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Daniel Raim
stereo downmix of a 4.0 channel mix
on May 27, 2009 at 2:05:08 am

Our mixers are sending us an LTRT sound mix for theatrical presentation.
Will the LtRt mix playback as stereo if the sound system doesn't support surround?
The goal is to have a stereo mix for DVD screeners for film festival submissions and other screening purposes.
Is there a way to create a stereo downmix in Final Cut Studio? If so can anyone point me in the right direction?

Thanks much!


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Ty Ford
Re: stereo downmix of a 4.0 channel mix
on May 27, 2009 at 2:48:08 am

Hello Daniel and welcome to the Cow Audio Forum.

Yes, that's the idea. It's stereo unless you have the decoder to unfold it.

About FCP. I'd take that to the FCP unless someone else chips in here. Don't see why not but I haven't done one yet.

Regards,

Ty Ford




Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Daniel Raim
Re: stereo downmix of a 4.0 channel mix
on May 27, 2009 at 7:00:47 am

Thanks for the feedback Ty!

I will be receiving version 1 of the LTRT mix and I need to QC it tomorrow.
(The mixers are in France and sending it over the net!)
Without access to a theater with proper surround sound, I will probably need to QC by opening the LTRT file in Quicktime and listening with my headphones or desktop speakers, nothing fancy.

Would opening the LTRT in Quicktime produce a stereo version that at least includes the 4 channels mixed down into a stereo file?

Thanks again for answering my questions... as you can probably tell I'm new to the audio/post world.
Cheers,
Daniel


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Ty Ford
Re: stereo downmix of a 4.0 channel mix
on May 27, 2009 at 11:12:38 am

Quicktime Pro has some very neat features. You need to pay the $29 to unlock the Pro version, but you can manipulate the audio and video. I'm not certain how that will play out for you, because I'm not entirely sure how the LtRt tracks will appear in Quicktime. DO let us know.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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JC Boulay
Re: stereo downmix of a 4.0 channel mix
on May 27, 2009 at 4:35:05 pm

Hi Daniel,

The LtRt mix is a stereo file, so your proposed QC procedure is exactly what you should do if you expect the recipients to listen to the mix in stereo. If the conversion was done correctly, stereo compatibility should be close to perfection. There is no software that will open a stereo LtRt file and see all folded discrete channels, though. To get to the surround information, you need to decode the mix through some kind of Dolby hardware or software.

If you expect the recipients to listen to the LtRt mix in surround, your DVD really should include the complete surround mix as well, in either AC-3, MP2 or discrete PCM. Unfolded LtRt really doesn't live up to true surround at all. In fact, I find it sounds like $#!t. That's why DVD's have eight audio tracks.

In case the LtRt mix will be upconverted, there is one thing you should watch out for. The information found in the surrounds will be treated correctly if you 4.0 mix is LCRS. If it's a quad mix (stereo front+stereo surrounds), it may not fold back up correctly, as LtRt sums the surrounds to mono. Something to watch out for.

If listening in stereo is your only concern, you should be quite OK. LtRt's are used very widely without issues.

Welcome to the oh-so-simple world of digital audio

IHTH

JC Boulay
Audio Z
Montreal, Canada
http://www.audioz.com


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JC Boulay
Re: stereo downmix of a 4.0 channel mix
on May 27, 2009 at 6:23:32 pm

just to add a link to a Dolby white-paper that could be helpful in untangling the formats for your DVD:

http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professio...

If you want to dive deeper or research other Dolby-related topics, this is where to start: http://www.dolby.com/technicallibrary.aspx?id=306

JC Boulay
Audio Z
Montreal, Canada
http://www.audioz.com


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Daniel Raim
Re: stereo downmix of a 4.0 channel mix
on May 27, 2009 at 6:33:00 pm

Jean,
I really appreciate all your feedback and information. And the links are great! A must read for any budding producer!
Daniel



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