BR-532: Disabling the built in Microphone
To use only a microphone connected to the MIC jack, you must first turn off the internal microphone.
1. Press UTILITY.
2. Press PARAMETER < or > to move the cursor to "SYS" and press (ENTER).
3. Press PARAMETER < or > to select "On Board Mic" and turn the setting to "OFF" with the TIME/VALUE dial.