Topic: Feelings on near coincident 'x-y'?

[achalsey]

I don't have a raiser at the moment to make my mics totally coincident.  How similar is running then right next to each other horizontally as opposed to in line vertically?  Seems like just visually there might be some physical blocking from the mic housings that close to each other.  I've certainly seen this set up used for drum over heads and even some band's official crowd mics by the board.

Would it be better to just run vertically coincident even if the mics are spaced a good 6 or so inches above and below each other?

Just thinking about this from the 'hyper cap' thread.  I've been running my 63s on stage but haven't tried xy and don't have an exact set up to make it 'real' xy.

[Gutbucket]

I typically usually use a Sure vert for X/Y with SD mics (a custom bar for the ADK TL).  However, I've done X/Y with SDs on a horizontal mic bar without spacers by pointing one up slightly and the other slightly down so one cap is over the other.  I figure the slight vertical angle difference is likely to be far less of a potential problem than having the capsules face into each other, especially for the angles I want to use between them which is almost always more than 90 degrees, and avoiding having each in the other's close reflection zone right at the on-axis capsule entry.  That worked fine.  I used the asymmetric on-stage setup of the band to my advantage by choosing which side pointed slightly up and which side slightly down and that made me feel better about it.

I've never run them spaced 6" apart vertically, but I see it done.  I think I'd still rather have the slight angle difference with the capsules placed as close together as possible.  I'd think proximity beats the slight vertical angle difference.

Probably like chicken nuggets, never really know what's in there but they are all pretty much the same. 
A good question is why a band would choose to use to run SD cardioids in X/Y as their 'official crowd mics' at the sound board?

[achalsey]

Cool, thanks for the input Gut.  I've just got a generic swivel t-bar so can probably make the angled set up work.

As for bands running xy by the board, I have no idea.  I've seen it a few times.  Basic ignorance I guess?  I've certainly had a random person or two ask why I had the mics spaced so far out (DIN) instead of xy.  I know I've read a similar story here somewhere.

[voltronic]

A good question is why a band would choose to use to run SD cardioids in X/Y as their 'official crowd mics' at the sound board?

Because that's what you always do with a pair of cardiods!   Or, if you're like any of the engineers working for the big-name acts I've been to recently, you don't really care about the sound quality anyway so long as it's deafeningly loud and the LF level is causing the audience's bowels to let go.

</rant>

I think many people simply don't know there are other ways to do a stereo recording that has good imaging.  I was one of those people.  Before finding TS, the only places I had ever seen things like DIN, ORTF, NOS, etc. discussed was on the Schoeps and DPA websites. 

[Gutbucket]

Yeah, their focus is mixing close-mic'd sources, where X/Y is 'safe stereo', in contrast to making good sounding ambient stereo recordings which stand on their own.

The irony is that if the intention of that 'official audience mic pair' positioned at the sbd is to improve a dedicated stereo bus mix for recording, the most useful contribution of that microphone pair is going to be room-sound and audience reaction that has sufficient decorrelation between the two channels.  And that's not something X/Y provides.

[DSatz]

Sorry I'm late to this thread. There are good reasons to separate the capsules at least a little, especially if they're cardioid.

If you're going to use coincident placement for whatever reason, though, definitely aim the capsules apart from the center line, not toward each other. When two microphones are placed close together and aimed toward a common center line, they partially block one another, which distorts their pickup patterns. Unfortunately there are still some articles and textbooks that show microphones placed "head to head" for coincident pickup. It's much better to place one capsule (or one microphone) directly above the other and aim them both outward from their common center. Ideally you want a common center line for the two diaphragms--an arrangement which many "coincident stereo microphones" create automatically (but see below about the dual-diaphragm capsules which are usually used in such microphones).

Back to why separate the microphones at least a little: If you don't absolutely need mono compatibility, recordings will generally sound and feel more spacious in playback over loudspeakers when the stereo effect is created partly from arrival-time differences between the channels in addition to amplitude differences. The explanation for this is fairly technical and has been discussed in many places including this board.

