There are times when you want to just have simple complete silence on an audio track. Perhaps there is a bit of background noise you want to remove, or perhaps you need to add more space for students to respond to a dialog. No matter the reasons silence can be added using the Generate -> Silence menu.
The generation command will add the silence at the insertion cursor, or the beginning of the selection. The amount of silenece added is specified in the dialog which appears. If you have a region selected then the selected length of time will automatically be placed into the dialog, otherwise a default of one second is used. The audio will appear at insertion mark to increase the size of the audio. If a region is selected then that region will be deleted before the silence is inserted. Thus, if a region is selected and the defaults used then the length of the audio will not change, but the selected portion will be changed to silence.