Topic: spaced omnis placement confusion

[WiFiJeff]

.. can't do it in this 3 dimentional space universe. 

Now this is only true for this 3 dimensional EUCLIDEAN space universe, some of the newer halls with a non-Euclidean metric allow all sorts of innovative mic placement.   However the mass or energy densities needed to sustain the local curvature of space in such halls can play havoc with unbalanced circuits, and you might as well kiss your time-code generator goodbye, unless you have something like the new Sound Devices Hyperspace 744 with a general relativistic invariant time-code function.  This will be useful if you want to keep the music on your tape from ending before it actually begins.

Jeff

does cell phone interference exist there?

See my upcoming piece in Phys. Rev. Letters "Cell-phone Interference in Audio Equipment Under the Most Fav Gerneral Relativistic Metric Space Structures - A Survey"

The short answer is that cell-phone interference is a universal constant and metric independent.  Although you can't make cell phone calls from a Black Hole, you can't avoid receiving them.

Jeff

[RebelRebel]

Search "spaced omnis vs jecklin type disc" or "jecklin disc"


1.) Omnis are technically the only microphones that when used can be called "proper" OSS/Jecklin Disc Technique. Who cares about that though..of course you can use any microphone you wish. I prefer omnis at all times with the disc because it sounds much more natural to me.
2.)that subject has been covered over and over...do a search on Jecklin Disc here http://taperssection.com/index.php?action=search;advanced

3.)My disc is a purchased one, and the Mics are angled outwards.yes, closer to the disc face= more seperation.

4.) an important point is that there are NO defaults here.Just use your ears and research and you cant go wrong...no static rules.

you guys simply lost me...

OK. no agreement if the 3:1 rule applies or not.
However, is it possible to say under which conditions a short spacing of 1 to 8 feet should be a good choice?

And of course I got very curious abt. the J Disc. The thread 'spaced Omnis vs. J/disc' has total 31 pages, so much info but I struggle to get the essence of it, I'd need a resumen stating all the important points. I'd be very happy to get clarified:

• Generally Omnis are used with J disc, but also subcard, even cards can be used. Should Omnis be the default choice, or when could cards be the better choice?
• Which would be the easiest to build but effective well working DIY J disc? Many build their own disc but modified it later. Why and how for which reason? Would a hard rubber disc make a good disc?
• Which would be your prefered Mic positioning using the J disc? Separation, pointing? Closer to the disc gives better separation, further away less separation and...? Would they usually be pointed streight forward?
• Is there any other important point?

Well, sure my questions are simplistic as the answers must depend on circumstances, but somethng like a dummy guide for J Disc would be just great.

[Chuck]

I tried J-disc with C-483's for Taj Mahal at Red Rocks a while ago. It sounded OK, but I may try C-481's next, since I don't have the CK-62's yet. I have a pair of MSH-1A's on the way that I really want to try baffled too.

[F.O.Bean]

I tried J-disc with C-483's for Taj Mahal at Red Rocks a while ago. It sounded OK, but I may try C-481's next, since I don't have the CK-62's yet. I have a pair of MSH-1A's on the way that I really want to try baffled too.

you'll love the j-disc bud, sounds real nice w/ the 62's i am gonna buy those omni's you got tho, they sounded sweet

[cgrooves]

I love the j-disc when running in a good sounding room with a crowd that isn't too rowdy and it isn't an acoustic sing along type of show.  Outdoors though, I like the sound of split omnis.  I've run mine split only 1' and liked the results.

[Church-Audio]

I am right damit just say it  
I know that under some situations it would be impossible to use it but, there are plenty of times when it can be used like recording a choir.

Easy now, didn't mean to raise anyone's ire.  It's a simple fact of geometry that it is impossible to have two mics three times as far apart as they both are from the same source (as would be the case with a stereo pair recording a single source).  Draw a diagram or get out the tape measure.. can't do it in this 3 dimentional space universe.  I completely respect your experience and the reputation of GEFELL, but the information on their site is wrong, perhaps their english translation is to blame. 

Now if the source is large like a chorus or orchestra, it is possible to have one part of the large source close enough to one of the mics to achieve a 3:1 ratio between that one part of the large source and the two mics.  Other parts of the source will have lower ratios.  That's not what we are really talking about, and confuses the issue by breaking up a single large source into multiple parts.

If you can show me a diagram or actual mesurements of a spaced pair setup you have used to record a single source with a spaced pair following the 3:1 rule you will convince me.. & we can dig up the bones of Pythagoras & Euclid and re-invent geometry.

No offense meant to you.  The rule does of course exist, it just doesn't apply to a spaced stereo pair.. not because anyone says so, but because it cannot be done.

