Apple Logic Express 8 - Manual (Page 529)

Chapter 21 Editing Audio in the Sample Editor 529
Reversing the Phase of a Selection Area
You will find the Invert command extremely useful for correcting phase cancellation
errors, or when several out of tune signals (or several signals processed through chorus
effects), are to be mixed down to mono.
To completely reverse the phase of all currently-selected audio material:
m Choose Functions > Invert.
All negative amplitude values become positive, and vice versa.
Note: This doesn’t audibly change the file, if heard in isolation. The process depends
heavily on the audio material.
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Tip: You can also use the Invert function to decode mono/stereo recordings, but it’s far
easier to use the Direction Mixer plug-in for this task. For more information on this
plug-in, see the Logic Express 8 Instruments and Effects manual.
Removing DC Offsets
Some audio interface hardware can layer direct current (DC) 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.
To center the waveform around the zero amplitude line:
m Choose Functions > Remove DC Offset.
Adjusting the Project Tempo
Just like automatic tempo matching functions in the Arrange, the Functions > Adjust
Tempo by Selection and Locators command adjusts the project tempo, in accordance
with the current locator positions and selection area in the Sample Editor.
The operation is similar to the Arrange function (see “ Setting the Project Tempo to
Match an Audio Region ” on page 554); but only applies to the selected area of the
audio file in the Sample Editor, rather than the overall length of the region.