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Author Topic: Thinking about taking the Schoeps or AKG actives plunge. Best options?  (Read 10769 times)

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Offline Gutbucket

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Re: Thinking about taking the Schoeps or AKG actives plunge. Best options?
« Reply #60 on: March 04, 2015, 10:48:35 AM »
^^^
Just want emphasize that I'm not trying to be a contrarian here.  I'm very interested in your thoughts on this Mr. Satz.

This is what I was trying to get at in the thread titled: Cardioids which are most natural sounding off-axis? On-axis sound secondary, before the discussion died without much talk about these particular aspects. Specifically in these two posts:

http://taperssection.com/index.php?topic=169175.msg2102771#msg2102771

http://taperssection.com/index.php?topic=169175.msg2103095#msg2103095
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Offline voltronic

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Re: Thinking about taking the Schoeps or AKG actives plunge. Best options?
« Reply #61 on: March 04, 2015, 05:11:42 PM »
[treading carefully]
I respectfully have a couple issues with just the extra credit part, and I value your thoughts on this-
 
First, keep in mind that the original poster is mounting the microphones onto the surface of an ~8" diameter spheroidal sound-absorbent baffle.  That microphone arrangement method is the most common way sub-miniature omnis are used for music recording around here at TS, and the only way many members use them.  And that's going to create a much larger far off-axis response difference than a omni embedded in a 40mm acrylic sphere, due to significant differences in size and acoustic properties of the materials, both increasing that directionality and extending it farther down into the lower-midrange.

Second, I remain open and ready to be convinced of the value of the "usual working concept of recording with omnidirectional microphones", but I find it's not the highest-frequencies but the midrange and especially upper midrange where a directional level difference is valuable.  When I have separate control over the sound from the sides and back compared to the direct sound from in front, it almost always works best to cut the midrange and especially presence range but increase high-frequency energy significantly from all the non-front directions (and low bass).  A sort of 'loudness curve' seems to work best and sounds most natural to me. That curve doesn't resemble the difference in response between on-axis and average off-axis response of typical non-miniature sdc omnis at all, which is more like a low-pass filter with a pretty high corner frequency (the M50 gets closer).

I also like the concept of a truly omnidirectional omni which I can use that way, or change the response as I choose and make it directional in all sorts of ways to differing degrees- like including embedding in small spheres, or placing near absorbant baffles, or mounting directly onto hard boundaries. 

Am I both incorrectly interpreting my experience AND it it's a fortunate coincidence that although imposed by the physical size of their diaphrams, the difference in direct and diffuse responses of sdc omnis occurs in the correct frequency range and has the correct shape and level to achieve the acoustic response we want for recording from a distance?

Isn't similarity of frequency response on and off-axis a basic design goal for directional microphones? I'm not asking rhetorically, It might be that shaped response differences are desirable in directional mics as well, for the same reasons.

Earthworks QTC series are very small diaphragm and extremely uniform response on- and off-axis.  I consider them the gold standard for omnis, at least equal in quality if not in some respects superior to DPA or Schoeps.  Not trying to stir the pot, just one man's opinion.
http://www.earthworksaudio.com/microphones/qtc-series-2/
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Offline DSatz

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Re: Thinking about taking the Schoeps or AKG actives plunge. Best options?
« Reply #62 on: March 04, 2015, 09:49:06 PM »
Gutbucket wrote:

> the original poster is mounting the microphones onto the surface of an ~8" diameter spheroidal sound-absorbent baffle. That microphone arrangement method is the most common way sub-miniature omnis are used for music recording around here at TS, and the only way many members use them.

Hmm, yes. I think I'm familiar with this type of spheroid--it has an uncannily similarity to that which many of us carry around on our necks, no?

My own recordings with omnis have been A/B with no solid object between the mikes, and that's the type of use for which I claim that having reduced off-axis response at high frequencies is valuable. I have no direct experience with "head-related" stereo recording, except for listening to binaural recordings over headphones, and some stereo sphere recordings made by Jerry Bruck using Schoeps microphones.

So on principle I'm not going to argue back. For that matter, people use all kinds of microphones with non-ideal characteristics, and they sometimes learn to make (or luck into making) good recordings with them nonetheless.

