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Author Topic: Actual frequency response of high end mics: how useful?  (Read 13714 times)

soapfoot

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Re: Actual frequency response of high end mics: how useful?
« Reply #30 on: June 03, 2013, 01:42:02 pm »

If your hearing bandwidth is 11k hz, I would use another person to gut check the tracks for me. It's no different than using another set of eyes to see the details your tired eyes miss.

Got a kid?

Last time I aligned a tape machine (about 2 weeks ago), I still had at least 16k (thank heavens).  Tim was the one who stated he didn't have much above 11k.
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Timtape

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Re: Actual frequency response of high end mics: how useful?
« Reply #31 on: June 07, 2013, 11:37:23 am »

If your hearing bandwidth is 11k hz, I would use another person to gut check the tracks for me. It's no different than using another set of eyes to see the details your tired eyes miss.

Got a kid?

Exactly. That was my point. I used the example of an FFT spectrum tool as an aid but a kid with great hearing is also a useful aid.


Now who else is going to give their ears the same unbiased  check I've been giving mine for years, and submit the objective results to this forum column? Dont all speak at once now!  ;)
 
Tim

 
   
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Timtape

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Re: Actual frequency response of high end mics: how useful?
« Reply #32 on: June 07, 2013, 11:52:58 am »

Last time I aligned a tape machine (about 2 weeks ago), I still had at least 16k (thank heavens).  Tim was the one who stated he didn't have much above 11k.

I've aligned a lot of tape machines over the years and it was in the course of doing that work regularly that I discovered the upper limits of my hearing.

But I assume that your reason for being thankful about still being able to hear 16khz is not primarily for its helpfulness in aligning a tape machine. In any case that task should be done using calibrated instruments which can respond to signals with quantifiable accuracy - in terms of level, frequency, distortion,  far better than any human ear can judge.
Still I'd always do a final A/B listening test between source and tape playback as confimation that the instruments were doing their job, which they nearly always did.

The point I was making earlier on was just this, that in the end there is no conflict between the measuring instruments and listening tests. It's when people try and place the "science" and the "listening" in opposition to each other that the problems start, I'd suggest.

Which brings us full circle to the reason I started the thread. There seems a strong view abroad that since "every human voice sounds different" which is undoubtedly true, therefore we need different microphones to capture those different voices. I dont see the documented evidence that that is true but I'm more than happy to be shown it.

Tim
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Jim Williams

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Re: Actual frequency response of high end mics: how useful?
« Reply #33 on: June 07, 2013, 12:31:30 pm »


Now who else is going to give their ears the same unbiased check I've been giving mine for years, and submit the objective results to this forum column? Dont all speak at once now!  ;)
 Tim

I went to an audiologist last year to get checked. Turns out I have very good hearing for my age. The results showed minimal loss in the left ear (road noise) and nearly perfect hearing in the right ear.

She commented that it was very unusual to test someone at my age with those great results. She also said that most teens now test with severe hearing loss, mostly due to loud enviromental noises and those dreaded 'ear buds'. Only small children still test well. That will end with their first 'ear buds', the quickest way to damage your ears, permanently. I don't have kids, but if I did, those would be off-limits until they turned 18. Any parent that provides those to their kids is sentencing them to permanent hearing loss. You might as well give them acid eyedrops for their eyes too.

I'm not one that was sheltered from loud sounds. I grew up playing rock music, but at an early age I decided ear protection was needed. That began in 1978. After several tours with Stevie Wonder, they became a part of life and where carried everywhere.

Now I'm in my 60's and still enjoy playing on "11", but with ear plugs always used. Same for shooting sports, no hearing loses from that either. ( I use suppressors and stuff there too).

Unfortunatly, these protectionist concepts tend to come later in life, usually after damage has occured. Smart kids are pro-active, as I was at an early age. That is not the norm as most kids don't think about this stuff until it's too late. We now know what hearing damage can do, same with sun exposure and tobacco use. Teaching the kids to be aware is 1/2 the battle.
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soapfoot

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Re: Actual frequency response of high end mics: how useful?
« Reply #34 on: June 07, 2013, 02:17:17 pm »

On a gig when I was 21, a drummer was really laying into a crash cymbal.  I had earplugs with me, but had forgotten to put them in.  That's the only time I felt physical pain, and it was in my left ear.  I reached for my earplugs and they fell behind my amplifier.

It still felt weird when I woke up the next morning.  Right then and there I decided that such a thing would never happen again, and I became very protective of my hearing.  I have custom ear molds from Westone, and I wear them walking around the city.  Subways and worn-out brakes on taxicabs and buses make incredible levels of noise. I wear them when I run the vacuum cleaner, and even if I have to use a hair dryer. I make my living mostly as a session guitarist, and I like to wear the custom plugs underneath my tracking cans, just in case the sound in the room tempts me to turn my cans up louder than is wise. There are so many potentially damaging environments that we don't ever pay attention to.

