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Author Topic: Oddball microphone techniques - part 1  (Read 165786 times)

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Offline Gutbucket

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Re: Oddball microphone techniques
« Reply #240 on: August 25, 2017, 07:10:41 PM »
On center mic forward spacing (all arrays not just spaced omnis + center 8 )-

As for spacing of the center mic forward of the L/R pair, I wouldn't worry overly much about it.  Play around with it, and with timing alignment of the center channel in post if so inclined, but I find it's far less significant than L/R spacing.  Much of that may be residual from Decca tree geometry history, intended to be flown over the conductor's head almost above and within the orchestra.  We are mostly recording from considerably further away, and the general trend is more L/R spacing with less forward spacing as the recording position is moved increasingly further back.  The most important basic mode of thought in this regards is IMHO good time-of arrival alignment for each side, independent of the other.  Spacing the center mic forward just enough to achieve good time of arrival between the center mic and outer mic on that side for the sound source(s) on that side.  Consider an imaginary line drawn between the Center mic and Left mic and arrange that to be perpendicular to an imaginary line drawn from the Left PA speaker to it's intersection with the line between the two mics.  Do the same for the right mic / center mic pair with respect to the right PA speaker.  With that arrangement, direct sound from the left PA speaker will arrive simultaneously at the Left mic and Center mic, yet will be just slightly delayed in the Right mic channel.  Vice-versa for the right side.  Doing that for arrays designed to be flown above an orchestra, with sound sources arrayed in a semicircle all around the recording position, one gets a deep triangular a Decca tree like arrangement, but from a recording positions further back, one gets an increasingly shallow but wide-based triangle.

This mode of thought concerns time-of-arrival alignment for the direct sound. When recording from further back that becomes easy to achieve when all mics are arranged more or less in the same plane.  Significant forward center mic spacing in that case may benefit from time-alignment in post by the addition of a slight center mic delay.  Play around with it.  Also consider Griesinger's 5-mics-in-a-row technique with no forward spacing of the center microphone at all works very well.   



OCT and Williams arrays are thinking more in terms of stereo image, but it's a fine-line in the real world between that and time of arrival as both work similarly.   If familiar with the OCT setup, consider that it's Stereo Recording Angle is tuned by varying the spacing between the L/R sideways facing supercards but the forward spacing does not change.  Basically the further away the recording position, the wider the L/R supercard spacing used, narrowing the SRA appropriately to accommodate the more distant perspective.  William's 3-channel MMAD extension of the Stereo Zoom is similar here, which is all about seamlessly linking the two Stereo Recording Angles (SRA) - that of the left/center mic pair and that of the center/right mic pair with out excessive gap or overlap.   I sometimes use Williams' MMAD charts when deciding on a good approximate forward spacing distance of a center mic between the omnis. 


From typical taper positions further back in the venue, I think increasing the forward spacing of the center microphone more than described above (possibly in combination with compensating alignment delay in post) may prove useful as a way to increase the distance between the three mics when it's otherwise difficult to space the outer microphones far enough apart, achieving good diffuse-field decorrelation (DFC) with a somewhat more compact overall foot-print than would otherwise be possible.  This is all about minimizing conflicts like comb-filtering between multiple mic sources (what the 3-to-1 rule is about, but in a different situation) as well as improving the sound of the ambient/reverberant content of the recording. One could also space the center higher than the omni pair instead of further forward of that pair to achieve this, which would retain good timing alignment for forward arriving sound without any need for timing compensation in post.

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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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Re: Oddball microphone techniques
« Reply #241 on: August 25, 2017, 07:55:31 PM »
OCT-

I think the OCT also looks pretty cool.

Love it outside where it's a primary basis of my current outdoor oddball setup.  Fantastically good imaging using 3 front speakers, and a really cool intense forward "presence" when mixed in to 2-ch stereo.  The 180 degree sideways-opposed facing supercards optimally reduce crosstalk reducing the need for a super-wide Left/Right spacing.  Because of that one can get away with spacings normally used with just two omnis of a just meter or less.  Just be careful indoors where those mics may be facing a reflective wall. I've had good results indoors from the sweet spot a few times but have not used it indoors extensively.  It was less good onstage for jazz trios in a small reflective room, where Williams 3-mic arrays using supercards pointing more at the on-stage sources worked better (sort of like a mini directional Decca tree arrangement).  I've considered increasing the L/R supercardioid spacing and angling them forward at something like a 90 degree angle between mics indoors to compensate, but haven't tried that extensively.

