Choose Process > Invert/Flip to reverse the phase of the sound data. Although inverting data does not make an audible difference in a single file, it can be useful for matching a sample transition when executing certain pastes, mixes, or loops.
If no data is selected, the entire file will be inverted.
In the following example, the red line represents the baseline, and the lower waveform is the inverted image of the upper waveform.