1) Highlight the track that you want to freeze
2) go to the VIEW > Track Freeze Switch... this will put the FREEZE icon on all tracks
3) click the FREEZE icon on the track that you want to be FROZEN
4) hit play on the transport
5) the timeline bar will go across the entire song from beginning to end and a dialog box will appear telling you that it is FREEZING the current file
6) once it is done, this track will still be present but it's processing will be removed from the CPU