Quote from: thatjackelliot
For that OCT layout . . . what does "omni directional" mean?

Also, on the left side we have two mics with complementary 100Hz high and low pass filters being summed. No such setup on the right side, just the "omni directional" mic. The asymmetry puzzles me. Perhaps that arrangement on the left side creates a single "omni directional" mic and we see it simplified on the right. It baffles science.

Same on both sides, just shown on the left.  The omnis are intended to extend the bass response of the supercards, arranged coincident with them and low passed at the point where the supers loose sensitivity.

I make a few oddball variants on standard OCT-
1) I use a center supercard instead of a carioid.  That increases center mic isolation from audience noise and room sound (more SBD-like direct sound from the center mic), and theoretically allows for a slightly narrower L/R supercard spacing to produce the same SRA linking.  Of these two aspects, the increased forward directivity thing with less side pickup is the most important aspect for audience taper positions by far.

2)I like the omnis spaced twice as wide (about 1.5 to 2meters), and don't  low pass them.  That makes for more involving wide-spaced omni stereo bass which I dig, and a more open pickup of ambient content.  I EQ and mix the omnis in to taste which contours their mid and high frequency contribution, EQing for both bass timbre and appropriate ambient air and room sound.  This wider spacing is difficult to achieve on a single stand with typical omnis, but is achievable using lightweight miniature mics.  The supercards and omnis are all in one plane so they can be arranged along one (long) bar.  For surround use I send the mids and highs from the wide omnis to the surround channels.

3) I add a backward facing center cardioid or supercardioid.  As mentioned above I like to have mix control over venue and audience ambience and a rear facing directional mic allows for that (the omnis pickup fantastically good ambience, but too much direct sound to provide really good mix control over the ambient balance). I figure a cardioid here is optimal for achieving maximum rejection of the direct sound arriving from the front, but the supercards I've used for this seem to work just as well if not better, so I now use identical miniature supercards all around for Left/Right/Center/Rear.  This keeps timbre the same all around and also makes the entire 6-mic array completely front/back symmetrical, producing both front and rear facing OCT arrays.

[edit]- the OCT surround array specifies two rear facing cardioids, spaced apart and a bit further back than the single rear-facing mic I'm using.  That's probably a better setup for both 5-channel and 2-channel mixdowns as long as one is capable of dedicating two recording channels to backwards facing mics, because it spreads that ambient surround content in the playback image out to the sides making it less likely to conflict with the forward facing center channel information.  In my oddball variant, in addition to using the omnis to provide stereo bass extension below the limits of the OCT supercards, the wider-spacing of the omnis than the supercards (the omnis are essentially spaced twice as wide) allows the omnis to serve as surround channels in combination with the single rear-facing mic.  The spacing between L/R supercards and L/R omnis is essentially insignificant at low frequencies where the wavelengths in question are long and the omnis are meant to extend the frequency response of the supercards, but significant at shorter wavelengths where the increased spacing serves to decorrelate the omni mids and highs (routed to the surround channels or mixed in to 2-channel as ambience) from the mids and highs from the L/R supercardioids.  So the omnis end up serving dual purpose as bass extension and as ambience/surround channels, and arguably do a better job in both rolls in this configuration as well as being more easily managed since they are positioned further out along along the same telescopic bar(s) as the L/R supercards.
 
« Last Edit: August 28, 2017, 04:23:30 PM by Gutbucket »
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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Re: Oddball microphone techniques
« Reply #242 on: August 25, 2017, 08:08:27 PM »
The Double MS looks interesting, I assume the three mics would be coincident, would the body of the reverse facing cardioid interfere with the front facing one in anyway (reflections, baffling, etc)? I guess you would just use the front facing M as a center channel in a 5.1 scenerio?

