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UMIK SPL with REW 7 years 2 weeks ago #20648

  • 72deluxe
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Hello

I received my UMIK today - great! I was hoping to use this for SPL measuring but I notice in Room EQ Wizard that this silent room that I am in is reading 54 db(Z) S (slow mode) with the HPF not enabled. Is this normal? This seems pretty high to me???

For reference I have loaded the calibration file on prompt when I plugged my UMIK in. When I press "calibrate" on the SPL screen it informs me "SPL is not required, REW is already calibrated for the USB mic you are using based on the sensitivity data in the mic cal file".

I am using REW 5.12, and the UMIK-1 is showing up as a "Umik-1 Gain: 18dB" in USB devices.

Any tips / advice more than welcome.

Thanks
Rich

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UMIK SPL with REW 7 years 1 week ago #20709

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I am experiencing the same. My mike shows as Gain: 12dB
I switched over to Real Time Analysis and below 20 Hz is a lot of loud noise over 60dB.
Switching to db(A) mode ignores this loud noise - that was not good enough for me so I modified a copy of my calibration file to attenuate anything below 30Hz by 40dB and that seems to help.

Did you find any answers elsewhere?

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UMIK SPL with REW 7 years 1 week ago #20710

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I did not find any answers anywhere but did notice from a topic on the forum (www.minidsp.com/forum/umik-questions/110...1-absolute-spl-error) that you can adjust the sensitivity via the text file but I was wondering what "normal" was myself! I was kind of hoping that the calibration file would dictate what "normal" was, else it isn't a calibrated microphone, surely?

I contacted support and provided two RTA plots from completely different rooms (different locations) and both show noise below 40Hz over 40dB, ~45dB to perhaps 50dB. I get a hump at 50Hz in one reading and that was from a room at midnight, with no traffic outside and a fridge in the room next door but with all doors shut. The 50Hz hump said 50dB but that should be as loud as my dishwasher being on and the room was NOT like this - it was completely silent.

I am still waiting to hear from Support because at the moment the microphone is pretty much useless to me as I cannot use it to take SPL readings with any accuracy at all.

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UMIK SPL with REW 7 years 1 week ago #20711

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Thanks for the reply. I will try to do some RTA plots during the night at the weekend and post them here for comparison.

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UMIK SPL with REW 7 years 1 week ago #20712

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Here are two plots I did - one at home in SILENCE very late/early so there was zero traffic outside, no rumble, entire area quiet apart from the fridge next door. No aircon (I don't have any, it is cold here). Nothing.

The other plot is at work in a quiet room (with a Mac Pro running nearby, idling so very quiet) and a guy about 8 metres away listening to music too loud on headphones (so hihats galore) but behind a few objects (desks, screens).

Plot 1: drive.google.com/file/d/0B2dUQpSGutXEaDN0TWwtdExFdWM/view
Plot 2: drive.google.com/file/d/0B2dUQpSGutXEOThJLVRKWm9LTWc/view

Spot the low end noise! This leads to crazy 50dB readings for SPL...??!?!

I had to upload the images to Google Drive because the "attachments" section of the reply in this forum appears to do nothing under Chromium/OSX.

EDIT: If any moderators or support want to chip in / reply / reply to my support email that would be very much appreciated....

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Last edit: by 72deluxe. Reason: Further text

UMIK SPL with REW 7 years 1 week ago #20714

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Hi, the ear is very insensitive to low frequencies at low levels. This is Fletcher Munson:

en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves

So even though you may think the room completely quiet, the microphone will pick up noise that you can't hear. A computer running nearby IS going to affect the measurements, which you can see in the difference between your two graphs esp 20-40 Hz.

With regard to background noise level, this may help:

www.engineeringtoolbox.com/rc-room-criteria-d_729.html

None of that is to say whether or not you are getting good readings, but to provide background info. With an Earthworks M30 I get a curve similar to what you have, at least as far as 20 Hz which is where I chopped off the graph last time I did it... It might be an interesting article to do this with different grades of gear, as I have an upgraded sound card as well now...
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UMIK SPL with REW 7 years 5 days ago #20741

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@ 72deluxe,

Similar to the tech support ticket that you started with this regards, the answer from John is very similar to what we'd say here. I don't believe that there is an issue with your microphone, it's most likely because it's the first time you ever see a graph from REW, and you start to worry thinking it's wrong data.. :-) Hearing that low frequency isn't actually easy to distinguish..

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UMIK SPL with REW 7 years 5 days ago #20763

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Thanks john.reekie and devteam (and thanks devteam for your reply to my support issue as well).

Do the readings at www.engineeringtoolbox.com/rc-room-criteria-d_729.html refer to "silent" rooms in those residences? I ask because I made the first measurement at midnight in my silent neighbourhood.

I am curious if anyone has a reference of comparable dB readings that I can use at all? I am looking to determine how loud this band is without deafening all of us, and if "silence" as I perceive it is actually 40 - 50dB, I truly wonder what levels my band is playing at (as I get ringing easily without ear plugs)!!!

I am looking for a chart where I can compare and say "wow, we are far far far too loud" compared to the readings I am picking up with my UMIK.

The values I am getting do not correspond anywhere near what Wikipedia lists under 'sound pressure', so if anyone could offer a proper chart, then I would appreciate it greatly.

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Last edit: by 72deluxe. Reason: Typo

UMIK SPL with REW 7 years 4 days ago #20770

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If you are doing noise measurements, I believe you should be using A-weighting (not Z) - ?
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UMIK SPL with REW 7 years 3 days ago #20783

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Yes you are spot on. I was using the wrong weighting. After changing it to A weighting, the values correspond to what I thought they should be. A useful explanation of terms and a chart for newbie/clueless first-timers like myself is at www.jimprice.com/prosound/db.html

I recorded the sound in "silence" at home and the very low frequency sound was there still so I pitch shifted it up and amplified it and I have no idea what it is. It makes me wonder what is running in my house and what noise I am subjecting myself to all the time.

Please excuse my inexperience and assumptions! Thanks again for all your help.

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UMIK SPL with REW 7 years 2 days ago #20797

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Nice point from John...We missed that statement at the beginning... We're getting old and blind I guess. :-)
Glad to hear that you're all set.

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