AC3 Questions

[Sakuya]

I read this tutorial:
https://www.videohelp.com/forum/userguides/140703.php

I was wondering, what happens after compressing the AC3 file into a WAV or MP2 file? Is it still stereo or is it surround? I know I'm making a VCD and Dolby Digital 5.1 is not possible, but still, what happens to the audio?

[Sakuya]

Also, would AVIMux work? In the past when working with AC3 audio, the resulting VCD's audio kept on pausing in my DVD player. I'm guessing that's what you call spikes? Is there a way to prevent that from happening this time?

[daamon]

Hi Sakuya,

I was wondering, what happens after compressing the AC3 file into a WAV or MP2 file? Is it still stereo or is it surround?

I'm pretty confident in saying that both WAV and MP2 are only 2 channels - i.e. standard stereo, whereas (as you know) Dolby Digital 5.1 AC3 is 6 channels (5.1 means 5 & 1, hence 6) which is your surround sound stereo.

Best thing to do is to check the specs of WAV (also known as LPCM, or just PCM) and MP2. They may well be on this site somewhere.

I hope that helps...

[Sakuya]

Actually, in the tutorial, it says to use either Virtualdub or avi2wav to extract the AC3 audio from the AVI file. And then rename it to movie.ac3? Would that really work?

Also, is it ok if I just use AVIMux and set the pre-roll and interleave settings at 100? Setting it at 100 would get rid of the spikes. But should I still rename it to movie.ac3?

[daamon]

Hi Sakuya,

Actually, in the tutorial, it says to use either Virtualdub or avi2wav to extract the AC3 audio from the AVI file. And then rename it to movie.ac3? Would that really work?

I've not used VirtualDub to extract AC3 to WAV (only the audio in DV AVI -> WAV), so you may want to check that out. But, I would suspect that (from VirtualDub) you will get an actual WAV format file. From there, I use ffmpeggui to convert WAV -> AC3 (2 channel) @ 192 - 256 kbps, depending on the source audio bitrate / quality. I find this little tool much easier to install and use than BeSweet.

In the tutorial, it actually says: "If the audio encoding is ac3, the avi2wav generated wav file is actually ac3 file. Rename it to movie.ac3" - Slightly different from what you quoted, but an important difference. Like I say, I've not done this so you'll just have to try it and maybe play a little.

Also, is it ok if I just use AVIMux and set the pre-roll and interleave settings at 100? Setting it at 100 would get rid of the spikes. But should I still rename it to movie.ac3?

I don't know AVIMux, so can't comment. Sorry. With regards to renaming, I'd suggest stepping into the unknown and trying a few things out - I find it's always the best way, and I learn other things in the process.

Hope that helps. Good luck...

[Sakuya]

I heard when you convert AC3 to WAV, the volume gets softer. Is there any way to increase the volume besides using TMPGEnc?

[offline]

I'm pretty confident in saying that both WAV and MP2 are only 2 channels - i.e. standard stereo, whereas (as you know) Dolby Digital 5.1 AC3 is 6 channels (5.1 means 5 & 1, hence 6) which is your surround sound stereo.

Nice try but no cigar
Dolby Digital Surround lives happy in a PCM .WAV file as does
DTS. More and more audiophiles are encoding DD and DTS as
standard wav files for buring surround onto a standard audio CD.

Wav & MP(1/2/3/4) are packages rather than pure formats - i.e. you
can have a multitude of flavours similar to .AVI allthough there are certain restrictions about compression and headers etc. You can also put surround 5.1 into MP2 but that is a whole different species of cake.

[Sakuya]

So what you're saying is that even if you convert them to WAV, the sound will still function in surround mode like its source?

[offline]

Not in your case. As the guide you are following directs you to "convert" using Headac3he or BeSweet to mp2, the resulting mp2 is stereo only. Depending on the source, you might keep some surround if you play your movie on a hometheatre that supports the old Dolby Pro Logic (I) format. Pro logic creates surround from stereo sources.

[Sakuya]

So how would you go about getting some Dolby Digital Surround-like sound on a VCD?

