Author Topic: High end rolloff measured  (Read 5234 times)

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r1ck083

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High end rolloff measured
« on: February 02, 2012, 03:52:32 AM »
Hi,
   Just a query regarding the some 20db roll off im seeing measured in the top octave. Does the SignalScope App reconise or have a calibrated mic file for iPod4 touch internally used mic. I'm seeing close to accurate result between 100-8000Hz range, but having that top octave would be nice.

Rick.

FaberAST

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Re: High end rolloff measured
« Reply #1 on: February 02, 2012, 11:16:43 AM »
Rick,

I would not recommend that you rely on the iPod's built-in mic for high frequency measurements, particularly because of diffraction effects you can expect from the body of the iPod, itself.

Ben

r1ck083

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Re: High end rolloff measured
« Reply #2 on: February 03, 2012, 02:35:38 AM »
I'm aware of that factor, although having the mic in the corner of the ipod body, and the curve of the back edge does help reduce any ripple.
Anyway is there a calibration or compensation for the mic characteristics in the SignalScope app? None would render the use of such a program on a mobile device inaccurate and useless, right?

rick

FaberAST

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Re: High end rolloff measured
« Reply #3 on: February 03, 2012, 10:04:47 AM »
Rick,

Compensating for microphone roll-off comes with tradeoffs. The body of the iPod increases the directivity of the microphone response, especially in the upper octave band. Amplifying certain frequency bands also amplifies the noise floor within those bands. Additionally, the inexpensive electret microphones in iOS devices cannot be expected to exhibit very tight tolerances in their frequency response curves. The response of a particular microphone element may also be altered by leaving the iPod in a hot car.

The goal of using a built-in mic on an iOS device should be to get a reading in the ballpark. It seems to me that you already confirmed that to be the case in your experience.

If accuracy is most important to you, I recommend that you use a proper measurement microphone, which can be connected to the iPod with suitable adapters.

Ben

r1ck083

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Re: High end rolloff measured
« Reply #4 on: February 05, 2012, 01:27:38 AM »
"If accuracy is most important to you, I recommend that you use a proper measurement microphone, which can be connected to the iPod with suitable adapters."

Ben

What mics would you recommend, with portability and connectivity in mind?
 I have a Behringer ECM8000 but its needs to be pre-amped and powered, not something that i would see as "ready to use" in a given situation. If there was an external mic to compliment this iOS program that would be i great idea. Maybe another money maker for Faber if they materialise the idea.


rick.