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Author Topic: Oddball microphone technique (OMT) - part 2  (Read 30736 times)

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Offline Gutbucket

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Re: Oddball microphone technique (OMT) - part 2
« Reply #360 on: March 28, 2019, 09:02:54 AM »
^ Cool.  Looks like a nice little music joint.

I'm going to play around with the use of a single omni channel option, but so far I definitely prefer how having the low-pass / high-pass line falling out at 120 Hz.

120 Hz seems more reasonable to my way of thinking, but whatever works and sounds right is right!  The single omni mono option may or may not be better, you'll need to give it a listen in the mix to find out. 

Unfortunately, I was unable get a chance to listen last night.
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Offline kindms

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Re: Oddball microphone technique (OMT) - part 2
« Reply #361 on: April 07, 2019, 07:01:49 PM »
So another OMT outing

This time we ran

AKG ck22s split 4ft >V2, We had AKG ck61s basically PAS split 2ft and then we ran the AKG c426 Blumlien fig8s 90degrees

Pretty good time. The cap is really being strict with the whole 7ft thing. kind of sucks as people like to chat there. But ultimately I think a solid representation of the room and music etc

https://archive.org/details/dbb2019-04-06.AKGc426AKGck22AKGck61
AKG c426, AKG414 XLS/ST, AKG ck61, ck22, >nBob colettes >PFA > V3, SD MixPre >  TCM-Mod Tascam HDP2, Sony M10
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Offline Twenty8

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Re: Oddball microphone technique (OMT) - part 2
« Reply #362 on: April 07, 2019, 10:05:48 PM »
So another OMT outing

This time we ran

AKG ck22s split 4ft >V2, We had AKG ck61s basically PAS split 2ft and then we ran the AKG c426 Blumlien fig8s 90degrees

Pretty good time. The cap is really being strict with the whole 7ft thing. kind of sucks as people like to chat there. But ultimately I think a solid representation of the room and music etc

https://archive.org/details/dbb2019-04-06.AKGc426AKGck22AKGck61

Nice recording!
I used to go see DBB all the time when I was in college.  Nice to see they are back and banging.
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Re: Oddball microphone technique (OMT) - part 2
« Reply #363 on: May 02, 2019, 03:47:12 PM »
From last night... I played around a wee bit with another improvisational rigging.

I was set up at the stage-lip, center.  I had Güde Head on his torso box, which i usually run "square" in relation to a imaginary line that closes a 180º hemispherical stage presence of the ensemble.
This time, I thought I'd turn Güdes chest 90º, such that it became diagonal, or rotated 90º from normal; see image 6743. In that thought I also thought that I would be able to utilize the box as a PZM-BLE stereo arrangement. Over the PZM-BLE arrangement, I flew the CM3 pair at 0º forward and 180º rearward.
I'm not sure that there needed to be a finished mix, as the PZM-BLE two channel stereo recrdong is quite a listen in its own right. But I mixed it down anyway, and, need time to check it out.

Güde in stealth mode, again; img6734
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Offline Gutbucket

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Re: Oddball microphone technique (OMT) - part 2
« Reply #364 on: May 02, 2019, 06:18:51 PM »
Cool technique using the "90 degree wedge" box orientation for boundary-mounting.

Similar to Pierre Sprey's Mapleshade recording setup using modified PZMs mounted on an acrylic-wedge-



PS- I mention this mostly as a technically, but "PZM" (acronym for Pressure Zone Microphone) is a Crown trademark, referring to their original design which mounts the capsule such that it is facing the integrated boundary/base plate just a fraction of an inch away from it.  The microphones in the photo above are modified Crown PZMs, taped to the larger lexan sheets forming the wedge.  In contrast, the technique itself is simply one of "boundary mounted omnis", regardless of the make of the microphones used in a boundary-mounted arrangement.  In other words, its technically "PZM" only if one uses Crown PZM microphones.
« Last Edit: May 31, 2019, 04:21:23 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<<

Offline heathen

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Re: Oddball microphone technique (OMT) - part 2
« Reply #365 on: May 31, 2019, 01:08:02 PM »
How narrow can we push it?

I've got Image Assistant up now, with L/R supercards spaced 31cm and angled a full 180 degrees apart.  I've switched the center microphone to a figure-8, as that is the only pattern available in Image Assistant which is tighter in front pickup than supercardioid, placed 8cm forward of the L/R pair.  In the taper world one might use a shotgun in the center with good reason, yet a fig-8 will be better behaved with regards to stereo imaging which is what Image Assistant is primarily about.  This produces an SRA of 138 degrees, which is still wide, but considerably more narrow than 180 degrees.

