When I import a video clip into the timeline, 4 audio channels automatically appear. How can I select just the original one? Thanks.
What is your camera or capture source? Post Mediainfo report if you are unsure per these instructions.
Please see https://www.vegascreativesoftware.info/us/forum/important-information-required-to-help-you--110457/ and provide the information requested under points B and C - and particularly a detailed MediaInfo report (a free app) of your media as linked in point C-1.
Otherwise, is the media MXF and you have 'Import MXF as multi-channel' selected 'on' in Options/Preferences/File I/O (tab)?