You need to change your recording source from 'mic' or 'line in' or 'aux' or whatever to 'soundcard' or 'whatuhear' (If you have a Creative brand SC).
Some third party programs allow you to do this (Goldwave, for example). I haven't used Audition in about a year so I'm not sure if it does. Regardless, you should be able to find the option somewhere in your soundcard audio properties:
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