Apple Logic Pro 7 - Manual (Page 401)

Chapter 11 Sample Editor 401
Silence
You can use Functions > Silence to remove all data from a selected area. The waveform
material contained in the selected audio passage and the corresponding amplitude
values are all set to zero. You can use this function to silence unwanted background
noise in quiet passages.
Invert/Reverse
Invert
Functions > Invert completely reverses the phase of all currently-selected audio material.
All negative amplitude values become positive, and vice versa. While this doesn’t
audibly change the file, if heard in isolation, you can use Invert to correct phase
cancellation errors, particularly if you’re mixing down to mono. This is extremely useful
when several out of tune signals (or several signals processed through chorus effects),
are to be mixed down to mono. The process depends heavily on the audio material.
You can also use the Invert function to decode MS recordings, but it’s far easier to use
the DirMixer plug-in for this task.
Reverse
Functions > Reverse reverses the selected audio passage.
Trim
Functions > Trim erases all Regions that aren’t selected. Use it to remove unimportant
passages from the start and end of your audio files.
Make sure that the areas you are about to delete do not contain any Regions that you
may need. Regions outside the selection will be lost, and Regions that fall partly
outside will be shortened. If any such Regions are being used in the Arrange, an alert
box appears, giving you the option to cancel the trim function.
Remove DC Offset
Poorly constructed audio hardware can result in direct current (DC) being layered over
the audio signal. This results in a vertical shift in the waveform position, which can be
clearly seen in the Sample Editor.
During playback, this can cause crackling sounds at the start and end of the audio
Region.
Functions > Remove DC Offset centers the waveform around the zero amplitude line, to
avoid crackling at cut points.