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Author Topic: XY Greater than 90 Degrees?  (Read 6785 times)

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Offline vantheman

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XY Greater than 90 Degrees?
« on: January 17, 2020, 02:57:32 PM »
I've created a little stealth rig that will let me pretty much leave it in plain sight in many cases. I don't keep it on my person. But in its current implementation, it basically demands XY config for the gear to be properly concealed. In most cases I'm pointing at one stack.

Frankly I don't mind a slightly narrower stereo image, but I'm also new to this and don't want to be kicking myself later if a few simple tweaks could have yielded better results on my earliest recordings. I had been hypothesizing about XY configs at greater angles than 90 when I saw a XY 120 option on the Stereo Mic Visualizations page: http://www.sengpielaudio.com/Visualization-XY120.htm

So I guess wide XY configs are a thing after all. With the small footprint of XY, and it seeming like a forgiving config, I would have thought that it would be more popular than it seems to be for recording stacks, up there with ORTF for example.

The question is what are the drawbacks of wide XY?
« Last Edit: January 17, 2020, 03:51:33 PM by vantheman »
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Offline dyneq

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Re: XY Greater than 90 Degrees?
« Reply #1 on: January 17, 2020, 03:51:54 PM »
Check out this excellent visualization tool: http://www.sengpielaudio.com/Fragen08.htm

You can plug in whatever mic type, angle and spacing you like and see how it affects the stereo image. Keep in mind that this isn't completely applicable because most of aren't recording an orchestra open where we can set up wherever we want, etc. Still, it does help to understand what will happen when you change each parameter.

I ran XY once, and didn't care for the result. It's useful if you think you might sum to mono, but I have otherwise stopped using it. For less than open recording, I have moved to Gutbucket's PAS (point at stacks) method here: https://taperssection.com/index.php?topic=167549.0

Offline billydee

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Re: XY Greater than 90 Degrees?
« Reply #2 on: January 17, 2020, 05:45:13 PM »
I use this AT2022 stereo mic from time to time which has both a 90 and 120 degree X-Y setting. Have only used the wide setting a couple times as part of a matrix recording with soundboard feed. Someone on the board here (don't remember who) advised using the wide setting when possible.
https://www.audio-technica.com/cms/wired_mics/a2c67abf775c91bf/index.html

Offline heathen

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Re: XY Greater than 90 Degrees?
« Reply #3 on: January 17, 2020, 06:03:29 PM »
The question is what are the drawbacks of wide XY?

It depends on the specific scenario in which it's used.  Depending on the circumstances, there might not be any drawbacks...in fact it might be the best configuration for that scenario.  I know this is a wishy-washy response, but it's true.  At the end of the day there is no single correct microphone configuration for every circumstance.  Sometimes ORTF is best, other times XY is best, etc.

That said, if you find yourself often recording in the same sort of circumstances (for example, always on stage, or always stack taping, etc.) you might find one configuration that gives you good enough results each time that you can use it as your default.  That's going to require experimentation, though, because no one can say what your ears/brain will prefer.

If you think wide XY will be the most convenient to implement, go ahead and give it a shot.  I'd bet that, barring some equipment problem, worst case scenario your recording will at least be listenable.  When you listen back to it, think about what it may be missing that you've heard in recordings you like.  Once you identify that you can go back to the drawing board and determine if you can correct those deficiencies, and if so what the best way to correct them will be (you might even be able to correct them in post without changing your configuration, for example with EQ or software that allows you to adjust the stereo image).

XY is just as valid as any other microphone setup, in a vacuum.  When it comes to real-world application, though, it's all going to depend on the specific circumstances and what you want to hear in your recordings.
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Offline Gutbucket

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Re: XY Greater than 90 Degrees?
« Reply #4 on: January 17, 2020, 08:01:05 PM »
X/Y angle is a tradeoff between center clarity and ambient openness and width.

X/Y = coincident arrangement, meaning both mic diaphragms arranged so as to be as close together as possible, typically one above the other in the same vertical plane.  X/Y does not specify any specific angle, 90 degrees is simply the most typical angle used.

Larger X/Y angles with cardioids sound more open, which somewhat helps counter what many folks don't care for in the sound of the configuration.  Somewhat larger angles help when using cardioids in comparison to tighter patterns like supercardioids and figure-8's.  If only using a single X/Y pair of cardioids for concert recording (rather than close mic'ing an instrument or something) I'd generally default to wide angle such as 120 rather than 90 degrees.. all else being equal.  With supercards I'd go somewhat narrower, and with figure-8s I'd default to around 90 degrees, which is Blumlein configuration, or even somewhat less.

If mixing with other stuff that is wide and ambient (like a pair of spaced omnis) a somewhat narrow X/Y angle like 90 degrees can work well to solidly fill the center.  The open, ambient stuff being provided by the other source.  If mixing with something that is mostly direct sound without much ambience (like matrixing with a SBD) a wide angle works better to provide more open sounding ambience, but I'd generally recommend a spaced configuration for that if possible.

All mic configurations are a trade off. X/Y tends to be good at tight phase-correlated direct sound, while spaced configurations are generally better at ambient reverberant sound portrayal.
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Offline vantheman

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Re: XY Greater than 90 Degrees?
« Reply #5 on: January 18, 2020, 12:24:49 PM »
This is really interesting, thanks. I think I’ll continue down the XY path for stealth for the time being. But I’ll open it up to 120 rather than 90. I really can’t wait to get into an open taping scenario to try other configs, I just tend to hit more shows that aren’t.
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Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #6 on: January 18, 2020, 02:23:55 PM »
I'd just like to confirm that X/Y = "coincident" as opposed to A/B ("spaced"); it's as simple as that. All that's implied is that the two microphones will have the same directional pattern as each other. There's no implication of what that pattern is, or the angle between mikes.

If you travel along the spectrum of first-order directional patterns--from omni at one end through cardioid in the middle to figure-8 at the other end--the farther you go toward figure-8, the narrower the front pickup pattern becomes. And the narrower the pickup pattern, the narrower the angle between mikes needs to be so that you get smooth, continuous coverage in the combined stereo pickup.

I think pretty much everyone knows that for figure-8 microphones, the angle that gives you that smooth coverage is 90° (the so-called "Blumlein" arrangement). That's a good point of reference to keep in mind. By comparison, if you take microphones with wider front pickup patterns and set a 90° angle between them, you'll get a more and more center-heavy pickup. The two channels will have more and more material in common between them, i.e. the recording will be more nearly mono, and correspondingly less spacious, less qualitatively responsive to the room's characteristics, AND less specific as to localization of individual sound sources.

Even with supercardioid microphones you can go well beyond 90° and still have smooth, continuous coverage, thereby getting a much more interesting, positionally definite, and spacious-sounding stereo recording. The idea of using 90° for X/Y cardioids as a "cookbook recipe" is just sad in my opinion; a much better starting point would be 120°, and in many situations one might well go beyond that angle, depending on the room, the recording distance and the particular microphones.

It's especially important, I think, to use loudspeaker playback as the basis for deciding this, rather than headphones, unless you're recording for the purpose of headphone listening specifically. With practice you can learn to correlate the two somewhat, and make decisions via headphones as to what angle between microphones might sound best over loudspeakers--though it's never the same as what sounds best through the headphones themselves, and I still get this wrong occasionally.

