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M/S EQ and Phase Equalizer Plugins
Old 6th August 2014
  #1
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Midnight Oil Audio's Avatar
 

M/S EQ and Phase

Hello all, just a quick question here for those more experienced.

When I bring in a track to 'pseudo' master, I use PRO-Q and have wanted to play with the M/S function to see if I can clear some of the low end from the sides which keeping the mid intact. Whenever I even engage the M/S mode, my phase seems to go bonkers and I lose all semblance of panning stability.

By that I mean, if I have a guitar panned hard L, and I engage the M/S mode on the 2 buss, and drag a HPF up to 100hz for the side channels, suddenly I have some hard panned L guitar also showing up in the right channel. Any idea's why this is?


*edit: One thing I hadn't thought about is the the linear phase mode on this EQ. I wonder if its necessary to use it in these situations.
Old 7th August 2014
  #2
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?
Old 7th August 2014
  #3
Well on Pro Q when u Switch to M/S Mode, u should also select on the Band itself if you cut the M or S. If you doing this already then yeah, its weird..
Old 8th August 2014
  #4
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Quote:
Originally Posted by the unik View Post
Well on Pro Q when u Switch to M/S Mode, u should also select on the Band itself if you cut the M or S. If you doing this already then yeah, its weird..
Yeah I am. Im going to try and make a short video tonight to demonstrate what Im seeing.
Old 8th August 2014
  #5
You simply can't encode an arbitrary stereo signal to Mid/Side. In fact, it's the wrong term. M/S is a microphone technique.

Just try it out. With a stereo signal, the resulting Sum DOES NOT represent the "middle" stereo image. And the stereo difference DOES NOT represent the stereo sides (although a million companies try to make you believe that it works like this, Mid/Side still a stupidly wrong metaphor for the process).

Take a mono sound, pan full left. Now listen to the "MID" channel => it still contains the hard panned sound. In other words, the "M" does not represent the center stereo image. Not at all.

accordingly, "S" does not represent the stereo side event, it describes the stereo width of the sum channel at a certain point in time (!).

So, as soon one introduces whatever form of delay between the sum channel and the difference channel, you are effectively de-correlating the stereo width information from the "meat" (the sum). In other words, the stereo image totally breaks and can result extremely weird effects. This also explains why compressing the "S" channel doesn't make much sense from the musical point of view, it really destroys the natural stereo poositioning.

M/S is totally overrated and most of all: misunderstood.
Old 8th August 2014
  #6
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Thanks for the response, Fabien. I have always had troubling results when trying to utilize M/S processing (hence my sig) but I recently wanted to try out a simple HPF on just the "side" info to clean up the low end. After watching one of the Fab-Filter tutorials, they made it look so simple, I thought, "I must be missing something". Indeed it seems I still am.
Old 8th August 2014
  #7
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That is darn good information FabienTDR, appreciate it!
Old 8th August 2014
  #8
Old 9th August 2014
  #9
Quote:
Originally Posted by FabienTDR View Post
You simply can't encode an arbitrary stereo signal to Mid/Side. In fact, it's the wrong term. M/S is a microphone technique.

Just try it out. With a stereo signal, the resulting Sum DOES NOT represent the "middle" stereo image. And the stereo difference DOES NOT represent the stereo sides (although a million companies try to make you believe that it works like this, Mid/Side still a stupidly wrong metaphor for the process).

Take a mono sound, pan full left. Now listen to the "MID" channel => it still contains the hard panned sound. In other words, the "M" does not represent the center stereo image. Not at all.

accordingly, "S" does not represent the stereo side event, it describes the stereo width of the sum channel at a certain point in time (!).

So, as soon one introduces whatever form of delay between the sum channel and the difference channel, you are effectively de-correlating the stereo width information from the "meat" (the sum). In other words, the stereo image totally breaks and can result extremely weird effects. This also explains why compressing the "S" channel doesn't make much sense from the musical point of view, it really destroys the natural stereo poositioning.

