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Author Topic: SPL, dBU, Pa, and overloading pres  (Read 4783 times)

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Offline ycoop

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SPL, dBU, Pa, and overloading pres
« on: March 14, 2019, 06:29:14 PM »
I’ve been having issues with my deck (PMD-706) that I think may boil down to being overloaded. I’m not sure exactly how to make sense of different units of sound/signal strength. Here’s what I posted on the 706’s thread:

I have a suspicion that what I’m seeing is the circuitry being overloaded from transients. That would explain why the clipping  doesn’t show visibly on the meters, but does show in the final waveform.

My CK-1s have a sensitivity of 15 mV/Pa and the 706 has a max input of -8 dBu when set to mic in. I figure the max SPL of a show is somewhere around 105 dB. The spec sheet also says that the minimum gain is +28 dB. When does that gain get applied? Would it potentially result in a clipping?

Thanks in advance for the input.
Mics: Avantone CK-1s, AT853 c+o
Pres: CA9100
Recorders: DR-60d mkII, DR-2d

Offline noahbickart

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Re: SPL, dBU, Pa, and overloading pres
« Reply #1 on: March 14, 2019, 11:57:51 PM »
Sounds like classic brickwalling to me. In the old days when I ran bluelines> da-p1 I ran pads on both microphones and deck to avoid it.

Try some 10 or maybe even 20db xlr pads

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F263150174657

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F321755704322
« Last Edit: March 15, 2019, 12:39:26 AM by noahbickart »
Recording:
Capsules: Schoeps mk41v (x2), mk4v (x2), mk22 (x2), mk3 (x2), mk21 & mk8
Cables: 2x nbob KCY, 1 pair nbob actives, Darktrain 2 and 4 channel KCY extensions:
Preamps:    Schoeps VMS 02iub, Naiant Littlebox, Naiant IPA, Sound Devices Mixpre6
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Offline ycoop

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Re: SPL, dBU, Pa, and overloading pres
« Reply #2 on: March 15, 2019, 01:49:21 AM »
I should have included the waveform, this doesn’t fit my understanding of what brickwalling looks like.

http://taperssection.com/index.php?action=dlattach;topic=179428.0;attach=134799
Mics: Avantone CK-1s, AT853 c+o
Pres: CA9100
Recorders: DR-60d mkII, DR-2d

Offline aaronji

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Re: SPL, dBU, Pa, and overloading pres
« Reply #3 on: March 15, 2019, 08:32:31 AM »
Check out this page on the Sengpiel site, particularly the table.  From that, a mic with a sensitivity of 15 mV/Pa will put out -8 dBu at about 120.5 dBSPL...

Offline ycoop

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Re: SPL, dBU, Pa, and overloading pres
« Reply #4 on: March 15, 2019, 02:30:58 PM »
Check out this page on the Sengpiel site, particularly the table.  From that, a mic with a sensitivity of 15 mV/Pa will put out -8 dBu at about 120.5 dBSPL...

Thank you, this was quite helpful. Is it possible that transients can reach 120 dB? I would imagine that there could be overloading before actually fully reaching -8 dBu, especially given the pro-sumer nature of the deck. Further,  the mics have a bump in frequency response in the high end. http://recordinghacks.com/microphones/Avant/CK-1
Mics: Avantone CK-1s, AT853 c+o
Pres: CA9100
Recorders: DR-60d mkII, DR-2d

Offline goodcooker

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Re: SPL, dBU, Pa, and overloading pres
« Reply #5 on: March 16, 2019, 11:08:36 AM »

120 dB is about like standing next to a prop plane.
130 dB is considered the pain threshold.
Concert volumes could definitely be in this range.
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Offline DSatz

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Re: SPL, dBU, Pa, and overloading pres
« Reply #6 on: March 16, 2019, 08:31:21 PM »
Hmm. People's math in this thread is right, but I for one can't stand to be in a place where the SPLs are 110 dB (let alone 120+) for longer than very brief intervals. It's possible that this is input overload due to high SPLs, but that wouldn't be my first guess.

More to the point, your waveform display is quite odd. It looks as if the music (the more or less continuous material) is peaking at rather low levels--around 20 dB below full scale. But some very strong impulse noise seems to be present as well, mainly in what I assume is the right channel of the recording (the one that's beneath the other one). The asymmetry of these impulses (mostly negative-going) is striking as well.

If this is an unaltered acoustic recording from a pair of microphones in the same recording space, I would say that something is seriously wrong with either the connections or the equipment. There's no ordinary way that your left microphone could (mostly) fail to pick up something so huge in the right microphone. No microphone in the world is that highly directional. So I don't think that those peaks represent an acoustical phenomenon.

Have you tried testing the setup at home, wiggling the cables at all the points of connection to see if something is intermittent, etc.?

