Electronic – Is it possible a microphone sounds different when user hold it(or not)

memsmicrophonesound

I am a computer-science student working on a signal processing project on smartphones based on recorded microphone signals. For my project, I need a really "reliable" recorded signal. The system works perfectly when I put phones on a table and don't touch it. However, when I touch the phone by my hands (e.g., press a button when phone is static in the table), the recorded data in microphone seems changed dynamically for unknown reason. For example, at certain time period, the received audio (sent from my laptop) is louder.

Since I am not an expert of electrical theory, I would like to know if there is any theory about this phenomenon (such as touching make the diaphragm hard to vibrate) I know the microphone is a MEMS microphone which operates as a condenser type microphone but not sure if there is any reason that the recorded signal changes depends on how user touch the microphone (or smartphone body).

Best Answer

I've flagged this question to be moved to a more appropriate SE site, but (to expand on what Eugene Sh. said) the answer can be deduced from the advice given to pro mic users:

Vibrations will not only reach the microphone through the mic stand. They can also enter the microphone body through the XLR connector and the cable, particularly if it is quite stiff. The best way to overcome this is to use the lightest and most flexible cable you can, and to clamp or tape it firmly to the stand to stop vibrations being carried into the mic. Location sound recordists for film and television use very light flexible tails between the mic and pole, and then a more robust cable back to the mixer, simply to avoid vibrations coming from this means of entry. Vocalists using a hand-held directional microphone can isolate cable vibration by making a loop of cable and trapping it between the fingers (not touching the microphone body) so that vibration along the cable is stopped when it reaches the hand, the onward loop to the mic being (hopefully) vibration-free. This technique also avoids straining the XLR connector with the weight of cable as the vocalist moves about the stage.

There are couple more things you need to know about MEMS:

  • Their natural frequency response is usually quite far from flat. So there's [mandatory] electronic post-processing. See this comparison of a MEMS mic and a [conventional/large] electret frequency response from a NASA study

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  • MEMS often get advertised as omidirectional, but that's only true of the sensor itself. Once it goes into whatever body (especially something as bulky as a phone), they stop being all that omnidirectional:

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