OK...Let me try to explain as simply as I know how:
The middle channel is a mathematical fact. You can look at stereo two ways:
The Left Channel is derived by adding Middle Channel to the Side Channel, while the Right Channel is derived by subtracting the Side Channel from the Middle Channel (mathematically, L=(M+S) and R=(M-S))
- or -
The Middle Channel is L+R and the Side Channel is L-R (mathematically: M=(L+R) S=(L-R))
Matter of fact, stereophonic sound was originally conceived as both LR and MS:
Quote:
Blumlein conceived stereo not just as a left (L) and right (R)
speaker signal but also in terms of a sum signal M (=
L+R) and a difference signal S (=L–R). The letters M
and S stand for 'mid' and 'side' signals (as in the M-S
microphone technique): M is the signal containing
information about the middle of the stereo stage,
whereas S only contains information about the sides –
since S=0 for a central signal.
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See this webpage (it's where I got the quote above)
Gerzon Archive if you're having a hard time wrapping your head around the math.
In the meantime, if you wanna experience this for yourself, try this:
- Load up your favorite mix
- pan the left and right channels to the center
- invert the polarity on one channel
That stuff that goes away is the middle channel. The stuff that's left over is the side channel.
Quote:
Originally Posted by Franco  P.S.:
"First of all, stereo absolutely has a center (or "middle") channel*.."
Uh, no. Stereo has a "central image", which is totally dependent on the only two channels in a stereo system, Left and Right. Shifting either speaker will change the central image and it will disappear with the absence of either channel. In case this isn't clear, you can't "solo" the central image on a stereo system (not talking about accessing the center frequencies that can be focused on a M/S matrix, but referring to fine-tuning the center image by placement of the left & right speakers), unlike a surround system which does have a central channel. |