Default installation of Linux Mint 16 (MATE version) does not allow to record sound played by the PC. To allow this type of operation, install pavucontrol.
When that's done, you can record playback sound following those steps:
- open PulseAudio Volume Control application
- start a recording application (audacity, for instance) and make it record
- under Recording tab of PulseAudio Volume Control, change Internal Audio Analog Stereo to Monitor of Internal Audio Analog Stereo
- you can now start the audio source
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