I'm not sure that any permanent damage was sustained in my left ear that night, but I can almost guarantee that the wake-up call I received has saved me from lots of damage.
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Timtape

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Re: Actual frequency response of high end mics: how useful?
« Reply #35 on: June 07, 2013, 08:24:46 pm »

Interesting comments Jim and Brad. This has turned into a thread on hearing loss and protection but that's fine by me.

When I was 25 I started work in the hearing aids industry. It was a good education to see of these people, often retired farmers with many tractor driving hours to blame for their hearing loss. It's not just the volume but the "dose". The longer the exposure at a certain level, the more damage.

Like Brad I've been using ear protection for years whenever I use the vac or any loud equipment such as a noisy air compressor, or when banging metals, using a hammer drill, tuning a car motor. etc.

I think there can be a psychological component here as well. I once played in a band with a guy who liked the foldback really loud, especially on his own vocals. As we shared the same foldback speaker it created a problem. I found the voulme ear splittingly loud and often ended up playing the gig way off axis from the speaker just to protect my ears. I concluded that for some, loud music is a sort of drug which excites them.
 Also that different people seem to have different thresholds for discomfort and pain in their hearing. Mine has  been fairly low.

The other thing not always appreciated by music and audiophile types is that our ears are sensitised to frequencies in the "presence" range, say 1khz to 6khz, and so that is the band that tends to be lost first, as it's easily overloaded. Many clients I dealt with in hearing care had acceptable thresholds at 1khz but a steep dive in response above that, especially around 2 to 4khz. It would often somewhat recover around 8khz and perhaps above that.
This band is critical to clear understanding of speech and of the ability to function in daily life. Someone who struggles to hear well around 2 to 4 khz has real problems. In that sense, a loss of highs say above 4 or 6khz is not nearly so critical. We often didnt test people above 8khz, for if there were sharp losses around 2 to 4khz there was not much point testing above that for we had located the real problems for their hearing in daily life.

Tim   
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leswatts

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Re: Actual frequency response of high end mics: how useful?
« Reply #36 on: June 12, 2013, 12:07:51 pm »

I just read this thread and want to comment. I am a microphone designer.

We do measure frequency response on every individual mic, particularly in the tuning process.

On axis response of course won't tell everything about the sound of a mic, but it's important data.
It should be carefully and tightly controlled in the manufacturing.

Do published responses mean anything? Well we electroacousticians have a joke about that....
"drawn by the marketing manager". In many cases that's not far from the truth.


A real frequency response chart will have many small sharp wiggles from mic stand or body reflections
unless steps are taken to reduce them. Many lower cost microphones have huge sharp 5-10 dB peaks
and notches in the mid and upper range. Some expensive ones too. And you can sure hear it. This might be a good thing depending...but in general a microphone is not a minimum phase network, so they can't really be eq'ed out. I tend to not like the sound of very sharp peaks or dips on many things.

Is there any standard method? Yes, a single free field plane wave. There are some problems doing this at very low
frequencies with gradient microphones, and much data has significant errors in it. The best way was and is a plane wave tube. For pressure microphones LF measurements can be done accurately in a small pressure chamber.

Can we isolate capsule distortion? Yes , in a limited fashion. Extrapolating from two speaker intermodulation is one way. With gradient mics the bigger issue is getting the tremendous SPL in a free field. The usual method
is powerful compression drivers feeding a resonant tube with multiple resonant absorbers tuned to harmonics.
At very high SPL the air itself creates harmonic distortion however.

Other thing that strongly affect the sound? Off axis response with multiple sources and room sound.
And distortion, which can be quite large in shunt or stray capacitance loaded constant charge condensers.
Many head amps produce large distortions (on purpose).

One thing i'll add...yes our super flat low distortion B&K/dpa reference mics sound horrible in the studio!

Les
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klaus

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Re: Actual frequency response of high end mics: how useful?
« Reply #37 on: June 12, 2013, 06:36:53 pm »

A fitting summation of this discussion. Thank you.
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Timtape

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Re: Actual frequency response of high end mics: how useful?
« Reply #38 on: June 17, 2013, 09:59:22 am »

I just read this thread and want to comment. I am a microphone designer.

We do measure frequency response on every individual mic, particularly in the tuning process.

On axis response of course won't tell everything about the sound of a mic, but it's important data.
It should be carefully and tightly controlled in the manufacturing.

Do published responses mean anything? Well we electroacousticians have a joke about that....
"drawn by the marketing manager". In many cases that's not far from the truth.


A real frequency response chart will have many small sharp wiggles from mic stand or body reflections
unless steps are taken to reduce them. Many lower cost microphones have huge sharp 5-10 dB peaks
and notches in the mid and upper range. Some expensive ones too. And you can sure hear it. This might be a good thing depending...but in general a microphone is not a minimum phase network, so they can't really be eq'ed out. I tend to not like the sound of very sharp peaks or dips on many things.

Is there any standard method? Yes, a single free field plane wave. There are some problems doing this at very low
frequencies with gradient microphones, and much data has significant errors in it. The best way was and is a plane wave tube. For pressure microphones LF measurements can be done accurately in a small pressure chamber.

