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View Full Version : DVD Authoring......PCM or AC3 audio?


tbrown4
2006-03-09, 06:47 PM
Hey folks,

I am authoring a DVD and would like to know which to use, AC3 or PCM audio. What is the difference here? Which is preferred? Thanks for your help!

-Tim

Chachi420
2006-03-09, 09:15 PM
Pcm

schmoe75
2006-03-09, 09:24 PM
Hey folks,

I am authoring a DVD and would like to know which to use, AC3 or PCM audio. What is the difference here? Which is preferred? Thanks for your help!

-Tim
probably not the 1 to answer this, since i'm still fairly new, but chachi didnt expound so....
AC3 will only encode at a max bit rate of 384 kbs
LPCM encodes at a max (correct) bit rate of 1.5 Mbs (1500 kbs)

AC3, though sounds good is still a compressed lossy rate where as LPCM is uncompressed and lossless.

think of it in terms of mp3...the 1st mp3 compression still sounds good, but its lossy and NO one wants that. unfortunately, there was an ass load of videos transferred before this was truly understood...now that it is more common knowledge, AC3 is unacceptable for new transfers.

you also want to encode the video stream at its max bit rate of 9000 kbs, this combination may result in having to split the show across 2 or 3 discs depending on how long it is...there is NOTHING wrong with having more discs as long as its all encoded correctly.

If the video stream is encoded at the max and the audio is encoded as LPCM, you can only get just over an hour per 4 gig disc.

good luck :thumbsup

schmoe75
2006-03-09, 09:35 PM
You can pm OPN (http://www.thetradersden.org/forums/member.php?u=12276) the VBT mod and he can answer any transfer/author/synch questions you may have

tbrown4
2006-03-10, 06:47 AM
Thanks guys!

yeltzin_4
2006-03-10, 08:41 AM
The maximum bitrate for AC3 is 448 kbit/sec.

I disagree that AC3 is unacceptable for new transfers. Even though AC3 is compressed (and lossy), how many commercial DVDs come with PCM audio? Most commercial DVD are AC3 or DTS, even music ones.

schmoe75 says that you want to encode your video at 9000 kbit/sec. Well if you use PCM audio then your total bitrate is 10536 kbit/sec which exceeds the DVD spec.

There's no one correct answer for all situations, you can make a case for both AC3 or PCM depending on your source audio.

For example if your encoding a satellite or cable television broadcast, then the audio has most likely already been compressed via a lossy codec. If you convert it to PCM, you still have a lossy source. But on the other hand if you encode it to AC3 you're introducing another level of compression. Tough call.

If you are encoding audio that has come from an in-camera mic then the audio quality isn't going to be optimal so PCM may be overkill. In this instance I would suggest using AC3 @<hidden> 448kbit/sec.

If you have a separate audio source (ie. a recording from a DAT deck, Microtrack, Edirol R-1) and you want to preserve the high quality recording, then you would have a very strong case to use PCM.

I guess you need to decide what is more important with your DVD and who it is aimed at. If you're authoring a DMB, Grateful Dead or Phish concert then your audience is probably biased towards the audio side so they would lean towards PCM audio.

Finally, I guess what you need to ask yourself is: Am I happy with video encoded at 8300 kbit/sec ? If you are (and don't mind only having 1 hour per DVD5 disc) then go with PCM. If you'd rather use extra bitrate on the video or add more than 60 minutes per disc then maybe AC3 is for you...

Hope this helps

krakhead
2006-03-10, 09:28 AM
The maximum bitrate for AC3 is 448 kbit/sec.

I disagree that AC3 is unacceptable for new transfers. Even though AC3 is compressed (and lossy), how many commercial DVDs come with PCM audio? Most commercial DVD are AC3 or DTS, even music ones.

schmoe75 says that you want to encode your video at 9000 kbit/sec. Well if you use PCM audio then your total bitrate is 10536 kbit/sec which exceeds the DVD spec.

There's no one correct answer for all situations, you can make a case for both AC3 or PCM depending on your source audio.

For example if your encoding a satellite or cable television broadcast, then the audio has most likely already been compressed via a lossy codec. If you convert it to PCM, you still have a lossy source. But on the other hand if you encode it to AC3 you're introducing another level of compression. Tough call.

If you are encoding audio that has come from an in-camera mic then the audio quality isn't going to be optimal so PCM may be overkill. In this instance I would suggest using AC3 @<hidden> 448kbit/sec.

If you have a separate audio source (ie. a recording from a DAT deck, Microtrack, Edirol R-1) and you want to preserve the high quality recording, then you would have a very strong case to use PCM.

I guess you need to decide what is more important with your DVD and who it is aimed at. If you're authoring a DMB, Grateful Dead or Phish concert then your audience is probably biased towards the audio side so they would lean towards PCM audio.

Finally, I guess what you need to ask yourself is: Am I happy with video encoded at 8300 kbit/sec ? If you are (and don't mind only having 1 hour per DVD5 disc) then go with PCM. If you'd rather use extra bitrate on the video or add more than 60 minutes per disc then maybe AC3 is for you...