Messing with the Image Assistant more today, I am surprised at the impact a level difference can have on an OCT2 array.  Bumping up the level of the center channel even just one db has a noticeable impact on the localization.

Maybe I should just record in mono and call it good  ;)
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Offline Gutbucket

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Re: Oddball microphone technique (OMT) - part 2
« Reply #366 on: May 31, 2019, 04:58:38 PM »
It does, but in reality I always end up adjusting the level of the center channel against that of the L/R pair afterwards by ear to best effect. While doing that, ideal image distribution is only one of several things I'm listening for- it's important, but not most important.  A higher priority is achieving an appropriate energy balance across the entire front soundstage with good center solidity, and sufficient clarity of the sources on stage dominating the center content.

Mono is simple in terms of gear, but really good mono is considerably more constrained and thus more difficult to pull off in a situation in which we have limited control than multi-channel surround!.. or 2-ch stereo. By contrast, making a really good single channel recording requires most everything be optimally balanced prior to reaching the recorder.

IMO, a large part of what makes OMT attractive for tapers is that although the setups and gear requirements are more complicated, it provides very welcome flexibility and options for manipulating things to best sonic advantage after the recording is made.  OCT2 intended for 2-ch is similar in that way, if a bit more specialized if the optional omnis aren't recorded as well, in that it is completely dependant on the totally side-facing supercard pair alone and no other channels for adding "stereoness".   

A fundamental philosophical as well as practical attraction of both OCT and OMT for me is that they essentially start with a single "mono-like" center microphone position and build upon that, with the additional channels providing extended dimensionality past mono to 2-ch stereo and on further still to multichannel playback.  Even if that "mono-like" center position evolves into a coincident pair rather than a single microphone.
« Last Edit: May 31, 2019, 09:11:36 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<<

Offline heathen

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Re: Oddball microphone technique (OMT) - part 2
« Reply #367 on: June 12, 2019, 01:31:30 PM »
After several outings now running an OCT/OCT2-type array, I'm on the fence about whether it's right for creating a recording meant for two-channel listening.  There is of course a certain "no duh" element to this because, as I understand it, OCT was made for multi-channel playback with a discrete center channel.  (Or maybe that's OCT2...or maybe both.)  That said, it also doesn't seem like two-channel playback should be out of the question.

The primary uncertainty I'm having with it is the stereo imaging on two-channel playback.  Now obviously right out of the gate there's a question here about how much stereo imaging was present from the source, since a lot of the mixes at shows I'm recording are mono or mostly mono.  Sometimes, though, I'm close enough to pick up stereo information from the stage.  Also there are sometimes stereo elements to the PA mix.

Another thing that's giving me pause about OCT/OCT2 for the type of shows I'm recording is that it introduces a lot of reverberant sound.  (Having said that I know that even when mics are pointed directly at the stacks we're still getting lots of reverberant sound, at least indoors.  Maybe the more accurate way of saying what I mean is that the side channels in OCT/OCT2 seem to pick up a greater ratio of reverberant to direct sound.)  The center mic, obviously, gets a lot of direct sound because it's pointed directly at the center of the sound source.  Listening to that on its own isn't fun because it's just mono.  In order to get some stereo sound, then, I'm bringing up the level of the side mics.  But doing that means bringing in a lot of reverberant sound.  So I'm ending up with a choice between largely mono-sounding playback or highly reverberant playback.

I'm rambling a bit here and I'm not really certain what my point is other than I'm not sure how appropriate OCT/OCT2 is for two-channel playback.  The reason I got interested in OCT/OCT2 to begin with is I want to have a really strong center to my recordings (partially because there's so much mono information at the shows I record, and partially because I think it gives recordings a really nice sense of presence? immediacy?  I'm not sure what term fits here).  At the same time, I do want to have good L/R information.  I think about what the sound is like at shows I attend, and usually it feels more like a wall than something with a lot of depth and dimension to it.  So, how can I capture that so that on playback there is this wall of sound coming at the listener?  That's what I'm trying to figure out, in the big picture context.
Recordings on LMA: https://archive.org/search.php?query=taper%3A%22Lucas+Lorenz%22
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Offline Gutbucket

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Re: Oddball microphone technique (OMT) - part 2
« Reply #368 on: June 12, 2019, 07:16:39 PM »
I think about what the sound is like at shows I attend, and usually it feels more like a wall than something with a lot of depth and dimension to it.  So, how can I capture that so that on playback there is this wall of sound coming at the listener?  That's what I'm trying to figure out, in the big picture context.