Can we isolate capsule distortion? Yes , in a limited fashion. Extrapolating from two speaker intermodulation is one way. With gradient mics the bigger issue is getting the tremendous SPL in a free field. The usual method
is powerful compression drivers feeding a resonant tube with multiple resonant absorbers tuned to harmonics.
At very high SPL the air itself creates harmonic distortion however.

Other thing that strongly affect the sound? Off axis response with multiple sources and room sound.
And distortion, which can be quite large in shunt or stray capacitance loaded constant charge condensers.
Many head amps produce large distortions (on purpose).

One thing i'll add...yes our super flat low distortion B&K/dpa reference mics sound horrible in the studio!

Les

Thanks for your comments Les.  Obviously mic stand or body reflections are independent of the mic itself and so would hardly be a reason to change to a different mic when recording.
In the same way, bad peaks and troughs in response in a cheap and nasty mic are also not what I was talking about.

Can you supply examples of a few typical good quality mics' response curves. Not the ones "drawn by the marketing manager" but the actual empirical responses with all the sharp peaks and troughs intact?

Do you also have a view on why as you say the B&K/DPA mics sound so terrible in the studio?

Cheers Tim
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Jim Williams

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Re: Actual frequency response of high end mics: how useful?
« Reply #39 on: June 17, 2013, 01:09:58 pm »

If you saw an un-edited mic response curve you probably wouldn't buy it. It looks like an audio waveform on an editor. Hundreds of spikes and troughs, no resemblence to any frequency curve you've ever seen. Most would have a tough time even finding the base line!

As I said before, the published curves are "normalized", like stretching a hose straight. Run enough passes and any wild, spiky looking curve can be "pulled straight". Is it honest? Your call. I don't find it any less misleading than any modern audio piece that's sold without any specs. Once I saw a Royer ad with a hand drawn curve and hand drawn frequency breaks, none of which resembled a log frequency curve, it was "made up" out of whole cloth. Didn't stop folks from buying them.

"Trust, but verify"  No truer words were ever spoken. That's why I have the Audio Precision analyzer here.
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Timtape

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Re: Actual frequency response of high end mics: how useful?
« Reply #40 on: June 18, 2013, 06:09:48 am »

Run enough passes and any wild, spiky looking curve can be "pulled straight".

Jim, what do you mean by this? Are you saying that  each pass gives a significantly different result to the one before? That could only implicate the testing procedure rather than the mic itself.

If so,  "running enough passes" and  averaged them out would seem a valid way of getting a  more accurate plot. If not, what did you mean here?

Tim
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Jim Williams

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Re: Actual frequency response of high end mics: how useful?
« Reply #41 on: June 18, 2013, 11:30:55 am »

An un-edited mic response curve is very spikey. Normalization software programs are used to "smooth out" that result. In my Audio Precision, it's called "compute smooth".

You can take any frequency reponse plot and apply that program. It can also be applied to any graphic plot on that system. Usually it's done to speaker and mic response curves. It makes the curve more "readable" but covers up a bunch of variations. Marketing folks love it as it takes away worrysome test results and makes it all pretty for the sales team.

The number of passes determines how "smooth" the end result becomes. The software is averaging the data and is "filling in the holes", so to speak. Passes means how many times you re-use the compute smooth function, not how many "tests" you sweep the mic with, that is done only once, then the computer takes over.

An honest plot would show before and after results, but most would not know how to interpret them or they might be scared off from those truthful results. Would you buy a mic that looked like a picket fence on a response sweep?
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Timtape

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Re: Actual frequency response of high end mics: how useful?
« Reply #42 on: June 18, 2013, 02:13:12 pm »

An honest plot would show before and after results, but most would not know how to interpret them or they might be scared off from those truthful results. Would you buy a mic that looked like a picket fence on a response sweep?

On the one hand Jim, you seem to be condemning the "smoothing" practice, and on the other, almost justifying it. I'm confused.
 
As I said earlier, I would like to see that " honest plot"  if as you imply the ones we are given are dishonest.

Tim

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klaus

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Re: Actual frequency response of high end mics: how useful?
« Reply #43 on: June 18, 2013, 05:28:53 pm »

It's been pointed out: the "honest plot", if it even exists, does not get published by manufacturers because it serves no purpose, other than maybe aiding in mic development to remove kinks.

I have never seen a graphs that were more detailed than those Sennheiser used to include with their mics. And even these were already so detailed that an untrained customer would only be tempted to overanalyze their jagged trace.

In summation of this thread, I think we can agree that, short of being useful during the research and development process, frequency plots are not helpful as indicators for the real-world performance of a mic.
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Timtape

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Re: Actual frequency response of high end mics: how useful?
« Reply #44 on: June 18, 2013, 09:41:50 pm »

I take it that the "honest plot" is the real world performance of the mic, with respect to frequency response, much more so than the smoothed plot.   Are you now saying that it isnt?

If so, of what use would such a plot be even to designers? I take it designers design their mics for the real world.

Tim
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