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Measuring microphone
Old 4 weeks ago
  #31
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kludgeaudio's Avatar
 
Quote:
Originally Posted by connloyalist ➡️
I realize that with my renewed interest in audio recording I am posting a lot of topics. If that is tiresome, my apologies. See it as a sign of enthusiasm that will probably decrease as my previous recording opportunity slides further and further into the past (I really feel for the forum members for whom this is their livelihood).

To the topic I have a question about.

From time to time I come across the term "measuring microphone". My understanding is that these are primarily intended for scientific applications and not for recording music. Measuring room acoustics for example. From what I gather these tend to have a wide and flat frequency response.

My question is this: I have always understood that to mean that these mics are not suited to recording music. But is that correct? And if so why? Because a wide flat frequency response might be a desirable thing under certain circumstances?
It used to be that if you saw something sold as a measurement microphone, you could be pretty sure it was an "IEC Type I Measurement Microphone" which is a very specific family of designs based on the Western Electric 640AA capsule. These microphones are omnidirectional; some of them are designed to be flat in the free field while others are designed to be used in a pressure situation like a sealed tube. In most cases the electronics are not designed for lowest possible distortion or lowest possible noise floor. In most cases these microphones require different powering than you would encounter in a studio.

Some of these microphones can be modified or otherwise adapted for recording use (and there is an article that I wrote on doing so in the July 2016 issue of AudioXPress magazine). They are not cheap, and they require a good bit of tinkering.

Now, there are some microphones based around IEC Type I capsules that are designed for recording work and those include the Josephson 617, the Sonodore, and the ACO Pacific 7052PH.
I am a huge fan of these designs. They are also not cheap.

Now... in the last decade or so, there has been a huge flood on the market of inexpensive "measurement microphones" that use generic omnidirectional capsules and rely on error correction tables to deal with the frequency response not being flat. Most of these microphones are not really as flat as you would want for recording and most of them are noisy and have comparatively high distortion since they are intended for things like room and speaker response measurements where noise and lowest possible distortion are not critical. These microphones aren't really all that great for measurement use let alone recording use, but you get what you pay for.

The catastrophically low-end example is the Behringer ECM8000... and actually there are at least three different microphones sold under that name. If you get a good one (and that means one of the later ones that don't have a transformer inside) they are very cheap and very omnidirectional and quite usable for loud sources like drums where the noise floor is not an issue. These microphones bear very little connection to the Bruel and Kjaer IEC Type I microphones but also sell for about 1/500th the price.
--scott
Old 4 weeks ago | Show parent
  #32
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kludgeaudio's Avatar
 
Quote:
Originally Posted by Klimermonk ➡️
Measurement capsules. I have been interested for a while in getting hold of some B&K (the 4145 is 1" diameter), perhaps with their old Falcon 2669 modular preamp, but not taken the plunge due to uncertainty of how worthwhile the effort would be. I have M296's, so it's not like I'm hurting in the LD true omni category, but I kinda wonder how close I could get to a DPA 4041.
Two B&K 4145 omnis with modified B&K 2627 preamps and modified B&K 2804 power supply with a Jecklin disc:
http://www.panix.com/~kludge/bk_examp.wav
This is on the distant side owing to some placement limitations and trying to avoid a flutter echo in the room. It's been high-passed too.
--scott
Old 4 weeks ago | Show parent
  #33
Gear Addict
 
"Catastrophically Low-End" should be a thread category here on Gearspace !

Very 'you are there' recording.
Old 4 weeks ago
  #34
Gear Guru
 
1 Review written
🎧 5 years
Quote:
Originally Posted by connloyalist ➡️
I realize that with my renewed interest in audio recording I am posting a lot of topics. If that is tiresome, my apologies. See it as a sign of enthusiasm that will probably decrease as my previous recording opportunity slides further and further into the past (I really feel for the forum members for whom this is their livelihood).

To the topic I have a question about.

From time to time I come across the term "measuring microphone". My understanding is that these are primarily intended for scientific applications and not for recording music. Measuring room acoustics for example. From what I gather these tend to have a wide and flat frequency response.

My question is this: I have always understood that to mean that these mics are not suited to recording music. But is that correct? And if so why? Because a wide flat frequency response might be a desirable thing under certain circumstances?

Please educate me

Regards, Christine
self noise is the only thing which might stop you from using measurement mics for recording purposes...

(i regularly use four b&k 4007's)
Old 4 weeks ago | Show parent
  #35
Quote:
Originally Posted by deedeeyeah ➡️
self noise is the only thing which might stop you from using measurement mics for recording purposes...

(i regularly use four b&k 4007's)
If stellar phase- and flat frequency-response up to 40K is what you are after, you indeed pay it with higher noise figures. Examples are DPA 4007 and B&K 4133. Self noise typical 22/24 dBA.

