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I've noticed that when using my smartphone the vibrations from my actions aren't picked up, or are picked up very faintly by the microphone. I've worked quite a bit with microphones and I know it must be a non-trivial problem. Does anyone have experience in this arena?

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  • \$\begingroup\$ Poor LF response is probably a big part of it... \$\endgroup\$ – Brian Drummond Jul 3 '15 at 15:52
  • \$\begingroup\$ Actually, they aren't that bad. You won't be making any hifi recordings with them, but I can pickup heartbeats with just the built in microphone on my cheap Samsung smartphone. \$\endgroup\$ – JRE Jul 3 '15 at 15:54
  • \$\begingroup\$ the raw microphone output probably does show these knocks and rubbing/vibration sounds, but the DSP done on the dedicated audio ICs and the firmware in your phone can do some neat tricks, like spike suppression and tuning out unnatural sounds \$\endgroup\$ – KyranF Jul 3 '15 at 16:04
  • \$\begingroup\$ When you make a call, sure it'll do some processing. It has to for the codec. The typical recording programs record to mp3, so they throw away a lot of stuff (under 100Hz is just GONE) but any program that uses the audio API directly gets pretty much raw audio (some high pass filtering, maybe some AGC, but no real heavy duty noise reduction.) \$\endgroup\$ – JRE Jul 3 '15 at 16:17
  • \$\begingroup\$ @JRE Very interesting about the raw data, I wonder if there is a way to ask for speech use filtering from some of the APIs? \$\endgroup\$ – KalleMP Jul 3 '15 at 17:58
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The microphones are generally mechanically decoupled from the housing.
If the mic is in the housing then it is usually in a soft rubber boot that reduces noise from carrying over.
If the mic is on the board, then there's already decoupling from all the mechanical barriers (noises have to go from the housing to the PCB to the mic, and there are losses at each stage.)

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