Pro Logic question.

[IKEA_boy]

I noticed today playing with my Gamecube that, using standard stereo RCA cables, that setting the output to 'mono' and my reciever on 'Pro Logic' that I would only get sound from my center channel. What I expected was that the same signal would be heard from my left & right channels. That got me thinking.
Can I leave my reciever on 'Pro Logic' (which changes to DD when I switch to my DVDs coax connection) will it decode a stereo signal and use only the fronts and, when applicable, use fronts & rears when a Pro Logic signal is sent?

[jonathan_little]

Part of the Prologic "scheme" is to put the same sounds that are heard in both the left and right channels at the same time into the center channel. This explains why you heard the mono sound collapsed to the center channel. If you want to hear the same mono sound from both channels, you'll have to set your receiver to stereo.

If you try to do Prologic decoding on stereo stuff that's not encoded with the surround channel, it will do a similar thing. The same sounds coming from both the left and right channels will be collapsed to the center. Sounds coming from either the left or right channel seperately will continue to emanate from their appropriate left or right speaker. The surrounds should remain mostly silent.

Dolby Prologic II is a bit better at handling Prologic-encoded and non-encoded stereo content than the old Prologic decoder. Some of the stereo surround effects it makes from a Prologic-encoded track are pretty good. Dolby Prologic II is still going to collapse mono sound to the center channel, but it can also make fake surround effects from non-encoded stereo content.

When your receiver goes into Dolby Digital mode, I believe there is a flag in the signal that tells the receiver if it's encoded for Prologic surround or not, and your receiver will enable the Prologic decoder automatically based on that. My Kenwood receiver ignores my analog choice for input (set for Dolby Prologic II) and automatically determines the mode (such as 5.1, Dolby Prologic Surround, or stereo) when using the digital connection. I can force it to use a different mode (like Dolby Prologic II Movie instead of Dolby Prologic) if I'd like. Your receiver could work differently.

[Jellodyne]

Incidentally, with Prologic II Music, you can specify the 'width' of the center channel, which sends some of the collapsed center channel back into the mains, more at a wider setting.