If you can live with less bandwidth (up to 20K) and can accept some phase shift within the audible audio range there are measuring capsules with less noise than a DPA 4006, examples are Micro-Rech Gefell MK221 and B&K 4189 or 4165. Selfnoise typical 14/15 dBA. Resolab, Sonodore and Josephson have models using equivalent capsules. It should be mentioned that on Ebay it is possible to buy for a couple of hundred dollars used 4165 models and preamps. One should only find a way to power these models. They need 120/200V.

If you look for lower noise than most music microphones and need a real omni directional capsule, the one inch measuring capsule is what you should look for. Typical self noise of 10dBA for a B&K 4145 and 6dBA for a DPA 4041. Unfortunately this capsule is discontinued, and no other manufacturers make this type.
Old 4 weeks ago
  #36
Gear Maniac
 
🎧 5 years
I understand (conceptually) the audible phase shift issue in context; others have discussed this as the main technical barrier to using benchmark measurement capsules for music recording. But honestly, I feel I'm not in a position to recognize, instinctively, phase- shift issues when I hear them! Simply - I do not have an acquired sensitivity to it. Last night I spent some time with the MAAT phase- shift plugin demos, trying to wrap my brain around this. The examples they give are dramatic, before/after are *not* subtle. But they are in a pop music context, (reamping, etc). I almost feel I would need to compare pairs of the 4145 to my 4006 side-by-side, with the MAAT phase plugged in for tinkering, to open my ears to what this is all about.

Edit: to clarify, I'm referring to phase shifts within specific frequency bands, not of the signal as a whole.
Old 4 weeks ago | Show parent
  #37
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kludgeaudio's Avatar
 
Quote:
Originally Posted by Klimermonk ➡️
I understand (conceptually) the audible phase shift issue in context; others have discussed this as the main technical barrier to using benchmark measurement capsules for music recording. But honestly, I feel I'm not in a position to recognize, instinctively, phase- shift issues when I hear them! Simply - I do not have an acquired sensitivity to it. Last night I spent some time with the MAAT phase- shift plugin demos, trying to wrap my brain around this. The examples they give are dramatic, before/after are *not* subtle. But they are in a pop music context, (reamping, etc). I almost feel I would need to compare pairs of the 4145 to my 4006 side-by-side, with the MAAT phase plugged in for tinkering, to open my ears to what this is all about.

Edit: to clarify, I'm referring to phase shifts within specific frequency bands, not of the signal as a whole.
The B &K lab mikes have -less- group delay than typical recording microphones; in part because the frequency response is so flat.

And no, group delay isn't very audible. It's a thing that is there, but it's the least of your worries.

The only time I have ever thought group delay in a microphone was an issue was with the Sennheiser MKH series microphones which have a tremendous amount of group delay in the lower midrange and are not even close to being minimum-phase. There's definitely something odd going on in the lower midrange sound, but it's not offensive, it's just odd. Considering the phase plot goes around several times for thousands of degrees of shift, if that's not an issue nothing will be.

I'd be more worried about the comparatively high IMD.
--scott
Old 4 weeks ago | Show parent
  #38
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kludgeaudio's Avatar
 
Quote:
Originally Posted by deedeeyeah ➡️
self noise is the only thing which might stop you from using measurement mics for recording purposes...
And some of that can be fixed with electronics alterations if you're willing to accept slightly poorer response above 18kc in exchange for lower noise.
--scott
Old 4 weeks ago | Show parent
  #39
Lives for gear
 
🎧 15 years
Quote:
Originally Posted by Klimermonk ➡️
I understand (conceptually) the audible phase shift issue in context; others have discussed this as the main technical barrier to using benchmark measurement capsules for music recording. But honestly, I feel I'm not in a position to recognize, instinctively, phase- shift issues when I hear them! Simply - I do not have an acquired sensitivity to it. Last night I spent some time with the MAAT phase- shift plugin demos, trying to wrap my brain around this. The examples they give are dramatic, before/after are *not* subtle. But they are in a pop music context, (reamping, etc). I almost feel I would need to compare pairs of the 4145 to my 4006 side-by-side, with the MAAT phase plugged in for tinkering, to open my ears to what this is all about.

Edit: to clarify, I'm referring to phase shifts within specific frequency bands, not of the signal as a whole.
If the entire signal is “phase” shifted the same amount then it’s just an overall time delay and there is no phase shift since all parts of the signal are still in the same relative phase to each other.
Old 4 weeks ago | Show parent
  #40
Quote:
Originally Posted by kludgeaudio ➡️
The B &K lab mikes have -less- group delay than typical recording microphones; in part because the frequency response is so flat.