--The one virtue of X/Y cardioids at 90° is that they pick up a very wide angle directly--essentially the entire front hemisphere. When your microphones are only a few feet from multiple or very wide sound sources, that can be a good thing. Recorders such as the Zoom units, or the Røde and Sony stereo mikes that have X/Y cardioids built in at 90°, are sold largely to people who want to record meetings or group discussions at relatively close range. Plop the recorder or the microphone down on the desk or table that people are gathered around, and it will pick up 180° nicely, with significant pickup still beyond that angle.

When you're a music taper and you mostly hang out with other music tapers, it's easy to forget that we're only one sliver of the market, and that the equipment available to us is often manufactured for speech pickup applications that have different requirements from ours. I've been on both sides of this, and any time I've written marketing copy where I could say, "This microphone has often been used successfully for ... " without lying absolutely, I've done so, or at least felt the pull to do so. But as someone who buys and uses this equipment, I try to be more critical of how things are marketed, and not rely too heavily on anyone else's conscience.

So if you keep seeing equipment with cardioids fixed at 90°, don't let that image seep too deeply into your visual cortex; use your ears instead.

--best regards
« Last Edit: March 28, 2020, 03:13:53 PM by DSatz »
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Offline Jammin72

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Re: XY Greater than 90 Degrees?
« Reply #7 on: January 18, 2020, 02:47:14 PM »
I don't recall where I heard this but in my head I had a rule that I liked for figuring out the optimal angle for the capsules themselves, not necessarily the subject material or room.  Double the included angle of the capsules at -3dB sensitivity at 1K.  It led me to run my akg's with larger than 90 deg included angles when i was running primarily XY.  For indoor nasty sounding venues, it doesn't get you a lot to go more than 90 deg in my personal experience.  But in nice sounding venues or outdoors it's worth a shot.   I ran this show X/Y at 110 deg. 

https://archive.org/details/aru2004-10-22.flac

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Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #8 on: January 18, 2020, 03:06:26 PM »
jammin, that makes sense, because the -3 dB point is where the microphone is down to 1/2 its power output relative to 0°. If all microphones had uniform polar response at all frequencies across the spectrum (i.e. if their directional patterns were completely independent of frequency), that would no doubt be the way to figure it. But in practice, such uniformity of pattern doesn't exist--especially with most cardioids, although small, single-diaphragm condensers come closest to it.

Dual-diaphragm cardioids become more or less wide cardioids at low frequencies (which is really bad for spaciousness when recording X/Y), and all but the smallest capsules of any pattern tend to narrow their pickup at high frequencies. So the very worst case is coincident large-diaphragm, dual-diaphragm cardioids--which unfortunately includes all large-diaphragm stereo microphones that I'm aware of--and the common use of such cardioids at 90° is sad IMO. Below about 100 Hz such recordings are essentially mono.

But this way of looking at things entirely backs up the idea behind "Blumlein" technique, since the -3 dB point for a figure-8 is indeed 45° off-axis--and when each microphone is 45° from center, then the total angle between them will be 90°, Q.E.D. (which, as my ex-wife once said, is Latin for "So there!"). And good figure-8 microphones often approach the ideal of "the same pattern at all frequencies" more closely than other patterns do.

Incidentally, for a mathematically correct cardioid the -3 dB point is a little more than 65° off-axis, which means that 131° (!) would be the optimal starting point for good small, single-diaphragm cardioids; as I said earlier, if you start out at 120°, you may sometimes decide to go even farther apart.

--best regards

P.S.: JFTR, for theoretically pure hypercardioids the angle between mikes would be 105° while for pure supercardioids it would be 115°, but I don't know of any such actual microphones; most microphones that are sold as either pattern are actually somewhere in between--usually more toward the supercardioid side, since that tends to sound less "thin".

P.P.S.: JFTR as far as I'm aware, Drs. Williams, Sengpiel, Wittek, and others who've worked out computational methods for recommended stereo miking setups all base their math on the idealized patterns that microphones may have at 1 kHz. If your microphones have significantly non-uniform directional patterns at different frequencies, all bets are off. The whole theory of coincident stereo recording is based on the assumption of uniform polar patterns across the audio range.

This is why I maintain that it's NOT merely a matter of individual taste or personal preference as to whether we use large vs. small microphones, or single- vs. dual-diaphragm microphones, for coincident and closely-spaced stereo recording--and incidentally it's also why professionals don't, as a rule, use pairs of shotgun microphones for stereo recording, though they might well use a shotgun as the center mike for M/S stereo.
« Last Edit: January 19, 2020, 04:23:27 PM by DSatz »
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Offline vantheman

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Re: XY Greater than 90 Degrees?
« Reply #9 on: January 18, 2020, 05:15:26 PM »
The idea of using 90° for X/Y cardioids as a "cookbook recipe" is just sad in my opinion; a much better starting point would be 120°, and in many situations one might well go beyond that angle, depending on the room, the recording distance and the particular microphones.

Exactly. You read up on mic patterns, XY is basically defined as a coincident pair specifically at 90 degrees. Which doesn't really make much sense if you think about it for a minute, even a noob taper like me. I think what I may do next time I take the rig out is try something like 110, which will still give me some margin for error if my aim is not true, but give me a wider image than 90.
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Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #10 on: January 18, 2020, 09:28:23 PM »
I don't think I've ever seen "X/Y" defined with any particular microphone pattern or included angle, as long as the mikes are effectively coincident, both having the same directional pattern (not omni), and not both facing the same direction as each other! 90° is a very common given example--too common in my opinion--but I would seriously dispute that it's a legitimate part of the definition as such.

All my recording textbooks are currently in storage, unfortunately. But https://en.wikipedia.org/wiki/Stereophonic_sound#X-Y_technique:_intensity_stereophony for example seems close to what I would call the consensus explanation, or at least the way it was often taught in the past (see the P.S. below if you really want to dive into some linguistic weeds).

--best regards

P.S. regarding "intensity stereophony": As a translator I avoid the German and French word "Stereophonie" as much as I can. I don't think that the cognate term "stereophony" ever really made it into comfortable English usage; the strong accent on the third syllable (a short vowel, no less), and to some extent the "-phony" ending, are just too odd and distracting.

These days, at least in the German-speaking part of Europe, there is also some objection to the continued use of the word "intensity" in this context. This objection was first raised by the late Prof. Eberhard Sengpiel, and I recall agreeing with it when I heard it spelled out, though I no longer remember the details for certain, sorry to say. Maybe it was that "intensity" is analogous to the voltage that a microphone puts out, while sound power is what really matters. (Hey, I promised you obscurity ...)
« Last Edit: January 18, 2020, 09:46:00 PM by DSatz »
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Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #11 on: January 18, 2020, 11:00:29 PM »
I'll go on a tangent.

Take a pair of coincident cardioids at 180º and mix them in mono, what do you have?  A dual diaphragm mic set to omni, and turned 90º. 

Make that a dual output mic, of which there are a few, pan the two outputs opposite and it's technically the same pattern as mid-side with an omni and a figure 8, mixed 50/50.  Introduce that concept to many engineers, and an argument will ensue, with profuse denials. 

As DSatz said, uniformity of pattern with respect to frequency makes all the difference. 

I ran the pattern experiment on the above dual output scenario once with an MKH 800 Twin. 
1) the two outputs hard panned.
2) an omni pattern created, and a figure 8 pattern created, then combined in a MS matrix at 50/50.
result: both sounded the same. 
« Last Edit: January 18, 2020, 11:23:42 PM by EmRR »
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Offline noahbickart

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Re: XY Greater than 90 Degrees?
« Reply #12 on: January 18, 2020, 11:03:26 PM »
Speaking of mid/side, perhaps it's greatest advantage over x/y is that the angle can be changed in post.
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Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #13 on: January 18, 2020, 11:20:23 PM »
Speaking of mid/side, perhaps it's greatest advantage over x/y is that the angle can be changed in post.

