Dolby Digital 2.0 mono Transcoding?

[joe55]

Hi, I have a DVD that is "Dolby Digital 2.0 mono" I have the
AC3 file and "azid" at the command line ..before with just one channel mono 1.0 files I would use:

azid -a -c normal -d1/0 -oc filename.ac3 filename.wav

and everything would be fine, how would I use azid for that Dolby Digital 2.0 mono AC3 to change it into a wav?

btw ..I'm just using the DOS command "azid"

Thanks!

[Skelsgard]

If its a Dual Mono then u don´t need the -d switch (since there´s nothing to downmix). Instead, u can use either "-m stereo" wich will send the Ch1 to the L and Ch2 to the R channels, or "-m ch1/-m ch2" to get Ch1 or 2 into the Left, to then output just Left channel. It´s more of a choice than a must.

U can perfectly use the commands u posted, in wich case u´ll get a C formed out of the muxing of Ch1 and Ch2.
azid -a -c normal -d1/0 -oc filename.ac3 filename.wav

considering that they´re already mono, u can also use:
azid -a -c normal -m ch1 -o L filename.ac3 filename.wav (to get a mono WAV).
or
azid -a -c normal -m stereo filename.ac3 filename.wav (to get a 2ch WAV wich is basically a 2 mono stream).

Cheers.

[joe55]

Great!! Thanks! Just trying that now, I'll check back :)

[joe55]

Okay, I used the command:

azid -a -c normal -m stereo filename.ac3 filename.wav

When I go to encode the file to an mp3 do I encode as mono or stereo? I am guessing mono? Thanks!

[Skelsgard]

For mono MP3 it would have made more sense to choose the -m ch1 -o L switches. The MP3 encoder is gonna mux it anyway if using mono encoding with a 2ch source.
Still, considering that the file is 2ch mono, there´s not much difference.
Cheers.

[Skelsgard]

That went fine, what should I use to encode this? This program I was using to encode it to mp3 ..It wasn't increasing the volume or anything I just told it to make an mono mp3 but the volume of the mp3 is very high and the voices sometimes sound crackly.
If u got this problem when encoding the -m stereo switch WAV u made first, it´s probably due to the downmixing the program makes as being a stereo source encoded to mono. The mathematical sum of both mono streams (L and R) makes a mono MP3 with twice the sound level, wich can easily lead to clipping (that´s when the audio surpasses the digital maximum volume level, wich causes the ditching or cutting away of the parts that go above the max level).

U shouldn´t have problems with the "-m ch1 switch" WAV.
Anyway, one of the standards today for MP3 compression is LAME. Is my encoder of choice. Wich one did u use?
Cheers.

[joe55]

Okay I think there may be something wrong at this point:

azid -a -c normal -m ch1 -o L filename.ac3 filename.wav

thats what I used then I used the command:

lame -b 96 --resample 32 -m dual-mono input.wav output.mp3

and when playing back the movie the audio still sounds louder than it should be, but for a Dolby Digital 2.0 mono file that "azid" command is correct?

Thanks

[Skelsgard]

I got your replies thru mail, but for some reason I can´t see your posts.
Anyway...

I find out later when viewing the ouput it just shows the center channel going ..that's just plain mono, if this is "dolby digital mono 2.0" how would you use lame.exe to encode that? I read somewhere it doesn't even support dual channel?

Is your file a real 2ch mono (as in i.e. english audio in Ch1 and other language in Ch2)? Or just the same mono in both channels? If it is the 1st option, then no, LAME doesn´t have a Dual Mono switch (at least, I´ve never heard of one). Still, u can get to use Stereo, then thru a matrix u can choose to play a desired channel (like with ffdshow). It´s tricky/hacky but works.
If it is the 2nd option, then u can just use one of both channels (since they´re the same) and encode with -m m to get a mono audio MP3.


and when playing back the movie the audio still sounds louder than it should be, but for a Dolby Digital 2.0 mono file that "azid" command is correct?