M/S is totally overrated and most of all: misunderstood.
Correct, and you can better understand what "Mid/Side" stands for if you look at the Original Microphone technique, as shown in this link for exemple :

Microphone practice - Wikipedia, the free encyclopedia

To say M is the "Center" and S are the "Sides" is incorrect, but an easy description in a "commercial" way I guess

So this would mean, maybe, that ur Guitar hard pan Left is not a mono signal but a stereo signal instead (recorded like that ?). Wich start to produce weird effect when you start touching the Side Signal...something like that
Old 11th August 2014
  #10
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Quote:
Originally Posted by the unik View Post
Correct, and you can better understand what "Mid/Side" stands for if you look at the Original Microphone technique, as shown in this link for exemple :

Microphone practice - Wikipedia, the free encyclopedia

To say M is the "Center" and S are the "Sides" is incorrect, but an easy description in a "commercial" way I guess

So this would mean, maybe, that ur Guitar hard pan Left is not a mono signal but a stereo signal instead (recorded like that ?). Wich start to produce weird effect when you start touching the Side Signal...something like that
I had this particular instance of Pro-Q inserted on the 2 buss. Maybe if I insert it on the GTR buss? Doesn't seem like it'll make a difference. I know Im doing something wrong, just not sure what yet.
Old 15th August 2014
  #11
As an experiment, maybe try testing the plug-in on some other mixes - even some commercial releases - to eliminate the possibility that it's something about the mix that's reacting strangely to MS processing. I say this because once I had a client who's mixes behaved similarly to what you describe, but it never happened to me before or since. I still don't know why, but it had to be something in his mixes... He was using a digital porta-studio FWIW...
Old 12th October 2014
  #12
AFAIK, the only reason engineers started using MS in mastering was to compensate for the slight difference signal paths had in mono or stereo EQ's due to component tolerances ....for example capacitors could have a tolerance of up to 20%...same for potentiometers...
Old 13th October 2014
  #13
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Hello Fabien,
that sounds interesting!
But i think, you can apply m/s to any stereo situation, not only microphone recordings. Why shouldn't you apply the exact same procedure (encoding&decoding) to a regular stereo file when the process is calculated properly?

Quote:
Originally Posted by FabienTDR View Post
You simply can't encode an arbitrary stereo signal to Mid/Side. In fact, it's the wrong term. M/S is a microphone technique.
Old 13th October 2014
  #14
Quote:
Originally Posted by cemski View Post
Hello Fabien,
that sounds interesting!
But i think, you can apply m/s to any stereo situation, not only microphone recordings. Why shouldn't you apply the exact same procedure (encoding&decoding) to a regular stereo file when the process is calculated properly?

OK, I'm not Fabien but I'll try to explain...First of all, M/S is not a stereo situation... That's were the confusion starts.

Second, as long as you just encode and decode it's OK. But I presume you want to process like EQ for example. Thing is, the decoding process needs both Mid and Side audio to recreate the stereo file. As soon as you start processing for example just the Mid audio, it will have effect on the side material as well during the decoding process. Basically, when processing the Mid audio your processing a whole lot more....especially when it's a lot of processing.
Old 14th October 2014
  #15
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The only way to EQ MS is to use linear phase, to avoid the problem of phases recombining out of place.
Old 14th October 2014
  #16
cemski, as Radiance already mentioned, M/S microphony is typically about tracking a perfectly centred source in addition to its ambient information. As such, the resulting M/S signal does typically not contain hard panned stereo events. And this restriction is the reason why in this specific case (and only in this case), the metaphor Mid vs Side really makes sense. As soon hard panned content comes into play, the metaphor breaks.
Old 14th October 2014
  #17
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Quote:
Originally Posted by FabienTDR View Post
cemski, as Radiance already mentioned, M/S microphony is typically about tracking a perfectly centred source in addition to its ambient information. As such, the resulting M/S signal does typically not contain hard panned stereo events. And this restriction is the reason why in this specific case (and only in this case), the metaphor Mid vs Side really makes sense. As soon hard panned content comes into play, the metaphor breaks.
Sorry FabienTDR, this is not correct. A M/S mic array captures directional cues just like any other coincident mic technique. Likewise, M/S processing can be applied to any stereo signal.

