For converting files into MP3, you will need LAME – a freeware MP3 encoder which provides high-quality output and fast encoding speeds.
Installing the codec on Windows
Installing the codec on Mac
LAME Encoder, while initially created as a set of patches, has been developed by the open-source community since 1998, and has quickly become one of the most renowned MP3 encoders.
After a codec listening test conducted in 2004 by Roberto Amorim, it was recognized that LAME makes the highest-quality MP3 files at mid-high bitrates (128 kbps and above). The test also established that LAME-encoded 128 kbps MP3 files showed results closest to the original (uncompressed) audio, compared with other encoders. You can find more information on LAME at lame.sourceforge.net.