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tgunn2760
2007-08-10, 11:10 AM
If the audio of a DVD has been encoded to AC3 and is then decompressed to LPCM, is the audio lossy or lossless? I would think it would no more lossy than the AC3 it was encoded to. Am I wrong?

Thanks.

U2Lynne
2007-08-10, 11:24 AM
It would be lossy. That's like taking an mp3 and decompressing it to wav - you just can't get back the stuff that was removed when it was compressed to mp3 (or ac3).

tgunn2760
2007-08-10, 12:01 PM
It would be lossy. That's like taking an mp3 and decompressing it to wav - you just can't get back the stuff that was removed when it was compressed to mp3 (or ac3).

Thanks...another question:

What if the LCPM is lossless and stereo, and reduced to mono.

Is that lossy?

Thanks again.

U2Lynne
2007-08-10, 12:07 PM
Well, it isn't lossy in the sense that if you look at an FA or SA of it, it will show frequency response in the range you want, however, you will never be able to go back to stereo from there. At least that is my understanding - you take the two channels and put them all into one.

tgunn2760
2007-08-10, 12:22 PM
Well, it isn't lossy in the sense that if you look at an FA or SA of it, it will show frequency response in the range you want, however, you will never be able to go back to stereo from there. At least that is my understanding - you take the two channels and put them all into one.

What if the original source had mono audio that was encoded to stereo was it was made into a DVD?

Is there a way to tell if the original audio was mono or stereo?

U2Lynne
2007-08-10, 12:34 PM
What if the original source had mono audio that was encoded to stereo was it was made into a DVD?

Is there a way to tell if the original audio was mono or stereo?
This I do not know. Someone more knowledgeable about this will have to answer.

tgunn2760
2007-08-10, 12:36 PM
This I do not know. Someone more knowledgeable about this will have to answer.


Thanks for your help.

paddington
2007-08-10, 01:06 PM
What if the original source had mono audio that was encoded to stereo was it was made into a DVD?

Is there a way to tell if the original audio was mono or stereo?



do you mean it was 'teased' into fake 'stereo' like TISDU or so you mean they simply doubled the mono track to 2 channels to make the DVD compliant?

If the latter - don't 'fold down', as that doubles the amplitude values - just extract the left channel.

The thing is, if you want it to go to CD, red book says it must have two channels - mono doesn't fly. So, you'd have to copy left to right again (which is what they did in the first place, so maybe leave it).

tgunn2760
2007-08-10, 02:12 PM
do you mean it was 'teased' into fake 'stereo' like TISDU or so you mean they simply doubled the mono track to 2 channels to make the DVD compliant?

If the latter - don't 'fold down', as that doubles the amplitude values - just extract the left channel.

The thing is, if you want it to go to CD, red book says it must have two channels - mono doesn't fly. So, you'd have to copy left to right again (which is what they did in the first place, so maybe leave it).

I don't know if the original recording was mono or stereo.

I have a DVD which has AC3 stereo audio, but the volume is very low.

I extracted the audio in wav and deleted a channel as someone suggested, ran it through Goldwave and then doubled the volume. It sounds great, but it's lossy.

I know there is a lossless LPCM audio file out there, but the size would make it too big for a DVD5, so I was wondering if after deleting one channel of the lossless stereo LPCM the audio would still be lossless, especially IF the original audio was in mono-and is there a way to tell if it was mono?

paddington
2007-08-10, 06:38 PM
yes. Take the LPCM audio file you suspect is dual-mono (exact same left and right channels) and open in Cool Edit Pro 2.0 (or Adobe Audition - whichever you have).

Highlight the whole thing and open the "channel mixer". Invert ONE of the channels and play. If the audio is exactly the same left-right, it will be completly silent since you are subtracting the inverse from one side to the other. Get audio, and you do not have a true dual-mono source.


Now, if that is the case and you have isloated a mono source, the only remaining question is whether you can include an LPCM mono track on a DVD and still be compliant with the standard. I know with a CD, that would NOT be compliant - you have to double to 2 channels - back where you started.

Maybe a video mod can chime in about whether a DVD can contain a 1 channel mono LPCM stream - or you can visit www.videohelp.com and look up the DVD-Video standards. I'll try to have a look later if I have a chance.

tgunn2760
2007-08-10, 07:26 PM
yes. Take the LPCM audio file you suspect is dual-mono (exact same left and right channels) and open in Cool Edit Pro 2.0 (or Adobe Audition - whichever you have).

Highlight the whole thing and open the "channel mixer". Invert ONE of the channels and play. If the audio is exactly the same left-right, it will be completly silent since you are subtracting the inverse from one side to the other. Get audio, and you do not have a true dual-mono source.


Now, if that is the case and you have isloated a mono source, the only remaining question is whether you can include an LPCM mono track on a DVD and still be compliant with the standard. I know with a CD, that would NOT be compliant - you have to double to 2 channels - back where you started.

Maybe a video mod can chime in about whether a DVD can contain a 1 channel mono LPCM stream - or you can visit www.videohelp.com and look up the DVD-Video standards. I'll try to have a look later if I have a chance.

