Speex

Speex is another product from Xiph.org, it is sort of the Ogg Vorbis answer to speech compression. As unlike music, speech is a lot simpler, and requires much lower bitrates to be aurally readable. As a result, it requires much lower bitrates and a different algorithm.

Speex is open source, and can be added to ogg container. It uses VBR (Variable Bitrate Encoding) process to provide the best combination with the best compression ratio. Its was mainly developed for VoIP, and uses a unique loss concealment technology that masks dropped UDP packets, to prevent crackling and breaking of voice data.