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Author Topic: The Myth of the Accurate Microphone  (Read 16438 times)

Offline Timtape

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Re: The Myth of the Accurate Microphone
« Reply #105 on: December 16, 2017, 11:16:30 pm »
Responding to your post Klaus:

Earlier I suggested that in mere music recording, the strictest accuracy in a mic is unnecessary.

In addition, many vocal artists want a mic that "makes me sound better than I actually am".  What characteristics in a mic make a particular vocalist "sound better"? Will a wide range of  listeners, producers, engineers all agree on which mic makes which vocalist "sound better", let alone "best"? We're now in subjective territory.

Then as many who  make recordings for release to the public know, other effects such as EQ, reverb and compression have been regularly applied to the vocal, and other instruments for many decades. These days, much more detailed "microsurgery" can be made. What we have been  hearing on many recordings for decades is not simply the raw output of the mic(s). 

Then there's the issue of the playback equipment used, and the general listening environment, which varies hugely. Then the preferences of the listener.

But all this is a long way from the original topic concerning the accuracy of microphones... which I thought we were getting back to.



« Last Edit: December 17, 2017, 03:58:35 am by Timtape »

Offline Marik

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Re: The Myth of the Accurate Microphone
« Reply #106 on: December 25, 2017, 01:54:56 am »
I'd like to nudge the discussion back to the original subject: accurate mics are a myth.

To start with, virtually all microphone products which emphasize claims of accuracy are not selling well, compared to other mics in the premium price class.

So what's the problem here? It's either that the product does not achieve the manufacturer's claim, and potential customers notice its shortcomings, or the claim itself is pointing in the wrong direction by appealing to a goal not perceived by a critical mass of engineers as either attainable or worthy.


Klaus,

First, earlier you mentioned that B&K/DPA are not popular--sure, they are not for everything and everyone, but there are uses with superb results--notably in classical music, Baroque Ensembles, orchestra recordings, piano, among others, i.e. where the least of color and max intelligibility between notes/different groups are of concern... For example, I have hard time of imagining putting mint original Elam251 on classical piano... In this respect, we can say that say, DPA, or Schoeps would be more accurate, which anyway, has rather relative meaning, to start with.

I don't have statistics on my hand, but I'd think they do not sell as much as some others just because they have uses in much smaller market, but of course, by no means it says that they are inferior.

Microphones are meant to transport sound waves that are ultimately meant for, and can only be interpreted by, human hearing.

I believe, the problem here is much more complex and a lot has to do with psychoacoustics. Ultimately, for us as listeners the idea of 'accuracy' in the end is how well the music source in real life (or our idea about it) translates into the recording. Here not the least plays obvious mismatch of translation of directionality of source, acoustics of the room, our hearing, and subsequent playback chain. I.e. mechanism of this translation is disturbed from the very beginning...

That is, our ears in real life in the room 'hear' the music source omni, with natural acoustics/reverberation of the room. When we need to translate music event of the given source through recording we put say, cardioid microphone, we place a singer into a booth, after that play back through the speakers (are they omni, cardioid, fig8, or what?) and then our 'omni' ears and our brain should answer main question--does it sound true to the source, or does it sound musical (mind you, in a completely different room)?

In a sense it reminds translation to a foreign language, say, Hamlet--take Wieland, Schlegel, and Flatter German translations of the monologue--all of them are completely different... but still Hamlet monologue. Is the translation accurate? After all any translation is just interpretation and the answer is if that interpretation finds our emotional response and if what we hear during the playback matches the image of 'ideal sound' in our brains...

BTW, aforementioned binaural heads did not get wider use exactly for that directivity mismatch. While they sound well in headphones they just did not translate through the speakers.

Best, Mark Fouxman
Samar Audio Design
www.samaraudiodesign.com
Omni8 Audio
www.omni8audio.com
« Last Edit: December 25, 2017, 04:04:33 pm by Marik »
Mark Fouxman
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Offline Jim Williams

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Re: The Myth of the Accurate Microphone
« Reply #107 on: December 25, 2017, 01:48:28 pm »
Two notable labels using B+K mics are Pony Canyon Classics and MA Recordings.

