All Audio that is coming through the Default Device in the Microsoft Playback Device Panel will be recorded. However, there are options to remove all audio, or just your microphone. In the Preferences under Audio you will have several options to choose from:
'Record All Audio' will include audio from all sources. This includes gameplay, music, and voice chat.
'Record Microphone' will only pick up audio from your microphone. 'Open Mic' will pick up microphone audio all the time, with a toggle to mute it.
'Push to Talk' will only record the microphone while you have a particular hotkey pressed.
Note: We currently do not have a method to filter out certain audio sources. You are welcome to let us know you would like this as a Feature Request though!