I would like to be able to say – quite correctly – that where surround sound exists, it is always on 2.0 as well as 5.1. Without attracting trolls, then getting banned for a month. So, perhaps the mods would like to read what follows, very carefully indeed, before simply making a knee-jerk reaction ? If u dont understand it ask someone who does! No shame in that .........
As everyone knows, pro logic 2 was invented by Jim Fosgate. So presumably, he should know how it works ……..
“Guttenberg: I guess this is a good time to ask: What, exactly, is the difference between the original Pro Logic and Pro Logic II?
Fosgate: They both have their roots in quad and SQ matrix-style encoding/decoding. The original Pro Logic had mono "band-limited" surrounds, PLII has "full-bandwidth" stereo surrounds. Since original Pro Logic was a film-oriented system, Dolby had to make sure the center/dialog channel was rock-solid. So they weighted the steering toward the center front channel, which shrank stage width on stereo recordings. When Pro Logic came out, it was a marvel of performance and stability”
http://www.stereophile.com/content/j...nd-mind-page-2
http://en.wikipedia.org/wiki/Jim_Fosgate
That’s right. The same matrix (more or less) is used in SQ, the 2.0 cinema analogue soundtrack version, and pro logic. All based on peter schrieber's original patents. There are minor differences in matrixing between sq, qs, and dolby surround (snce there is only 1 way to matrix 4 channels into 2!) But there are very big differences in how the various different decoders work!
The main difference with pro logic is an absence of projector weave effects, allowing the two surround channels to be full bandwidth, if this is on the original material. Plus the analogue noise reduction has already been stripped out, if it was there at all, of course.
“REGULAR MATRIX: DOLBY SURROUND
This was originally developed to make "Star Wars" under the name Dolby Stereo. It quickly became the preferred surround system for movies. Home movies were encoded in it, as were many phonograph records, cassette tapes, and CDs. Most soundtrack recordings are encoded in Dolby Surround because the movies they came from were so encoded. There are more recordings in this matrix than any other.
One difference from other systems is that the decoder adds a delay in the back channel before it goes to the speakers, and that back speakers (called surround speakers) are placed on both sides. This removes the problem of localizing the side images that other 4-corners matrices have. Also, applying identical signals to all of the inputs produces the nadir (n) modulation”
Of course, a pro logic decoder will also play sq and qs!
“If you play a matrix style quadraphonic record, (Stereo-4, SQ or QS), through your Dolby Pro-Logic II matrix decoder you will get 5.1 channels of sound. Actually, this works quite well. My experience is that the Dolby Pro-Logic II decoder works better at playing back matrix style quadraphonic records than the many of the purpose-built decoders of the quadraphonic era. Some records decode better than others. That is true whether one is playing back the quadraphonic records using the original matrix decoders or using a Dolby Pro-Logic II decoder. One can also us the Dolby Pro-Logic decoder to play back quadraphonic records. My experience is that the Dolby Pro-Logic II decoder is much superior”.
"Indeed, Dolby Pro-Logic was essentially the ultimate implementation of matrix quad :-"
http://www.audiokarma.org/forums/sho....php?p=5453602
Now on to wrongly named “mono surround”, which confuses lots of people. Obviously, there is no such thing, because it is a contradiction in terms! So Please pay close attention:
“The last stage splits the signal in two with ± 90-degree phase shifts before adding to the left and right outputs. Thus the surround signal is encoded in opposite polarity on the left and right channels, but is also phase-shifted in respect of the original left, right and centre channels. This last point is essential
as it would not be possible to 'fly' sounds overhead from surround to centre, or from one side to the rear, without it.”
http://www.soundonsound.com/sos/sep0...oundsound2.asp
In other words, the “mono” channel is fully phase encoded with positional information, which is then matrixed in with +j and –J (see diagram). Which is how you get spaceships whooshing around the back of your head in star wars. As I previously explained, the haas (precedence) effect doesn’t work in smaller living rooms, which is why the entirely different pro logic decoder - used only in homes, not cinemas note ! - was developed! Even on the earliest cinema decoders, which DID just have one rear output for parallel wired speakers (not in series, obviously!), the phase encoding still gives quite good surround sound.
Pro logic uses "steering" instead !
There IS actually such a thing as “mono surround”, ie the rear effects channel on Todd AO (early 6 track magstripe). If this were mixed into either dolby surround or 5.1, it would give a very odd “point mono” source at the rear! So usually, it isn’t.
I trust this clears up the confusion.