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DVD Downmixing
post Sep 20 2010, 21:03
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I popped "The Fellowship of the Ring" Extended Edition in my Macbook Pro the other day, and noticed I had the choice between Dolby Digital 5.1 and "Dolby Surround". Am I safe in assuming that the Dolby Digital is down-mixed to Dolby Pro Logic II on my Mac? And if so, what at the advantages/disadvantages of this down-mix vs. the special made "Dolby Surround" track? I'm wondering why the included a "Dolby Surround" track at all? I guess I should mention I'm just listening via analog headphones.

Thanks much!
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post Sep 20 2010, 23:37
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The 2.0 track might be a completely different mix. When listening in stereo, the 2.0 mix is probably intended & recommended, but you might prefer the mixed-down track on any given movie. Or with headphones, you might prefer the 5.1 track with Dolby Headphone if your Mac has it.

Pro Logic works by "steering", and if you simply mix-down you might not get the proper surround effect. For example, if there are dominant rear-channel effects during dialog (or during music), the dialog (or music) might get steered to the rear.

If the mix is done in Pro Logic (while monitoring in Pro Logic), then the same mix can be encoded as both 2.0 and 5.1. Then, 5.1 can be down-mixed and decoded-back from 2.0 to Pro Logic surround. But, this approach limits what the mixing engineer can do.

I'm now working on up-mixing a concert video from mono to 5.1.* In the 5.1 mix there is rear-channel reverb and additional applause that I'm leaving out of the 2.0 mix. (My plan is to set the mix-down parameters so that the rear-levels are still there, but reduced in mix-down mode.) Neither the 2.0 or 5.1 mix is being done with Pro Logic in mind so any Pro Logic steering is likely to mess-up the sound. The proper playback choice will be between 2-channel stereo and true 5.1 digital. (Or. perhaps one of the non-movie Pro Logic modes that doesn't use steering).

* Of course, I can't un-mix the mono or create a proper stereo image. But, I can do some little tricks with EQ and I can pan the announcer to the center, and pan the applause to the rear (and add/move applause from other parts of the recording)... I'm just "playing around", and I still have the original mono for the purists who might not like my gimmicks. tongue.gif
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