You are 100% incorrect The 3:1 rule does exist argue your point with GEFELL one of the most respected names in audio.
I have been a sound engineer for 20 years I know my mic techniques and not because I read them from a book because I have used them. This rule can be applyed to close micing and to distant micing BUT it is only a guidline I was only trying to say that this rule dose exist and it is used sometimes. The fact that someone says this rule does not exist does not make it so. Furthermore this rule does not always have to be used it depends on your situation.



Chris Church

Here is the url for the info I have posted. http://www.gefell-mics.com/stereo_mic_techniques.htm


Wide stereo
Set-up: Two directional or omnidirectional spread using the 3:1 rule
Primary use:  STEREO RECORDING OF ENSEMBLES AND ORCHESTRA'S
Stereo image: EXCELLENT
Center image: OKBest for: Working with the mid to far field
Advantage:   Better stereo imaging

Notes:
The wide stereo employs a 3:1 rule whereby the distance between mics is 3 times greater than the distance of the source. For large orchestra, an additional center mic is often used. This provides better stereo imaging but does not make for good mono compatibility.

Actually RESPECTFULLY, you have it backwards phase cancellation happens when two mics pick up the same source at the same exact time and amplitude and frequency. The polar patterns overlap making this happen. This normally happens at one frequency like for example if I had two Omni mics on a single singer and he or she was hot at 2.5k I would need to apply the three * to one ratio to avoid phase cancellation and the peek frequency or dominant frequency.

Your scenario of the rule needing to be applied with two different sources would be almost impossible to get any kind of phase problem.  Hence the need to space mics with such open polar patterns (OMNI) in the first place. This is the reason why you never see a true stereo one point Omni mic; it would be a phase cancellation nightmare.

Aaah, I see, the much misunderstood 3:1 rule.

And now, sorry for the emphasis.

The rule of thumb is ONLY of any use when you use two mics to record two DIFFERENT sound sources and want the two sources to be SEPARATED. So if you want one channel to have the lead singer and one to have the backup singer it is applicable. If then the singers are each one meter away from his/her mic, then the mics should be at least three meters from each other. Then each mic will basically only have one singer, allowing you to mix and match without much problem with phase issues and bleed between the mics. As with any rule of thumb it certainly does not work in every circumstance. It is a useful starting point for mulitmicing things in the studio or on the stage.

It has ABSOLUTET NO RELEVANCE for the distance between the two mics that make up a stereo pair. Here we want both mics to capture every source to some degree. The arrival time and volume differences are queues for our brain to recreate the stereophonic landscape. How to setup the mics is ruled by what stereo image you get, and then both mics need to get at least part of the picture, exactly as your ears.

Once more, sorry for shouting -- this seems to be a very common misconception.

Gunnar

Sorry Chris, but Gunnar is correct.  The 3:1 rule is for multiple mics on separate sources.  it is a multi-miking rule and does not apply to a single stereo pair. You are correct in noting that comb filtering is caused by the interference pattern of a single source, picked up by two mics and then summed again (either electronically or in air).  The 3:1 rule works by getting each source/mic pair far enough away from the next that any inevital bleed is or or less inconsequential for phase issues.  The rule has nothing to do with polar patterns other than more discriminating patterns can, by attenuation, help to reduce bleed and limit the comb filtering that the 3:1 rule aims to achive using distance.  The different path lengths between the source and the 3:1 separated mics proivides both attenuation and phase differences between the signals of all the mics that are picking up that souce, both intentionally (mic on that source) and unintentionally (bleed from other mics). 

It is physically impossible to apply the 3:1 rule to stereo micing, follow me here:

For stereo miking where some part of the source (say, the center of the stage) is equidistant from each mic, you cannot have more than a 2:1 ratio of source to mic vs. mic to mic distance.  The only geometry that would acheive a 2:1 ratio would be to put the mics in a line with the source on the midpoint of that line, centered between the mics.  As soon as you move the source away from the line the ratio drops. An equilateral triangle of source and mics would have a 1:1 ratio.

[china_rider]

Ok... I'm not a very handy guy and doubt I could make my own but would love to try a JDisk with my 482s or the TLs I have on the way.  Anyone out there that has made one that would like to make another that won't break the bank?  PM Me....

Stay Kind,
Dana

[RebelRebel]

Ok... I'm not a very handy guy and doubt I could make my own but would love to try a JDisk with my 482s or the TLs I have on the way.  Anyone out there that has made one that would like to make another that won't break the bank?  PM Me....

Stay Kind,
Dana

Dana, it isnt hard really. you just need an embroidery hoop, a piece of threaded rod, a coupler, foam, and some felt..

[Chuck]

Ok... I'm not a very handy guy and doubt I could make my own but would love to try a JDisk with my 482s or the TLs I have on the way.  Anyone out there that has made one that would like to make another that won't break the bank?  PM Me....