Double MS is very cool for 2-channel coincident stereo.  All three mics need to be as coincident as possible.  It is Ambisonics without height - think SoundField or TetraMic but horizontal plane only.   It's primary advantage is it's very compact size, and the ability to change the microphone configuration in post, both of which have obvious advantages for tapers. Point virtual mics of any pattern from omni to 8 in any direction in post!  That makes it super useful for tapers where setup is rushed and one can't monitor during setup.  Place it in a good spot and tune it to any coincident configuration later.

Drawback is that it's limited to coincident mic configurations only.   It works for surround but isn't optimal for more than 4 channel playback as it doesn't provide enough separation between channels.   You need spacing between mics to optimize for that.. and maybe for 2-channel stereo as well depending on your feelings about coincident verses near-spaced mic configs.

I think it would be best combined with spaced omnis.  Use it like a super configurable center pair.  You also get a rear facing mic at the same time if you want one.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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Re: Oddball microphone techniques
« Reply #243 on: August 25, 2017, 08:18:42 PM »
^ That requires 6 channels total, same as my OCT+ variant.  I'm considering setting up a second rig using the TetraMic + spaced omnis into my old DR-680 mk1.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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Re: Oddball microphone techniques
« Reply #244 on: August 28, 2017, 12:25:07 PM »
I was only able to get the omnis spread about 20 inches, and the figure 8 was only a couple inches in front of the omnis (there's a picture in the Rig Pictures subforum). 

Not being able to get the microphones spaced as widely as desired is probably the most common taper problem with omni setups using more than 2 microphones, in which case the introduction of a center mic can make the stereo recording overly monophonic.  But that doesn't mean it shouldn't be tried or can't be a helpful addition - I listen first to the omnis alone to determine how well they work on their own just with some EQ, then compare that to mixing in some center mic.  To my way of thinking, EQing the omnis alone first is important when making this comparison so as to minimize the timbrel influence of the center mic addition.  That's because I feel the center mic should be helping in ways other than just in terms of simple frequency balance which could be alternately be achieved just with EQ.  Comparing after EQing helps remove timbre from that decision process, since it is one of the more most predominant aspects I immediately notice before more subtle things like stereo image width, depth, solidity, precision. 

If I can't mount the omnis as wide as I'd like, I look at tweaking the mounting to get as much spacing as possible with the current setup.  Can I clip the mics to the ends of the bar instead of to the top of it? I'll also angle the omnis outwards, which often increases spacing by a few inches more and introduces some directional difference at high frequencies.  If I have a center mic, I don't hesitate to point the omnis fully sideways 180 degrees apart (just like the L/R supercards in the OCT setup) even if they are spaced widely enough.  That "makes perceptual room" for the direct high frequency stuff from the center mic in the middle of the stereo image, and also makes the ambient room sound more open.  A directional mic with a more-narrow front pickup angle such as a bidirectional or hypercardioid helps with less than ideally-wide-spaced omnis as well.  Another strategy is to use subcards or cardioids in place of the omnis, and point them 180 degrees apart.  The opposite pointing directionality helps counter the minimal spacing with level differenece substituting for timing differences, and the forward pointing center mic takes care of the direct arriving HF information.

[edit] Another thing which can be tried with an overly-narrow spaced omni pair to do some Mid/Side stereo widening on it, especially when mixing in a center mic.  That increases the difference information so that the addition of the center mic doesn't make the recording overly monophonic / Mid-channel dominant.

« Last Edit: August 28, 2017, 12:37:33 PM by Gutbucket »
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

mfrench

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Re: Oddball microphone techniques
« Reply #245 on: August 28, 2017, 12:40:49 PM »
Give up on spacing them... baffle them, instead. 
A baffle gets the omnis close enough together that they can very well be thought of as a coincident pair.  The baffle provides amplitude differences that are substantial enough to give great imaging. With the spaced mic timing issue drastically diminished with the baffle, that gives a lot more control over omni's.

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Re: Oddball microphone techniques
« Reply #246 on: August 28, 2017, 12:48:45 PM »
Give up on spacing them... baffle them, instead. 
A baffle gets the omnis close enough together that they can very well be thought of as a coincident pair.  The baffle provides amplitude differences that are substantial enough to give great imaging. With the spaced mic timing issue drastically diminished with the baffle, that gives a lot more control over omni's.

