it all again.

[SEALs1230]

Does that mean I can get rid of the 2 channel then? and if i do that, keeping the 5.1, will it play the audio even if i dont have the surround sound system?

[Gurm]

The 5.1 channel is ALWAYS (on modern discs) the default audio. Players will ALWAYS (whtout reservation) downsample it.

So yes, it's ALWAYS safe to pick the 5.1, as long as it's the first on the list.

[HatchetMan]

When using DVD Shrink, you can right click the movie picture while previewing a title, then independently select each audio stream to listen to find out exactly what each is for - commentary, music only, optional languages. If the 2 channel sounds exactly like the 5.1 channel coming out of your little computer speakers, then go ahead a pick the 5.1, it will sound best on any home theater.

[SEALs1230]

Cool, I had no idea you could do that...thanks alot.

[curlyween]

I didn't know that either. You learn something new every day...

[Gurm]

If the 2 channel sounds exactly like the 5.1 channel coming out of your little computer speakers, then go ahead a pick the 5.1, it will sound best on any home theater.

Not if you don't have 6 speakers. If you're working with a stereo setup, the 2-channel that's mixed in the studio is going to sound better than the 5.1 that's downmixed on-the-fly by your $100 Sony receiver.

[HatchetMan]

If the 2 channel sounds exactly like the 5.1 channel coming out of your little computer speakers, then go ahead a pick the 5.1, it will sound best on any home theater.

Not if you don't have 6 speakers. If you're working with a stereo setup, the 2-channel that's mixed in the studio is going to sound better than the 5.1 that's downmixed on-the-fly by your $100 Sony receiver.

I doubt that. The one in my bedroom is hooked up 2 ch stereo and the 5.1 mix sounds much better, meaning louder for some reason, dts sounding even better than that. To each his own I suppose.

[Gurm]

Your experience is unusual. The odds that your DVD player can do a better downmix than an experienced studio technician with hundreds of thousands of dollars worth of mixing equipment... is slightly larger than zero. Y'know, like 0.0000001% larger.

[HatchetMan]

I very rarely see both 2 channel and 5.1 soundtracks anymore, I was originally under the assumption that in that case it may have originally been recorded in 2 ch stereo and them upmixed to 5.1. I couldn't imagine why anyone would want to downmix 5.1 to 2 ch considering how well it sounded in the first place. Gurm, maybe different equipment handles it differently, I didn't realize mine was so superior to everyone else's, yours included. My lame $20 COBY player hooked directly to my old azz TV even sounds great playing a 5.1 soundtrack, DD or DTS.

[Cinemagic]

You both are right, IMO. AC3 2 channel on a simple stereo system will have all the audio information contained in the two channels. The AC3 5.1 has some of the audio allocated to other speakers. Usually the audio allocated to other than the main speakers is significant when listening on a 5.1 system, but relatively insignificant to most people when listened on a 2 channel system. If the audio from the 5.1 is boosted slightly, then it will be somewhat louder. To the average person, louder sounds better. If you were to play both 5.1 and 2 channel at the same volume level and listened, the 2 channel would sound better when played on a 2-channel system. Since the 5.1 volume is usually boosted, it sounds better to most people. So both of you are right, one from a quantitative standpoint and the other from a qualitative standpoint.

[HatchetMan]

^ nice

[Gurm]

I'm speaking from a "DVD player running into a beefy stereo but only have three speakers hooked up because we had to rearrange the house for the new baby" standpoint.

With no rear speakers, 5.1 is a waste. I just pick the 2.0 soundtrack when it's available, and use the Pro Logic II 3-channel mode.

[Cinemagic]

You let a new baby take precedence over video/stereo? What's wrong with you?

[Gurm]

I know, I know. I'm trading in the BMW coupe for a Volvo Wagon, too. Sad.

[guns1inger]

I think I'm gonna cry. I got my first DVD player in the lead up to our second kid. Told wife I could geta good deal if I got a DVD player at the same time as a new dishwasher. The fact that it cost twice the price of the dishwasher thankfully never became clear to her.