calibration IMM-6 on Audio Tool

[Matthias]

I bought the IMM-6 mic and loaded the calibration file. I did it on a galaxy S10, S7 and a Google Pixel 3a. There different results. Not only the level is different but also the curve differs a litte bit. But how do I know which is the right offset? Is there a table with all important phones on the market to get a nearby offset value or do I have to find out by calibrating in a studio - then there is no need of buying a calibratet mic!?

I read in this forum that there is no difference betwen "front mic" and "main mic" setting in Audio Tool. On my Galaxy S10 it has a huge effect especially at arround 2.5kHz. It measures 10dB+ on "main mic" What is the right setting then. The funny part is, apart from the selection the IMM-6 is always the one which is active. That means samsung is already adjusting the curve even before the signal reaches Audio Tools - which makes a calibratet mic even more ridiculous.

Is anybody out there to help me with my questions? ;)

Thanks,
Matthias

[Julian Bunn]

There are two different use cases for a calibrated mic: either you want to correct for the frequency dependent response of the mic, and aren't interested particularly in the absolute level, or you want both. In the latter case you must calibrate AudioTool using the Global Offset by comparing with an external SPL meter. Not everyone is interested in absolute SPL measurements: many are interested only in, say, the response curve/shape.

All Android phone models are different when it comes to audio internal circuitry, and of course AudioTool has no control over the internal circuitry. There *IS* a difference between Front and Main mic ... and you can select which you want in the AudioTool Menu. Whether the internal audio circuitry respects the SDK/API choice is a different matter. You should expect to see a difference in the response curves and levels between the two. Normally, the Main Mic is the channel that is used when you plug in an external mic like the iMM-6. But for a given phone that may not be the case.

Hope this part way helps?

Julian

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