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Author Topic: XY Greater than 90 Degrees?  (Read 1759 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

Yes, but what do you HEAR?

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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Online 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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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?

 

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