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ORTF plus omni
Old 3rd July 2014
  #1
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ORTF plus omni

Hey guys,

I'm sure this has been done before, but I just did a quick test with an ORTF rig plus an omni mic centered between them and was very happy with the results.

The reason I even attempted this was because I love what an omni mic gives me with regard to low frequency extension and trueness of sound, but I have issues with the mono compatibility that putting multiple omnis up in space causes (for SFX recording specifically)

I used a pair of line audio CM3s for the ORTF setup, and a Schoeps CMC6.MK2 omni for the center.

What I found was that the addition of the omni tended to push the image a little more center, and it added tons of information in the middle that now feels missing with a straight ortf setup. It also (of course) greatly contributed to the low end.

The thing I was most interested to find out though, was phase coherence in mono, and this setup passed that test with FLYING colors.

the other nice thing is that you can still get a surround setup running from this just by adding a fig8 to the mix and decoding against the omni for the rears.

Wind protection still an issue with this rig, but sonically I couldn't be happier right now.
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ORTF plus omni-door-opening.jpg   ORTF plus omni-modified-ortf-setup.jpg  
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Old 3rd July 2014
  #2
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boojum's Avatar
Add another CMC62, space them as AB at 38 - 40 cm with the ORTF in the middle and you will have a stereo feed from the omnis. You will also be able to vary one array against the other to suit the venue and desired tone.
Old 3rd July 2014
  #3
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@boojum, while I'm sure that setup would sound lovely in stereo - the problem I'm trying to solve is how to incorporate omnis in to SFX recording in a mono sum compatible kind of way. I don't think adding an AB pair would alleviate that issue - hence the addition of only a single omni.

why is mono compatibility so important? because sfx get summed to mono all the time for any number of reasons. editors sum fx to mono when they spot, mixers sum fx to mono when they mix or when they pan, and playback systems sum to mono on PAs and on phones. When I release libraries, I release mono compatible ones.

I'm just playing with the idea of getting away from all of this cardoid stuff and going with that true sound that omni capsules bring. It'll come to me one way or the other.
Old 3rd July 2014
  #4
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pkautzsch's Avatar
 

I'm not convinced that the spaced component of the ORTF, in addition to the even smaller spacing between each cardioid and the omni in the middle, doesn't matter at all - ie. that the setup is truly mono compatible.
Have you actually tried with one single speaker, or panned through a theatrical 5.1 setup? What does the correlation scope display?
Actually, this setup - getting two channels from three non-coincident mics by summing the center mic to both L and R - introduces comb filtering at least theoretically. With such a close spacing, the difference between L and omni should be quite small, so phase issues would arise.
How audible is this in reality? Is it possible the existence of comb-filtering in stereo makes the additional comb-filtering when summed to mono just less obvious?

The safest way to get mono compatible SFX is MS. You can use an omni for M, or add one to a directional M mic.
Old 3rd July 2014
  #5
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boojum's Avatar
Quote:
Originally Posted by pkautzsch View Post
The safest way to get mono compatible SFX is MS. You can use an omni for M, or add one to a directional M mic.
The true answer. Of course, OP will have to run out and buy a figure-8 now. But if he is serious about SFX that is a must. Perhaps the ORTF plus center omni was a kludge attempt to arrive close to what MS would render. OP, was it?
Old 3rd July 2014
  #6
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Don S's Avatar
 

If these are CM3's then are they are not cardioids, but wide cardioids and little too close together. Try them at 12-14 inches. In regards to adding mics, I would start with the Faulkner or Boonjum array. Both topics have threads on GS.
Old 3rd July 2014
  #7
Gear Addict
 

If the OP wants to use an omni to fill in bass, then he should use high cut filter on the center omni mic, say at around 140Hz, mix it in with a pair of ORTF. In this case the omni mic is only being used as bass fill. This way, the center channel will not make the image narrow because of the high cut.

If he wants to try MS with two cardioids and one omni, then he should put two cardioids as close as possible but pointing opposite way to mimic figure 8 microphone. In the mixer, the right side pointing cardioid should be phase reversed. Do a hard left and right panning on the two cardioids, but with no panning on the omni, mix all three to form MS configuration.


Da-Hong
Old 3rd July 2014
  #8
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Quote:
Originally Posted by boojum View Post
The true answer. Of course, OP will have to run out and buy a figure-8 now. But if he is serious about SFX that is a must. Perhaps the ORTF plus center omni was a kludge attempt to arrive close to what MS would render. OP, was it?
I have the Schoeps fig 8 capsule as well, and I do a fair amount of MS recording, for whatever that's worth. This is not a kludge, just an experiment.

MS is fine for spot recording IMO, but the wider spaced mic options tend to sound better than MS for sfx ambiances and for things like bys.

AB omni is one of the best pure stereo solutions, but again, mono compatibility is problematic there.

@donS - I'm intrigued by the idea of faulker or boonjum arrays. I'll have to look more deeply into those.

@pkautzsch - panning all channels to my center speaker creates no audible phasing artifacts, at least in this test. The real acid test is car bys.

thanks all for your input.
Old 4th July 2014
  #9
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If you want more mono compatibility, wouldn't XY be better, as the left and right capsules are effectively coincident, so there'd theoretically be no (or at least much reduced) phase difference in the pickup ? As Don S says, a NOS arrangement probably gives better stereo with the CM3's, at the risk of a bit more phase cancellation.

