When editing sound, you may need to remove the sound before and after the sound. For example, you made final edits and you want to discard some extraneous sound before and after your edited sound. You can make these adjustments by cropping sound with Crop to Selection by selecting the sound you want to keep. All sound in the waveform not selected is replaced with the selection. Your selection set can be across frames which allows the frame markers to be preserved.
If no sound is selected, the icon is disabled.
To crop the sound in a frame: