I've heard that Audacity, which is free, can do that.. I've never tried Audacity though so I can't confirm it for you. I use Reaper (which is also free) for all my recording purposes now, there's a possibility that it or one of the many free plug-ins available could do it too.. but again, as I have never used it for that purpose I can't confirm it.

Audacity:
http://audacity.sourceforge.net/

The Reaper forums:
http://www.cockos.com/forum/