Incremental audio is analogous to incremental video. You can use incremental video to process audio information from YouTube, or you can use a dedicated extractor bar in sound components to import and process sound files (e.g. MP3, WMA, WAV, etc.).
Working with sound files is the same as working with video files. The only difference is that you will use sound components instead of video components. Those will be created for you automatically at import with File : Import : Files and folders (available from the main menu). For details see: Incremental video with video files: Outline.
See: Incremental video with YouTube: Outline to find out how to use YouTube material in incremental audio process.