Channel View Options
On the left of the waveform display, you can find the view options for the waveform.
If you use multi-channel samples, the buttons on the left of the sample display let you decide which channel is displayed and used for wave extraction. The channel setting is remembered for each extracted wave. This way, you can extract one wave from the left and another from the right channel, for example. By default, the wave is extracted from the sum of the audio channels.