Use Trim Silence to remove leading and trailing silences from the ends of the selection. Unlike other trim commands, Trim Silence works within the selection and does not remove anything outside the selection. Be sure the selection contains all the leading and trailing silences to be removed. and are recommended before using this effect to ensure a consistent silence level.

To remove all silences throughout the selection, use instead.

Trim Silence Settings
Setting Description
Silence to keep (s) Sets the amount of silence to leave on the ends. Use zero to remove all silence. Extra silence is not added if the existing silence is less than this amount.
Threshold (dB) Sets the highest of background noise that should be considered silence. If the audio has a lot of background noise or hiss, use values above -30dB. If the audio is clean, use values below -40dB.
Leading silence,
Trailing silence,
Both
Sets the end of the selection to trim. Leading silence removes the silence at the beginning of the selection. Trailing silence removes the silence at the end of the selection. Both removes silences from both ends.

If only some channels are selected in a stereo or multichannel sound, then only that channel is trimmed. Since it is not possible for one channel to be longer than another, the ends of the trimmed channels are padded with silence, which results in trailing silence. All channels must be .
To completely trim silences from both ends of the entire file:
  1. Use from the Edit menu.
  2. Choose Trim Silence from the Edit menu.
  3. Enter 0 for Silence to keep.
  4. Enter -40 for the Threshold.
  5. Select Both.
  6. Choose OK.