Most of the instances I'm recording is in an audience with people behind me, and I don't feel great about blocking their view more than already occurs with a normal setup.  From what I've read, a baffle needs to be a pretty decent size to be effective.
Mics: AT4050ST | AT4031 | AT853 (C/SC) | Line Audio CM3 | Sennheiser e614 | Sennheiser MKE2 | DPA 4061 Pre: CA9200 Decks: Zoom F8 | Roland R-05

Offline Gutbucket

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Re: Oddball microphone techniques
« Reply #247 on: August 28, 2017, 01:05:39 PM »
^Moke makes some really tiny baffles work well, but that's really achieving an entirely different thing than what one gets from spaced omnis.  At high frequencies it is essentially the same as pointing a pair of mics further apart rather than spacing them more.  Normal baffles don't have any effect at all at low frequencies, where only mic-spacing or pattern directivity works.  Pointing full-bodied omnis 180 degrees apart is very much like using a tiny baffle- the mic diaphragm itself, mic-housing and amplifier-body effectively act like a small baffle.

Baffled omnis are are near-spaced or coincident setups and have some similar qualities to those setups.  But the omni pattern lends a naturalness that differs from many near-spaced cardioid setups.  Perhaps the best comparison with baffled omnis are other nearly-omnidirectional near-spaced or coincident setups in terms of overall room sensitivity, such as Blumlein 90-degree crossed bidirectionals, which are fully omnidirectional with respect to the room.


« Last Edit: August 28, 2017, 01:22:01 PM by Gutbucket »
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline heathen

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Re: Oddball microphone techniques
« Reply #248 on: August 28, 2017, 01:10:29 PM »
I'm going to try running omnis in a DIN config for the fun of it this week.  Maybe closely-spaced omnis will become the real oddball technique  ;)
Mics: AT4050ST | AT4031 | AT853 (C/SC) | Line Audio CM3 | Sennheiser e614 | Sennheiser MKE2 | DPA 4061 Pre: CA9200 Decks: Zoom F8 | Roland R-05

Offline Gutbucket

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Re: Oddball microphone techniques
« Reply #249 on: August 28, 2017, 01:18:23 PM »
^ That can work well, but will definitely benefit from a baffle if you can rig one.

.. and perhaps some Mid/Side widening too.  Blumlein's original stereo technique before bidirectional microphones were made available to him used baffled head-spaced omnis + Blumlein difference shuffling, which is basically Mid/Side widening.  Jorg Jecklin also experimented with difference shuffling in his re-adoption of Blumlien's original baffle technique 40 years later.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

mfrench

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Re: Oddball microphone techniques
« Reply #250 on: August 28, 2017, 01:21:40 PM »
Give up on spacing them... baffle them, instead. 
A baffle gets the omnis close enough together that they can very well be thought of as a coincident pair.  The baffle provides amplitude differences that are substantial enough to give great imaging. With the spaced mic timing issue drastically diminished with the baffle, that gives a lot more control over omni's.

Most of the instances I'm recording is in an audience with people behind me, and I don't feel great about blocking their view more than already occurs with a normal setup.  From what I've read, a baffle needs to be a pretty decent size to be effective.

I don't want to highjack this thread, but, here is a show where my smallest baffle was tested against a pair of Schopes in a near-coincident array, in extremely loud conditions (Widespread Panic).  The miniature baffle held its own.
How much audience site blocking is that thing going to do?
I run baffles in front of the most discerning audiences in music in the classical/chamber world.  I've never heard a single utterance of blocking views.
Regarding what "they" say about baffle size, don't believe a word of it without trying it for yourself, especially not anything that Jurg Jecklin might have to say on the matter. I've proven him wrong on all of his stringent standards with my own parallel baffled omni experiments dating back to the mid-80's.

First two images: mini baffle at WsP concert
last three images: Large baffle for large diaphragm mics. Why? Because Jecklin said it would not work.