And no, group delay isn't very audible. It's a thing that is there, but it's the least of your worries.
One can only wonder why CEO Viggo Kjaer gave a panel of designers millions of Danish Kronor to design a few new microphones for music recording from scratch if they already had the 4165 and 4133 lying ready on the shelves. A simple adaptation to 48V with some DC/DC converters would have done the trick, or with a 4155 not even necessary, since it was a back-electret. Instead years of development, including test recordings made by Peter Willemöes and Onno Scholtze, blind audio listening tests under the direction of Poul Ladegaard, that finally resulted in the 4003, 4004, 4006 and 4007.
Old 4 weeks ago
  #41
It's pretty common to measure 90 degrees of phase shift at 20k hz in many pieces of audio gear that was designed with a limited bandwidth. Any roll offs below 200k hz will show that phase shift. Maintain a 2 hz to 200k hz bandwidth and there is no electronic generated phase shift.
Old 4 weeks ago | Show parent
  #42
Quote:
Originally Posted by Jim Williams ➡️
It's pretty common to measure 90 degrees of phase shift at 20k hz in many pieces of audio gear that was designed with a limited bandwidth. Any roll offs below 200k hz will show that phase shift. Maintain a 2 hz to 200k hz bandwidth and there is no electronic generated phase shift.
Jim, how will it sound when a piece of audio electronics had a phase shift of 90 degrees already at 11K ?
Old 4 weeks ago | Show parent
  #43
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Orgeltonmeister ➡️
Jim, how will it sound when a piece of audio electronics had a phase shift of 90 degrees already at 11K ?


Record something at 96KHz or higher sample rate. Now, listen to the recording with and without an analog type highcut filter set to 20KHz, or higher. Don’t use linear phase type filter. This is a quick dirty demo since inserting a hicut filter will also introduce other sonic byproducts but you will get an idea.
Old 4 weeks ago | Show parent
  #44
Gear Maniac
 
🎧 5 years
Quote:
Originally Posted by Orgeltonmeister ➡️
One can only wonder why CEO Viggo Kjaer gave a panel of designers millions of Danish Kronor to design a few new microphones for music recording from scratch if they already had the 4165 and 4133 lying ready on the shelves. A simple adaptation to 48V with some DC/DC converters would have done the trick, or with a 4155 not even necessary, since it was a back-electret. Instead years of development, including test recordings made by Peter Willemöes and Onno Scholtze, blind audio listening tests under the direction of Poul Ladegaard, that finally resulted in the 4003, 4004, 4006 and 4007.
This is not an unserious consideration, and it's this kind of thing that's kept my curiosity at bay for a long time. Yes - they obviously didn't reinvent their very expensive wheels for no aesthetic reason. But let's not forget the 1" capsule in the 4041 though, as well, in addition to the ones you listed! I'm interested in learning the Ways of the Large Diameter Omni... without the price tag of a pair of the big dogs :P

Forget FR - where is the phase shift in the 4145? Is it under 20k? If it's over, who thinks it really makes a difference?

Or should I just stay in my sandbox with the 296 and stop gazing longingly at the nice Danish grass?
Old 4 weeks ago | Show parent
  #45
Quote:
Originally Posted by Klimermonk ➡️
This is not an unserious consideration, and it's this kind of thing that's kept my curiosity at bay for a long time. Yes - they obviously didn't reinvent their very expensive wheels for no aesthetic reason. But let's not forget the 1" capsule in the 4041 though, as well, in addition to the ones you listed! I'm interested in learning the Ways of the Large Diameter Omni... without the price tag of a pair of the big dogs :P

Forget FR - where is the phase shift in the 4145? Is it under 20k? If it's over, who thinks it really makes a difference?

Or should I just stay in my sandbox with the 296 and stop gazing longingly at the nice Danish grass?
The phase shift of the 4145 is specified as 90 degrees at 11K. Comparing the 4006, it is specified as 90 degrees at 24K.
Old 4 weeks ago | Show parent
  #46
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kludgeaudio's Avatar
 
Quote:
Originally Posted by Folkie ➡️
If the entire signal is “phase” shifted the same amount then it’s just an overall time delay and there is no phase shift since all parts of the signal are still in the same relative phase to each other.
This is the whole point of the studio process. You put that tape on, and there's John Coltrane shifted in phase by fifty years coming out of the speaker.
--scott
Old 4 weeks ago | Show parent
  #47
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kludgeaudio's Avatar
 
