Apple Soundtrack Pro 3 - Manual (Page 214)

As you drag, the left (upper) channel of the audio file becomes darker in the waveform
display.
Part of left
channel selected
To select the right channel of an audio file
1 Move the pointer near the lower edge of the waveform display.
The pointer changes to the letter “R.”
2 Do one of the following:
• Double-click in the lower part of the waveform display to select the entire right channel.
• Drag the pointer to select the part of the right channel with which you want to work.
As you drag, the right (lower) channel of the audio file becomes darker in the waveform
display.
Part of right
channel selected
214 Chapter 8 Working in the File Editor