[Karl Morkunas]

I read and tried the solutions prevented above, but found this solution to work best for Soundbooth CS4:

Adobe Soundbooth: Mono to Stereo

1. Drag and Drop Audio into Interface
2. Right click and choose “Insert Channels into New Multitrack File”
3. Delete the Empty Channel
4. Copy and Paste the channel with the audio (i.e. L1) & drag and drop into the empty channel (i.e. R1)
5. You now have Stereo sound with audio in both channels