Topic: Split omni with card center?

[Cobiwan]

I just read through all the threads I could about running split omnis, and from what I gathered Gutbucket had recommended running the split omnis with a center set of cards in XY. Is this the only config that would work well when mixing the split omnis, or can you use others- DIN/ORTF/NOS, etc? Your help is always appreciated TS!
-Coby

[bhtoque]

I've run cards din in the middle with great results both stage lip and farther back. Also done it with hypers AB in sheds/at festivals. Don't think there is an "only" way at all.

JAson

[capnhook]

Split omnis, and mono center cardioid is fun, too.

[Bruce Watson]

I just read through all the threads I could about running split omnis, and from what I gathered Gutbucket had recommended running the split omnis with a center set of cards in XY. Is this the only config that would work well when mixing the split omnis, or can you use others- DIN/ORTF/NOS, etc? Your help is always appreciated TS!
-Coby

Look up Faulkner phased array.

[Hypnocracy]

Split omnis, and mono center cardioid is fun, too.

What Capt'n said...

https://archive.org/details/tauk2014-06-27.Avenson_Gefell

[Gutbucket]

You can put anything in the center, really. 

Conceptually you are either starting with your typical stereo pair and adding wide omnis, or
starting from spaced omnis, and adding something in the center. 

I find the second approach more productive and more flexible.  Spaced omnis are my starting point.  A microphone or pair in the center lets me space the omnis wider without problems for more wide omni goodness, and provides up front clarity and articulation in the center of the stereo image, sweetening things up.

I use a single cardioid or supercardioid facing directly forward in the middle like the capt'n mentions.  Having a single microphone facing directly forward maximizes the on-axis clarity of the center, more tightly focusing on just the sound coming from directly in front.  That nicely complements the omnis which are picking up everything, and it keeps things simple and easily manageable.  You can use the 4th channel to record a mono SBD feed.

[Gutbucket]

My suggestion to use X/Y in the center is a simple extension of the single forward facing center cardioid (doesn't have to be a cardioid BTW, it could be any pattern at all, it's just that a cardioid or supercardioid works nicely).  Actually I'd preferably do it as Mid/Side by just adding a fig-8 to that forward facing center microphone, but X/Y cards or X/Y supers would be fine.  That uses all four channels so the taper won't feel like they are 'wasting' an empty channel on the recorder or leaving a mic unused, but still keeps things manageable and simple and allows for some center image spread adjustment if you want- pan them both center and it's as if you had a single forward facing sub-card in the middle, or pan them out a bit or all the way hard left/right for more center image spread.  You can pan them like that without problems since they are coincident and won't have phase issues as they mix with each other, yet there is still the good timing and phase difference info provided by the combination with the wide omnis so the recording won't sound flat and lifeless like a pair of x/y cards would alone.  At least an X/y pair of cards used alone sounds that way to me. 

Here's the technical part- regardless of any panning of the X/Y (or M/S) pair, there are only two phase relationships being mixed electrically- the coincident center pair with left omni and the coincident center pair with right omni.  Electrical mixing is where the potential phase problems occur for the most part.  There are three phase relationships going on in total including the phase relationship between the two omnis, but the omnis aren't mixing electrically with each other. 

A near-spaced pair plus wide omnis can work fine too.  In that case, in order to minimize potential phase problems, it will usually be best to just route the near-spaced pair hard left/right so each center microphone mixes only with one omni on the same side.  But even doing that, the phase relationship is more complex than having a single microphone or X/Y pair in the center.  If direct-routed or hard panned left/right, there will still only be two phase relationships being mixed electrically- the near-spaced left card with left omni and the near-spaced right card with right omni.  But there are now not only three but six phase relationships in total.  Tony Faulkner leverages that complex phase relationship intentionally, somewhat like the way a phased-array radio antenna works.  By very careful spacing and close listening during setup he avoids phase problems.  Concert tapers don't have that same ability to carefully monitor and adjust things on setup before recording, so it becomes somewhat more of a gamble.  It may work fine though and sound great.

