Choose Insert > Silence to insert a section of silence in a sound file.
Choose Edit > Mode > Time (or click the Time Mode button in an editor's playbar).
Choose Insert > Silence. The Insert Silence dialog is displayed.
In the Insert box, specify the length of silence that you want to add.
Choose a setting from the at drop-down list to specify where the silence should be inserted:
Cursor: inserts silence at the current cursor position.
Start of file: inserts silence at the beginning of the file.
End of file: inserts silence at the end of the file.
Click the Insert button.
Any markers or regions that exist after the insertion point will be rippled to preserve their position.