AC3 reencoding, how is the quality?

[MvB]

How becomes the quality (theoretical) of an 448 kps AC3 file,when i convert it to 6 wavs and then the 6 wavs to an 448 kps AC3?

Is the quality much worse than the original AC3?

Thanks

[mikecito]

I actually do this all the time when I edit dvds - I can't tell a difference at all. AC3 is a pretty high standard when it comes to quality, to the compression isn't lossless, but it's good. I doubt there is an ear out there that could tell you had recompressed it, unless you were to drop the bitrate or something. But where you're leaving it at 448 - I wouldn't worry about it.

[ChristianHJW]

while this is probably right ( sound quality will be worse, no question, but maybe be acceptable for most purposes ) if you are using a very good encoder, may i ask what the purpose would be of doing so ( curious ) ?

[mikecito]

The reason I do it so often is the following:

I edit DVD's to make them more family friendly. see www.mikecito.com

In the process, I seperate the ac3 to 6 distinct waves so that I can mute just the center channel, or right channel, or whatever channel I want. 99% of the time, I can remove a swearword by muting the center channel, because that's usually the only place it's found. That way, the music and sound effects continue, and it's pretty transparent that I edited anything. Then - after I'm done, I export the six waves and reencode them at the original rate. It sounds dang good, and I can't tell a difference between the original and reencoded file. It's the only way I can think of, also, to maintain Dolby Digital 5.1 after I've edited parts from the movie. I don't think you can edit ac3 directly anyway.

If you're interested in the process, I plan on putting a step by step walk-through with screen shots on my web site. Give me a couple weeks and check back.

[MvB]

@Chris

There is a simple reason for me to do this:

I want do convert PAL DVDs to NTSC with full AC3 sound (you know, the speed difference). So I've laid out, which way to do this if you convert the AC3 to WAVs in Thread
http://forum.doom9.org/showthread.php?threadid=24535
Now i just want do slow down an AC3 by splitting it in 6 separate WAVs and using the procedure. there i was interested whether the sound would be acceptable with recompression.

[DJ Bobo]

@ mikecito
Sorry, but I don't like censoring. If you don't like your children to hear or see something, don't even let them see the movie -.-
If you ask me, I hate all censors, censoring is ridiculous IMHO (when I think about what is done to DBZ, I must ... :angry: )

[Alestrix]

Originally posted by DJ Bobo
If you ask me, I hate all censors, censoring is ridiculous IMHO (when I think about what is done to DBZ, I must ... :angry: )
I 100% agree!
Censorship was one of the things that freaked me out most when I lived in the states. If children don't hear some things in a movie or a song, they hear it somewhere else. I think it's important to learn how to deal with such things moderately at home rather to be impressed by kids in school who make excessive use of swear words...

But I'm far off topic here, so I'll shut up now...

My 2¢
- A

[mikecito]

You know, I think it's great that you want to make me feel bad for cleaning up some of the best movies ever made so that they are appropriate for all audiences, but you fail to see my point. You can go rent all the porn you want, and I won't interefere with your actions. That's your choice.

But when it comes to my home, I do what I want. I choose to let my kids see movies that have a positive impact on them. For instance, Rain Man is a great movie. Edited, it has the SAME effect and feel as it does with all the swearing and partial nudity left in. I simply remove those half-second chunks, and it comes out great. Another good example - Good Will Hunting.

See, these movies have a great theme and moral, but they have a couple spots that I don't want my kids to watch. If they choose to watch it when they're older, fine. But I won't be the one to corrupt their young minds, IMHO.

Thanks for the feedback, though. If you ever want to try it yourself, you'll see more than enough information on how - on my website.

[Eye of Horus]

I think it is not only about censoring !
The method mentioned is the same I use when I want to make a copy on DTS of the music only.
Take for instance The Wall, The movie DVD.
When you want to listen to the music only, you have to skip parts in the movie that contain speech and / or silence.
So I ripped the complete soundstream. Edited it (removed the silence and speech) and re-encoded it to DTS. Or you can re-encode to DD, but as the original post asked about quality loss, I think that for music only DTS is a better choice.
So now I can listen to the music only and I preserve my valuable DVD !

Eye of Horus

[DJ Bobo]

@ mikecito
You do what you want, but I think, if a director makes a film with a given amount of language/violence/sensuality, then he's having a given audience in mind, and censoring won't do, it will only make the movie valueless! so in my opinion, when you think a movie isn't suited for an audience, don't show it to them and basta!
Talking about DBZ, It's a shame to see that kids of 5 and 6 years are watching the series when the uncut version was originally thought for ages 13 and up, you can imagine how I feel then! I mean the series was brought down to kid level, this is awfull and absolutely unacceptable, no matter what the reasons are!

@ Eye of Horus
Well, you may go for DD5.1 @ 512kbps or 640kbps if you feel like 448kbps isn't enough. I can't test, but I think 640kbps DD5.1 will be pretty close to DTS in quality.

[Eye of Horus]

Originally posted by DJ Bobo
@ Eye of Horus
Well, you may go for DD5.1 @ 512kbps or 640kbps if you feel like 448kbps isn't enough. I can't test, but I think 640kbps DD5.1 will be pretty close to DTS in quality.

I don't think the difference will be hearable (correct english ?) with decoded DD streams and then re-encoded.

But with original source material..... I prefer DTS.
It just sounds a bit clearer, more fresh, more like ..... the source :-)
An excellent DVD where you can hear this difference is : The Ultimate DVD Platinum. It is a test DVD to adjust your setup perfectly and contains a lot of samples in all formats.

And..... the encoder I use for DTS is a lot faster than the one for DD 5.1.... !! (I do 4 DVD's to DTS and to VCD or SVCD a week !)
(Sonic Foundry Soft Encode compared with Minnetonka's Surcode Pro)

I know there are different opinions about if the difference can be heard, but that speed difference is for me just as important.
When I don't have to skip speech or silent parts, I use of course Besuresweet (!), but then too to DTS.

Also the fact that 99% of the "Quad conversion guys", convert to DTS makes you wonder, huh ?


Eye of Horus

[DJ Bobo]

If DTS encoding is a lot faster, I'm 100% behind you ;)