[offline]

You can't. You can run your stereo vcd through a DVD connected to a home theatre with a receiver. If you have Pro Logic II, you can enjoy a limited surround effect. If you have Pro Logic I, you can also have a limited surround effect if you have a vcd or svcd that has its mp2 soundtrack converted from an 5.1 AC3 file.

[Sakuya]

You did mean DVD PLAYER right because you put "DVD". Yes, I do have a home theatre and a receiver with Pro Logic. Not sure if it's I or II. Last time I checked, I think it just says "Pro Logic" and "Pro Logic enhanced". So I just convert my AC3 5.1 file to MP2. That's it?

[indolikaa]

offline,

Supposedly (it says so on the button to the left titled 'SVCD'), you can have a 5.1 surround audio stream on an SVCD using an MPEG-2 audio stream. This of course being different from an MP2 stream which is MPEG-1 Layer-II.

After repeating three times to ensure clarification:

VCD cannot have Dolby Digital soundtracks,
VCD cannot have Dolby Digital soundtracks,
VCD cannot have Dolby Digital soundtracks,

how practical is it to have 5.1 on SVCD? Ever heard of it being done?

.indolikaa.
Still an (S)VCD Fan

[offline]

Sakuya,
for example see guide at doom9 -
http://www.doom9.org/mp2-hac3.htm

After repeating three times to ensure clarification:

VCD cannot have Dolby Digital soundtracks,

Correct. However miniDVD and xSVCD can hold DD, but it
only works on a minority of DVD players. I have a stack of
xSVCD and miniDVD disks with the original ac3 5.1 DD sound
muxed with a mpeg-2 stream and they play perfectly on my
Hitekker & Conia DVD Players. I even got an old JVC to play
back DD audio by making a CVD/d1 res. mpeg-2 stream at 2300kps
muxed with 448kps AC3 and renamed as .VOB on a normal data
CDR - this also worked on an old Hitekker 700.

you can have a 5.1 surround audio stream on an SVCD using an MPEG-2 audio stream.

I tried this but it would only work on a friend's Philips DVD player
and even then the subsonics were poor. Waste of time imho.

These days I only work with DTS 8)

[Sakuya]

Sakuya,
for example see guide at doom9 -
http://www.doom9.org/mp2-hac3.htm

Thanks a lot! If you don't mind, I have some more questions. In the past when I dealt with AC3 audio (Dolby Digital 2.0), I had to use AviMUX to extract the WAV. I set the pre-roll and interleave at 100ms. Before, I set it at something much higher and when I played it on my DVD player, the audio got spikes. When I set it at 100ms, it played fine. Now, is there a function like this in HeadAC3he? Because I don't want spikes.

Also, if my source AVI file has Dolby Digital 5.1, why must I downgrade it to surround 2 and 2 channel?

[offline]

I had to use AviMUX to extract the WAV

No idea. Never extracted AC3 from a .WAV that has been interleaved under AVI. I was only talking about 16bit 48Kz AC3 or PCM. Not even sure the surround will transfer & what quality- let us know.

why must I downgrade it to surround 2 and 2 channel?

Down mixing is required to make a stereo signal that is mixed in a way that both cues ProLogic I for surround and holds the signal from all channels. 2 channels are all you can have at the one time for standard VCD or SVCD spec's.

[Sakuya]

Ok then. If I used avi2wav to extract the AC3 audio file and then use HeadAC3he to convert it to MP2, how can I make it so there won't be any spikes when I play it on the DVD player? And how do I know how much delay (whatever that is) to add?

[RabidDog]

AFAIK INEx

Supposedly (it says so on the button to the left titled 'SVCD'), you can have a 5.1 surround audio stream on an SVCD using an MPEG-2 audio stream. This of course being different from an MP2 stream which is MPEG-1 Layer-II

No i think mp2 is mpeg1 layer2 like mp3 is mpeg1 layer3
If you search for mpeg2.5 you might find some results IIRC.
pre-roll = pre load?

[Sakuya]

In HeadAC3he, it's so slow encoding. The yellow bar isn't moving... But it didn't freeze...