However, if you were to try to pan that near-spaced center pair like I mentioned doing with an X/Y pair, say to fine tune the center image width or maybe solidify the middle or whatever, you are much more likely to get phase interaction problems because you'd then be mixing five of those six phase relationships between microphone positions electrically, instead of mixing just two of three. 

Things get complicated quickly when you electrically combine (mix) multiple microphones which aren't placed very far apart from each other.  That's the basis for the 3:1 rule for microphone spacing when mic'ing individual sources on stage that will be mixed together.  The 3:1 rule doesn't apply to stereo recording microphone setups because stereo uses those phase differences intentionally and the two stereo channels are kept separate and aren't electrically mixed with each other, but when more than two microphones are used in a stereo recording array, at least some of those microphones will be mixed together electrically, and the same phase interaction issues that the 3:1 rule is intended to minimize will be in play.

[Cobiwan]

Thanks GB, as always you provide stellar information. Would there be any phasing problems if you ran DIN or ORTF in the center vs XY?

[Gutbucket]

I can't say decisively whether you'll have problems or not.  Both DIN and ORTF are "near-spaced" configurations.  When combined with a pair of spaced omnis, the spacing between those two center microphones makes for four different microphone positions in total which will all be interacting with each other in various ways.  There will most definitely be more complex phase relationships going on in that case than if you were to use a single microphone or a coincident pair in the center, where you would only have three microphone positions in space interacting with each other.

Phase interactions are not necessarily bad.  Good phase interactions are in large part what makes near-spaced configurations like ORTF, DIN, etc, and spaced omnis sound pleasurable.  The resulting recording might sound fantastic, in which case those phase interactions are either working to your advantage or at least not causing any major problems. 

What I can say for certain is this- the possibility of unfavorable phase interactions will be greater than if you were to only have only three microphone positions interacting with each other.  As mentioned above, if you are using a near-spaced ORTF or DIN pair between spaced omnis with the intention of mixing both pairs to a single 2-channel stereo mix, you reduce the probability of having problems by routing or panning both the omnis and your ORTF or DIN pair to the hard-left and hard-right positions in the resulting stereo mix. 

With only a single center microphone position, you get plenty of the good phase interaction going on in combination with the omnis, with less potential problems, and if you use a coincident pair you can also gain some additional flexibility in mixing, which is there if you need it.

I'm not saying that using a near-spaced pair in the center is wrong or that you'll definitely have problems.  I'm only explaining a few of the advantages of using a single center microphone position instead.

Here's a closely related thought-
Regardless what kind of stereo pair technique you choose to use in the center between the omnis, it's probably best to choose one which when listened to in isolation without the omnis tends more towards a narrow playback image with a strong and very well defined center (more narrow sounding and mono-like), rather than wide sounding but with a less solid middle (more diffuse sounding and more super-stereo-ish).  The omnis will provide the "big wide-open soundstage" qualities that will offset any "narrowness or lack of width" in the center pair and the center pair's job is mostly to solidify the center, add forward presence and maybe improve some imaging across the middle.  So a narrow-angled near-spaced PAS pair (as PAS is typically setup) may be generally more appropriate than a wide-angled ORTF pair.  And for the same reasons, a single mic which when listened to in isolation is all mono with no width at all, or an otherwise narrow and rather boring-sounding X/Y pair of cardioids works quite well in the center once combined with the omnis.

[Cobiwan]

Awesome, thanks for the advice.

[Gutbucket]

The other approach is to start with the near-spaced pair configuration you like and would normally use, say your normal ORTF or DIN setup, and consider that as your primary pair.  Then also run wide omnis in addition to that, and if it doesn't work just throw the extra pair out.

If both pairs work well in combination with each other then great.  If not then just use the center pair alone, or just the omni pair alone.  And be psychologically ready to do that if necessary, don't feel like you have to mix both pairs together just because you recorded both.

That's a safe way of hedging the bet if you are more of a "near-spaced guy" than a "spaced-omni guy".

Using three mics or a center coincident pair which you normally wouldn't care to listen to in isolation by itself is more of a move away from the concept of "my favorite near-paced stereo pair technique + extra omnis" towards "spaced-omnis improved by adding something in the middle" with some other potential advantages.