I would make an exception to that statement for the Blumlein method with coincident, crossed figure-8s at 90 degrees, though. In those (unfortunately relatively rare) recording situations where the geometry of that type of setup is appropriate to the recording environment, Blumlein tends to work very nicely. The pickup regions of the two microphones are so strongly independent of each other that the signals that the two mikes pick up will automatically have low correlation between the channels--which is what you want.

That is definitely not the case with cardioids, however. A cardioid pattern is relatively broad. If you set up a coincident pair of cardioids and aim them 180 degrees apart (back to back)--thus getting the greatest possible difference in what the two channels will pick up--about half of whatever you pick up in either channel will be in the other channel as well. As a result, when you play back the recording, even for sounds that originated far to the left or right in the real world, the apparent source of the sound never quite reaches either speaker position. Instead it tends to "puddle" in the middle; there is always a strong central (i.e. mono) component to the recording. For this reason I feel that X/Y with cardioids at 90 degrees is a poor choice of a "cookbook recipe"; I would suggest starting at 120 degrees instead (of course, always adjusting this for the actual circumstances).

This effect is even worse when the cardioid microphones use dual-diaphragm capsules, as in most switchable-pattern microphones, because such capsules have a true cardioid pattern only in the midrange. At low frequencies the pattern tends to "bloom outwards"--it becomes a wide cardioid. That's nice for studio vocals, since it tends to warm up the sound, but for coincident stereo recording, at low frequencies the pickup will be even closer to pure mono than what I described above. This is a serious problem with coincident stereo microphones even from such high-end manufacturers as AKG and Neumann, who use dual-diaphragm capsules to provide multi-pattern capability. X/Y cardioid recordings should be made only with single-diaphragm cardioids (the most common type of single-pattern cardioid).

Anyway, putting some space between the mikes helps to reduce all these problems.

--best regards

[voltronic]

I can share an even worse example: I have a friend who for years has used large-diaphragm AKGs (414s and 214s) on a short stereo bar intended for pencil mics.  He mounts them on the bar and angles them at 90 degrees to one another facing inward, so picture a DIN spacing but with the mics facing the opposite way they should.  It does not sound good at all.  He thinks that is X/Y, and I've tried to explain that it is not, and he doesn't even have the necessary mount to do X/Y with his mics.  I've also tried to explain how he would get superior results with DIN, ORTF, etc. but I'm not sure he quite understands.   I recommended he join TS, as I didn't fully understand these concepts either until I became acquainted with you nice people here.

My point in sharing all of this is that the person I'm speaking of is an extremely intelligent individual, but somehow has been mislead down the path that if you buy a product labelled as an "X/Y bar" and angle your mics in toward each other, you're getting X/Y.  Furthermore, he like so many others has been sold on the idea that X/Y is just "what you do" with cardioid mics.  I think manufacturers (at least the big ones) ought to be doing more in terms of educating consumers in proper stereo techniques through manuals, sales literature, etc.  Yes, there are forums with knowledgeable people like this one and some manufacturers have great info on their websites, but it's not consistent, and not everyone knows to look in those places.  For example, right now I pulled up the manual for the AKG C414, and it has several good descriptions of studio techniques for solo instruments, but nothing about recording an ensemble.  AKG does not have any info on their website on stereo techniques that I could find either.  My friend who is looking at said manual would have absolutely no guidance on how to use his 414s in a stereo array.  DPA, on the other hand, does a good job supplying this information with their Microphone University.

[buckster]

Back to why separate the microphones at least a little: If you don't absolutely need mono compatibility, recordings will generally sound and feel more spacious in playback over loudspeakers when the stereo effect is created partly from arrival-time differences between the channels in addition to amplitude differences. The explanation for this is fairly technical and has been discussed in many places including this board.

Good to know and thanks for the reassurance.  I assembled my rig in September and was recording at the rear of my local venue using DIN + hypers.  A couple of shows ago I moved up closer, maybe 12 feet from the stage, and thought I would try x-y + cards, being that I was much closer.  I've been shy of getting a perfect x-y alignment, so good to know having some space helps with the stereo effect.     