According to "The New Stereo Soundbook"by Ron Streicher and F Alton Everest, using the NOS method...'the narrow angle still provides primarily intensity cues, although the wider spacing produces phase differences that become evident at lower frequencies, beginning at approximately 250 Hz-around Middle C- as compared to the ORTF technique, in which audible comb filter effects occur two octaves higher, around 1000 Hz. Thus monophonic compatibility of the NOS technique is more noticeably affected than with the ORTF'
The fact that the CM3 is wide cardioid might come into play to minimize these phasing issues, compared with a straight cardioid....just a guess ?

XY miking gives you best possible phase integrity, because the lack of spacing gives you stereo derived solely from intensity differences. With your 3rd mic (omni) also aligned vertically with the XY pair (and perhaps rolled off above 140 Hz as has been suggested) you might get the best of all worlds ?

Do you have a goniometer (stereo phase meter) available to you in software..I know Wavelab 5 and later have such a device. This gives you a Lissajous picture of the phase relationship between left/right and is a great visual tool for comparison of the various methods (as well as your ears of course !)
Old 4th July 2014
  #10
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pkautzsch's Avatar
 

Quote:
Originally Posted by studer58 View Post
The fact that the CM3 is wide cardioid might come into play to minimize these phasing issues, compared with a straight cardioid....just a guess ?
Actually, the more directional the outer mics are, the less phase issues will arise in combination with the center omni. This is due to sound from most directions being attenuated more than with a wider pattern.
Three omnis in a row, close together, are most prone to phasing issues. This becomes most obvious for sound at 90°, hitting one capsule after the other.
Old 4th July 2014
  #11
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Plush's Avatar
I cannot endorse the use of an omni mic in the center of an ORTF pair. The stated aim to improve mono compatibility should instead be sought by using an array such as a MS set-up.

Besides--what is shown is not ORTF. It is a variant of NOS.

The stereo picture portrayed by an ORTF type main microphone is not made to be ruined with mixing in a mono component.
Old 5th July 2014
  #12
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Quote:
Originally Posted by renec View Post
AB omni is one of the best pure stereo solutions, but again, mono compatibility is problematic there.
Easy fix, use one of the mics only.
Old 4th May 2016
  #13
Here for the gear
Flame Bait

Hey guys - I stumbled across this article a couple of years late, but found it really interesting.

I've been using an ORTF pair for a while and as a sound recordist for video and TV projects I often need a little more than ORTF cardioids can provide, but it needs to be a manageable sized mic array.

Before you leap to respond, I just don't like the sound of MS. I love the sense of space that coincident arrays mostly kill off in their mathematical perfection. And no, I'm not blaming maths (at least not for this - I've had a few currency deals not go my way that should not have been on me!)

What really struck me about the tone of the conversation was the number of folks championing theory and proper technique - I've gotta say I think you're missing the point.

OP had a need, and he found a solution. That's what gets you paid in TV and film land (I may not know enough about what some of y'all do to make money

Theory is great - but it's a great starting point. Reality is how does it sound - and for me and OP - do the folks higher up the food chain find it flexible/useful to add a completely optional 3rd channel of info for free?

Some of you surely just mean to offer up what's written as best practice, but don't forget it's a real world and flexibility keeps you alive - remember OP was sharing VERY helpful experience.

Perhaps we could embrace that instead of telling him all the things he was theoretically doing wrong.

If we don't experiment, fail, occasionally succeed, and SHARE this information, guys like me with incredibly limited resources can't learn from you all.

I'm not looking to get yelled at, but I am looking to see folks embrace the idea of being able to share without be belittled or corrected when he was so up front about his unique personal needs.

I found proof in OP's idea and recording that lets me spend money on some omni's to augment our limited resources.

Thanks for that.

Perhaps one day I will have the courage to transgress the pages of this site with my own technically imperfect technique so we can all enjoy sound and music as fans, not mathematicians. Ok, that was rude
Old 8th May 2016
  #14
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Quote:
Originally Posted by DCPatterson View Post
Hey guys - I stumbled across this article a couple of years late, but found it really interesting.

...

Perhaps one day I will have the courage to transgress the pages of this site with my own technically imperfect technique so we can all enjoy sound and music as fans, not mathematicians. Ok, that was rude
I can agree with you on this. Although some time ago, maybe Renec could do 3 "mixes" (NOS+centre omni, NOS only and a summed mono of all 3 mics).
And maybe a moving and more "familiar" sound could help to hear more clearly the quality/veracity of the resulted sound of the mixes...?
Old 8th May 2016
  #15
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surflounge's Avatar
Quote:
Originally Posted by Strabinsky View Post
I can agree with you on this. Although some time ago, maybe Renec could do 3 "mixes" (NOS+centre omni, NOS only and a summed mono of all 3 mics).
And maybe a moving and more "familiar" sound could help to hear more clearly the quality/veracity of the resulted sound of the mixes...?
Love to hear 3 omni mics mixed to mono, also NOS+centre omni. Some rooms are too small for a decca tree.
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