Hard panned content arises when the M signal has equal amplitude as the S signal. When they share the same polarity, the signal is sent 100% to the left speaker. When they are opposite polarity, the signal is sent 100% to the right speaker.
Old 14th October 2014
  #18
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Quote:
Originally Posted by PyneBoxx View Post
By that I mean, if I have a guitar panned hard L, and I engage the M/S mode on the 2 buss, and drag a HPF up to 100hz for the side channels, suddenly I have some hard panned L guitar also showing up in the right channel. Any idea's why this is?
By putting a HPF up on the side channel, you're making the low frequencies mono, you're not making them go away. If you want to attenuate low frequencies on the left channel, you need to HP the left channel, then but guess what happens to your kick and bass guitar?

This is really stuff that should be solved in the mix.
Old 14th October 2014
  #19
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Quote:
Originally Posted by OpusOfTrolls View Post
The only way to EQ MS is to use linear phase, to avoid the problem of phases recombining out of place.
Unless, like, you prefer the sound of minimum phase EQ. Point me to something that says IIR EQ "recombines out of place"?

Does this mean that phonograph mastering engineers couldn't narrow the lows on the way to the lathe prior to the advent of digital linear phase EQ?
Old 15th October 2014
  #20
Quote:
Originally Posted by 2pulse View Post
Likewise, M/S processing can be applied to any stereo signal.
Of course it can. The point of my posts was that it is important to understand the meaning of sum and difference. The terms mid and side are misleading in the case or arbitrary stereo.

BTW, how do you capture two signals coming from the front, both having perfect opposite polarity with a M/S setup?

You can't. The system will record some ambient garbage, but loses a huge part of the information. Try to MS de-code this signal and you'll find out that something is missing. M/S microphony is absolutely not equivalent to LR microphony.

And accordingly, there's no such thing as true M/S encoding. Typical M/S recordings feature a strong center image and no anti-phase at all - they can't capture anti-phase (given an accurate M/S setup and low amounts of reflection). That's a relevant difference, believe it or not.
Old 15th October 2014
  #21
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Quote:
Originally Posted by FabienTDR View Post
Of course it can. The point of my posts was that it is important to understand the meaning of sum and difference. The terms mid and side are misleading in the case or arbitrary stereo.

BTW, how do you capture two signals coming from the front, both having perfect opposite polarity with a M/S setup?

You can't. The system will record some ambient garbage, but loses a huge part of the information. Try to MS de-code this signal and you'll find out that something is missing. M/S microphony is absolutely not equivalent to LR microphony.

And accordingly, there's no such thing as true M/S encoding. Typical M/S recordings feature a strong center image and no anti-phase at all - they can't capture anti-phase (given an accurate M/S setup and low amounts of reflection). That's a relevant difference, believe it or not.
M/S with a figure-8 for the mid, which is a perfectly commonplace implementation. Any direct event that arrives from 45 degrees off-axis will decode as hard-panned, and anything more than 45 degrees and less than 135 degrees off-axis contains antiphase, with 90 degrees being pure antiphase.
Old 15th October 2014
  #22
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To expound on that: In the scenario of M/S with a fig-8. When sound arrives at 45 degrees to the right of the array, it's captured equally by the mid mic and the negative lobe of the S mic, thus you have perfect antiphase signal. When decoded, that signal is only heard from the right speaker.
Old 19th November 2014
  #23
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BOMI's Avatar
Hello everyone, I was wondering if anyone can give advice on the use of gml 8200 and 8900 gml insert mid side. Anyone know how to behave these 2 pieces of hardware?
Thank you and sorry for my English.
Old 20th November 2014
  #24
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Quote:
Originally Posted by mollyer View Post
Hello everyone, I was wondering if anyone can give advice on the use of gml 8200 and 8900 gml insert mid side. Anyone know how to behave these 2 pieces of hardware?
Thank you and sorry for my English.
Works fine as it's dual mono.
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