SoundIn is a convenience UGen to read audio from the input of your computer or soundcard. It is a wrapper UGen based on In, which offsets the index such that 0 will always correspond to the first input regardless of the number of inputs present.
"open -a 'Audio MIDI Setup'".unixCmd; // execute this to launch it
the channel (or array of channels) to read in. These start at 0, which will correspond to the first audio input.