That said, I don't know of any professional-quality dummy head or sphere recording system that uses free-field-equalized (i.e. flat on axis) pressure transducers. They all use diffuse-field-equalized transducers, which, when measured in a free field on axis, show a rise of several dB at high frequencies depending on size. So I would be really surprised if the MK 2 were the best choice among Schoeps capsules for this application; I would still think that the MK 2 S would be distinctly preferable--for some people, maybe even the MK 3, depending on how they were oriented during recording.

--best regards
« Last Edit: March 04, 2015, 09:52:38 PM by DSatz »
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Offline Gutbucket

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Re: Thinking about taking the Schoeps or AKG actives plunge. Best options?
« Reply #63 on: March 05, 2015, 12:28:28 PM »
Thanks.   I value your expertise, experience and contributions here highly, and figure you're my best shot at digging deeper into this!

The free-field verses diffuse-field eq aspects I totally agree with, and I noted the head-mounted technique only as clarification of how the OP is using any of the microphones mentioned in this thread, which will effect response more strongly than off-axis differences due to capsule size.

However, although off-topic to the thread, what I'm really most interested in is discussing the part quoted below, in regards to the broader issue of on-axis vs off-axis response differences in general, in which A-B omni technique falls-

DSatz wrote:

> [snip] the usual working concept of recording with omnidirectional microphones is to WANT the microphone to have some directivity at high frequencies. You don't normally want to pick up reverberant, off-axis sound with the high frequencies at full volume; that clutters and confuses the result. So having identical high-frequency response at all angles isn't traditionally considered a virtue in an omnidirectional microphone, except by the marketing departments of certain manufacturers. In fact, the most historically highly revered omnidirectional microphones (the Neumann M 50 and its various successors and imitators) have pressure transducers embedded in 40 mm spheres specifically to increase the difference between frontal response and the response from all other directions, and to extend that directivity downward toward the midrange. That comes from many decades of practical experience in making live recordings from a distance.

Below is the jist of what I'm interested in, addressing that part. Quoting from my previous post-

"I find it's not the highest-frequencies but the midrange and especially upper midrange where a directional level difference is valuable.  When I have separate control over the sound from the sides and back compared to the direct sound from in front, it almost always works best to cut the midrange and especially presence range but increase high-frequency energy significantly from all the non-front directions (and low bass).  A sort of 'loudness curve' seems to work best and sounds most natural to me. That curve doesn't resemble the difference in response between on-axis and average off-axis response of typical non-miniature sdc omnis at all, which is more like a low-pass filter with a pretty high corner frequency (the M50 gets closer)."

And this (slightly rephrased for clarity)-
"is it a fortunate coincidence that although it's a 'side-effect' imposed by the physical size of their diaphragms, the difference in on-axis verses off-axis responses of non-miniature omnis just happens to occur in the correct frequency range and has the correct shape and level to achieve the acoustic on-verses-off-axis response we'd most like to have?" 

I can understand that a shaped response off-axis verses on-axis might be desirable for both directional microphones and omnis, rather than having an identical frequency response from all angles, with only level differences when moving off axis for a directional microphone.  But I'm looking for some deeper justification for the rolled-off off-axis upper response of omnis being most appropriate response for acoustical rather than historical reasons.  Partly because it needs to counter my personal experience that it's upper midrange and not the upper high-frequency range where increased directionality is truly appropriate and useful for omnis.  It's one reason I suspect the M-50's became more highly valued over other omnis where it's use is appropriate- being closer to an optimal on-verses-off-axis response for those situations.

Here's a new way of phrasing the question: Ignoring all historical and current mechanical manufacturing constraints, what would be the most desirable polar response, allowed to vary with frequency, for an ideal microphone designed to be used in situations where a stereo array of M-50 microphones has historically been most appropriate?

