Built-in and external microphones, overrange

  This application measures sound from an external microphone if one is inserted, or from the iPhone's built-in microphone otherwise.
  The sound pressure value displayed is calculated to be equivalent to that of the built-in microphone if the external microphone is SONY ECM-SP10. If the * symbol appears to the right of the dB value displayed, it indicates that it is recognized as an external microphone.
  The built-in microphone cuts low-frequency sounds at the input and suppresses loudness at the input, so overrange rarely occurs. If overrange occurs frequently, press the Attenuate button. This will lower the gain by approximately 12 dB. Note that the Attenuate button will only appear on the screen in an environment where the gain can be adjusted. Pressing it repeatedly alternates between AttenuateOn and AttenuateOff.

The right side of the figure shows Attenuate ON. Even when Attenuate is turned on, the dB value displayed is corrected and is almost the correct value.
  When saving a file, the file name is distinguished as
    ES_yyyyy-MM-dd_hhmmss.wav for the built-in microphone,
    es_yyyyy-MM-dd_hhmmss.wav for the built-in microphone and AttenuateON,
    LS_yyyyy-MM-dd_hhmmss.wav for the external microphone,
    ls_yyyyy-MM-dd_hhmmss.wav for the external microphone and AttenuateON.
  The application's display sound pressure is compensated by reading the differences in these file names.