Xrecode is a free audio conversion tool for Windows that can convert almost any audio formats. It supports vast number of audio conversions and can convert multiple files by taking full advantage of multi-core CPU(Parallel processing). Apart from audio-to-audio conversions, it can also extract audio from video files (avi, flv, mov, etc). This can come useful if you want to extract audio from music videos.
Just click Open and select multiple audio files that you want to convert. In the screenshot below you can see that I have selected 120 .mp3 audio files and 1 .wma audio file.
To check which file types to accept, click Settings. Now you can select all file types that you want to accept, you can also accept non-audio files.
After you have selected all the files for conversion, select the Output destination. You can enable pre processing of the files if you have a fast system. Now lastly select the format to which you want to convert. Under every format there is Settings where you can change the quality and modify other settings. Once ready, click Start and you are done.
If you have a fast computer with more than one core, you can take full benefit of parallel processing. Suppose I have Core 2 Duo @ 2.26 Ghz CPU, it means I can easily run 4 files in parallel.
It uses Lame for encoding to MP3 format, Vorbis for encoding to OGG and FLAC format, MonkeysAudio for encoding to APE format, and WavPack for encoding to WV format.
It also has full unicode support for input and output files under Windows 2000, XP, and Vista. Being one of the most stable, feature-rich, and easy-to-use tool, it has now become one of my default audio converter. Enjoy!