Godspeed you fellow knight chasing the dragon's tail. Having drunk from the same chalise I wish for the same. If our listening experience at a concert is an immersive one of a large all-encompassing wall of sound in front supported by live audience and room ambience all around us, then expecting a strong emulation of that experience from two speakers placed in front of us (and neither directly in front) is a quite tall order.  The best way I've found for translating the "big solid wall of sound" experience aspect you describe is to use a reproduction system which enables a more robust emulation of the original experience, tailoring the recording setup to suit that playback arrangement.  I do that using three to five speakers across the front, seven to nine in total all the way around.  I also realize this is not the answer you are looking for.

It's the answer hardly anyone accepts, including tapers, which is ironic in that I find the most useful application of surround reproduction, other than movie sound and gaming where it has achieved acceptance, is the enjoyment of "live performance from the audience perspective" recordings.  Its best for the stuff we do.

But enough pie-eyed thinking, lets talk OCT/OCT2's suitability for 2-channel stereo playback.. or more specifically, it's suitability for the situations in which you are recording...
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<<

Offline Gutbucket

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Re: Oddball microphone technique (OMT) - part 2
« Reply #369 on: June 12, 2019, 07:50:47 PM »
Quote
Another thing that's giving me pause about OCT/OCT2 for the type of shows I'm recording is that it introduces a lot of reverberant sound.  (Having said that I know that even when mics are pointed directly at the stacks we're still getting lots of reverberant sound, at least indoors.  Maybe the more accurate way of saying what I mean is that the side channels in OCT/OCT2 seem to pick up a greater ratio of reverberant to direct sound.)  The center mic, obviously, gets a lot of direct sound because it's pointed directly at the center of the sound source.  Listening to that on its own isn't fun because it's just mono.  In order to get some stereo sound, then, I'm bringing up the level of the side mics.  But doing that means bringing in a lot of reverberant sound.  So I'm ending up with a choice between largely mono-sounding playback or highly reverberant playback.

I concur with your observations-  OCT can be pretty 'verby.  When mixed to 2-channel, the L/R side-facing supercardioid pair pretty much acts in a way similar to the Side channel of a Mid/Side pair and its polarity inverted copy, except with the two channels physically spaced away from each other rather than being coincident.  Think of it like dialing in a Mid/Side matrix- only a small range of ratios works well, and although the ability to make that adjustment is a godsend, we are essentially stuck with the direct/reverberant ratio present at the location in which we recorded.  We can choose clearer and more solid but overly monoish or over-verby but with good stereo width. (EQing the center and sided differently can help somewhat if you want to try that)

Other than selecting a different recording position, the answer is essentially the same regardless of the number of microphones used: Point the directional mics that are intended to provide directional stereo imaging aspects more toward the sources, and compensate for the reduced angle between those microphones with increased spacing.

I think of OCT as especially well-designed in concept, and very good for its intended use, yet rather specific in appropriate application.. sort of like Blumlein in the real world.  Variations on it are more useful for me than it is on its own, but its an excellent conceptual 3-microphone starting point.  I never run OCT on its own, just like I never run M/S on its own, yet both are core components of my setup.  I no longer run just a single pair of omnis either, so I guess it apples there as well.

Quote
I'm rambling a bit here and I'm not really certain what my point is other than I'm not sure how appropriate OCT/OCT2 is for two-channel playback.  The reason I got interested in OCT/OCT2 to begin with is I want to have a really strong center to my recordings (partially because there's so much mono information at the shows I record, and partially because I think it gives recordings a really nice sense of presence? immediacy?  I'm not sure what term fits here).  At the same time, I do want to have good L/R information.

TL:DR-
If you want to give OCT a few more goes, try revising the setup by angling the supercards forward 45 degrees while moving them wider apart.  That will trade away some L/R channel separation and level-difference stereo for a less verby, more direct sound by pointing all three mics closer to on-axis with the sound sources, yet compensates for the loss of stereo difference information by moving the three microphone positions farther apart to help achieve a similar Stereo Recording Angle.   Also consider trying a PAS X/Y pair in place of the center microphone.  Actually you might want to try a coincident center pair first.  Do both.  It's then no longer OCT, but these changes should help improve the aspects you are seeking.

