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Author Topic: Smaart 7 - setting up mic and interface sensitivity  (Read 12157 times)

Mark McFarlane

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Smaart 7 - setting up mic and interface sensitivity
« on: September 14, 2013, 04:52:27 am »

I've been playing around with the SPL readings on Smaart 7 and am trying to enter my mic sensitivity.  I haven't had any problem entering my mic's frequency response (calibration curve)

Double clicking on the SPL meter in the upper right window corner brings up the Sound Level Options Dialog.  Clicking 'Calibrate" brings up the the Amplitude Calibration dialog.  The Microphone field is disabled and I am unable to set the Sensitivty for my mic as provided by my factory calibration (5.7mV with 94db) because the field doesn't take any input. 

Smaart's integrated help system says I can only set up a microphone and its sensitivity if the electrical sensitivity of the interface is known.

1) How exactly is the mic's sensitivity used? Is it a simple multiplier to transform delta voltage to delta SPL?
2) Is there a way to measure/estimate and then specify to Smaart an interface's electrical sensitivity? 
3) What interfaces does Smaart actually know the electrical sensitivity of?

I have been able to manually calibrate SPL using the offset field (the auto calibration is off a few db, but then I manually adjust the offset) using my analog Radio Shack meter.  However, the calibration only works within a few db of the reference I calibrated at.  For example, if the room background noise I'm measuring is 20db lower than where I calibrated, the SPL measurement is way off.  I assume this is what the mic and interface sensitivities account for.
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Mark McFarlane
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Mac Kerr

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Re: Smaart 7 - setting up mic and interface sensitivity
« Reply #1 on: September 14, 2013, 11:08:25 am »

I've been playing around with the SPL readings on Smaart 7 and am trying to enter my mic sensitivityI have been able to manually calibrate SPL using the offset field (the auto calibration is off a few db, but then I manually adjust the offset) using my analog Radio Shack meter.  However, the calibration only works within a few db of the reference I calibrated at.  For example, if the room background noise I'm measuring is 20db lower than where I calibrated, the SPL measurement is way off.  I assume this is what the mic and interface sensitivities account for.

I don't know how you set it just from electrical sensitivity specs, the most common way to calibrate for SPL is with a calibration piston. It is a device that seals around the mic capsule and provides a known SPL (generally 94dB). You set the SPL in Smaart to 94dB while the calibration piston is running and you're done.

If your RS meter and your measurement system disagree about SPL over wide ranges I would suspect the RS meter not a good measurement mic. The sensitivity only sets the reference, it doesn't change with level.

Mac
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Timo Beckman

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Re: Smaart 7 - setting up mic and interface sensitivity
« Reply #2 on: September 14, 2013, 12:18:05 pm »

I did the calibration and saved it but as it turns out i need to calibrate each time i do a alignment .
I can put in the sensitivity but if i verify with a calibrator (piston@94db) it doesn't match al the time . It's always a bit of .

If i punch in the numbers on sim3 and then verify spl read out on the mic it's off and the same within smaart compared to the piston@94dB .
The smaart i/o's are great . First calibrate and after that you joggle the gain settings all you want . The spl read out will still be valid .
http://wp.me/a178jh-zC
http://wp.me/a178jh-zD
http://wp.me/a178jh-zE
http://wp.me/a178jh-zF

Which version of smaart7 do you use ?

In the help file it says as you already found :
"The Microphone selector is normally disabled unless you are using an input device with known electrical sensitivity, in which case you will be able to store and recall sensitivity values for named microphones that allow you to essentially calibrate Smaart to SPL (or some other reference) without a sound level calibrator."

I suspect you'll need to use the smaart i/o because i can put in a voltage/p.
Maybe ask the people from rational
« Last Edit: September 14, 2013, 03:51:47 pm by Timo Beckman »
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Gustaf Kempe

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Re: Smaart 7 - setting up mic and interface sensitivity
« Reply #3 on: September 14, 2013, 04:58:57 pm »

I think you only can put in the sensitivity of the mic if you are using the Smaart I/O. I use a Piston, if I recheck like the next day it's allways within +-0,1 dB. You should however allways check before and after a measurement if you are measuring to please the government.
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Chris Tsanjoures

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Re: Smaart 7 - setting up mic and interface sensitivity
« Reply #4 on: October 09, 2013, 10:52:15 am »

I think you only can put in the sensitivity of the mic if you are using the Smaart I/O. I use a Piston, if I recheck like the next day it's allways within +-0,1 dB. You should however allways check before and after a measurement if you are measuring to please the government.

You are correct, using microphone sensitivity to calibrate for SPL and storing of a microphones sensitivity data is only available with the Smaart IO. You can save microphone correction curves for use with any IO device, however the calibration/sensitivity information cannon be saved because Smaart cannot communicate with generic input devices the way that it can with the Smaart IO (namely known gain and tolerance).
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I am employed by Rational Acoustics. Besides being a Product Manager for the Smaart Platform, I operate as a fully deployable Smaart Ninja (aka Instructor/System Guy).
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