Media.io allows you to convert audio files to MP3, WAV, WMA and OGG formats without the need to install any software on your desktop, while fre:ac (for Windows) and Max (for OS X) are highly rated downloadable converters. Installing an application may speed up your conversion process.
Media.io is a Web-based application that lets you convert WAV files into MP3 format simply by selecting a file to upload, and choosing the output format and bit rate. It then uploads your WAV file, converts it and allows you to download the converted MP3 file.
Using a software-based audio converter has the advantage of eliminating the need to upload your files to an external server for conversion.