Check the paper in this link.  Referred to as 'INTENSITY STEREO RECORDING TECHNIQUES'.  There's a list of advantages and disadvantages for both X/Y and MS. 

https://www.gearslutz.com/board/showpost.php?p=14445763&postcount=6
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Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #14 on: January 18, 2020, 11:37:45 PM »
Thank you all for very nice posts. I have been thinking a long time about xy and mid/side. When we are changing mid/side ratio in post of stereo track of mics in xy, are we changing a resulting angle and directionality of mics? Can we use for example cardiods in xy at narrow angle and then change it in post to virtual hyper cardiods at wider angle?

Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #15 on: January 19, 2020, 12:19:17 AM »
Thank you all for very nice posts. I have been thinking a long time about xy and mid/side. When we are changing mid/side ratio in post of stereo track of mics in xy, are we changing a resulting angle and directionality of mics? Can we use for example cardiods in xy at narrow angle and then change it in post to virtual hyper cardiods at wider angle?

Another great paper to find and look through is Wes Dooley's AES paper about mid-side.  It has pages and pages of equivalent mic patterns.

Control involving both mic pattern and angle is more the territory of ambisonics, and you can get most of that with a native B format array using two figure 8's and an omni, then encode with one of the many ambisonics plugins.  You just won't get the height element of full ambisonics.   You can also create multiple virtual patterns for surround, or if you need a center mic along with a widely angled hyper pair, etc. 
« Last Edit: January 19, 2020, 12:24:58 AM by EmRR »
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Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #16 on: January 19, 2020, 01:59:48 AM »
Thanks EmRR. It is helpful document. I found it on google, here it is:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=2ahUKEwiyw7i1gY_nAhWLEVAKHfT8AigQFjAEegQICBAB&url=https%3A%2F%2Fwww.gearslutz.com%2Fboard%2Fattachments%2Fall-things-technical%2F156765d1265402712-excellent-x-y-stereo-sdc-cardioid-mic-field-use-schoeps-x-y-clone-technique.pdf&usg=AOvVaw0gH9AYQVXAHF2ZnM4y5ipu

It is difficult to imagine it. I just guess the following. We can decompose the directional pattern on an omni and a fig8. So, if we mute mid in xy track, the result are two crossed fig8. And we can decode two crossed fig8 in mid/side as one forward facing fig8 and one side facing fig8 (Fig 2a in the Wes's document). So is the final result side facing fig8? And if we mute side in xy track we get some directional pattern facing forward?

Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #17 on: January 19, 2020, 02:27:38 AM »
I promise this will get to an interesting and useful place after a moment.

Do "kids today" know how stereo FM radio works? FM broadcasting was introduced as a mono-only medium, and then stereo was "grafted on" as a retrofit. The way this was done is very similar in principle to M/S. To simplify somewhat: At the radio station, the left and right program channels are fed into a matrix. One output of the matrix is L+R (the "sum"), while the other output is L-R (the "difference"). The "sum" signal would modulate the station's carrier frequency directly if it was a mono station--as they all were originally, and then there were several transitional years during which only some FM stations were stereo, while all others remained mono and only gradually converted.

If the station was broadcasting in stereo, the "difference" information would modulate a second, somewhat higher-frequency carrier, and the result would then become part of the signal that modulated the main carrier--all happening in real time, analog processing, so that it was really synchronized and simultaneous. Finally, a 19 kHz "stereo pilot" tone was added in at a low-ish but constant level (and possibly a secondary program channel which could be entirely unrelated if present; I'll leave that mess out, though).

A mono receiver simply demodulates the received signal, chops off everything above 15 kHz, and plays that back as mono; no problem.

A stereo receiver demodulates the signal, chops off everything above 15 kHz (which produces L+R a/k/a mono as above), but also checks for a 19 kHz stereo pilot signal. If it's present, the receiver knows to lock onto the secondary carrier (38 kHz above the baseband as I recall) and demodulate that as well, producing L-R a/k/a the difference channel. It then matrixes the two received signals together; (L+R) + (L-R) = 2L, while (L+R) - (L-R) = 2R; and voila, you have the original stereo signal back again.

As this illustrates, ANY two-channel signal--in fact anything that you can stuff into two channels, whether it's the left and right halves of the same program, or two completely unrelated signals (!)--can be matrixed into L+R (sum) and L-R (difference), then transmitted and/or recorded, and finally dematrixed back to the original signals (e.g. L and R) again on the receiving end. So this is certainly true for X/Y microphone signals. But in principle it doesn't even need to be two coincident microphones, or even microphones that are (or were) at the same concert at the same time!

However, if you do use this trick (matrixing / dematrixing) with a coincident (X/Y) pair of microphones that are at the same concert at the same time, then the nice thing about the L+R sum is that it is (if you've set up appropriately and the acoustics gods are with you) a listenable mono signal in case there's a use for that. Conversely, back in the 1950s when recording engineers were first learning to record stereo for FM broadcast and classical record production, they were all experienced as mono engineers (since that's all there was for many years), and M/S allowed them to continue using those skills while producing mono-compatible stereo recordings. This method was used very widely in Europe, while spaced-microphone stereo became the norm in the U.S. due to the influence of Bell Labs.

Back to our world today: Any X/Y recording may be translated (matrixed) to M/S "signal format" and vice versa without limit. You can derive the sum and difference from any X/Y recording, then (if you like) process the M or S channel separately, then recombine them to L/R stereo. I typically like to boost the low frequencies in the "S" channel to improve spaciousness; it doesn't really matter whether I'm starting from an X/Y or an M/S recording, although starting from M/S saves me a processing step.

--Dr. Noah said: > Speaking of mid/side, perhaps it's greatest advantage over x/y is that the angle can be changed in post.

X/Y and M/S are equivalent in principle--just different "encodings" of the same information. There's really nothing that you can do in one that you can't do in the other.

The technique that you're referring to involves changing the overall proportion of M signal to S signal. And when you do that, you not only change the stereo image width, you also change the amount of reverberation in the stereo recording. If you increase "S" in post, it's as if you've time-traveled back and spread your original X/Y microphones farther apart--but at the same time, altered their pickup pattern toward a greater degree of reverberation and a lower proportion of direct sound. You can't have one without the other in conventional M/S <-> X/Y.

In my experience this has been a real limitation; only one narrow range of M-to-S gain ratio settings yields a plausible degree of reverberation for the image width that you get with it. So you can sometimes use this approach to improve an X/Y recording up to a point--but it won't give you independent control over these two important parameters of the recording separately from one another. If you want fully independent control over the stereo image width AND the amount of reverberance in the recording, you need at least three microphones--either "double M/S" as Schoeps calls it (a regular M/S pair plus a separate, rear-facing capsule with its own recording and processing channel) or so-called "horizontal Ambisonics". (Or real Ambisonics, of course.)

--best regards
« Last Edit: January 19, 2020, 09:27:02 AM by DSatz »
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Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #18 on: January 19, 2020, 04:50:04 AM »
Thank you very much David. It is nice from you that you take your time to explain mid-side manipulation. It is very helpful.