Offline klaus

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Re: The Myth of the Accurate Microphone
« Reply #108 on: December 25, 2017, 04:46:13 pm »
...And two notable audiophile labels that use(d), pardon my language, "subjective" mics on pianos: Chesky (SM69) and Windham Hill (U67). 

B&Ks/DPAs, in my opinion, are just another flavor that works well in some applications, and not so well in others. This proves to me my point again: there's no such thing as an accurate mic, only ones that, in a particular situation, translate musical intention well, or not so well.

Merry Christmas, and a healthy New Year, everyone, and thanks for keeping things lively around here!
« Last Edit: December 25, 2017, 06:23:23 pm by klaus »
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Offline Timtape

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Re: The Myth of the Accurate Microphone
« Reply #109 on: December 26, 2017, 10:19:53 am »
Again, a mic's "accuracy" or "fidelity"  relates to  how well its electrical output conforms to the sound pressure waves presented to it. National and International standards are based on this objective criterion. Here, tastes, preferences and opinions are irrelevent.

Interestingly Chesky has been making and marketing dummy head recordings using small Bruel & Kjaer mics:

"In 2011, Chesky Records incorporated High Resolution Technology in their label, and introduced binaural recordings. The Binaural+ masters are captured in high-resolution (24-bit/192kHz) sound using a binaural dummy head nicknamed "Lars". David Chesky collaborated with Princeton professor Edgar Y. Choueiri to begin producing binaural recordings. The purpose of the technology is to capture three-dimensional sound and imaging."

Ref: https://en.wikipedia.org/wiki/Chesky_Records
« Last Edit: December 26, 2017, 03:05:28 pm by Timtape »

Offline soapfoot

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Re: The Myth of the Accurate Microphone
« Reply #110 on: December 28, 2017, 08:59:44 am »
Again, a mic's "accuracy" or "fidelity"  relates to  how well its electrical output conforms to the sound pressure waves presented to it.

But how would one measure "the sound pressure waves" for comparison except with a microphone?

If there's no other way, isn't any assertion of "accuracy" a textbook demonstration of the logical fallacy "petitio principii," also known as "begging the question?"

A scholarly conversation does not look like this:

Person A: "How do you know that a microphone can give an accurate measure of the sound pressure?"

Person B: "Because I also measured the sound pressure with a microphone, and it was accurate."

That won't do.

The central question then becomes: what is your reference for "the sound pressure waves," and how was it obtained?

Because unless we have a reliable, precise, and agreed-upon method of measuring "the sound pressure waves" that does not rely on microphones (i.e. "the device under test,"), then any reference is arbitrary, and any comparison not-so-meaningful.
« Last Edit: December 28, 2017, 10:07:43 am by soapfoot »

Offline Timtape

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Re: The Myth of the Accurate Microphone
« Reply #111 on: December 28, 2017, 11:20:54 am »
(Note from KH: Soapfoot deleted sections of his post after Timtape responded. I therefore removed comments of Timtape which referred to these sections.)

Your question about absolute sound pressure levels is an excellent one. As I understand it the basic answer is that we create the sound pressure waves via methods that are known and repeatable.

For a start, you could Google key words like "pistonphone" and "electrostatic actuator" as I did. That should get you into the general field. There's a particular standards article I came across last week. Will try and track it down tomorrow.
 
It's half past midnight over here so I need to hit the sack. To be continued.

Tim



« Last Edit: December 28, 2017, 03:01:16 pm by klaus »

Offline Jim Williams

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Re: The Myth of the Accurate Microphone
« Reply #112 on: December 28, 2017, 11:32:03 am »
I consider a standard microphone a "snapshot" type device. It only captures from one perspective and ignores the surround location information.

An omni pattern will pick up air motion from all angles but does not provide any directional cues. The human ear can do that with only one working ear. That is why when you bury one ear in a pillow you can still determine the sound's directional source.

There were/are some directional sensing microphone designs, one was the "henry" from the 1980's. A recording from that mic provided all the 360 degree directional cues in a standard stereo playback format. It even worked well on cassettes. I recall studying those waveforms for the hidden directional cues but could not seperate them.

