Mid & Side

This may help http://www.fabfilter.com/.deo/mid-side-demystified

The Fabfilter article is pretty good... but just in case you want more:
 
Mid-Side processing is used all over the place in audio.
 
A front facing cardiod can be paired with a side-facing bi-directional microphone to record both the mid and side signals. This provides almost infinite control over the stereo width during mixing.
 
Electronically realized mid and side signals are used for FM stereo broadcasting, and were once used to encode stereo material for storage on broadcast cartridges (which were notorious for their terrible stereo performance - the tape would slide up and down and make a real mess!)
 
And the much respected Fairchild 670 provided a way to create Mid and Side signals for processing to make it easier to cut a record... meaning quite literally cutting the vinyl.
 
Let's do a little bit of math (just a little!)
 
The Mid signal, in all of these cases, consists of the mono equivalent, what you'd hear if you put up only one microphone. It can be created, after the fact, but adding the left and right channels (and you will see it referred to as L+R)
 
The Side signal is created by subtracting the Right from the Left. This is also what you get from a side-facing bi-directional microphone.

So why is it useful?

Mid is monophonic - and compatible with mono radios, which is why it is the primary signal broadcast by FM stations.
 
If you add Mid and Side you can, in effect, decode the Left channel:
(L+R) + (L-R) = 2L - since the right channels will cancel out
 
If you subtract Side from Mid you can decode the Right channel:
(L+R) - (L-R) = (L+R) + (-L+R) = 2R - since the left channels now cancel out
 
That's how stereo FM receivers work. It also turned out that even with the tape slip-sliding around if you encoded the stereo into Mid and Side you could recover a pretty darned good facimile of the original stereo from a cart machine.
 
None of which is all that valuable to us today.

But what is valuable is we can now work on four different channels of a stereo signal! We have Left and Right, of course, but we also can have Mid, which is the mono equivalent, and Side, which is the ambiance, if you will. (yeah, not a great description, but my brain is off for the weekend.)

So I can apply equalization or compression or delay or whatever to the MID channel and only affect those things that appear in both the left and right channels, the "center" channel if you will. That's pretty powerful! And I can do the same to the side channel, but that's not always as useful<G>. All the while I can also still process or effect the left and right channels.

Clear as mud??
 
PS- Carver and Polk Audio (among others) used to use this matrix idea to create a "bigger than stereo" effect. It sounds cool, for a little bit anyway.

Is it possible that one can use Channel Tools to create mid/side tracks by cloning a track and placing CT on both tracks, then turn mid way down on one, and side way down on the other? It seems like that would be true, but I'm not certain how CT is processing the audio and if the end result id the same as using a true MS encoder.
 
Regards,
Dan

Somehow I'm not "demystified".
I'm not complaining!
I'm glad (well not really, more relived I guess) that I'm not the only one who's
head hurts when trying to "wrap" it around this.
I guess I AM one of the "Geezers".
 
T
fine print
AM is a registered trademark of bapu etc., etc.
end fine print
:-}

I'll give it a go to explain it simply as a microphone technique.  
 
We know that flipping polarity cancels out sound.  That is negative voltages added to equally positive voltages results in no voltage. 
 
In the membrane of a figure 8 microphone, sound coming from the front of the mic results in standard polarity.  When the sound waves push the membrane, you get a positive voltage, when they pull it, you get a negative voltage.  The opposite happens on the rear lobe.  Pushing results in negative, and pulling results in positive.  
 
In mid side, the figure 8 microphone points the front lobe to the left and back to the right.  The channel this microphone is recorded to is duplicated.  One is panned hard left, and the other copy hard right.  On the right channel, the polarity is switched to make the rear/right lobe act like a second front lobe, but exactly opposite.  If these two channels were centered now, you would hear no sound because they cancel each other out,  but they are panned left and right on separate channels.
 
What we need now for a stereo image is a center reference. So a mid microphone is added.  It can be any pattern but is traditionally cardioid.  Since it is panned center, it occurs on both left and right channels equally.  Now anything that is similar on the left and center is equally canceled out on the right.  And anything that is similar on the center and right is equally canceled out on the left, resulting in a stereo image.  
 
Hope that makes sense.
 
MS was the very first stereo experiment Alan Blumlein divined.  Created before there was even a stereo playback format or stereo mixers.  Quite ingenious.  

mike_mccue
You can use Channel tools to do something like this:
 

hint: Right click view image in new tab to see the image at full size.
 
You can put effects in the bins of the mid or side bus.
 
There are other free Mid Side decoders. Voxengo has a good one called MSED.
 
Although this routing is easy to do, you may find that any FX with built in mid side processing saves a lot of time and routing and so they may be preferable.
 
best regards,
mike

I get it now. Thanks for this. I think I dimly remember seeing this a long time ago, but I've only recently gotten comfortable enough mixing to add another tool to the arsenal.
 
Regards,
Dan
 

The King or the Holding Company*?
 
 
 
 
 
 
 
 
 
 
 
*Geezer humour
 
 

King!
Big Brother is one of the 60's acts I never saw live.
I WAS mere inches from Janis once, she was driving that cool Porsche the Fool had painted for her.
But that is another story...
T

A correlation meter (also called a phase meter) shows how different the left and right channels are from one another.
 
If both sides are exactly the same (mono), you can say that they are fully correlated, having a correlation ratio of 1:1, or a correlation factor of 1. If both sides are completely different, they are said to have a correlation of -1. A correlation meter reads from -1 to 1, from fully uncorrelated to fully correlated.
 
Real mixes bounce around between 0 and 1, showing that the L-R differences are varying, as you'd expect them to be. Correlation meters have persistence, meaning instantaneous values stay onscreen awhile so you can see the accumulated range of values over the past N milliseconds. The wider the range of values, the wider your mix is going to sound. A mix that sticks over to the -1 side has polarity problems and is not mono-compatible.
 
A goniometer (sometimes called a vectorscope) is a variation on the same idea, except that it displays a Y axis in addition to the X axis of a correlation meter in order to add amplitude into the information. You use it the same way, except that a nice wide mix will have an oval shape, and a mono mix will show as a vertical line. It also has the advantage of showing L-R balance, although if you have two ears and two speakers you've probably already got that covered.
 
 

^

I've been in the middle of issues? And I've been on the side... I'd rather be on the side? Things can get bumpy in the middle.