Open Sony Soundforge and load the song you wish to edit. Select "File" then "Open" and select the song from the browser. Use a high quality wave file for best results and because not all versions of Sony Sound Forge 9.0 support MP3 file editing.
Double-click in the center of the wave to select the entire song. Alternatively, click once on the wave form and select "Edit" then "Select All" from the top menu.
Select "Process" then "Channel Converter" from the file menu. From the Channel Converter drop-down menu, select "Stereo to Stereo Vocal Cut." From the Channel Converter dialog screen, select the box marked "Invert" on the right channel.
Process the audio file and remove the vocals by selecting "OK" from the channel converter dialog screen. When the file has finished processing, preview the track and test the results by pressing "Play." The audio has been removed by canceling out the center channel where vocals are usually mixed. Drums and bass also occupy the center channel so you may notice the song sounds slightly different.
Save the processed song by selecting "File" then "Save As" and renaming the file. Selecting "Save As" prevents you from overwriting the original file with the vocals.