Channel selection lets you operate on any subset of the channels in a multi-channel audio file, by excluding channels as desired. Excluded channels are unaffected by the operation, meaning their samples remain untouched. Only the following commands support channel selection: Amplify, Fade, Invert, Normalize, Reverse, and Plugins. For all other commands, channel selection is ignored.
By default, all channels are selected. To toggle a channel's selection state (from selected to excluded or vice versa), use Ctrl+left-click, i.e. press the Ctrl key, and while holding it down, left-click anywhere within the channel. To extend the resulting selection state to adjacent channels, drag the cursor over the adjacent channels while continuing to hold down the left mouse button. The cursor changes to a vertical double arrow, indicating drag channel selection mode. This lets you quickly select or exclude a group of adjacent channels, useful when editing surround audio. To select all channels, use the Fit Vertically command (View/Fit Vertically or Shift+0).
Excluded channels are indicated by an alternate color scheme, which can be customized. The channel selection needn't be contiguous, i.e. it's possible to select the first and last channel in a surround file. At least one channel must be selected at all times, and WaveShop enforces this by modifying your selection if necessary.