Hi Goner,
on my KB it's "-", go figure.. you can always remap it via the clipboard..
However, what ever key you use (default is the one next to the RH shift), you can modify it three ways to give four channels. On my Danish KB it's "-", as I said, so I get "-";"shift -", "alt - " and "cntrl -". The fifth channel, vox, doesn't have a key combination.