I was thinking about a non-standard thing that sounds strange. I have only cardiod and omni mics. If I need to record in xy with more directional microphones, I could use cardiods. I could set narrow angle and then lower mid/side ratio. Probably not a win with cheap microphones. But maybe it would work a little bit. Maybe it would be a small help for hobby taper.
« Last Edit: January 19, 2020, 04:53:41 AM by kuba e »

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Re: XY Greater than 90 Degrees?
« Reply #19 on: January 19, 2020, 09:51:23 AM »
kuba, yes, you could record with coincident cardioids, then afterward matrix to M/S, boost S, then rematrix back to L/R stereo. This could make the recording more interesting and fun to listen to, particularly if your cardioids are single-diaphragm and (preferably) small or small-ish.

(If they're dual-diaphragm, unfortunately you won't have much low-frequency energy in the S channel. That's because the cardioid patterns of dual-diaphragm microphones "widen out" at low frequencies, particularly in microphones that use a shared-single-backplate capsule design; the result is an S channel with attenuated bass, since both microphones are picking up mostly the same stuff at the same time, and the matrix simply cancels it all out.) (Again, forgive me for being repetitious, but this is why I maintain that large-diaphragm, dual-diaphragm cardioids are a poor choice for coincident or closely-spaced setups.)

But there's a limit to how much you can stretch things with this technique and still have it sound natural. Try listening to that S channel signal by itself some time--it's not entirely wonderful sounding, since it contains a large helping of far-off-axis pickup, which in many cardioids can be somewhat "bright and boomy". Boosting it a few dB can be a big help; boosting it many dB, not so much. Past a certain point the stereo playback can start to sound "phasey". Injecting large amounts of the same signal into both channels in opposite polarity isn't a lot better than injecting it into both channels in like (equal) polarity; you never want that component of your signals to become obvious, let alone dominant, in the playback.

All in all it's still best if you can put optimal microphones in the optimal position(s) before pressing the "record" button.

--best regards
« Last Edit: January 19, 2020, 04:21:41 PM by DSatz »
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Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #20 on: January 19, 2020, 12:11:47 PM »
--Dr. Noah said: > Speaking of mid/side, perhaps it's greatest advantage over x/y is that the angle can be changed in post.

X/Y and M/S are equivalent in principle--just different "encodings" of the same information. There's really nothing that you can do in one that you can't do in the other.

In theory, yes.  In practice I find a lot of cases with XY or Blumlein comparing stereo versus collapsed mono (or even a narrowed image) reveals an unhappy loss of high frequency information.  If I'm combining multiple recording passes in the studio and don't know what the client is going to want (insist?) regarding stereo spread, MS is the more reliable path to a sound I'll be happy with anywhere from mono to hard panned stereo.   Same goes for post-processing of 2 track live recordings.    That's my only caveat.  If you're not ever changing width, you don't need MS. 

Back on topic, XY at concerts where XY orientation may be pretty much a PAS situation, XY may win. 

Then as you mentioned, DMS or horizontal Ambisonics (native B format as I called it) give many more options after the fact....cue the dual output mic once more...    Again, ruler flat mics with great pattern control really help both techniques. 
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Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #21 on: January 19, 2020, 02:20:13 PM »
Yes you mean manipulating left/right components vs. manipulating mid/side components. And David means encoding left/right vs. encoding mid/side.

This is for someone who is like me. This discussion was good for me to realize that a pair of directional mics (cards, hypers, blumlein) in XY has always twin in a M/S pair (directional mic + fig8). XY pair has parameters - polar pattern and angle. M/S pair has parameters - polar pattern of mid and mid/side ratio. And there is always possibility to recalculate XY parameters to M/S parameters and replace XY pair with M/S pair and vice versa.  The relationship between XY parameters and M/S parameters is interesting. All can be derived from the fact that each directional pattern can be decomposed into omni and fig 8. So for example it si possible to show when we lower mid/sid ratio of XY pair that it is equal as another XY pair with wider angle and more directional polar pattern.  Of course all this is valid only for theoretical profiles, practice profiles differs. I hope I didn't write it confused or wrong.

Please, do you know whether there is Ambisonic plugin that is able to show how is changing XY pair when we are changing it's mid/sid ratio?

Back on topic, XY at concerts where XY orientation may be pretty much a PAS situation, XY may win. 

Please, XY may win compared to what configuration?


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Re: XY Greater than 90 Degrees?
« Reply #22 on: January 19, 2020, 02:53:52 PM »
Please, do you know whether there is Ambisonic plugin that is able to show how is changing XY pair when we are changing it's mid/sid ratio?

Ambisonics plugs show intended pattern and angle, but won't do anything with a 2 channel MS signal.  I don't know of any MS plugs that show pattern and angle, but there may be one. 

Back on topic, XY at concerts where XY orientation may be pretty much a PAS situation, XY may win. 
Please, XY may win compared to what configuration?

Mid Side, which, depending on the mic, may not have optimal response at the angles of the PA compared to the mics.
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Re: XY Greater than 90 Degrees?
« Reply #23 on: January 19, 2020, 03:34:23 PM »
I think it is equal. If we choose right mid/side ratio of M/S pair we get optimal response at the angles of the PA. We can also control the response outside this two angles. This can be controlled by choosing the right mid/side ratio together with the right polar pattern for mid microphone. It is the same as choosing the right angle and the right polar pattern for a XY pair. It is just entered in a different encoding.

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Re: XY Greater than 90 Degrees?
« Reply #24 on: January 19, 2020, 06:36:10 PM »
I think it is equal.

Not if the treble pattern of the mic is very beamy in nature, it isn't.  You won't get equal results from LDC's. 

'Perfect' mics, yeah, it's equal or close to it. 
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Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #25 on: January 19, 2020, 08:16:05 PM »
EmRR, thank you and yes: One can always translate between X/Y and M/S signals in either direction--but each particular, actual X/Y or M/S setup still has its own particular characteristics. It is a little like the famous line at the start of Tolstoy's Anna Karenina: "Happy families are all alike; each unhappy family is unhappy in its own way."

As an example to clarify this, think of an M/S pair with a shotgun microphone as its M microphone. Shotguns, as we know (or should know) have directional patterns that become increasingly irregular at upper-mid and high frequencies; taken on a broad average, they get narrower than the low- and low-mid-frequency pickup pattern--but at any one frequency above that, they have "lobes" at various odd angles--a rather wild pattern which is ultimately the reason why professionals avoid using them indoors whenever possible. If you make an M/S recording like that and matrix it to X/Y, the equivalent "microphones" of your virtual X/Y pair will have directional characteristics unlike those of any real-world microphone, and of course quite different depending on which frequency above the midrange you consider.

(I am assuming, perhaps incorrectly, that people here are conscious of the ways in which the directional patterns of most microphones vary across the frequency range--with large and/or dual-diaphragm and/or interference-based microphones being the worst offenders, and cardioid being the midpoint on the spectrum that often shares the defects of both extremes rather than escaping them. "He who stands in the middle of the road gets hit by trucks going both ways.")

So I'm not saying that for each X/Y or M/S pair that we could set up with microphones that you or I happen to own, there's an exactly equivalent setup of the other kind that we could also make with microphones that we happen to own (or which even exist at all). There are still reasons to choose particular microphones and particular setups in particular situations!

But matrixing can give you the sum and difference of any two inputs--and if those inputs are a symmetrically arranged coincident pair (X/Y), the outputs will be functionally a mid-side pair of signals (M/S) and vice versa, and you can flip back and forth between the two realms and perform the kinds of processing that belong to each realm.

