Playback options deal with volume. Set Loopback allows selections to be repeated. The Effects menu begins with choices to modify the current selection. The Effects menu also has tools for generation. Noise creates sound like static.
Silence adds quiet.
From the Windows menu, a Control palette allows clips to be recorded, played, paused or stopped. A Selection palette gives time for start, end, and duration. Sound Edit also allows QuickTime sound recording, editing and synchronizing. One can add a soundtrack, effects, narration and music to movies. Audio CD tracks can be made into sound-only movies too.