My current thinking about increasing the flexibility of the OMT setup I'm using in order to make it rapidly adaptable to all the typical open recording situations I encounter, is to figure a way of easily adjusting angle and spacing of the OCT-style 180-degree opposed supercardioid pair within a small but sufficient range of adjustment.  I want to be able to run an straight OCT-like center microphone triplet outdoors or in a really great room, yet be able to angle the L/R microphones up to 45 degrees forward for most things indoors or on-stage, while increasing the spacing between them to compensate.  Using a coincident pair at the center microphone positions helps too.
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Offline heathen

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Re: Oddball microphone technique (OMT) - part 2
« Reply #370 on: June 12, 2019, 09:45:20 PM »
I think about what the sound is like at shows I attend, and usually it feels more like a wall than something with a lot of depth and dimension to it.  So, how can I capture that so that on playback there is this wall of sound coming at the listener?  That's what I'm trying to figure out, in the big picture context.

Godspeed you fellow knight chasing the dragon's tail. Having drunk from the same chalise I wish for the same. If our listening experience at a concert is an immersive one of a large all-encompassing wall of sound in front supported by live audience and room ambience all around us, then expecting a strong emulation of that experience from two speakers placed in front of us (and neither directly in front) is a quite tall order.  The best way I've found for translating the "big solid wall of sound" experience aspect you describe is to use a reproduction system which enables a more robust emulation of the original experience, tailoring the recording setup to suit that playback arrangement.  I do that using three to five speakers across the front, seven to nine in total all the way around.  I also realize this is not the answer you are looking for.

It's the answer hardly anyone accepts, including tapers, which is ironic in that I find the most useful application of surround reproduction, other than movie sound and gaming where it has achieved acceptance, is the enjoyment of "live performance from the audience perspective" recordings.  Its best for the stuff we do.

But enough pie-eyed thinking, lets talk OCT/OCT2's suitability for 2-channel stereo playback.. or more specifically, it's suitability for the situations in which you are recording...

Actually I've thought very seriously about moving to, at a minimum, three-channel L/C/R playback for exactly the sort or reasons you're talking about.  I still can't help but think about the fact that most other listeners will be using two-channel playback, but how much I should care about that is a whole 'nother philosophical discussion...
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Offline Gutbucket

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Re: Oddball microphone technique (OMT) - part 2
« Reply #371 on: June 14, 2019, 07:53:15 PM »
Actually I've thought very seriously about moving to, at a minimum, three-channel L/C/R playback for exactly the sort or reasons you're talking about.  I still can't help but think about the fact that most other listeners will be using two-channel playback, but how much I should care about that is a whole 'nother philosophical discussion...

This gets to the crux of my own recording journey, with the open taping part of it reflected in this thread.  I ventured into 3+ channel reproduction out of curiosity, exploring whether it made a significant improvement for listening to my own recordings as well as the processes of making them. I was similarly concerned about complications and potential problems in diverging from the standard 2-channel stereo reproduction path.  Yet the improvement of having three identical speakers set up correctly across the front was so compelling for a number of reasons that I couldn't let that go, even if it was only for my own listening.  I began to feel that stereo reproduction over speakers really should have been 3ch LCR from the start (the conclusion Harvey Fletcher's Bell Labs research group reached back in the 1930's) although the limitations of 30's-50's era tech imposed a maximum practical of channel count of two. Once stereo was commercially realized via the stereo LP in the late 50's and widely adopted by the mid to late 60's, two channels had become the de facto standard for music.  Commerce had spoken.

IMHO it would have made better conceptual and engineering sense to achieve stereo and beyond by building upon mono in a hierarchical way.  Start with single channel mono, and rather than discarding that and starting over again in the move to stereo, instead build upon that basic foundation by adding Left & Right channels to the already established strong center, extending it to 3ch stereo (LCR).  And further extended to 4 channels with the addition of a single ambience channel.. and so forth.