--best regards
« Last Edit: January 20, 2020, 01:02:38 PM by DSatz »
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Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #26 on: January 20, 2020, 08:11:01 AM »
Thank you all, it is starting to be more clear for me. EmRR, I read the documents you recommended. There is one example of advantage/disadvantage of XY/MS - XY with large angle. The disadvantage of XY with large angle is "the microphones are then mostly addressed from the side which causes the directional properties to be very frequency dependent." And second addition "The directional characteristics of the S microphone are almost ideal since its figure-of-eight polar pattern is almost frequency independent. For that reason the S microphone can record objectively even from the side". I understand this.

Just because of my curiosity - when we reduce the microphone types only to good quality small diaphragm and target only to stereo playback - are there more general practical rules when to choose XY or MS or is there only little difference (except the first case)? In general, in the terms of bass response, is there any advantage / disadvantage?
« Last Edit: January 20, 2020, 08:39:38 AM by kuba e »

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Re: XY Greater than 90 Degrees?
« Reply #27 on: January 20, 2020, 12:21:04 PM »
Generally speaking with SDC's and distance, the closer to omni you are the more bass you have, with less as you pass from cardioid through hypercardioid on to figure 8.    Mics like the MKH30 are the rare 8's with reasonably flat bass, but in comparison to other MKH series mics they are still the thinnest sounding.....until you get up close (within a meter or so) and then they have the greatest proximity effect, and can give more bass than an omni.   So as always, there are interconnected variables. 
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Offline Gutbucket

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Re: XY Greater than 90 Degrees?
« Reply #28 on: January 20, 2020, 12:49:14 PM »
Bringing it on home in the taper world-

Go full on Russian literature and leverage family unhappinesses to personal advantage.. the lovely princess Stereophonie working her influence and charms to singular effect. 

Consider this approach:
Given a relatively distant recording location (aka typical "taper" in a bar positions), start with P.A.S. - that is to say, angle the microphones so that they are pointed directly at the PA stacks, placing those primary sound sources directly on-axis, which also serves to keep on-stage sound sources relatively close to on-axis as well in the shared overlap region.  Then adjust the other variables around that practicality-driven starting-point.   What other variables?  Choice of pickup pattern, choice of spacing between microphones (including no spacing at all for coincident X/Y), and choice of mid/side ratio re-adjustment.  These variables all interact with one another. One is forced to decide on the first two prior to making a recording, but the last needn't be decided upon until after the recording has been made.

Once back at the bat cave, convert Left/Right X/Y to Mid/Side and adjust the Mid/Side ratio while listening to dial in the desirable stereo width.  That Mid/Side representation is converted back to Left/Right prior to listening.  In pointing directly at the PA speakers, the physical microphones have been aimed with the real-world behavior of imperfect polar patterns, taper recording locations in real-world rooms.  One then effectively (re)points virtual microphone patterns to achieve the prefered stereo spread.  This is the pursuit of a best of both worlds approach.

^Taking it a step further, one can EQ Side differently than Mid , affecting stereo width by frequency range, such as boosting low frequency Side content to increase low frequency spaciousness without mid and high frequency content being portrayed as overly wide.

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Re: XY Greater than 90 Degrees?
« Reply #29 on: January 20, 2020, 12:59:25 PM »
As mentioned by others above, when choosing an appropriate mid/side ratio for a straight stereo pair, the range in which an optimal adjustment can be found is relatively small, and when such a mid/side ratio-readjustment is performed on stereo material recorded using non-coincident spaced microphone techniques, the range is typically smaller yet.

Regardless of the nature of the stereo signal, this poses no problem for properly received and decoded stereo FM radio because the encoding and decoding ratio is identical on both ends of the transmission.  There is is no change of overall Mid/Side ratio when the transmission is received correctly.  However, if there is a problem with FM transmission such that the stereo sideband carrier cannot be properly received and only the primary mono band is heard (the monophonic sum of Left and Right, equivalent to a change of Mid/Side ratio to 100:0), there might be issues with comb-filtering in the mono sum of content recorded using non-coincident microphone techniques.

It's not so much Mid/Side verses X/Y (both representing coincident configurations) but coincidence versus non-coincidence of a microphone pair which is a more important differentiator considering how much of a mid/side ratio readjustment one might be able to make without introducing unwanted problems.
« Last Edit: January 20, 2020, 03:33:03 PM by Gutbucket »
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Re: XY Greater than 90 Degrees?
« Reply #30 on: January 20, 2020, 01:53:18 PM »
With regards to adjustment of Mid/Side ratio of an X/Y recording (as well as direct recording in Mid/Side), I think it helps to think of the actual pickup pattern of the physical microphones and the setup angle between them, verses the virtual microphone patterns and angle between them which result from the Mid/Side ratio used.  If the Mid/Side ratio is altered, the virtual patterns and angle will differ from the actual microphone patterns and X/Y angle.

Using the term virtual helps keep the relationship between the physical microphone configuration and the virtual output configuration straight in my mind.

Bringing this back around to the original topic..
I found one of the most interesting things to mess around with when listening back to an ambisonic recording is changing the virtual microphone pattern/angle relationship.  With an ambisonic recording, the stereo output produced is always some virtual X/Y stereo pair. Output can be thought as being a choice between various combinations of a virtual pair of microphone patterns and inclusive angles between them.  What makes it different than Mid/Side in this respect is the inclusion of the omni microphone 3rd or 4 channel which effectively allows one to change virtual angle independently of virtual pattern, and vice-versa.  So one can hear what changing the virtual angle between microphones sounds like while the virtual pattern is held constant.

For example, one can choose a pair of virtual cardioids and play with various angles between them without altering the cardioid pattern.  Alternately one can hold the virtual angle between microphones constant while adjusting the shape of the virtual pickup patterns.

Doing this with "typical taper scenario room recordings" I found I generally ended up gravitating to virtual pickup patterns which landed somewhere between supercardioid and hypercardioid, with a typical inclusive angle of anywhere from around 110 to 120 degrees or so.  With cardioids I needed a 130-140 degree angle in an attempt to achieve a similar stereo-width and ambient-openness, yet the microphones were then typically too far off-axis from the source.   A subcardioid pattern with a 150 degrees or so angle seemed to work better than cardioids most of the time, and I'd frequently find myself going back and forth between virtual super/hypercard-like patterns with a more narrow angle between them and virtual subcardioids with a wide angle between them, homing in on what sounded best.

I ended up thinking a lot about a seemingly inherent "cardioid compromise" that defines the less attractive region between the above points on the continuum of X/Y patterns and angles. A few times I combined the two, using a wider angled pair of virtual subcardioids for low frequencies transitioning to a pair of more narrowly angled virtual hyper-cardioids at high frequencies.
« Last Edit: January 20, 2020, 02:14:22 PM by Gutbucket »
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Re: XY Greater than 90 Degrees?
« Reply #31 on: January 20, 2020, 02:13:19 PM »
^My intention in posting this is not so much as an endorsement of ambisonics, but rather as a way to share what was for me a rather enlightening exploration of the general relationship between X/Y pickup-pattern and microphone angle.  Pretty much the only time I ended up liking a 90 degree virtual angle was with very hypercardioid-ish pattern that approached figure-8. 

Interestingly, I generally liked a somewhat smaller angle than the standard 90-degree specified as Blumlien for crossed fig-8s, sometimes as narrow as 70 degrees.  That helped better define a solid center, yet most of the time overall pickup of crossed-8s didn't provide enough forward sensitivity bias in typical taper scenarios, and something between supercardioid and hypercardioid tended to work better.
« Last Edit: January 20, 2020, 02:27:00 PM by Gutbucket »
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Offline EmRR

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Re: XY Greater than 90 Degrees?
« Reply #32 on: January 20, 2020, 03:17:25 PM »
^ yup to that.
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Offline DSatz

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Re: XY Greater than 90 Degrees?
« Reply #33 on: January 20, 2020, 07:19:49 PM »
^ yup to that as well.

