Topic: spaced omnis placement confusion

[RebelRebel]

 

you can, though, using spaced omnis , get a cool comb filtering so bad that it sounds like Galaga when you record a solo instrument...

[muj]

HAHAHAHAHAHAHAHAHAHAH.... nice one

[Church-Audio]

+T for catching that one Ted.

Hey I said 3:1 not 2:1 

actually it is 3:1, not 2:1, Chris.

Just remember the two to one ratio, that Omni mics should be twice the distance apart as they are from the source.

That rule basically tells you to use AB spaced omnis only close to the sound source.  If you try to follow this rule at any significant distance, you'll have your mics out of the building, or if it's outdoors, you'll have a huge hole-in-the-center effect.

A more realistic rule might be the one from the New Stereo Soundbook that references keeping the spaced omnis apart by between 1/3 and 1/2 the width of the soundstage (ie: the PA in most cases).

- Jason

Just remember the two to one ratio

[mmmatt]

I LOVE split omni's.  I would never go 3:1 though.  The widest I have gone was a 15' split and that was about 100' back.  Here is a pretty good example of that http://www.archive.org/details/ddbb2005-05-28.mbho.flac16 .  The soundstage is quite wide at a 15' split, and I actually like it but I don't think I would want to go any wider.  This was part of an 8 track multi/matrix but ddbb said no to posting the matrix.  The other recordings from the fest used the omni's in conjunction with board and 2 other pairs of mics on stage.  It was a nice treat being able to manipulate the image and kind of layer the soundstage.  I LOVE split omni's outdoors either alone or in a matrix.
     I have also used splits many times on stage.  The thing with stage placement of any config is you can get too much of some of the instruments and not enough of others.  When there are vocals don't bother, but for amplified jazz it is the shit IMO.  I did a 3 night series of Fareed Haque group last year and the first 2 nights I ran mono board + stage corner omni's + center-stage x/y.  The Tabla's player was set up center stage so I got way too much of him the first 2 nights.  It was a tight club and I didn't have a lot of option.  The third night was at a small outdoor stage and I ran split omni's at the lip and an ORTF pair from the audience.  That recording was much better.  I had a chance to listen to the other two from previous nights and noticed I was light on a few of the instruments, so I place the splits a little closer to instruments that I felt were light from previous nights and away from the tablas player!  When just going split on stage I usualy try to stay around 6-8 ft spread and just position the mics so I am away from direct sound sources.  Also, if possible I like to be centered on the drumset because I like to hear the placement of each cymbal and drum.  I guess the key to a good split omni stage recording IMHO is to think of each mic individually for what it will record, and try not to split them so far as to create that hole in the middle.  I would never go 15' spread on stage, but 6-10 is probably just fine depending on the spread and depth of the stage.
     I recorded fhg again a few months later and they set up after the opener.  Knowing the blunder I had made on the first two by using x/y I set up splits.  Turned out that the keyboard player wasn't there that night and the tablas player set up off to the side and was again to heavy in my mix!  Another nice perk of recording split omni's over a card/hyper config is that you get a little more crowd responce.  For a wild rock show this is not an advantage, but for an instrumental show this is often a big plus.  Getting crowd at appropriate times without a lot of room-boom is a nice thing to my ears.
     As for being too close, I once forgot to change the caps to cards for an x/y recording and did x/y omni's.  Surprisingly enough it was not a bad image!  It was far from what I got with splits but certainly not mono.  I recorded a multi/matrix using onstage x/y omni for the opener, and then split omni's for the headliner.  I can pull out just the mic tracks and do a comp if I can find the time in the next couple of days.  I think people here will be surprised.  I know I was.  That effor was with Brian Ska, and MattD at the Metro in Chicago for Goran Ivanovic Group and Andreas Kapsalis Trio.  Goran got the splits.  Actually my current avitar is from that show.

Matt

[kuuan]

I am very happy that my question sparked this discussion, or rather disclosures of experienced tapers.
To me personally much of what is said is above my horizon as I am a beginner, but I try to assimilate and to study.
Certainly above all Moke also got me also interested in the Jecklin Disc. Here in hardware store they are selling solid rubber rectangular and also round pads, which I believe are sold to put underneath furniture or the like to prevent it from sliding or to absorb movement (?? - well, this is an earthquake prone country ) They are made of solid, heavy black rubber, come in various thinkness starting abt. 2mm untill 1 or 1,5 cm. Do you think this would make a good J-disc? ( if yes - o.k. I should research this, but why not ask at once: which diameter would you recommend? )

[ghellquist]

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

[mmmatt]

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

I was gonna say!  Thanks for the proper clarification Gunnar.  +T

Matt

[F.O.Bean]

i have never ran split omni's, but i do own a j-disc and ran it a few times last summer and loved the results, speaking of, i have to hit up grider and borrow his ck62's for a few months

as moke said, it gives a spaced feel w/ a LOT less hassle and i can never see myself splitting omni's too much PITA for me

[Church-Audio]

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

[Chuck]

I almost have everything I need to start experimenting with J-Disc omni's and split omnis more. I wonder if the pan feature on recording software would be able to fix the hole in the middle thing if the mics are spaced too far apart. Specifically add a bit of the Left signal into the right channel and visa versa.

I have to say that Moke has been a real champion of omnis and baffled omnis in particuliar. I for one have paid attention and soon will be doing my own recording and experimenting. To me, no cardioid or hyper-cardioid has the same realistic representation of the way things really sound than omni's. For some this is not the goal, to have realistic representation. But, I always hear the compromise when listening to most two track live recordings made with anything other than omnis.

[pfife]

a successful split omni's recording, in an amplified situation, is going to depend greatly on the acoustics in the venue.  I've had good luck with it from balcony of a medium-sized club in detroit.  However, I've had less than stellar luck running them from a balcony of a local theater.  It's actually not much of a pain with DPA 406x's - in the smaller club I just taped them to the railing of the balcony, prolly 5' spread.  At the larger theater, I taped them to the lip of the balcony, about 6' spread. 

that being said, in general, jeklin is way easier, and in smaller venues (amplified sources) it gives me a might tighter sound, if that makes any sense.

[Gutbucket]

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.

[Church-Audio]

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.

[RebelRebel]

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.

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.

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.

[Chuck]

Maybe one of you omni gurus can answer a question:
DPA offers various "grids" to place in front of their omnis to alter the response of the microphone. For example, they have a diffuse-field grid that raises the response above 15 kHz when recording farther away. What's up with that? Can this be done for other microphones? How does this work? I think it would be great to have that option available on any omni, to tilt it's response up a bit when you run them farther back than you would like.