Speex

Speex is an Open Source/Free Software patent-free audio compression format designed for speech.
The Speex Project aims to lower the barrier of entry for voice applications by providing a free alternative to expensive proprietary speech codecs. Moreover, Speex is well-adapted to Internet applications and provides useful features that are not present in most other codecs.
Speex is a useful audio compression utility that will come in handy. Speex is based on CELP and is designed to compress voice at bitrates ranging from 2 to 44 kbps.
Here are some key features of "Speex":
ï¿­ Narrowband (8 kHz), wideband (16 kHz), and ultra-wideband (32 kHz) compression in the same bitstream
ï¿­ Intensity stereo encoding
ï¿­ Packet loss concealment
ï¿­ Variable bitrate operation (VBR)
ï¿­ Voice Activity Detection (VAD)
ï¿­ Discontinuous Transmission (DTX)
ï¿­ Fixed-point port
ï¿­ Acoustic echo canceller
ï¿­ Noise suppression
Note that Speex has a number of features that are not present in other codecs, such as intensity stereo encoding, integration of multiple sampling rates in the same bitstream (embedded coding), and a VBR mode.