Despite certain ideal properties, in my work it has been rare that Blumlein was the most fitting solution. It has a relatively narrow stereo pickup angle, yet requires closer placement to the sound sources than most other types of setup because of the large amount of room sound that it naturally picks up--the rear lobe of a figure-8 being equally as sensitive as the front lobe, of course. And of course the closer you get to your sound sources, the wider the angle they represent from the microphones' point of view.

--best regards
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Offline vantheman

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Re: XY Greater than 90 Degrees?
« Reply #34 on: February 07, 2020, 05:24:29 PM »
I took the XY 110 rig for a spin last weekend in Las Vegas for Van Morrison. All in all I’m pretty happy with the results, you can check it out here: https://drive.google.com/drive/folders/12u6Kxxg9-95TfLRjAPyYh5BwKnjxkzLg

I was front row balcony dead center in line with the center stack, and you’ll see that the music is pretty center heavy. It’s almost like a M/S recording, so mastering it was pretty straightforward once I realized this, as it harkens back to my MV88 days.

In this case I dropped the low mid range frequencies of the sides by about 6db, in an attempt to reduce the chatter, which isn’t all that bad to begin with. I lost hardly any musical information by doing this, maybe just a tad bit of “air”.

What I’m wondering is, what if anything did I really gain by going with 110 instead of 90? Yes, there is a nice stereo effect with the audience off to the sides, but I found myself wanting more center. Do you find that too? Due to where I was positioned, I only stood to capture one stack anyway.

These are things I’m considering before he comes up to Oakland next week. My approach for those shows will be pretty similar, just thinking about mic angle.
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Re: XY Greater than 90 Degrees?
« Reply #35 on: February 10, 2020, 01:13:03 PM »
Sounds good here, listening on cheap Samsung phone headphones straight out of the computer.

What I’m wondering is, what if anything did I really gain by going with 110 instead of 90? Yes, there is a nice stereo effect with the audience off to the sides, but I found myself wanting more center. Do you find that too? Due to where I was positioned, I only stood to capture one stack anyway.

I suspect the 110 angle helped achieve the "nice stereo effect with the audience off to the sides" aspect you describe. I don't detect any lack of center, but I'm not listening over speakers where I'd prefer to make that kind of critical judgement.

If you plan to re-adjust stereo width in post with a M/S ratio adjustment anyway, you can let the geometry of the recording location relationship to the PA be the biggest influence in determining the X/Y microphone angle. Capture maximum clarity by keeping the microphones angled so that they are relatively close to on-axis from the PA source(s), then adjust virtual angle afterward to achieve the wider stereo effect with the audience off to the sides, but limit the ratio readjustment to the extent that sufficient center clarity and focus is retained.

If you are in a recording position where most of the energy is coming from a single PA stack position in front of you, a narrower (say 90 degree) X/Y angle combined with increasing Side ratio afterwards to achieve a similar perception of width as recording with a 110 degree X/Y angle and no ratio readjustment might be a good bet. 

Just remember to keep both the actual X/Y microphone angles and the ratio readjustments made afterwards within a reasonable range.  This method of optimizing for one aspect when recording, then optimizing for another when mixing afterwards can work quite well until it is pushed overly far.  In order for you to be able to increase either Side or Center contribution later, there has to be a sufficient amount of it in the raw recording ito start with.  If you were to start with a zero-degree X/Y angle because that would place the microphones on-axis with the only significant PA stack located directly in front of you, the recording will have no significant Side information at all, and there will be no Side information captured that you can emphasize later.
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Offline kevinsinnott

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Re: XY Greater than 90 Degrees?
« Reply #36 on: April 06, 2020, 12:19:06 PM »
My short answer is experiment and don't be too concerned about 90 versus 120 XY stereo. These are approximations I'm convinced were chosen mostly to generalize about image based upon some suppositions about how a recording might be made, which would differ completely in most of your applications.

I'm more accustomed to field audio for documentary audio, rather than recording live music, but I'm interested in this topic and otherwise enjoy this site. Historically, there have been lots of theories on stereo mic placement. A look at classical music recording philosophies, including French Radio's ORTF, Holland's NOS, so-called X-Y and Blumlein have gotten attention among sound enthusiasts, but whenever I read interviews with old sound engineers from stereo's early recording days, it's clear those are just a few. Heck, we've never really settled on how far apart speakers should be, or rather some stereo listening guides may have, but given the amount of listening done in automobiles and, particularly headphones, there's obviously no true one-size-fits-all recording methodology. I'm still astounded that after all these years the vast majority of public radio documentaries are done in plain vanilla monaural! BBC seems to have discovered stereo, but recording notes are almost nonexistent. I know a retired BBC engineer, who claims he did a lot of Mid-Side recording, but the shows I hear are all over the place.

I collect stereo microphones. One company who departs from XY slightly is Audio Technica. I own a couple of their mics that feature 120 degrees. The hole in the middle isn't a problem. Some image wavering is and can sound weird if you're, say, recording an interview and the subject wavers back and forth. Otherwise, no problem, and the backdrop is wider, which can be appealing. Sony has issued a number of Mid-Side mics, which allow you to electronically dial-in a soundstage. I find something between 90 and 120 is ideal for most of my purposes. At 120 still no problem. There is some mono incompatibility above 120. My favorite monitor phones are AKG DJ phone with a stereo-mono switch so I can judge summing compatibility in the field. 

Offline datbrad

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Re: XY Greater than 90 Degrees?
« Reply #37 on: April 06, 2020, 06:50:32 PM »
I agree, don't get stuck on angles, unless SRA is a big concern to you. The key trait of XY stereo  is the pure coincidence of the capsules (intensity). When capsules are positioned on the same vertical plane, usually one over the other, there is no comb filtering or phase issues when summed and played back in mono. Since spaced and near coincidence patterns are known to produce audible comb filtering, for decades in traditional broadcast radio, XY was usually favored because it made tracks playable on single speaker radios without loss of fidelity.
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Re: XY Greater than 90 Degrees?
« Reply #38 on: April 06, 2020, 08:18:34 PM »
With wide X/Y angles there isn't really any mono incompatibility or hole in the middle issue in the traditional sense of those terms.  However, because the microphones are pointed further off-axis with respect to centrally located sound sources there is somewhat less sensitivity and possibly less linear response across the center, in combination with increased pickup from the sides and an increase in Side in comparison to Mid information in the resulting recording.

Pushed too far, the center may become somewhat less distinct while the sound arriving directly from the sides and around back becomes louder and more clear.
« Last Edit: February 23, 2022, 01:08:08 PM by Gutbucket »
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Re: XY Greater than 90 Degrees?
« Reply #39 on: February 23, 2022, 12:58:37 PM »
Revisiting this thread a few years later, I would like to add..

In the same way that we can EQ the Side channel of a Mid/Side pair, or an X/Y pair converted to Mid/Side (typically boosting low-frequencies to improve spaciousness), it can be useful to EQ the Mid channel differently from the Side channel.  This will modify the sound of the content dominating the central portion of the stereo image, which can be useful for things like clarifying vocals.

Here's something to be aware of when doing this- Similar to the way that making a Mid/Side ratio adjustment modifies both the virtual pickup pattern of the microphones and the inclusive angle of the pair simultaneously, EQ'ing the Mid and Side channels separately will simultaneously effect both width and level in the frequency range being EQ'd.  If you boost the lows in the Side channel to increase spaciousness you will also be increasing the overall low frequency content of the recording.  Likewise, if you make a boost in the Mid channel to increase vocal clarity, you will simultaneously be narrowing the stereo width in that frequency region.

