See INSTALL file for instruction on how to install Speex.
The Speex is a patent-free, Open Source/Free Software voice codec. Unlike other codecs like MP3 and Ogg Vorbis, Speex is designed to compress voice at bitrates in the 2-45 kbps range. Possible applications include VoIP, internet audio streaming, archiving of speech data (e.g. voice mail), and audio books. In some sense, it is meant to be complementary to the Ogg Vorbis codec.
To use the Speex command line tools:
% speexenc [options] input_file.wav compressed_file.spx
% speexdec [options] compressed_file.spx output_file.wav