I don't have either of the programs you suggested, and I don't have the lossless LPCM now so I will worry about it when I get it..IF, I get it?

As for the mono audio being compliant on a DVD, it is. I made one. I overwrote the AC3 audio in Tsunami DVD author Pro with the decompressed AC3. In fact, when I run the DVD files through GSpot it doesn't recognize the LPCM audio, it reads it as AC3.
And I know it is NOT AC3, I burned a copy of the original DVD with the AC3 audio, and played them both, the difference is impossible to miss.

Thanks again for your help.

paddington
2007-08-10, 07:49 PM
I'm confused.. if you decompress AC3 (I assume you mean to 48kHz WAV), you don't get back the audio data that was discarded when it was compressed to AC3.

It should sound the same. Unless you then RE-encoded to AC3 again.. THAT would sound terrible.

KoolKat
2007-08-10, 08:11 PM
AC3>LPCM = Not lossy,just a bloated AC3
Some VHS's used to say Dolby on Linear tracks

But tgunn,between you & me(hopefully),i wouldn't do what i 100% know you are thinking.The definitive is being worked on......Shhhhhh ;)

K_K

paddington
2007-08-10, 08:16 PM
AC3>LPCM = Not lossy,just a bloated AC3


It doesn't make it more lossy, but it doesn't exactly put the audio back either. Unless we are talking about lossless AC3, then? :hmm: I assumed he was talking about the standard lossy AC3 you find on nearly all DVDs with AC3 sound?

KoolKat
2007-08-10, 08:26 PM
It doesn't make it more lossy, but it doesn't exactly put the audio back either. Unless we are talking about lossless AC3, then? :hmm: I assumed he was talking about the standard lossy AC3 you find on nearly all DVDs with AC3 sound?

Agreed J,i see what your saying chap

K_K

paddington
2007-08-10, 08:34 PM
I really wish all these lossy codecs weren't suddenly available as lossless, too (AC3, WM9 (WMA), AAC, etc) it REALLY is going to confuse a lot of people soon, once stuff starts spreading that way... makes it much harder to tell what is crap and what is not without having to analyze each file :disbelief :down:

KoolKat
2007-08-10, 08:47 PM
Yeah i know what you mean & why call these sudden lossless ones the same bloody name.That's a boggler too

____________________________
"There are some of these recordings where it is just a whirring and you cannot hear the music. " - Jimmy Page, 2007.JUL.26

"yes, but making copies of copys of copys of audio cdrs, then extracting WAV>FLAC, putting it on the internet, burning that to audio cdr, oops I lost the info & screwed up the date, mailing that, copying it again to audio cdr, put this in my cd player & what's that sound? click, crackle pfffft oh shit maybe we should avoid this. - FIVE, 2007.JUL.28

"it sounds ok to me" - Demonoid member 2007.JUL.29

tgunn2760
2007-08-10, 10:12 PM
AC3>LPCM = Not lossy,just a bloated AC3
Some VHS's used to say Dolby on Linear tracks

But tgunn,between you & me(hopefully),i wouldn't do what i 100% know you are thinking.The definitive is being worked on......Shhhhhh ;)

K_K

Exactly. If the original audio was mono, then reducing the lossless stereo LPCM to mono would not make it lossy, and it would fit on a DVD5. I HATE DVD9s and splitting one into two DVD5s. I do it when I must, as I recently did with CologneShark's Steve Miller DVD9.

I quadrupled the volume on that one.

I hope whoever is working on the "definitive" increases the volume in Goldwave, it makes a HUGE difference. I will probably DL it even if it's a DVD9, just to extract the audio. My "decompressed" AC3 version sounds great, I sincerely hope the one being worked on sounds as good or even better. I'm also curious to see if my ears can tell the difference.

Thanks for replying.

tgunn2760
2007-08-10, 10:20 PM
I'm confused.. if you decompress AC3 (I assume you mean to 48kHz WAV), you don't get back the audio data that was discarded when it was compressed to AC3.

It should sound the same. Unless you then RE-encoded to AC3 again.. THAT would sound terrible.

Yes, the AC3 was decompressed to wav, when I dropped it into Tsunami DVD Author it said "LPCM" mono, as I deleted one channel and doubled the volume.
(as Bob the Guru suggested. On account of this I wondered if the original audio was mono.)

The full file was 1.2 GBs, the mono about 585 MBs, it fit perfectly onto a DVD5, with motion menu it came to 4.27 GBs, and sounds great.

But you do get back some of the compressed data. The AC3 audio is about 1/4 of the LPCM.

Anyway, KK knows what this is all about, so if says the definitive version is being worked on, expect something really exceptional to happen. The video on this DVD is excellent, and I expect the audio will be too.

Thanks for replying.

KoolKat
2007-08-10, 10:20 PM
then reducing the lossless stereo LPCM to mono would not make it lossy

Thanks for replying.

Now thats a different ball park & would

K_K

tgunn2760
2007-08-11, 01:19 AM
Now thats a different ball park & would

K_K

If the original audio was stereo. Was it? I don't know, this is what I have been wondering about.