One of the more interesting sound samples was an electric shaver run from the top of the head downward. It showed as a mono source but one could easily hear the sound moving from the top of the head centered downwards, just like a real shaver would.

Part of that mic's design was the inclusion of location reference tones as produced by the human ear. Although inaudible, they were part of the mic's technology. I'm not sure what ever happened to those designs but they were very impressive.

Offline Timtape

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Re: The Myth of the Accurate Microphone
« Reply #113 on: December 29, 2017, 02:51:33 am »
An omni pattern will pick up air motion from all angles but does not provide any directional cues. The human ear can do that with only one working ear. That is why when you bury one ear in a pillow you can still determine the sound's directional source.

Yes some facility  remains but the directional sensing enabled by the pinna (outer ear) seems to be limited mostly to the vertical plane (above, level, below the head). It seems the brain senses partial frequency cancellations varying between about 6kHz to 10kHz.  So while undoubtedly useful it is  inferior on its own compared to the full 3D location sensing abilities of two fully working ears. (See F. Alton Everest, 1989, pp 19 and 20.)

Interesting that dummy head recording microphones include the outer ears to presumably capture the location cues in the vertical plane, as well as the left/right.



« Last Edit: December 29, 2017, 06:01:28 am by Timtape »

Offline klaus

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Re: The Myth of the Accurate Microphone
« Reply #114 on: December 29, 2017, 02:44:26 pm »
(...) but the directional sensing enabled by the pinna (outer ear) seems to be limited mostly to the vertical plane (above, level, below the head).

Have you tested and confirmed the claim that directional sensing of an individual ear is mostly limited to the vertical plain?

How about trying this:

Rub your thumb against your index or middle finger, move it in the horizontal plane from front to rear, back to front: can you follow the rustling sound?
Do you get any less directional sense from rustling horizontally than making the same move in the vertical plane? I certainly don't. I hear them both equally distinct.

(Not that any of this has much to do with the thread's subject).
« Last Edit: December 30, 2017, 01:31:51 am by klaus »
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Offline Timtape

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Re: The Myth of the Accurate Microphone
« Reply #115 on: December 30, 2017, 06:04:31 am »
Have you tested and confirmed the claim that directional sensing of an individual ear is mostly limited to the vertical plain?

Not formally. I was simply replying to Jim's post on sound localisation with information on sound localisation from a well regarded audio reference book I own which is now in its Seventh Edition.

How about trying this:

Rub your thumb against your index or middle finger, move it in the horizontal plane from front to rear, back to front: can you follow the rustling sound?
Do you get any less directional sense from rustling horizontally than making the same move in the vertical plane? I certainly don't. I hear them both equally distinct.

I tried it briefly but  realized it's not a blind test since I already know where I have placed my fingers. I cant be sure it's not that prior knowledge which is helping me to cheat a little. It seems to me a fairer test would be asking an assistant to make the sounds for me, and for me to be blindfolded.

 

(Not that any of this has much to do with the thread's subject).

As I said I was replying to Jim's post on sound localisation. And I took your earlier post about candy wrappers to mean microphones are poor at translating sound localisation information. Hence my earlier surprise that nobody had mentioned dummy head microphones in that context. For as we know they are specifically designed to preserve localisation cues. If you meant something other than sound localisation, fine, but in that case it might help if you explain what you did mean.

« Last Edit: December 30, 2017, 08:18:30 am by Timtape »

Offline Timtape

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Re: The Myth of the Accurate Microphone
« Reply #116 on: January 04, 2018, 05:55:57 am »
But how would one measure "the sound pressure waves" for comparison except with a microphone?

As mentioned, here is the paper on measurement microphone calibration standards I referred to but temporarily mislaid.

Calibration of Pressure and Gradient Microphones by Victor Nedzelnitsky.

https://www.nist.gov/sites/default/files/documents/calibrations/eacous.pdf

Offline soapfoot

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Re: The Myth of the Accurate Microphone
« Reply #117 on: January 04, 2018, 11:08:18 am »
As mentioned, here is the paper on measurement microphone calibration standards I referred to but temporarily mislaid.

