viking99

Hopefully this is the appropriate forum for this question....

My Sony 5.1 receiver has can toggle between the following modes:

"Auto"
"Dolby ProLogic"
"Prologic II - Movie"
"Prologic II - Music"

The owners manual does a very poor job of explaining these. Let me tell you what I think they mean, and then I'll invite the experts out there to either correct me or confirm my understanding.

"Auto" appears to try to detect a 5.1 encoding. If it finds one, it plays the 5.1 using my my five speakers plus subwoofer. If it does not find a 5.1 channel, it plays everything as 2 channel stereo plus a subwoofer output.

The "Dolby ProLogic" appears to use the right and left speakers, subwoofer and center channel for anything, including DVD's that aren't "surround sound" (non movie DVD's in my collection). I don't understand ProLogic very well.

The "Prologic II - Movie" setting appears to take a normal ProLogic-Surround soundtrack and alter the signals to the surrounds to make it "act" more like a 5.1 track.

The "ProLogic II - Music" appears to be intended to take a simple 2 channel stereo soundtrack and create synthetic center and surround signals.

Am I close?? Thanks!!

uli2000

thats pretty much it. Pro logic is 4.0 (center,right, left, and a matrixed rear channel).

Josh Z

You should use the 5.1 "Auto" setting for movies so encoded, and "ProLogic II - Movie" for everything else.

viking99

Thanks Josh. While it doesn't come right out and say it in the owners manual, I believe that leaving the receiver on "auto" with a non-5.1 track results in a simple two channel stereo playback - ignoring prologic encoded tracks.

I do have some non-movie DVD's that have only a stereo (or mono) track (i.e. there is not even ProLogic surround). Am I correct in assuming that those should be played with the Prologic II - Music setting??

Josh Z

It's possible. Every receiver is a little different. My Denon can be set to default to ProLogic II for all 2-channel input signals. Maybe your Sony can't. You'll have to check the manual to see how that works.

If you have ProLogic II, there's really no sense in ever using old ProLogic for anything.

Are they music or concert DVDs?

The ProLogic II matrix does a good job with just about any 2-channel signal. If the signal in mono, the track should default to playback only through the center channel. If it's stereo, you'll primarily just get audio through the front left and right, though perhaps a bit of ambiance bleed to the surrounds. Dolby 2.0 Surround mixes will have activity in both the front and back soundstages.

The "ProLogic II - Music" setting steers the front soundstage to the side speakers and away from the center. The "Movie" setting uses all three front speakers; any signal that goes to both channels in equal amplitude (like movie dialogue) collapses into the center speaker, while anything with stereo separation goes to the sides.

If they are music or concert DVDs, the "Music" setting may seem a little fuller or warmer. But if it's something like a TV show, the "Movie" setting is still best.

viking99

Thanks for the explanation Josh. The part I just quoted (above); is that how the center channel for regular old Pro-logic is generated as well?

Also, it sounds like older movies with a mono soundtrack might be better played with the Prologic II - Music, as otherwise the LF and RF speakers might not be utilized(?). Is that a correct understanding?

OldDude

Prologic is not (strictly*)encoded, it is "faked" from two channel stereo. Nothing wrong with that if you like the effect, but you may get mixed results on music, some are OK in Prologic, others sound better in two channel stereo, which is all they are to begin with.

*Knowing how it decodes, there are some things (manipulating 2 channels) that can be done in mastering to affect how the two channels will decode to four, but there are only two channels.

viking99

Thanks OldDude! Drifting from the original topic a bit....., is there a simple explanation for how ProLogic is used to produce the center and surround signals? Is the center simply that part of the left and right channels that is identical in composition and amplitude (maybe already answered above)? How does prologic create the surround signal? This is very educational for me.

stevevt

Pretty much. The center info is derived by figuring out the parts of the L&R that are identical in frequency and phase.

The surround info is similar, but uses out-of-phase info.

viking99

Thanks. This is starting to make sense. I remember a (somewhat) similar technical discussion of 8mm video where the "normal" mono camcorders would record a "left plus right" audio track. Stereo versions would record a second track that was "left minus right". For playback on a stereo device, the tracks would be added to produce the left stereo channel and the second subtracted from the first to produce the right stereo channel. It's been years since I had read about that, but it stuck in my mind as being both very logical and very clever. Now, ProLogic isn't the same, but does appear to involve similar comparisons, subtractions, etc. to generate the final channels.

Josh Z

Yes. The difference between ProLogic and ProLogic II is how the surround channel is extracted. ProLogic II allows for stereo separation in the rear speakers, while old ProLogic has a strictly mono surround channel.

If you have a good center channel, just use the Movie setting and let it handle the whole soundtrack. You're better off this way for clarity of dialogue.