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M/S Processing for non m/s sources

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noahbickart:
Hi everyone:

As I've been thinking about modified PAS and OMT techniques, and doing more multi-microphone recordings, one of the things I'm thinking more and more about is the degree to which a good tape depends on the right mix of direct and reflected sound.

We set up our microphones arrays in such a way to provide a good balance between the “dry" direct sound from the PA and "wet" sound of the room. If done well, yay!! If not, well try again.

But there's an easy way to adjust this stuff in post, by using a M/S plug in on a Stereo L/R signal. With the Magic of modern DAW plugins, there's no need to convert to M/S first.

So, too much ambience/audience chatter? Decrease the S component and/or bump up the M. Recording too Monoish? Decrease the M and/or increase the S.

Here are some great resources:
https://klanghelm.com/contents/products/VUMTdeluxe/VUMTdeluxe.php (This is what I use, as the channel knobs can be L/R or M/S)
https://www.voxengo.com/product/msed/
https://hofa-plugins.de/en/plugins/4u/

**edit to add more resources:**
Here's a good free parametric eq which allows for different EQ setting for M and S:
https://www.ikmultimedia.com/products/trclasseq/

If you prefer a free graphic, the same folks who do MSED make this:
https://www.voxengo.com/product/marvelgeq/

Here's a free VST which does M/S level, eq & dynamics in a single plugin:
https://www.soundonsound.com/news/internet-co-release-free-ms-eq-comp-plug

I find the toneboosters eq to be really easy to work with and is only ~$35:
https://www.toneboosters.com/tb_equalizer_v4.html

Gutbucket:
Any stereo file can have it's balance re-adjusted in this way. IME lots of live recordings made with narrowly spaced and angled microphones can benefit from some adjustment.  Just listen carefully to determine if it is doing what you want without introducing other problems. 

It can sometimes be helpful to think of this in terms of manipulating the basic Sum/Difference balance between the two channels rather than Mid/Side.  Mid/Side representing the higher-order categorization of the sum and difference components.

And if you want to get really fancy, you can apply inverse EQ curves to the Sum and Difference channels so as to adjust stereo width in different amounts by frequency, without changing the overall frequency balance.  Probably easiest to do that by adjusting EQ of the difference channel to obtain the width result you want (typically by emphasising the low frequencies in the Side channel), then EQing the re-combined output to whatever sounds timbrally appropriate overall.  Otherwise, there are plugins which do that for you, providing controls for varying width by frequency.

noahbickart:
Isn’t another way of saying "mid," "sum" and side another way of saying "side," "difference?"

Gutbucket:
Yes, just different terms for the same thing:
Sum = Mid = L+R
Difference = Side = L-R (and/or R-L)

This past weekend I was considering running a setup using two sideways-oriented Mid/Side pairs, which would have decoded as Front/Back rather than Left/Right.  In talking about this with Nick D over the phone it became confusing describing a sideways-facing Mid and forward-facing Side. 

wforwumbo:
All phenomenal information in this thread so far.

First thing I have to say: don't trust that "Nick D" character. He has no idea what he's talking about.

Mid/side processing is also useful for equalization, especially on stereo equalization. Some EQ plugins - I'm pretty sure the default Logic EQ plugin will do it, and I want to say Fab Filter Pro-Q 2 will as well - will also encode/decode and mix in M/S for you as well. Particularly useful if you want to address mid/side differently, and still have the information presented in traditional L/R.

What's interesting to me about M/S, has to do with coherence. The "mid" channel is the amount of "coherent" signal between left and right, while "side" is about "incoherent" or "decorrelated" sound. Practically speaking, this is similar enough (if not identical) to using "sum/difference" terminology - where the waveform aligns in sum it reinforces, and where it does not it cancels.

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