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Re: Oddball microphone techniques
« Reply #251 on: August 28, 2017, 01:30:09 PM »
Thanks for the info Moke.  That small baffle definitely seems unobtrusive.  Is it just a piece of foam or is there more to it on the inside?  I'd appreciate more info so I could give something like that a try.
Mics: AT4050ST | AT4031 | AT853 (C/SC) | Line Audio CM3 | Sennheiser e614 | Sennheiser MKE2 | DPA 4061 Pre: CA9200 Decks: Zoom F8 | Roland R-05

Offline Gutbucket

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Re: Oddball microphone techniques
« Reply #252 on: August 28, 2017, 01:35:05 PM »
Mr Jecklin isn't actually much of a stickler for conformity at all.  I've corresponded with him about baffles and shuffling.  He has simply related what has worked for him, and actually modified his setup considerably over the years.

I think it's others reporting what he's done in an overly specified manor, reporting whatever the dimensions of his setup are as some sort of gospel instead of the more important concepts underlying them, just because that's so much easier than understanding and translating the underlying principles at work.  I feel it's somewhat similar to Tony Faulkner being branded with the oft-reported super-specific spacing of the "Faulkner Phased Array" (near-spaced parallel bi-directionals) which he himself dismisses in every interview I've ever seen or heard when hes asked about it.  He understands how things work and shifts things around until they do.  It's others who attempt to saddle what he does with exact measurements and other specifics.

All that said, tiny omni baffles most definitely qualify as odd-ball!

[edit] extra-credit for identification of the TS member in green in Mokes first photo above, but only to new member's here (say joined post 2010).  Hint- it's not Moke, and he doesn't live anywhere near him.
« Last Edit: August 28, 2017, 01:38:58 PM by Gutbucket »
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

mfrench

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Re: Oddball microphone techniques
« Reply #253 on: August 28, 2017, 01:38:55 PM »
Its just foam.  THe mount is a piece of scrap aluminum flat stock, and screwed together with some construction screwws, and silicone adhesive. If I spent an hour at it, it meant that I took a fifteen minute break half way through it.
Truth,... Its the middle of a seat from a PortaBote (one of those 12' folding boats). THe seats ahve that foam on them, for floatation requirements.  I cut the foam out, and replaced it with those throwable float/seat pads.  This met my requirement for a throwable preserver on board, and saved that room in the small boat.
The foam consistency is of a fairly large air pocket, and the foam is firaly rigid, but still flexible. 
I've got to dig out the pics (in folders on my desktop after the rescuing them from Photobucket)
I'll post them here.

did I say that I can highjack a thread, or what?

mfrench

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Re: Oddball microphone techniques
« Reply #254 on: August 28, 2017, 01:42:32 PM »
Mr Jecklin isn't actually much of a stickler for conformity at all.  I've corresponded with him about baffles and shuffling.  He has simply related what has worked for him, and actually modified his setup considerably over the years.

I think it's others reporting what he's done in an overly specified manor, reporting whatever the dimensions of his setup are as some sort of gospel instead of the more important concepts underlying them, just because that's so much easier than understanding and translating the underlying principles at work.  I feel it's somewhat similar to Tony Faulkner being branded with the oft-reported super-specific spacing of the "Faulkner Phased Array" (near-spaced parallel bi-directionals) which he himself dismisses in every interview I've ever seen or heard when hes asked about it.  He understands how things work and shifts things around until they do.  It's others who attempt to saddle what he does with exact measurements and other specifics.

All that said, tiny omni baffles most definitely qualify as odd-ball!

[edit] extra-credit for identification of the TS member in green in Mokes first photo above, but only to new member's here (say joined post 2010).  Hint- it's not Moke, and he doesn't live anywhere near him.

Lets just call it,... Monday Morning Surliness.

When I first read his works, his was entirely stringent.  That was back in the early-mid 90's at a time when I was having to repair the cancer stricken circuit board of my MKE2002 pair (circuit board peeling and lifting; eventually solved by point to point wiring). I was having to face the reality that my old binaural comanions were dying, and I started into looking into alternate baffled omni theories beyond HRTF/Binaural.
At any rate,... Moke might be a little surly this morning. Sorry to all.

 

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