Apple Logic Express 9 - Manual (Page 560)

As long as the mouse button is held down, the drawn waveform can be replaced by the
original waveform—by moving the pointer to the left.
Trimming Audio Files in the Sample Editor
The Trim function is used to edit areas of the audio file that are not selected.
You can use the Trim command to remove unimportant passages—generally
silence—from the start and end of your audio files. Trim can also be used to remove
portions of audio files that are not used by regions.
To erase all unselected portions of an audio file
µ
Choose Functions > Trim (or use the corresponding key command, default
assignment: Control-T).
Important: Make sure that the areas you are about to delete do not contain any regions
that you may need. Regions outside the selected area will be lost. Portions of regions
that fall partly outside the selected area are also removed, resulting in a length reduction
of the region. If any such regions are being used in the Arrange area, a warning dialog
will give you the option of canceling the trim command.
Silencing an Audio File Selection in the Sample Editor
You can use the Silence command to set all amplitude values to 0, rather than removing
(with Cut, Delete, or Trim) all data from the selected area of an audio file. This function is
generally used to silence unwanted background noise in quiet passages.
To silence the selected area of an audio file
µ
Choose Functions > Silence (or use the corresponding key command, default
assignment: Control-Delete).
Changing the Level of Audio Files in the Sample Editor
You can use the Change Gain command to change the level of an audio file. Typically
used on an entire audio file, this command can also be used to boost portions of it.
To raise or lower the level of the selected audio file (or area) by a specific amount
1 Choose Functions > Change Gain.
560 Chapter 17 Editing Audio in the Sample Editor