how do I record my computer audio and my screen?

So, I've been making lyric videos using Keynote because they look a lot cooler that with iMovie. The Problem is, I'm trying to use QuickTime to Record the keynote along with the audio I have set up with it. However, I can either record all outside sounds (the song and, shuffling, background noise), and the song sounds really muffled. The other option is to record nothing at all. Can some one help me record only the computer noise and the screen?