5.1 surround pan/channel assignment in Sony Vegas

[mltwitz]

I extracted a 6 channel (5.1 surround) .ac3 audio track from an HDTV video file which I want to use for a render job in Sony Vegas Pro 9. When I drop it into the Vegas timeline, all 6 channels show up as single audio tracks, with the surround pan in the center for all tracks. I've never done 5.1 rendering before, so excuse my ignorance: How do I now apply the right panning for each track. Is there any way to know what the original channel assignment is?

[edDV]

I extracted a 6 channel (5.1 surround) .ac3 audio track from an HDTV video file which I want to use for a render job in Sony Vegas Pro 9. When I drop it into the Vegas timeline, all 6 channels show up as single audio tracks, with the surround pan in the center for all tracks. I've never done 5.1 rendering before, so excuse my ignorance: How do I now apply the right panning for each track. Is there any way to know what the original channel assignment is?

Ideally would will be doing this by ear with calibrated 5.1 speaker soundfield.

[mltwitz]

I don't have the means to do that. I only have headphones for the job. I can tell which is left and right, but not front or rear. Isn't the speaker/channel assignment information embedded in the ac3 file?
If I've identified a channel, do I slide the pan pointer all the way to that speaker symbol, or at an intermediate position? What about the center, does that stay in the center of the field or right at the center speaker?

[edDV]

When you import raw PCM files into a project you have all positioned in the center and it is your job to place the tracks in the sound field.

But if you import an existing AC3 5.1 file (e.g. this TV commercial) the front LR and Center track will be positioned to the front and the surrounds in the back. The LR and surrounds load as stereo pairs.

[mltwitz]

Sorry, I misspoke. It's not an ac3 file it's a 6 channel .wav file converted from a 5.1 ac3. I had to convert it to .wav, because when I drop the ac3 file into Vegas all I see is 6 silent tracks. Any idea why that could be? Anyway, so I'm assuming that why the speaker assignments got lost?

[edDV]

Yes if you convert to wav, track positions in the sound field are lost. You can brute force it by assigning each track to a speaker.

[poisondeathray]

If you convert 6-ch AC3 to mono wavs with eac3to , it will automatically write the original channel assignment into the filename of each wav. C, L, LFE, R , SL , SR

[poisondeathray]

Ideally would will be doing this by ear with calibrated 5.1 speaker soundfield.

What edDV says is important, because every now and then the channel mapping is incorrect in the original file. So if you "blindly"/"deafly ?" go assuming the original channel mapping was correct, sometimes it can produce unintended results

[mltwitz]

Why is it that when I drop 5.1 .ac3 files into Vegas, I only see 6 empty/silent audio tracks? I tried it with several files. If I mux the the ac3 file with the corresponding video (.h264) it won't import it at all, message says "...could not be opened"

[edDV]

Why is it that when I drop 5.1 .ac3 files into Vegas, I only see 6 empty/silent audio tracks? I tried it with several files. If I mux the the ac3 file with the corresponding video (.h264) it won't import it at all, message says "...could not be opened"

Don't know. An unsupported format I assume. What does mediainfo say?

Most AC3 files I drop work but these aren't from Blu-Ray.

It could be an issue with version 9. I forget what it supports.

[poisondeathray]

Why is it that when I drop 5.1 .ac3 files into Vegas, I only see 6 empty/silent audio tracks? I tried it with several files. If I mux the the ac3 file with the corresponding video (.h264) it won't import it at all, message says "...could not be opened"

Not sure, maybe something wrong with the audio? header issue ?

Maybe try re-wrapping the video & audio e.g .with tsmuxer in .m2ts transport stream

What is the source from ? How was it recorded ?

[mltwitz]

It's an HDTV recording, not mine, so I don't know too much about it, below is the info from MediaInfo. It was originally an .mkv file, since Sony Vegas won't support that, I extracted the ac3 audio with MKVExtractGUI2. Vegas will only show 6 silent tracks, so I converted it to 6 channel .wav with AC3Tool. Vegas will import the .wav file, but then I get to my original question...not sure which track corresponds to which speaker.

Complete name : C:\***.ac3
Format : AC-3
Format/Info : Audio Coding 3
File size : 57.9 MiB
Duration : 21mn 4s
Overall bit rate mode : Constant
Overall bit rate : 384 Kbps

Audio
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Duration : 21mn 4s
Bit rate mode : Constant
Bit rate : 384 Kbps
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Compression mode : Lossy
Stream size : 57.9 MiB (100%)

[poisondeathray]

As mentioned above , use eac3to instead, and the channels will identified and written into the filename

eac3to input.ac3 output.wavs

(notice it's "wavs", not "wav", this will give you mono wavs)


If you don't know how to use command line, here is simplified procedure for batch file

1) Download eac3to package
2) copy your ac3 files to be converted into the the eac3to folder
3) download the zip file, unzip, and copy the batch file "eac3to_ac3towavs.bat" into the same folder, and double click it

This will convert all ac3 files in that directory to mono wavs, each with their channels written into to filename

[mltwitz]

Thank you sir, you are a scholar and a gentleman!

[mltwitz]

As mentioned above , use eac3to instead, and the channels will identified and written into the filename

eac3to input.ac3 output.wavs

(notice it's "wavs", not "wav", this will give you mono wavs)


If you don't know how to use command line, here is simplified procedure for batch file

1) Download eac3to package
2) copy your ac3 files to be converted into the the eac3to folder
3) download the zip file, unzip, and copy the batch file "eac3to_ac3towavs.bat" into the same folder, and double click it

This will convert all ac3 files in that directory to mono wavs, each with their channels written into to filename

Trying to figure this eac3to out. Your batch file worked great. Now, what would be the syntax to combine/multiplex 6 mono wavs back to one 6 channel ac3?

[poisondeathray]

you can use any audio dolby encoder that accepts mono wavs, I can't recall if vegas can do this out of the box (you might need 3rd party plugin)

e.g. besweet, audacity, avisynth + soundout, soft encode

the free ones are all based on aften

or you can export a 5.1 wav out of vegas, and any audio program will be able to encode it to ac3 (dozens to choose from, but all based on aften). There is a gui for aften, this is probably the easiest method for you

here is an old guide for besweet & several other methods for mono wavs
http://www.schudy.de/dts/dts2ac3-e.htm