Stay Kind,
Dana

I might be tempted to sell this one or make another just like it...

11" plexi-glass square, with the corners cut off, covered with placemat rubber backing, covered with three layers of 3/16" felt on each side, then I sewed some green fleece over that. To hold the microphones I used 2 Radio Shack desk mount threaded mic holders. It attaches to the stand with a standard mic clip assembly that I took apart.

[Gutbucket]

You just need some pockets on the corners and a set of miniature billiard balls

[Chuck]

You just need some pockets on the corners and a set of miniature billiard balls

Yeah, my choice of that green was based on the mark-down bin in the fabric dept. at Walmart. I kind of like it that color. 
I got 2 yards for under 2 dollars.

[Gutbucket]

Yeah, my choice of that green was based on the mark-down bin in the fabric dept. at Walmart. I kind of like it that color. 
I got 2 yards for under 2 dollars.

Funny, I bought a big load of bargin bin fabric for sewing hammocks and the best of that was green, same price.

[ghellquist]

I agree with Chris. It applies to both situations.

Gunnar was right on the fact that it applies to seperate sources, but was wrong about it not applying to stereo micing.

Hmm.

Teddy, seriously, how often do you use this 3:1 rule in a stereo pair? Could you make a drawing of how the two mics are setup in relation to the single source (which might be smallish like a guitar or large like a symphony orchestra). Let us together once and for all kill the idea the 3:1 has anything to do with the two mics in a single stereo pair.

Anyway, the spaced stereo technique of two omnis is one of my favourites. It is sometimes called AB. Depending on the room, the mics may be about a foot apart or up to many feet, maybe as much as 20 feet in extreme situations (far from the sound source).

Anyone experimenting should try this. As the distance increases you often end up in a situation with a "hole" in the middle of the sound stage. This is clearly heard on a good pair of monitors, but sometimes not noticed in headphones. When the hole is there, you know you are too far apart. On the other hand, as the mics get closer to each other, the stereo width decrease, finally collapsing into mono.  When the mics are really close you may end up with some quite interesting phasing phenomena and wandering stereo images (one sound, say the S-sound of a chorist may wander from left to right in the stereo image). Somewhere in between too close and too far apart is the optimum. Sadly enough there are no rules really, you need to listen to get the right distance. In a hurry I tend to go for about 2 foot, usually works.

Gunnar

[ghellquist]

You are 100% incorrect The 3:1 rule does exist argue your point with GEFELL one of the most respected names in audio.
I have been a sound engineer for 20 years I know my mic techniques and not because I read them from a book because I have used them. This rule can be applyed to close micing and to distant micing BUT it is only a guidline I was only trying to say that this rule dose exist and it is used sometimes. The fact that someone says this rule does not exist does not make it so. Furthermore this rule does not always have to be used it depends on your situation.
m the line the ratio drops. An equilateral triangle of source and mics would have a 1:1 ratio.

Sure, the rule is there. Simply make me a drawing showing where it applies to the two mics in a single stereo pair recording one source (with a certain spread as otherwise it would not need stereo).

Anyway, that page from Gefell is wrong about "wide stereo". I have mailed the company asking them to remove it. I have a belief that the text is copied from a course material used in one of the audio engineering 101 courses (might be SAE, no idea really). The person writing it clearly had no idea.

Do read DPA-s mic university instead. They are slightly wrong about the "lacking bass" of cardioid mics, but their description of AB stereo is correct.
http://www.dpamicrophones.com/
(Sorry, I find no way to point directly down into the mic university texts on their web page).

They tend to regard "optimum distance" between two omni mics to be between 40 and 60 centimeters (a foot is about 30cm). I tend to end somewhere about there as well.

With regards
Gunnar

[mmmatt]

so many less rules to remember with baffled omnis!

I run splits on stage a lot and it is a big advantage in many cases to be away from the center of the stage, or closer to one instrument that you know is going to have less stage volume.  Many times you can avoid monitors and the overpowering of a particular instrument that may be located in the center, while highlighting another instrument off to the side that would otherwise be light in the mix.  I usually go cards center stage or splits if I need a little more versatility.  For stage taping I would think a j-disc would be a far larger distraction than mics without.  From the section or FOB, a j-disc may be best so you can run easily from a single stand.
     All these rules people are talking about for splits are bunk in my mind.  I think your ears tell the tale, and there is a huge window of acceptable placement.  I think the actual logistics of the event are the biggest determining factor for actual mic placement.  Trial and error, and knowing your gear is what will make for good recordings with any config.  The average person hearing a recording won't be able to tell any difference between a 10' spread or a 2' spread.  We are geeks so we know what to listen for and since we record in strange places it is a crap shoot no matter what.

matt