7.1 Surround and Vegas

[futon88]

I've started work on a disc that provides 7.1 audio, but Vegas only supports 5.1. I'm not sure what I should be doing with the extra channels. Should I be down-mixing the back four somehow, or can I simply ignore two of the back channels?

 

[krausfadr]

You should downmix, instead of ignoring channels since you'll lose some content.

I use this tool a lot:

dmMediaConverter - v2.4.1

dmMediaConverter is a crossplatform FFmpeg frontend (GUI) exposing some of its features. It is ...

dmsimpleapps.blogspot.com

 

[addiesin]

I would definitely check and see if there's also an officially produced 5.1 track on the disc along with the 7.1 track and use that instead if possible. That way there would be no margin of error.

 

[futon88]

I'll double check, but I only saw 7.1 and 2.0

 

[unfair]

You should downmix, instead of ignoring channels since you'll lose some content.

Are you sure you're not going to get unintended positioning of sounds by doing that? 7.1 is 5.1 plus one more speaker in between on each side, so if you mix the sounds from those into the others you're basically repositioning or increasing the volume on the other tracks. I would think that at least some of the sound from those two middle speakers would already be in front or rear tracks, but I guess that might not universally be true.

I'd probably run some tests before doing the edit just to see the impact of downmixing vs dropping the tracks on key scenes. I avoid downmixing if possible, since if you do dolby to stereo for instance you often lose some clarity. I just try to avoid 7.1 audio though since Premiere doesn't play nice with it either.

 

[futon88]

Thanks, all.

I should see what happens when I explicitly ask ffmpeg for 5.1 via "channelsplit=channel_layout=5.1[FL][FR][FC][LFE][BL][BR]"...

 

[krausfadr]

Are you sure you're not going to get unintended positioning of sounds by doing that? 7.1 is 5.1 plus one more speaker in between on each side, so if you mix the sounds from those into the others you're basically repositioning or increasing the volume on the other tracks. I would think that at least some of the sound from those two middle speakers would already be in front or rear tracks, but I guess that might not universally be true.

I'd probably run some tests before doing the edit just to see the impact of downmixing vs dropping the tracks on key scenes. I avoid downmixing if possible, since if you do dolby to stereo for instance you often lose some clarity. I just try to avoid 7.1 audio though since Premiere doesn't play nice with it either.

I’ve listened to the actual content in just those two extra speakers. Trust me. You’re over thinking this.

 

[unfair]

I’ve listened to the actual content in just those two extra speakers.

So what's the result when you downmix it, does it shove the middle left track in the front left, back left, or both?

 

[asterixsmeagol]

Are you using MakeMKV to rip the video from your disc? I think I've seen 5.1 audio nested under a 7.1 track before, but I'm not sure. It might have been a DTS track nested under DTS-HD or something.

If you can't get a real 5.1 track, you could just import the two extra tracks and just set the fader halfway between front and back on each side to let Vegas do the mix for you. You'd just need to preview a couple of scenes with your surround setup to make sure you have the panning done correctly.

 

[futon88]

I used makemkv to pull the files, and tsmuxer to put them back together (disc has both theatrical cut and director's cut playlists). tsmuxer only shows 7.1 or 2.0 for audio, and that's backed up by what's printed on the back of the case. Oddly, the case says the director's cut is 2160p, but all of the .m2ts files I pulled are 1080p. A puzzle for another day.

Alas, I don't have a surround setup to do a proper test, but I can do an A/B back and forth against the source in my headphones to ensure it's close.

 

[krausfadr]

So what's the result when you downmix it, does it shove the middle left track in the front left, back left, or both?

It combines the 4 “rear” channels into two. If you want to really control the percentages and mix, nugen halo downmix can do that. But no one’s likely ever going to notice the difference.