Sound Converter is an open source tool available from Ubuntu Software Center that can be used to convert audio files from one format to another.
Example usage is to generate different formats of same audio file to be used in case of HTML5 <audio> element.
Install it from Ubuntu Software Center
Add a file to be converted, from the browser dialog after clicking on "Add File"
Select the format, the audio file is to be converted to and the place to be saved and then click the "Convert" button in the main window to begin the process.