* USB microphone. By default, the demo will produce a square wave test tone
* when the board button is pressed. If USE_TEST_TONE is not defined in the
* project makefile, incoming audio from the ADC channel 1 will be sampled
* USB microphone. By default, the demo will produce a square wave test tone
* when the board button is pressed. If USE_TEST_TONE is not defined in the
* project makefile, incoming audio from the ADC channel 1 will be sampled