Must be installed in your MAIN GAME FOLDER, not saved games. Use JSGME or other manager so you can back it out if needed.
Reduces just the radio effects volume. Jesters voice is not changed, because it can be controlled by the ICS volume control knob.
Note that the volume is highly dependent on what you set your "Helmet" volume to and your other sound settings. So edit the sdef files to suit your own setup accordingly.
Passes normal integrity checks for MP, but haven't tested with pure scripts since all the good servers I use don't enable that anyway.