However, we can use a second EQ instance in L/R mode to re-adjust the overall frequency balance to whatever we want. The combination of using two EQ instances in this way is powerful. For instance, we might make a low frequency boost in the Side channel to increase spaciousness, only to find that the spaciousness is now much better but there is too much low frequency content overall.  We can fix that by making a low frequency cut in the L/R EQ to corrects the overall frequency balance without changing stereo width.  Or, if we have a problem with vocal clarity in the center verses the clarity of audience chatter to the sides, we might boost the Mid channel for improved vocal clarity in the center a bit more than we really want, then correct the overall timbrel change by making a corresponding cut in the L/R EQ.  The L/R EQ brings the timbre of the center part of the image back to what we want, and effectively reduces the same frequency range in the wide portions of the image.  You can work this balance between the two EQ's to your advantage.

Extra credit-
Instead of following the Mid/Side EQ with a L/R EQ to "undo the timbrel change" the same can be achieved in a single Mid/Side EQ instance by applying an inverse curve to the other channel.  If the exact inverse curve is applied to the other channel, only stereo-width/pickup-pattern is altered while overall timbre remains about the same.  That's great if using an EQ which can be set to automatically apply the inverse curve to the other channel, in which case the Mid/Side EQ is pretty much only effecting width, and the difference in timbre of the center verses the sides, while not strongly effecting the overall frequency response of the recording.  Follow that by L/R EQ to fine tune the overall frequency balance as desired.  Cool stuff, however that kind of automatic application of inverse curve in a Mid/Side EQ just a nicety.  It works just as well to first make a regular, non-inverse curve Mid/Side EQ adjustment followed by a L/R EQ adjustment for correcting overall frequency response and adjust the two in an iterative way to achieve the desired result. 
« Last Edit: February 23, 2022, 01:08:56 PM by Gutbucket »
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Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #40 on: March 29, 2022, 04:51:16 PM »
In the same way that we can EQ the Side channel of a Mid/Side pair, or an X/Y pair converted to Mid/Side (typically boosting low-frequencies to improve spaciousness), it can be useful to EQ the Mid channel differently from the Side channel.  This will modify the sound of the content dominating the central portion of the stereo image, which can be useful for things like clarifying vocals.

If you boost the lows in the Side channel to increase spaciousness you will also be increasing the overall low frequency content of the recording.  Likewise, if you make a boost in the Mid channel to increase vocal clarity, you will simultaneously be narrowing the stereo width in that frequency region.

Gutbucket, thank you very much for continuing this thread. I started thinking about it more. I'm just not sure about the equalization. I don't know what is overall frequency balance. Is it sum of left and right channel? Then that would be the mid channel. When we do the eq of side, we should just emphasize the difference in the right and left channel but the overall frequency balance (mid channel) should be maintained.

I was thinking, when we equalize the mid (or side) and add the second eq in the stereo left/right, it's the same result as equalizing only the side (or mid).

I'm confused. Maybe I'm looking at it wrong. I'll think about it more.
« Last Edit: March 29, 2022, 05:10:40 PM by kuba e »

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Re: XY Greater than 90 Degrees?
« Reply #41 on: March 29, 2022, 05:31:29 PM »
Yeah, I'm the thread starter and just saw this recent reply myself. I really want to experiment with that mid/side EQ technique. It hadn't occurred to me but it makes sense. I have a show coming up next week so I'll plan on doing 2 versions so I can A/B them (also using it as practice because I generally suck at EQ).
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Re: XY Greater than 90 Degrees?
« Reply #42 on: March 29, 2022, 06:33:47 PM »
Hi guys, yeah this Mid/Side EQ stuff can be a challenge to wrap one's head around.. let me try to explain it better.

Kuba e-
By overall frequency balance I mean the general frequency balance or tonality of the entire recording.  That would be both Left and Right channels, or both Mid and Side channels in the overall collective tonal sense.

We essentially have 3 variables in play here: Stereo width, the tonality of the center verses the sides, and the overall collective tonality of the recording as a whole.

If we EQ Side only, we affect both width and the tonality of the sides of the playback image differently than the center of the playback image.  If the Mid remains the same as it was before when we do that, we also affect the overall tonality of the recording (say as heard from an adjacent room through an open door, devoid of all stereo imaging).  One way to avoid that overall tonality change is to make a complementary inverse EQ adjustment to Mid which offsets that overall tonal change.  If we do that, the overall tonality of the recording (as heard from the adjacent room) will remain the same, and only the stereo image width will be changed - actually by twice as much as it was when only EQing Side only (in this case of boosting one channel and cutting the other by the same amount, both work together in a complementary way in altering stereo width, while working against and offsetting each other with regards to the overall frequency balance as a whole). 

But unless the Mid/Side EQ is set to do so automatically, instead of carefully EQing the Mid with an exact inverse of the curve applied to the Side, another way of achieving the same thing is to use a Left/Right EQ with the same EQ setting applied to each channel, adjusted so as to "undo" the overall tonality change.. or push it toward whatever overall tonality you want.  This is simpler in practice.  Adjust stereo width (along with center/side tonal balance) with a Mid/Side EQ, and the overall collective tonality of the recording with a separate Left/Right EQ.

Here's the thing- If we EQ either Mid or Side differently from the other, we change stereo width in the affected range- Boosting frequencies in the Mid channel not only emphasizes them across the center, it also reduces their stereo width, while cutting frequencies in the Mid channel not only reduces them in across the center, it simultaneously increases their width. Likewise, boosting frequencies in the Side channel emphasizes them to either side while also increasing stereo width, while cutting them reduces them to either side and reduces stereo width.

It's all about the ratio between the Mid and Side channels in the frequency range of interest, regardless of exactly how that ratio is changed.

Not sure if that helps, but I hope it does.
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Re: XY Greater than 90 Degrees?
« Reply #43 on: March 29, 2022, 07:38:35 PM »
 :coolguy:

I have a stereo mic or two (card patterns @ 100'), and have observed a image improvement since running them that way.  It's like what you can accomplish with a smidgen of Ozone Imager width in post.
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Re: XY Greater than 90 Degrees?
« Reply #44 on: March 30, 2022, 04:38:01 AM »
Thank you Gutbucket! All is starting to be clear to me now. I misunderstood tonality. I mistakenly thought that tonality was the sum of the left and right channels (the mid channel). But now, I realize that tonality should correspond to the sum of the absolute values ​​of the right and left channels. And that's something different. For example, when I sum two identical signals of opposite phase, I get zero. It is mid component. But when I sum the absolute values ​​of these signals, I get a double signal. This could correspond to the tonality.

I am sorry, I look at it more from the view of the numbers. I hope my idea is correct. When I eq for example +2db bass in stereo left/right, the same result is as when I add +2db bass in the side and +2db in the mid. But when I eq +2db bass only in the side component, it will expand the stereo width for bass (it increase the difference between the left and right channels) and also eq stereo image sides by some amount (if I understand right, stereo image sides contain the side and also the mid component, the mid component is zero only when left and right channels are in oposite phase). The tonality influence of the side eq is reduced towards the center of the stereo image because the influence of the side component decrease there. The very center of the stereo image will not be affected, because it is created only by the mid component.

