Quite possibly the best free audio converter available, Freemake Audio Converter is certainly the easiest to use.

Users who don’t want to install third-party software can easily pull audio from YouTube with an online video-to-MP3 converter. These free, cross-platform solutions work with Windows, Mac, iOS ...

Step 3. Choose “MP3” or “WAV” in the Audio section and select a quality. Then, click the “Download” button to save this YouTube audio on your computer.