Connect your audio source to the first input of a mixer. You may use any device from a microphone to a hand-held tape recorder, just ensure that you have the correct cable to connect your audio source.
Plug the power cord from the mixer into a power outlet.
Plug the RCA end of an RCA-to-1/8-inch cable into the mixer's Audio Out RCA jacks.
Insert the 1/8-inch end of the RCA-to-1/8-inch cable into the line-in jack of your computer's sound card.
Open an audio recording program of your choice.
Set the recording input in the audio recording software to "Line In."
Press the "Record" button in the audio recording software.
Play audio from your audio source and adjust the levels on the mixer and sound editing software until you reach the desired recording level.
Press the "Stop" button in the audio recording software.
Cue up your audio source to the point where you wish to begin recording.
Press the "Record" button in the audio recording software.
Activate your audio source.
Press the "Stop" button in your audio recording software when you have reached the desired stopping point.
Click on the "File" menu, select "Save As," type a name for the audio file, select a save location and press "Save."