I never realized the tonal influence in M/S editing. But now it reminded me that sometimes when I expanded the stereo image for bass, the center of the recording was cleaned up from bass hum and everything there was more clear. I thought it was because the change in the stereo image, but there's also effect of eq. I will pay more attention to the change in tonality on the sides and center.
« Last Edit: March 30, 2022, 05:12:20 AM by kuba e »

Offline kuba e

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Re: XY Greater than 90 Degrees?
« Reply #45 on: March 30, 2022, 04:59:57 AM »
:coolguy:

I have a stereo mic or two (card patterns @ 100'), and have observed a image improvement since running them that way.  It's like what you can accomplish with a smidgen of Ozone Imager width in post.

Yes, it's similar. Ms for xy is a natural (we change the ratio of the pressure and pressure gradient component of the microphone capsule) and is lossless. It is always possible to change the ratio to the original state. Imager makes artificial adjustments and it cannot be returned to its original state. For xy is the best ms, it is the clearest edit. (The Imager never sounded good to me personally, maybe only very small stereo changes sounded good)
« Last Edit: March 30, 2022, 08:32:29 AM by kuba e »

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Re: XY Greater than 90 Degrees?
« Reply #46 on: March 30, 2022, 10:17:53 AM »
I haven't used the Ozone Imager and am not certain how it works, but most stereo imaging tools convert L/R to M/S, make a Mid/Side ratio adjustment, then convert M/S back to L/R again.  Some of them are mulitband, spliting the frequency range into multiple bands prior to doing that with each band, allowing one to affect a different ratio modification for highs verses mids verses lows, for example.  In that way a multiband imaging plugin is doing something very similar to EQing Mid/Side, only across specific bands rather than as a continuous EQ curve.

Conversion from L/R to M/S and back again without any ratio change made is looses no information.   And if one changes the ratio by a reasonable amount, and leaves that ratio change in place (which is what we are talking about here for the most part), there is no effective loss of signal to noise ratio in the resulting recording..  However if one wanted to revert the modified recording to its original ratio again for some reason, and performs another conversion from L/R to M/S and back to make a ratio modification that is the inverse of the first one, doing so will return the ratio to what it originally was, however the noise floor in whichever channel was reduced will increase by the amount of that reduction.  In practical terms this will rarely matter.  For one thing we could just go back to the original files.. and even if we did want to do this it probably wouldn't be noticeable with reasonable ratio modifications. 

But, think of it this way- If you were to convert from L/R to M/S, then change the ratio to 100% Mid or 100% Side, you are completely eliminating the other channel and there is no getting it back when you convert to L/R again.  Same as if you were to pan a stereo recording all the way Left then record that output, there is then no way to pan back to center again later, you've thrown away all Right channel information by panning fully Left.  Changing M/S ratio or panning (which is changing L/R ratio) by lesser amounts which don't eliminate the other channel completely will reduce signal to noise ratio by the amount of the change if you later undo that change.
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Re: XY Greater than 90 Degrees?
« Reply #47 on: March 31, 2022, 12:26:34 AM »
Thanks all for the super informative thread. Learned a lot reviewing it.
I recorded many shows from '83-'92 using km84i's xy PAS and was pretty happy with the results. Biggest issue was that indoor large rooms often sounded distant and vocals got lost.
I've remastered a few using rx music rebalance and adding more of the vocal stem back into the mix. Good result.
Thinking to try converting to ms and adjusting ratio and then comparing.
Some of those recordings from outdoor venues like the Greek or Frost sound amazing 😀

Thanks again!
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Re: XY Greater than 90 Degrees?
« Reply #48 on: March 31, 2022, 10:32:03 AM »
You are right, I was wrong. Ms is not lossless. I forgot the noise and also the high frequencies. At high frequencies, there will be a phase shift because small gap between the capsules in xy. Maybe it's in higher up 20kHz. I think Imager is widening stereo by phase shift. It can also turn mono into stereo with it's algorithm.

I am still thinking about changing the tonality with ms eq. It's not easy at all for me. I'm sorry, the following is just a theoretical consideration. I am only thinking loudly.

I've probably figured out what confused me. Ms eq can be analyzed using the basic relationship:
left = mid + side
right = mid - side

Eq of mid channel manifests itself equally in the left/right channel. We cant say how much, because left and right are composed of mid and side. Mid eq can be corrected by an additional left/right eq for overall tonal balance. (I would guess that the left/right eq correction will be the opposite of what we used for mid eq. It is because how behave the side eq.) The side eq is a different case. We add side channel to the left and subtract from the right. So the overall tonal balance should be maintained in left/right channel. This would then mean that if we equalize the side, we do not have to make additional adjustments. There is one exception. When the side is louder than the mid (mid - side is negative value, this does not happen in xy, only with a strong ms eq) then the right and left channels are in opposite phases. And overall tonal balance is not maintained.

I would be happy if somebody correct me. We can also look at ms eq from point of view of changing virtual directional patterns and angles. And patterns and angels shouldn't cause a change in tonality on their own.
« Last Edit: March 31, 2022, 10:40:05 AM by kuba e »

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Re: XY Greater than 90 Degrees?
« Reply #49 on: March 31, 2022, 01:00:11 PM »
Easiest just to think of it in practical terms-

Use Mid/Side EQ as a more advanced way manipulating Mid/Side ratio of a coincident pair, by frequency range.  That affects image width and spaciousness.  It will also affect the frequency balance of the center of the image differently than the sides.  Those two aspects are interlinked.

Then use regular EQ to adjust the overall frequency balance (both center and sides together) to whatever you want.

You might go back and forth in an iterative way when adjusting the two EQ instances to home-in on exactly what you want.


To more specifically address your points [my comments below in italics]..
Eq of mid channel manifests itself equally in the left/right channel. [as does EQing the Side channel]

Mid eq can be corrected by an additional left/right eq for overall tonal balance. (I would guess that the left/right eq correction will be the opposite of what we used for mid eq.) [the EQ applied for tonality should be whatever sounds right. If using it specifically to 'undo' some unwanted tonal change imparted by whatever Mid/Side EQ was applied to manipulate the spatial qualities, it will address the tonal changes imparted by both Mid and Side EQ channels]

The side eq is a different case. We add side channel to the left and subtract from the right. So the overall tonal balance should be maintained in left/right channel. This would then mean that if we equalize the side, we do not have to make additional adjustments. There is one exception. When the side is louder than the mid (mid - side is negative value, this does not happen in xy, only with a strong ms eq) then the right and left channels are in opposite phases. And overall tonal balance is not maintained. [This is incorrect.  Side channel has opposite polarity in Left and Right channels, but that does not affect its tonal qualities.  There can be more Side information than Mid from an X/Y pair, which is likely to happen as you increase the angle of Blumlein to wider than 90 degrees for instance.. if you were to use a 180 degree  X/Y angle with fig-8's the result would be 0% Mid /100% Side]

We can also look at ms eq from point of view of changing virtual directional patterns and angles. And patterns and angels shouldn't cause a change in tonality on their own. [For all practical purposes, as soon as you start EQing things you are going to create tonal changes.  As mentioned earlier in the thread, with M/S a lot of variables are interrelated. Ambisonics breaks those interrelations, making it in some ways easier to mentally relate to theory and the mathematic concepts]
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Re: XY Greater than 90 Degrees?
« Reply #50 on: April 01, 2022, 03:00:41 PM »
Thank you very much Gutbucket. It is very kind from you to comment my thinking. I need some time to understand it deep. This thread is very helpful.

Yes, I totally forgot that there is negative lobe from hypercardiod  to fig 8. I was wrong, xy can have opposite signals.

 

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