Quote:
Originally Posted by Orgeltonmeister ➡️
One can only wonder why CEO Viggo Kjaer gave a panel of designers millions of Danish Kronor to design a few new microphones for music recording from scratch if they already had the 4165 and 4133 lying ready on the shelves. A simple adaptation to 48V with some DC/DC converters would have done the trick, or with a 4155 not even necessary, since it was a back-electret. Instead years of development, including test recordings made by Peter Willemöes and Onno Scholtze, blind audio listening tests under the direction of Poul Ladegaard, that finally resulted in the 4003, 4004, 4006 and 4007.
Well, for one thing the 4165 and 4133 are very expensive to make... and secondly that whole capsule design is not really possible to adapt to make it directional and people don't really want an omni most of the time in the studio.
--scott
Old 4 weeks ago | Show parent
  #48
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kludgeaudio's Avatar
 
Quote:
Originally Posted by Orgeltonmeister ➡️
The phase shift of the 4145 is specified as 90 degrees at 11K. Comparing the 4006, it is specified as 90 degrees at 24K.
Yes.  This is down in the noise floor. Worry more about the microphones with thousands of degrees.
--scott
Old 4 weeks ago | Show parent
  #49
Quote:
Originally Posted by Orgeltonmeister ➡️
Jim, how will it sound when a piece of audio electronics had a phase shift of 90 degrees already at 11K ?
Depends on the filter slope and it's deviation from linear phase. Nearly all analog filters used in converters use a 2 or 3 pole butterworth low pass filter. Butterworth slopes show maximally flat response but contribute a non-linear phase slope. That will show ringing with a square wave as harmonics are "re-arranged" into another form.

Bessel filters are less steep but generate a linear phase response. That requires more poles to obtain the same attenuation at a fixed frequency. Therefore those are not found in recording gear, they are usually reserved for the high end playback converter market.

Older audio gear with transformers tends to create the most non-linear phase curves, 90 degrees or more at 20k hz is common. There is also a non-linear phase curve generated in the low end as well. The deviation from linear phase causes a smeared midrange, a common complaint of earlier transformer designs.

Interested readers should ping the AES for reprints of Dean Jensen's groundbreaking research on phase response.
Old 4 weeks ago | Show parent
  #50
Quote:
Originally Posted by Klimermonk ➡️
Or should I just stay in my sandbox with the 296 and stop gazing longingly at the nice Danish grass?
I just looked up the specs of the Miceotech Gefell M296. Except from the noise, the 4145 is a bit less noisy, I don't think you really can go so wrong with the M296. If you still want 4145, they are on Ebay from time to time.

About danish grass, look here: https://www.grasacoustics.com
Old 4 weeks ago | Show parent
  #51
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Quote:
Originally Posted by Orgeltonmeister ➡️
I just looked up the specs of the Miceotech Gefell M296. Except from the noise, the 4145 is a bit less noisy, I don't think you really can go so wrong with the M296. If you still want 4145, they are on Ebay from time to time.

About danish grass, look here: https://www.grasacoustics.com
The M296 is an excellent microphone and I agree you can't go wrong with it. But unfortunately you can't compare noise specs between manufacturers because they all measure them very differently. Both B&K and MG have honest and accurate specs but they are measured under very different conditions because there is no standard. And manufacturers have fought the AES's attempt to establish a standard method too. This really annoys me.
--scott
Old 4 weeks ago | Show parent
  #52
Quote:
Originally Posted by kludgeaudio ➡️
Both B&K and MG have honest and accurate specs but they are measured under very different conditions because there is no standard. And manufacturers have fought the AES's attempt to establish a standard method too. This really annoys me.
--scott
B&K and MG, two companies that manufacture measuring microphone capsules for industrial purposes follow the standards of the International Electrotechnical Commission (IEC). If B&K measures noise of a MG capsule or vice versa, the outcome is the same. They do not need any standarisation by the AES.

All those companies that mainly/only are involved in microphone manufacturing for the music industry, they have their own ways of measuring and specifying there you can not trust on for 100% but I think Schoeps and Neumann do pretty well.
Old 4 weeks ago | Show parent
  #53
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kludgeaudio's Avatar
 
Quote:
Originally Posted by Orgeltonmeister ➡️
B&K and MG, two companies that manufacture measuring microphone capsules for industrial purposes follow the standards of the International Electrotechnical Commission (IEC). If B&K measures noise of a MG capsule or vice versa, the outcome is the same. They do not need any standarisation by the AES.
In the case of measurement microphones, this is the case. B&K and MG both measure their measurement microphones according to IEC 60194 and the numbers are comparable, yes.

The M269 is not rated that way, though, because it's not a measurement microphone even though it uses a capsule similar to the IEC measurement microphones... the data sheet has only weighted S/N which doesn't really tell you that much because the dominant noise is all at low frequencies anyway.

You could probably say the M269 geometry is CLOSE TO the MK102 geometry and say the capsule numbers are similar and then all you have to do is compare the effective noise floor of the electronics....

Don't even get me started on IEC 60268 which has so many loopholes in it that it's worse than no standard at all. Everyone wants to measure things to make them look as good as possible on the datasheet!
--scott
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