--best regards
« Last Edit: April 02, 2019, 08:21:51 PM by DSatz »
music > microphones > a recorder of some sort

Offline ycoop

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Re: SPL, dBU, Pa, and overloading pres
« Reply #7 on: March 16, 2019, 09:07:25 PM »
^I just took a look at my mics, and somehow a screw has come missing from each, resulting in the XLR jack wiggling slightly. Perhaps this is the source of my issue. At a different show I saw the clicking in both channels, both looking now both mics have the loose end.

Edit: I’m taping a show tonight and wrapped some gaffer’s tape around the end portion of the mics, it seems to (for now) keep things stable. I also turned on the mics’ 10 dB pads. I’m running another set of mics (though not into the XLR inputs), so I feel okay doing some experimenting.
« Last Edit: March 16, 2019, 10:17:54 PM by ycoop »
Mics: Avantone CK-1s, AT853 c+o
Pres: CA9100
Recorders: DR-60d mkII, DR-2d

Offline DSatz

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Re: SPL, dBU, Pa, and overloading pres
« Reply #8 on: March 16, 2019, 10:35:18 PM »
Good luck tonight. But the pads in the microphones aren't necessary or relevant, and will add ~10 dB of noise to your recording, whether or not you turn up your record levels to compensate for the lost signal level. The pads built into condenser microphones are designed to prevent the electronics of the microphones from being overloaded by the signals coming from their own capsules.

If a preamp or recorder is being overloaded by the undistorted output of a microphone, an in-line resistive pad should be used at the input of the preamp or recorder. The pad will reduce the microphone's noise along with its signals, whereas the pad in the microphone will reduce the microphone's signal but NOT its noise.

--best regards

P.S.: Speaking of high sound pressure levels, see https://www.politifact.com/truth-o-meter/statements/2019/mar/15/joe-cunningham/yes-airguns-used-oil-gas-exploration-are-16000-tim/
« Last Edit: March 16, 2019, 10:37:34 PM by DSatz »
music > microphones > a recorder of some sort

Offline ycoop

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Re: SPL, dBU, Pa, and overloading pres
« Reply #9 on: March 16, 2019, 11:12:14 PM »
Thanks for the that! Pads turned off and rig set up. We’ll see how it goes.

edit: Things seem to have gone well! Looks like the deck may not have been the issue after all. It was a relatively quiet show (though only compared to the other shows I've taped with this deck) but it seems more likely that the mic wiggling was the issue.  :smash:
« Last Edit: March 17, 2019, 04:17:50 AM by ycoop »
Mics: Avantone CK-1s, AT853 c+o
Pres: CA9100
Recorders: DR-60d mkII, DR-2d

Offline DSatz

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Re: SPL, dBU, Pa, and overloading pres
« Reply #10 on: March 17, 2019, 10:09:18 AM »
Glad to hear it.

Now for some unsolicited advice about follow-up. Intermittent signal output is an extreme situation. The milder forms of this problem (shielding / grounding / irregular contact) can cause severe radio frequency interference. It's not something to be casual about, if you value the time and effort that you put into your recordings.

These are "Avantone" mikes, no? I've never dealt with them myself--but among the hundreds of Western importers and resellers of mikes from the same handful of Chinese factories, I get the impression that they're more serious than many of the others. Especially since this happened to both of your microphones, it's something that they should be told about, so that they know that there's a problem with this model, or the production batch or series that your mikes came from.

Ideally they would want to see the mikes and make things right for you. An alert company will realize that this is a chance to make a "friend for life".

--best regards
« Last Edit: April 02, 2019, 08:23:33 PM by DSatz »
music > microphones > a recorder of some sort

Offline ycoop

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Re: SPL, dBU, Pa, and overloading pres
« Reply #11 on: March 18, 2019, 12:46:51 PM »
Contacted Avantone and they are sending “replacements.” Though it is unclear to me if they mean replacement mics or replacement screws. I’m hoping for the former.
Mics: Avantone CK-1s, AT853 c+o
Pres: CA9100
Recorders: DR-60d mkII, DR-2d

Offline DSatz

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Re: SPL, dBU, Pa, and overloading pres
« Reply #12 on: March 21, 2019, 06:20:45 PM »
I would bet that they're sending screws; if they were sending microphones, they probably would have asked you to agree to return the ones you have.

But I will be very glad for you, and impressed with Avantone, if I lose this bet.

--best regards
music > microphones > a recorder of some sort

Offline ycoop

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Re: SPL, dBU, Pa, and overloading pres
« Reply #13 on: March 22, 2019, 11:19:09 AM »
I would bet that they're sending screws; if they were sending microphones, they probably would have asked you to agree to return the ones you have.

But I will be very glad for you, and impressed with Avantone, if I lose this bet.

--best regards

After further emails they are definitely sending screws. Got a little over-excited 8)
Mics: Avantone CK-1s, AT853 c+o
Pres: CA9100
Recorders: DR-60d mkII, DR-2d

 

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