[Sakuya]

Ok, I've got a new issue and I thought I would re-use this thread that I made some time ago. Well, a few months ago, I burned a DVD with Dolby Digital 5.1 surround sound. The voices and sound effects are loud and impressive, but the background music is faint and cannot be heard with all the explosions. I want to rip the DVD and edit the volume.

Dafreak mentioned that I rip the DVD, demux the audio as a WAV, open it in Goldwave, maximize the volume, then convert it back to an AC3 and burn it to DVD again. I used DVD2AVI to decode the AC3 to WAV. Once I did this though, I lost the 5.1 surround sound effect. It is now a PCM WAV, 2 channels. Is there any way to increase the volume as well as keeping it at 5.1 channel?

[johns0]

Just extract the ac3 and use it as the source audio,dont re-encode it.

[Sakuya]

Huh? But how do I maximize the volume? That's the point of this whole thing.

[johns0]

You shouldnt maximize ac3 cause it has a wider dynamic range.

[Sakuya]

Then what else can I do to increase the volume? What does a wider dynamic range mean? I just want to increase the background music so it can at least be heard over the voices and explosions. When I play the AC3 file on the computer, I can hear the music pretty well. But when I burn it to DVD, the music is almost non-existant. So hopefully, if I maximize it, it will be better but then I can't save it as a 5.1 channel AC3 in Goldwave.

Ignore the first post of this thread and instead, read the post right above yours.

[Sakuya]

I tried using BeSweet and set the boost factor at 6 and I also checked to attenuate the volume by 2dB. But still, the background music is still so soft. For the Downmix Levels in BeSweet, I checked the "LFE to LR channels" and put it at 3db. I left the others unchecked because I don't know what they are. Should I be checking the Center/Surround Downmix? The output sound is not supposed to be like this.

I'm willing to go through any kind of work as long as someone guides me in the right direction.

[Sakuya]

I found a cool tool called AC3Machine. Would that work to increase the volume a bit? I did a gain of 7db but the output sounds exactly the same as the original on the computer. Why is that? Maybe I should do the surround downmix at 3db? 0db is normal while anything above 0 is louder right? And anything below 0db is softer? I'm currently testing it using a surround downmix of 3db.

If anyone has some other ways to help me, it's greatly appreciated.

[fritzi93]

You could get AC3Filter. Go into Configuration and set Master Gain to +20db, Output as 2/0-stereo, and tick the Normalize box. That solved the problem for me, both for playback on the computer and for playback on a stereo TV using extracted AC3 for authoring the DVD. Good luck.

[Sakuya]

I already have the AC3Filter. It plays fine on the computer but the background music's volume decreases on the home entertainment system.

But, did you say that by setting the AC3Filter and then extracting it, the result would be different? Then should I be setting AC3Filter to 3/2+SW 5.1 channels since the output is 5.1 channels? Would it really make a difference?

Edit:
I used DVD2AVI to demux the AC3 with Dynamic Range Control at Off. Since I have 2 VOBs for that one movie, only DVD2AVI can merge them temporarily to extract the AC3. But, I don't think AC3Filter will affect anything other than playback on the computer which is not what I'm looking for.

[fritzi93]

Hmmm, afraid I can't answer your questions, perhaps the AC3Filter help files may address them (?) Haven't looked at them for some time...

Here's the scenario where it helped me: A couple AVIs with AC3 had a dynamic range that went from barely audible to very loud, and all I have is plain old stereo. All I did was install AC3Filter, and change settings as outlined above, also, if memory serves, AC3Filter was set as the default for handling such files. This was on the suggestion of Baldrick in response to a similar question someone else had. It was a few months ago, as I recall.

The problem was fixed thereafter, both for playback of such files on the computer and for DVDs authored with extracted AC3. Sorry if this didn't help you.

[Sakuya]

I downloaded AC3 Machine and it sounds like it can do the job. However, no matter how much gain or whatever that I apply, everything else just goes louder with it.

Is there a guide anywhere to tells what each function does in AC3 Machine and what they're for?