The links above to my posts in the other threads here are questioning is same aspect, exploring the shape of that response difference in a bit more detail.  I've never gotten good answers or discussion of those things either here or at GS when I attempted to discuss it over there long ago.
« Last Edit: March 05, 2015, 12:41:58 PM by Gutbucket »
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Offline DSatz

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Re: Thinking about taking the Schoeps or AKG actives plunge. Best options?
« Reply #64 on: March 06, 2015, 08:26:47 PM »
I don't think that the answer to your question is likely to come from any form of theoretical analysis that I'm aware of, although the type of omni that you're describing was designed in a laboratory (NWDR's--and then Neumann got the contract to manufacture the M 50 for them). As far as I'm aware it was a completely pragmatic design, not a theoretically-based one.

So I think it's fair to say that this type of microphone is its own model or ideal, in effect.

The one thing that has varied significantly in this design has been the capsules--Neumann used numerous different types in the different versions of the M 50/M 50a/M 50b/M50 c, and yet others in their latter-day recreations. Initially the capsules were fully equalized for the diffuse sound field, but fairly soon the curves became less highly emphasized on axis.

That might be due to the capsule types that Neumann happened to be making for other purposes at any given time, and/or to the difference between mono and stereo recording practices--no one would ever record stereo from the distances that were sometimes used for pickup of large-scale performances in the pre-stereo era, and the full diffuse-field equalization gives harsh, metallic-sounding results when used at conventional A/B stereo recording distances. But German broadcasters were required to use mono-compatible stereo recording methods, so it seems that this type of microphone passed out of favor altogether for a while, until A/B stereo and "Decca Tree" recording techniques became more prominent outside of Germany.

Do you know Martin Schneider's AES paper from 2001, "Omnis and Spheres - Revisited"? It's available for download from Neumann's Web site as "lect0043.pdf".

--best regards

P.S.: As you know, any first-order pattern can be created by summing the signals from a coincident omni and figure-8 pair in various proportions. As you may also know, some years ago Jörg Wuttke at Schoeps came up with the idea of breaking this down into three frequency ranges so that the summing formulas (and thus the resulting pickup patterns) could be made frequency-dependent at will. This was implemented with digital signal processing; specific equalization could also be dialed in to the various frequency ranges. The system was unfortunately quite expensive, but it was by far the best "microphone emulator" ever made, and as with M/S, it could be used either during recording or in post-production ("choose the microphones after the session is over"). -- More recently, Schoeps has come out with a software-based version of this approach (http://www.schoeps.de/en/products/categories/polarflex) which wouldn't be too expensive for someone who already has pairs of their omni and figure-8 capsules.
« Last Edit: March 06, 2015, 08:29:38 PM by DSatz »
music > microphones > a recorder of some sort

Offline Gutbucket

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Re: Thinking about taking the Schoeps or AKG actives plunge. Best options?
« Reply #65 on: March 13, 2015, 01:21:12 PM »
I am aware of Martin Schneider's AES paper from 2001 and will probably revisit it, it's been a long time since I read it.

Reading the information available on the Schoeps website for the Polarflex system has been very informative.  That is exactly the kind of tool needed to answer the questions I'm posing above in a empirical, non-theoretical way.   Can you point me to any discussion of how users have found it to be most useful to them, or other 'application notes'?

Polarflex is pretty much an answer to the first of two questions I recently asked of the ambisonic research experts on the 'sursound' mailing list,  concerning tools which could do similar things for 'virtual' microphones derived from ambisonic recordings.  I asked:

Can anyone point me to B-format tools which can produce a virtual
microphone output which has the following specifications?

1) Specify a changing polar response that varies by frequency, morphing
smoothly between two specified first-order patterns set at two specific
frequencies.

2) Specify a changing frequency response that varies between two user
specified equalization curves: a direct on-axis curve and a 180-degree
off-axis curve, so that the frequency response of the virtual microphone
varies smoothly by the angle of incidence.



Reading about the signal processing technique used by the Schoeps CMIT microphones has also been enlightening and informative.  I was aware of the CMIT 5 U, but only noticed the superCMIT 2 U after checking for more detail on how the system works.  These seem to be 'shotgun mics' which might actually have more application for music recording from a distance (as so often done around here due to setup constraints) than traditional shotguns that traditionally have such badly compromised off-axis behavior.  Any thoughts on that?

Thank you very much for all your help with this!
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