If you are going to be serious about creating a successful YouTube channel, then YES you need a microphone, and it needs to be a good one. Fortunately, it does not have to cost the earth. A Power DeWise lavalier mic is about $22. A Deity V-Mic D3 short shotgun mic costs under $100. And the Blue Yeti condenser mic is also about $100. You can pay a lot more, but these microphones will allow you to record good audio for YouTube videos.