Like my addition of the center channel, the introduction of a single recorded "room and audience channel" was a similarly large improvement.. one of a very complementary but different nature.  I introduced this at the same time I added the front center channel - after all I was using a 4 channel recorder.  A single ambience channel can do a very good job of capturing and carrying the ambient information.  The L/C/R channels are all somewhat similar in their role.  They are direct-sound focused and define the reproduction quadrant in which clarity, solidity and good directional imaging are key attributes. The ambience channel(s) is perhaps most useful in representing the opposite of that LCR stuff.  What is important for it to contain is not imaging, solidity, and up-front LCR stuff, but rather the exclusion of as much of the direct-sound present in the LCR channels as practical, allowing the ambient sound to be captured clearly and not masked by redundant front-arriving direct sound.  In the big picture, this ultimately allows it to serve a sort of a perceptual negative feedback role in relation to the primary sound arriving from the front, making the sound presented through the LCR quadrant perceptually clearer, less cluttered, less reverberant and more open.   The immersiveness it provides, with audience reaction coming from all around is cool too, as is how it frequently makes the bass sound more correct, but what is really interesting to me is how the inclusion of a channel which ideally contains only reflections, audience reaction and reverb makes the perception of the front quadrant material clearer and more like the real thing.
 
The ambience channel is also categorically different from the center in that it is ideally reproduced very diffusely, with its content spread all around the back of the room via a number of speakers.  This is another from of stereo information, an entirely different aspect than directional imaging and just as valuable..  which becomes increasingly valuable the more distant and reverberant a recording is, where directional imaging sharpness becomes minimal.  In a way, its focus is the opposite of imaging.. representing the "anti-front" stuff.  Ironically the front stuff becomes stronger with its inclusion rather than less so, the opposite of what most tapers assume when they see an extra microphone or two pointed directly away from the stage and PA.

I took some time trying to determine which additional channel would be more important to me if I were limited to a total of three channels rather than four- the center channel or the ambience channel?  This was much more difficult to decide than I thought it would be. I initially figured the center channel would certainly be the top choice, and eventually concluded that is indeed my preference, but not at all to the degree I expected. It wasn't like the addition of each channel altered one particular set of aspects in isolation, such that it was easy to choose the more-solid imaging, stronger center solidity and increased clarity that the center channel addition provided over what the ambience channel added.  Because what the addition of the ambience channel provided was not more ambience for an already reverberant AUD, but rather something more like a cleaning up of the ambience already in the recording, resulting in increased spatial clarity, openness and dimension (in addition to the immersive aspects of extending the reproduction of ambience and audience around the sides and back to envelop the listener).  Mostly, the additional channels helped everything work together in a better way..  a case of the whole being greater than the sum of its parts.  If I was really forced to choose I'd grudgingly take the center channel over the ambient one in most cases.  However, my actual conclusion was that I was unwilling to sacrifice either, and fortunately had no need to do so.

I still feel to this day that 4 recorded channels (LCR + dedicated ambience channel) are where things really blossom strongly compared to 2 channel, and for the past decade all my stealth recordings have been made in a LRCB format ("B"=back-facing "ambience" channel).  Yet I'd not hesitate to record 3 channel LCR instead of 2 channel stereo if I were limited to 3 channels.  The issue later became wanting to run the center position as Mid/Side + L/R directional microphones, which left no available channels for the ambient information.

With that LRCB scheme, "B"=back, specifying the directional aspect of that recording channel. I used that convention to differentiate it from LRCS, which is 4-ch matrix surround ("S"=surround, the single channel of ambient surround information), which is closely related, yet not quite the same in important ways.

The open taping OMT rig I run now has grown to 8 channels, which is at the edge of my practicality and cost restraint envelope.  Yes it is better, which I why I do it, but I admit I am chasing the dragon's tail at this point.  4 or 6 channels are probably an good OMT channel count for most folks wanting to try these ideas.
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Offline Gutbucket

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Re: Oddball microphone technique (OMT) - part 2
« Reply #372 on: June 14, 2019, 08:15:43 PM »
^ That's mostly about the capture and multichannel playback side of things.  As for suitability for mixing to 2 channel stereo, I've found almost everything that works well recording for LCR stereo or multichannel surround playback also applies and works well for 2-ch stereo. The areas where there are different are few and relatively subtle. I'm happy to discuss them if you like.

Actually, rather than think of it as mixing to stereo, I think of it more like mastering from stems in comparison to mastering from a 2ch mix where things are more fixed.  It gives me more control and that's especially useful for recording in live taper situations where I cannot check the setup beforehand like in a professional recording situation.
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

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Re: Oddball microphone technique (OMT) - part 2
« Reply #373 on: June 14, 2019, 11:53:18 PM »
I began to feel that stereo reproduction over speakers really should have been 3ch LCR from the start (the conclusion Harvey Fletcher's Bell Labs research group reached back in the 1930's) although the limitations of 30's-50's era tech imposed a maximum practical of channel count of two.

