Editing individual AC3 5.1 DD channels

[lacywest]

I've got a AVI video with 5.1 DD AC3 audio. I was told before I obtained it that the left back channel was barely audible but I decided to get it anyways.

I can open it up in ... TMPGEnc Video Mastering Works 5 and see how the 6 channels behave and yes ... it seems that the left back channel is lower while the right back channel is ... louder.

I've done some checking and the latest version of ... Audacity ... with the correct plugins included can display the 6 audio channels ... been wondering if I can boost the left back channel with it.

Anybody here ... have any suggestions ??

[yoda313]

You may have already done it but if you can't simply increase the volumes in audacity I would export the ac3 to wavs. ac32wav is an old I think for doing that. I'm sure a million other programs can I just can't think of them right now. I believe besweet uses ac32wav. There is also eac3to of course.

From there load the offending wav channel to a an editor that does have volume booster ability and save the new file. Than use besweet or eac3to to mux a new ac3.

Are you sure there aren't volume booster abilties in audacity? I would keep checking. Otherwise you'd have to use some other audio program to do it. I have an old version of payware software Cakewalk Pyro that does volume boosting. I'm sure there are plenty out there that can.

I think there might be gain boosters just for ac3 files as well. though I don't know if you can specify which channel to boost. Might be worth doing search for "ac3 volume booster" or something like that.

Good luck.

[lacywest]

Thanks yoda ... something I'd like to try ... and I know it may be wrong to do it this way but I'd like to ... load both left and right back channels and treat them like normal stereo channels and then work on them.

I've got ... Sound Forge 10 ... Cool Edit Pro 1.2a ... and Cool Edit Pro 2.1 ... to work with and a whole bunch of DX plugins.

I guess what I need to do is ... extract the ... left and right back channels .. do some work on them and then when they seem okay ... replace them with the ones that are in the 5.1 AC3 DD audio file.

Sound Forge 10 ... displayed all 6 channels ... but I didn't see any way of or it didn't jump out at me ... to boost the back left channel.

[hello_hello]

My method would be to open the audio using an encoder which can re-encode it via DirectShow. With ffdshow installed I'd use it for decoding. ffdshow has a "volume" filter which can be used to adjust the volume of each channel individually. Once I'd balanced the audio as desired, I'd just re-encode the whole thing. It'd probably be easier to use a video player such as MPC-HC which will also let you use DirectShow for decoding, as then you can play the audio while adjusting the channel volume, and once you're happy apply the ffdshow configuration and encode with your DirectShow encoder of choice. Just make sure ffdshow's "mixer" filter isn't active, or doing something you don't want it to do such as mixing the multichannel audio down to stereo.

MeGUI is one encoder GUI which lets you set the preferred decoder when encoding audio. DirectShow is one of them. There's no doubt many programs which will re-encode via DirectShow.

[yoda313]

load both left and right back channels and treat them like normal stereo channels and then work on them.

I dunno sounds like an iffy proposition to me. They could have the headers written incorrectly upon saving. You might not be able to resave them as individual channels.

Check out what hello_hello is suggesting. Though I don't know if that is more for realtime playback instead of reencoding.

[lacywest]

load both left and right back channels and treat them like normal stereo channels and then work on them.

I dunno sounds like an iffy proposition to me. They could have the headers written incorrectly upon saving. You might not be able to resave them as individual channels.

Check out what hello_hello is suggesting. Though I don't know if that is more for realtime playback instead of reencoding.

I did some more messing around ... yeah ... my idea wasn't the best idea ... I did load them as separated tracks in CEP 2.1 but didn't fly the way I was thinking.

Audacity ... extracted 6 separate wav files ... problem was trying to figure what each file was ... Center ... SL ... SR ... LFE [not hard ... most low sounds] ... I'm still not sure if I got the ... center channel right in reference to the FL and the FR and if the SL is SL and not SR ...

[johns0]

You can adjust the level of any of the tracks in audacity without having to extract to 6 wavs,just select the track you want adjusted and effect/amplify and export as 5.1 ac3.

[hello_hello]

Check out what hello_hello is suggesting. Though I don't know if that is more for realtime playback instead of reencoding.

He seems to have it sorted now but there's no reason why you couldn't use ffdshow to adjust the volume of a channel while encoding as long as the encoder can decode the original audio using DirectShow. When all else fails I've used ffdshow's mixer to mix multichannel audio down to stereo while encoding. Every so often I come across an audio file where the channels were assigned incorrectly during (a stereo channel and the center swapped around, for example), so I use ffdshow's mixer to fix them while encoding.

[lacywest]

Yes ... I am making progress ... but ... Audacity doesn't actually say ... which channels are what ?

The top 3 are heavy in content ... so of the 3 channels ... which is which ... just looking at them doesn't help.

Is the center in the middle ... as number 2.

And then at the bottom ... I've got 3 channels that have me wondering too ... it is not hard to figure out the LFE channel ... it's all low frequencies.

But which channel is LS and RS.

Okay here is an idea ... of the bottom 3 ... the LFE is not hard to figure out.

So now to figure out which is LS and RS ... well since I know the LS is flacky and lower in volume as compared to the RS ... I guess I could assume [ I hate the word] ... the weak channel is the LS and the RS is the one that is ... not weak.

I then can extract the 6 channels as mono wav files and then enchance them with CEP 1.2a or CEP 2.1 or Adobe Audition or Sound Forge 10.

And then from there ... use ... SurCode for Dolby Digital ... to create a AC-3 audio file.

Or ... use ... EncWAVtoAC3-5.0.exe and run it to install it. In my start menu it looks like ... WAV to AC3 Encoder

So the only problem left actually is ...

... the top 3 channels on the top ... when viewed in Audacity ... which one is ... FL ... FR ... Center ... anybody know that answer ??

[hello_hello]

I'm pretty sure when playing multichannel audio such as AC3 using foobar2000, (according to the output meters) it's always front left, front right, center.