This is pasted from the help files in RB.

Solo Mode



Note: The Solo button solos a group of all selected tracks, not just the current track.

You can toggle RealBand in and out of Solo mode by pressing the Solo button. When in Solo mode, you will only the currently selected group of tracks (assuming you haven't muted them). You won't hear any of the other tracks. The Solo button will remain pressed to indicate RealBand is in Solo mode.

Solo BB Bass and Drums Tracks

To hear just the BB tracks for bass and drums tracks hold down the Ctrl key while clicking on the Solo button.