You're in good company.  Paul Klipsch did a lot of work with three channel, for example: http://www.aes.org/e-lib/browse.cfm?elib=235 http://assets.klipsch.com/files/Dope_611120_v2n13.pdf?_ga=2.195201452.1609077799.1560570380-259552099.1560570380

I spent a bit of time reading about the Meridian Trifield system, and went so far as to look for an old Meridian preamp with it but didn't end up pulling the trigger.

I still may very likely implement a center channel, but it would require some serious lead time to get one that perfectly matches my L/R.
Recordings on LMA: https://archive.org/search.php?query=taper%3A%22Lucas+Lorenz%22
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Re: Oddball microphone technique (OMT) - part 2
« Reply #374 on: Yesterday at 06:07:56 PM »
I've also been curious about Trifield.  As I recall it is essentially an equal-energy-vector Mid/Side upmixing scheme derived by Gerzon.  The patent should be expired at this point, with parole-board release from commercial proprietary prison following. It shouldn't be very complex, maybe someone will make a plugin available for us to play around with outside of Meridian gear.  [edit- link to Trifield article describing the Meridian implementation, and discussing the Bell labs stereo experiments, Klipsch, Hafler.. http://www.meridian-audio.info/public/trifield%5b2563%5d.pdf]  Similarly, I'd like to play around with Logic 7 without being tied to Harmon gear and gear-related specific implementations of it.

I had lots of fun years ago playing around with the two recorded channels feeding more than two speakers thing, using Klipsch/Hafler sum/difference wiring setups. Most often ended up using a pair of difference channel speakers (L-R & R-L) spliced into a standard 2-ch stereo setup bouncing off the walls.  Later played with matrix surround modes (Dolby PLII, DTS neo, etc) which sometimes worked very well but often seemed overly tied to the specific implementations, varying from device to device, setup to setup, tweaking for different material. Three identical speakers in front helped a lot for arrangements trying to derive a center, as did using more speakers than ambience channels around the back.

The commercial surround matrices do a pretty good job of extracting ambience from a stereo difference signal, but I suspect something like Trifield would be far better at deriving a pseudo-discrete center channel in comparison to a simple (L+R) mono sum or the similar schemes used by the standard upmix matrices, which sometimes mess with the purity of the primary L/R channels too much.

In messing around with all that stuff, playing with the recording side of things, and playing around with what manipulations might be done in the processing phase in between I've put a lot of thought into the fundamental relationship between recording and playback.  Ignoring multi-take/multitracked panorama/mixed material (the majority of modern music) and modern proprietary 3D object-based cinema rendering schemes for material recorded using a single microphone-array (of which taper stuff is subset), consider that there are the following points at which the number of channels can vary:

The number of microphones used
The number of channels recorded
The number of channels used for processing/mixing
The number of channels delivered
The number of speakers used

The Bell Labs guys doing initial stereo research in the 1930s explored various combinations of that in a simplified form:
Number of mics
Number of transmission channels
Number of speakers
[edit- see the article linked above which has some description of the Bell experiments with regards to this]

Simple parity is the obvious straightforward solution: 2 mics > 2 channels > 2 speakers (or  3>3>3; 5>5>5; 7>7>7..)
This is standard stereo taping, and also me plugging my 4-8 ch multichannel recorder directly into the 5/7ch analog DVD inputs of a home theater receiver for playback.

But the asymmetric configurations get interesting:
~Recording few microphones, yet playing back through more speakers. ex: 2ch stereo > upmixed multichannel playback via Trifield, matrix surround upmixing, etc.
~Recording more microphones, yet playback using a lesser number of speakers. ex: OCT/OMT/SBD matrix > 2ch stereo.
   ^
The first is standard 2ch taping played back via a matrix surround mode, Trifield, Hafler, etc. The second is mostly what this thread is concerned with, likely to be the focus of most tapers reading it, and what you were posting about above concerning the suitability of OCT mixed down to 2ch.

~As does an "hourglass shaped" (many channels > fewer channels > many channels) symmetrical arrangement.
  ^
  This one has always interested me in that it fits standard 2-ch stereo distribution, making it universally compatible.  Likely not as good as a pure symmetric (many > many > many) arrangement, yet could it be made good enough to be acceptable (to me) if I could find an appropriate way to matrix encode it?  I could then mix to a single 2-ch master delivery format regardless of playback.  Everybody wins.  I've not been able to answer this yet.
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