[Gutbucket]

^^
The right amount of space is important, remember there are three interrelated variables which play off one other: pickup pattern, angle between microphones, and capsule spacing.

To use your example above, keeping one variable constant- from the rear of your venue, try hypers with minimal angle and more spacing between them, and from up close try the same hypers with a wide angle and minimal spacing between them.  More spacing and less angle than DIN from far in back, maybe X/Y with hypers at ~120 degrees at the stage-lip.  Then imagine seemless variations between those two extremes as you move your imaginary recording position between the two locations.

X/Y with hypers at ~120 degrees is a reasonably spacious sounding coincident stereo setup for the same low inter-channel correlation reasons DSatz mentioned with regards to Blumlein X/Y fig-8s at 90 degrees, but it's geometry is often more appropriate to common recording environments, because it is more sensitive to sound arriving from in front than sound those arriving from the rear, were Blumlein is equally sensitive to sound arriving from all horizontal directions.

[F.O.Bean]

I know of a men's choir that uses two Oktava MK319s on a stereo bar feeding a mono PA.  What's better is that they have them aimed in "XY" as if they were end-address microphones, with the on-axis orientation of the mics thus randomly aligned somewhere between ceiling and floor.  I've explained the problem to them before, but they don't seem to get it, so I gave up.

So one mic facing the ground and the other the ceiling? How could ANYONE think that sounds good AND continues to do it ?!?!?! I ran XY my first recording with a full rig[481>DMIC>D8] Phish/Hampton 1999 the first night, and when I was setting up for the second night[12.18.1999, one of my favorite shows of ALL time BTW], someone suggested that I run near coincident and try a DIN-ish config! HOLY SHIT what a HUGE difference! It was night and day! Ever since then, I think I've run XY MAYBE 3 times, if that. So I've been taping that many years and have only run XY a total of 3 times EVER! Obviously everyone hears things differently, but if that doesn't say anything, I don't know what does lol

I did have to run XY once in a college bar because there was NO where to setup. So I ran my ck63s in XY, about 1' away from the left speaker against the wall, just to get some kind of stereo separation. But if there is ANY way to run anything but XY, then that's what I do!

[voltronic]

This has been posted here before, but to me it is one of the most convincing examples of why X/Y is also not a great choice for a purely acoustic ensemble recording.  They switch to X/Y at 3:45 and you hear the space completely collapse into a tiny box.  Out of all the arrays they go through, I my preference is: 1) 80cm spaced omnis 2) DIN 3) NOS 4) ORTF. 
https://www.youtube.com/watch?v=fguw5I6MxEo

[buckster]

More spacing and less angle than DIN from far in back, maybe X/Y with hypers at ~120 degrees at the stage-lip.  Then imagine seemless variations between those two extremes as you move your imaginary recording position between the two locations.

Thanks, I know there are all of these variables involved that I admittedly haven't fully grasped, so I appreciate the guidance.  I've only done two recordings at the closer location and I went with the cards as I wanted to try to avoid the chatty conversations behind the mics.  I'm recording over the dance floor now and there's generally less chattiness there, than behind the mics, which is a seating area with tables.  I'm thinking now maybe give the hypers a try (x/y @ 120°) just to see how it turns out. 

[Gutbucket]

Here's a bit more to go on- That basic two-way correlation: widely-spaced with little angle verses closely-spaced with a wide angle, is about attempting to maintain good stereo image and width in the resulting recording, while accommodating for other variables as the recording position is moved.   Of those variables, I think the most important is managing the balance of sound between what comes directly from the band (and/or PA) and what comes from all other directions making up the rest of the room.  The biggest influence on that by far is the location of your recording position in the room.  Beyond changing the recording position, we have some influence over that balance by choice of microphone pattern and choice of the angle between microphones. Those are arguably the next two most influential things we have control over.

