One of the abilities many users miss from Sony Vegas is the ability to record audio from a microphone directly into the editor. It's mostly used for narration, dubbing, and other video-synchronized speech tasks. But perhaps the most surprising fact is that KDEnLive already supports the microphone, although in a very unintuitive way. The program, curiously enough, already supports recording from a webcam, with audio included. Which means that, for recording from a microphone, the hacky workaround is to record a video, then removing the video part. Is it too complicated to create a mode to record audio only?

Under the "Record monitor", choose FFmpeg capture and enable audio only. Then move back to the project monitor and hit play. You can now record audio only while the clip is playing and create a voice over.
http://kdenlive.org/mantis/view.php?id=2910