Hope this helps



if audio only use pcm !


if video use ac3


one correction ac3 is 448 kbit/sec but thats for 5.1

it is only 192 kbit/sec stereo

saltman
2006-03-10, 01:35 PM
ac3 sounds like GARBAGE. If you don't mind your DVD sounding like GARBAGE go for it. Do a test sample and see if you can tell a difference.

keep in mind the DVD spec is 10800 kbs max. which includes the video + audio + any menu info, etc...

some DVD players can't handle bitrates higher then 8000
so 8000 + 1536 is under the DVD spec and will produce the best DVD.

I bet you will find that you can't tell much difference between video encoded at 8000 vs 9000..... but you sure can tell a difference in audio encoded in ac3 vs pcm

AAR.oner
2006-03-10, 02:27 PM
^^^what saltman said...

for the average show, you can typically set the video bit rate at 8Mbps [8,000Kbps] & choose LPCM audio...this will give you the greatest quality while still keeping it cmopatable with everyone home set ups

Five
2006-03-10, 02:35 PM
Pcm

planetearth
2006-03-10, 03:01 PM
I'd go with AC3, I agree with yeltzin_4, in fact some dvd authoring programs such as Encore require you to transcode the audio if it's pcm to ac3. Some dvd players or television speakers have a tough time with pcm audio as a compatiblity issue.

Five
2006-03-10, 03:36 PM
^it would have to be a dvd player compatability issue

what dvd players have trouble with pcm? First time I've ever heard of this. Has this happened directly to you using your player, then the problem was solved by reauthoring to AC3? Sounds a litte far-fetched, especially the bit about PCM compatability with TV speakers. :wtf: :roflol:

schmoe75
2006-03-10, 03:45 PM
he probably has a HUGE collection of mp3's he wants to share as well
:roflol:

willndmb
2006-03-10, 07:06 PM
i rather have better video then better audio
ac3 over pcm if you would havwe to compress the video more to fit pcm

schmoe75
2006-03-10, 07:29 PM
i rather have better video then better audio
ac3 over pcm if you would havwe to compress the video more to fit pcm
you say that as if its a big deal to put a show on 2 or 3 discs instead of 1, so other than that, why exactly would you have to compress the video? :hmm:

i personally want the BEST video AND the BEST audio COMBINED! :thumbsup

FUCK AC3!! i have yet to hear 1 legitmitate reason to use it for any new transfers, other than the 'satellite tv broadcast' that are already in AC3

schmoe75
2006-03-10, 07:31 PM
I dont know what part of 'AC3 is LOSSY' you peeps arent getting...but if thats what you really want, find a site that doesnt care about quality and mp3's are considered a great thing :thumbsup

STLBlues
2006-03-11, 02:05 PM
If you have Pink Floyd's The Wall on DVD, I'm sure most people have that one, it's essential in life. Compare the PCM to the Dolby or DTS on that DVD. The PCM just blows the others away, completely! Using a good system always helps. I can't stand it when music DVD's (commerical..especially) don't have PCM, it's so much better.

ssamadhi97
2006-03-11, 04:58 PM
FUCK AC3!! i have yet to hear 1 legitmitate reason to use it for any new transfers, other than the 'satellite tv broadcast' that are already in AC3
Multichannel audio. So there. :P


That aside, most available AC3 encoders suck badly which gives AC3 a worse reputation than it deserves, though the format itself isn't that bad (potentially even on par with DTS, seems nobody ever bothered do a proper formal test of this though). It certainly helps to use a good encoder and a sufficiently high bitrate.

On a related note, the same also helps when it comes to the video. (because, you know, mpeg2 video is lossy too, ohoho </Sherlock>) I'm very much not impressed with the performance of commonly used mpeg2 encoders. More often than not, throwing more bitrate at these doesn't help either - it's not all that uncommon that you could get away with significantly lower video bitrates and still end up with better quality by using a good encoder.


...my point? Err, I dunno... something like "I wish more people would actually know what they're doing or talking about when making codec and bitrate choices or recommendations," I guess.

Five
2006-03-11, 05:42 PM
:clap:

AAR.oner
2006-03-11, 06:50 PM
:lol absolutely correct ssamadhi, but for the purposes of 99% of the stuff that goes thru this site, i'd still have to say PCM over AC3...

Unidecker
2006-03-13, 03:50 AM
pcm is best hands down ac3's only benefit is 5.1 and a smaller file size for the audio files...but also "compressed"...while pcm is pure "un compressed goodness" nice job guys ...keep up the good discusions. PCM is KEY 2 Sucess as far as i see it.....multitrackz brauh :)

LocalHero
2006-03-13, 11:27 AM
Let's just AC3 blows and LPCM rules.

Don't get me started on the compression issues of AC3. :disbelief

If it was up to me we would all be watching uncompressed avi files with LPCM audio! :lol