5.1 legit downmix to Lt/Rt

OTL wrote on 5/12/2009, 10:41 AM
Hey, appreciate your help at your earliest convenience.

I urgently need to create a proper Lt/Rt mix from my 5.1. Not just a preview... 2 AIFF's - 1 for L 1 for R.

I have my 5.1 Stems (6 channels L; R; C; Ls; Rs; LFE) and I'm wondering if there's a way to render the selected reagion automatically into 2 MONO AIFF's for the Lt/Rt?

Is there a quick way to do this? Or do I have to mute the right while I'm rendering the Left into 1 AIFF and vice verser etc...

I always thought Lt/Rt was a 5.1 mix folded into a stereo-esq mix... seems like the obvious way of rendering with muted channels wouldn't create a true Lt/Rt.

Thanks for your help and suggestions.

Comments

newhope wrote on 5/12/2009, 4:39 PM
First a quick question on your terminology.

LtRt (Left total Right total) means a stereo Dolby Surround (Prologic) encoded signal which will play correctly as a stereo file but which will also decode into LCRS surround (not 5.1) via a Dolby Prologic equipped decoder/amp etc.

Straight stereo which won't decode into surround is called LoRo.

So which of these do you want and why do you want either as separate mono files?

Vegas can output a relatively acceptable LtRt (though not strictly 'legal' in the Dolby sense) stereo file from your 5.1 mix by choosing to Render as... an AIFF file and selecting enable multichannel mapping. This also works for WAVE files.

Click on the Channels...button and select Surround Master (Stereo downmix) and click OK. Then if you do need separate mono files, as opposed to a single stereo interleaved file, in the Template drop down select 44,100 Hz, 16 Bit, Mono, PCM (multiple) then click on the Custom... button and change the sample rate to 48,000 (assuming you want to maintain 48KHz sample rate) and click OK. Now name and save your file.

The result is an acceptable, though not strictly legal, Dolby RtLt downmix of your 5.1 original.

You can do this directly from your master mix session, without the need to output the separate 5.1 stems as individual files, though you may want to do that for other reasons.

Alternatively have a look at Neyrinck, but their software for Dolby etc is not particularly cheap.

New Hope Media
OTL wrote on 5/12/2009, 6:52 PM
Thanks for your response.

I need Lt/Rt not Lo/Ro and totally understand that it won't be decoded into 5.1 etc...

Lt = 1 Mono Rt = 2nd Mono (That's the way our post sound originally gave us the Lt/Rt files. 1 Lt/Rt labled L (MONO) and the other R (MONO). The short version is I had to remix some of the 5.1 stems and conseqently now need a new Lt/Rt that corresponds with the 5.1 remix changes etc...)

Our distibutors have requested AIFF hence I can't give them WAV's.

AIFF does have the Multichannel mapping, when I enabled it... then selected "Surround Master (Stero Downmix" (Ch: 1&2) its only giving me 1 file.

If money wasn't an option I'd have many encoding software choices to play with, but unfortunately I have to try and do this with Vegas only.

Thanks again.
newhope wrote on 5/12/2009, 11:54 PM
The reason that you've been given two mono files is most likely because the originals came from ProTools in your Sound Post suite (or possibly an AVID edit system) which always split their stereo audio into separate mono .L and .R files.

AIFF does have the Multichannel mapping, when I enabled it... then selected "Surround Master (Stereo Downmix" (Ch: 1&2) its only giving me 1 file.

If you follow the instructions below AFTER selecting multichannel mapping you should get two mono files output.

In the Render as... dialogue box select the Template drop down select 44,100 Hz, 16 Bit, Mono, PCM (multiple).

Then click on the Custom... button and change the sample rate to 48,000 (assuming you want to maintain 48KHz sample rate) and click OK.

Now name and save your file.

The result is an acceptable, though not strictly legal, Dolby RtLt downmix of your 5.1 original and should be output a two mono files.

If you can only output a stereo AIFF file then import it back into Vegas in a new session, drop it on a track and right click on it. Select Channels and Left Only then Render as... a mono AIFF. Then do the same thing, right click and select channels but select Right only and Render as... a mono AIFF.

That will give you your two sides of the LtRt file as mono tracks and you can name them .L and .R appropriately.

Mind you any AVID or ProTools system will import interleaved stereo and separate the files into .L and .R stems as they are imported so interleaved stereo really isn't a drama usually.

New Hope Media
OTL wrote on 5/13/2009, 3:22 PM
Hi and thank again,

Unforunately I've already tried the Mono (multiple) route, with multichannel mapping, without it, with it again but selecting surround master (stereo down mix) under channels... all three choices give me 6 rendered files (L, C, R, Ls, Rs,LFE) which is very odd.

I also tried the creating a stereo filme and rendered each side (L then R) which is my back up etc... my only concern is it's not really a real Lt/Rt in the sense that I dond't believe it will unfold into a psudo 5.1... LCRS etc...


I'm at a total loss... the only thing I can think of is it's somehow related to busses?!
newhope wrote on 5/13/2009, 4:35 PM
Without seeing your session setup it's hard for me to decipher why it is that you are getting a six track render.

I did a short film, Death's Requiem, mixed in 5.1 with Vegas and, as well as the 5.1 mix, I also rendered a stereo mixdown using the method I described. It gave me a two channel mix which did decode reasonably accurately as surround LCRS when played through a Prologic amp.

No it isn't the real deal Dolby version but as Dolby Surround (Prologic) largely relies on phase difference for detecting the mono rear channel (signal is 90 degrees out of phase to front channels) the downmix appears to be doing that with the surround from the 5.1 mix.

My film started with a phone ringing behind camera and as the camera tracked around the room I panned it from the rear through right to front centre in the 5.1 mix. The stereo mix down approximated this though, because the surround in LCRS is mono, the effect of the pan from rear to right was less accurate though what I'd expect from LCRS.

If I read this correctly you've also tried just outputting a stereo file using Multichannel Mapping stereo downmix ... not multiple mono, and it still gives you six channels?

When you are in the multichannel stereo down mix it should indicate channels 1,2 in the dialogue box to the right of the selection for stereo downmix.
I'm booted into Mac OSX at the moment so can't load Vegas for better info.

If you can get a stereo file you can use the method I described, reimporting it into Vegas, earlier to create the two mono stems.

New Hope Media