 

[Gutbucket]

This may be helpful conceptually, or maybe just more than you care to read- 

Start by picturing the idealized shape of your microphone's pickup pattern.  It's not really that perfect and well-behaved at all frequencies, just as DSatz mentions concerning the behavior of switchable dual-element large diaphragm condensers and why they aren't the best choice for X/Y stereo recording, but  that's unimportant for the more basic issue I'm getting at here.   Okay so you have omnis or cardioids, or supercards or 8's or whatever, the next conceptual step is to consider the shape of the combined pattern of both microphones together, as if they were going to be mixed together into the same channel.  Ignore the distance between the two microphones for now. Unless you are using omnidirectional microphones, that combined shape is going to vary depending on the angle between the two microphones.  If you have two cardioids and point them in opposite directions, the combination of the two is sort of oval, and almost omnidirectional.  If you point them directly ahead, in parallel, the combination is cardioid shaped just like a single microphone since they both overlap completely.  Two figure-8 microphones angled 90 degrees apart end up being omnidirectional in this sense.  If they were pointed in parallel, they'd combine to form a single "8" shape, if pointed in opposite directions they also combine to form an "8" shape.  Ignore polarity or phase differences for now and just think about the combined pattern of both microphones.

So the combined pattern shape of a pair of supercardioids can range from that of a single supercardioid, with both microphones arranged parallel to each other, to a pattern resembling sort of sideways facing figure eight, thicker in the waist than a normal 8, sort of a squashed jelly bean-ish shape, with them pointed in opposite directions.  At a certain angle between the microphones, where a back facing 'null' angle of both supercardioid pattern line up and points directly backwards, the combined pattern will look like a single forward facign cardioid, with it's single null facing directly backwards, even though the two microphones are supercardioids.  Got it so far?

It is the shape of that combined pattern which indicates the sensitivity of your microphone pair to sounds arriving from all different directions in the room as a pair.  And it's usually NOT the same shape as each individual microphone's pattern.

[Gutbucket]

If the room-reverberance and audience-reaction sounds good and is in perfect balance with the direct sound from the band and PA at your recording position, then a combined pattern which is more open (more omni or subcardioid-like) can be appropriate.  How you achieve that combined pattern is influenced by other factors, and is part of the creative art of recording.  You could use spaced omnis, or you could use an X/Y pair of fig-8's, both of which combine to an overall combined omni shape with regards to their overall directional sensitivity in the room.  Using a pair of directional microphones this would be equivalent to moving toward placing them closer together and angling them wider.  The overall combined pattern becomes less directional.

Once you decide on what overall pattern is most appropriate for getting the direct sound and the reverberant(and audience) sound balanced as best as possible, move on to figuring out how you want to achieve that overall shape with the microphone patterns you have available.  Then you can determine how much spacing between microphones is appropriate, to get the sense of stereo width and imaging you want given the mic patterns and angles.

Of course tapers probably never or very rarely go through all this explicitly.  But that's what's going on 'under the hood' and is a good conceptual basis for understanding the interactions as well as an argument for optimizing things in essentially that order.  Lots of variables, and that order helps prioritize optimization of the most important things (the direct/reverberant pickup) first, over the less critical but 'nice to have' things such good stereo width and nice imaging which isn't overly mono or whatever.

In many real-world recording situations dealt with here at TS,  the recording position is constrained, the room isn't great, the audience is distracting, and you are struggling to do everything you can to maximize the pickup of direct sound from the band and PA as much as possible, while minimizing the room-revebrerance and audience sound coming from all other directions.  In that case it helps to point your most directional microphones directly ahead at the band or PA.  The microphones will either be parallel or much closer to parallel than angled apart very much.  That's the PAS (point at stacks) method and why it works well for recording PA amplified stuff from less than ideal locations in less than ideal rooms.   The key to getting better stereo image width with the PAS technique is getting the right amount of spacing between the narrowly angled PAS microphones.  The simple answer to that is usually more than most tapers are using with a mounting bar used for DIN/ORTF/NOS or any standard configuration that uses an angle of at least 90 degrees between the microphones.  An easy to access but more refined answer to that, based upon the relationship of pattern and angle is what this TS thread is meant to help with- PAS table (printable) - good imaging with high direct/reverberant pickup ratio