The -a switch is maximizing the sound levels. It raises the volume so the loudest sound reaches 0dB. And, including that it´s being combined with the "-c normal" switch (wich lowers and raises the audio to get all the sounds to basically play at the same volume), u end up with a audio stream that is loud.
U can lose the -a switch and use -g # (i.e. -g 0.90) to normalize at a certain percentage (-g 0.90 will normalize to 90% of maximum volume, 0.80 to 80%, and so on).

[joe55]

This is off a DVD and it just says "Dolby Digital Mono 2.0" ..it's the same mono in both channels, no english audio/other language. I downloaded LAME version version 3.97 beta 2 and it has an option for "dual-mono"

So I used:

lame -b 96 --resample 32 -m dual-mono input.wav output.mp3

so in that case what command should I use then with azid ..the -m stereo one? Thanks!

[Boulder]

Why don't you encode it as mono?

[joe55]

Okay, I just tried again using:

azid -c normal -m mono filename.ac3 test.wav

lame -b 96 --resample 32 -m mono test.wav test.mp3

and everything seems okay

[Boulder]

Yep, because you don't need to output a 2ch mp3 file if you have a mono source. You could actually do with a lower bitrate because 96kbps is quite a lot for 32kHz. Use the --alt-preset nn or --vbr-new -V n option.

[joe55]

One more quick question Skelsgard..

I used the two commands:

azid -c normal -m mono filename.ac3 test.wav

lame -b 96 --resample 32 -m mono test.wav test.mp3

should I use what you said with:

azid -a -c normal -m ch1 -o L filename.ac3 filename.wav

and then the lame command? Thanks :)

Another thing is the log from azid it shows..

[00:00:00.000] | Input channel configuration:
[00:00:00.000] | Left : None compression, +0dB gain
[00:00:00.000] | Center : None compression, +0dB gain
[00:00:00.000] | Right : None compression, +0dB gain
[00:00:00.000] | Sur Left : None compression, +0dB gain
[00:00:00.000] | Sur Right: None compression, +0dB gain
[00:00:00.000] | LFE : None compression, +0dB gain
[00:00:00.000] | Output configuration: 2/0
[00:00:00.000] | Ch0 [Left ]: Normal compression, +0dB gain
[00:00:00.000] | Ch1 [Right ]: Normal compression, +0dB gain
[00:00:00.000] | Output Dual mono mode: Mono
[00:00:00.000] | Output Stereo mode: Dolby Pro Logic
[00:00:00.000] | LFE levels: To LR -3.0dB, To LFE -INF
[00:00:00.000] | Center mix level: BSI
[00:00:00.000] | Surround mix level: BSI
[00:00:00.000] | Dialog normalization: No
[00:00:00.000] | Rear channels filtering: No

It says mono..but it also says "dolby pro logic" when I actually go to encode the WAV using LAME it says "converting from stereo to mono" is this messing anything up, like making the file louder/adding distortion..etc?

[Skelsgard]

If u´re already satisfied with the results u have, u don´t need to. Remember that is always on a what-u-like-best basis, there´s nothing mandatory.
As the source is "mono 2ch" when using the "-m ch1 -o L" switches u would just be choosing one of those 2 channels to send to the encoder. Therefore the "-m m" switch in LAME wouldn´t be necessary, since u were already encoding a mono source.

Output Stereo mode: Dolby Pro Logic
I think is just reporting what would be used if u were exporting using the Stereo options. It shouldn´t be there but doesn´t have any effect whatsoever.

It says mono..but it also says "dolby pro logic" when I actually go to encode the WAV using LAME it says "converting from stereo to mono" is this messing anything up, like making the file louder/adding distortion..etc?
Don´t know exactly how LAME works with the downmixing. U can ask the developers.

[joe55]

Yeah, I'm getting some other DVD's that are "Dolby Digital Mono 2.0" so I'll see how that goes lol ..thanks for all the help, I'll be sure to check back :D