Calibration of Pressure and Gradient Microphones by Victor Nedzelnitsky.

https://www.nist.gov/sites/default/files/documents/calibrations/eacous.pdf

Thank you for sharing! I read the whole paper (though perhaps not a close, detailed read). A few things jumped out:

(section 2.1)

The paper acknowledges that there's no perfect way to calibrate a microphone, so that a calibration procedure must be selected to "correspond... to the pertinent critical conditions of intended use of the microphone" (section 3.1).

This is, of course, subjective and speculative in every case, because the testing procedure must account for the inherently subjective questions of "how is this microphone most likely to be used?" and "what's the appropriate way to measure for that application?"

For example, in section 4.1 uncertainties in the measurement of pressure sensitivities are detailed. It's acknowledged that discrepancies can arise as a result of such measurements being "critically dependent on different choices made in different laboratories with regard to rather complicated details of method and apparatus."

In other sections outlining other procedures, the reader is advised of several similar uncertainties and discrepancies.

All of the testing procedures outlined require the excitation of a second transducer of some sort (read: speaker or a second microphone), which can (read: most certainly will) introduce its own unintended characteristics to contaminate the measurements. The significance of these errors (or the appropriateness of methods undertaken to compensate for them) will, of course, be at least somewhat subjective (section 7.3 is also of particular interest here).

Also important is section 8, the only section to deal with the concept of phase (as opposed to just frequency response). This very brief section serves chiefly to acknowledge that (paraphrasing) the state of the art in calibration of phase response in measurement microphones is highly immature (at the time of writing), and that "there  must be further development of these primary standard methods."

This is crucial, because real-world experience has instilled in me a sense that phase errors and off-axis coloration may be as important as on-axis frequency response to a microphone's subjective performance.

The paper was first published two decades ago, so it's unclear whether any substantial advancements in the state of the art have occurred since its publication (I'd assume they likely have).

But I didn't personally come away from this paper convinced that there's any sort of universally agreed-upon standard and procedure for establishing what constitutes "accuracy" in a microphone. Remember, "best available information" does not necessarily correspond to "perfect information."

The paper outlines the best available procedures (contemporaneous to its writing) for evaluating measurement microphones. I'd be hesitant to ascribe more importance to it than that.
« Last Edit: January 04, 2018, 11:16:38 am by soapfoot »

Offline klaus

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Re: The Myth of the Accurate Microphone
« Reply #118 on: January 04, 2018, 01:15:17 pm »
Thanks for picking through the paper for the rest of us.
Unless I am mistaken, don't all these calibration methods rely primarily on sine wave reproduction? I.e. a singe tone is fed and the accuracy (yes, an appropriate use of the term in this context) of the response is recorded and compared.

I pointed out decades ago the fallacy of single-tone reproduction as criterium for the quality of a recording mic: The frequency graph accompanying a Radioshack condenser at $99 (this was when Radioshack was still in business) looked identical to a B & K measuring mic, or a top-notch studio mic by a major manufacturer: ruler-flat response, low noise floor... 

But I have found that the quality of a mic can best be judged with our ears: how that mic processes complex waveforms arriving at the same time: a timpani's spike, a violin's scratchy bow, a trumpet's overtones, etc. all at the same time. Is that multitude processed without smear? Does the soundstage collapse? Can I still pick out individual nuances of each instrument from the whole?

Tell me how you would measure the dynamic ability of a mic- processing complex events in real time, and "accurately". You cannot possibly get a clue from a rather primitive, static, sine wave feed, a frequency at a time?

What other device but our ears can judge a mic's ability in this regard?
« Last Edit: January 08, 2018, 09:52:54 pm by klaus »
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Offline Jim Williams

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Re: The Myth of the Accurate Microphone
« Reply #119 on: January 05, 2018, 11:46:53 am »
Another measurement error is the sine wave generator. That requires a form of speaker. Speaker distortion is a magnitude of error beyond the mic capsule's THD.

We end up measuring both with each contibuting to the errors.