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G.729 is an ITU Telecommunication Standarization Sector standard used for speech compression and decompression. The technology is used in digital transmission systems and for coding analog into digital signals. G.729 is widely used in voice over Internet Protocol applications because of its low bandwidth requirements.
G.729 includes patents by several companies and is licensed by Sipro Lab Telecom. In certain countries, the use of G.729 requires a license or royalty fee.
The extensions of the G.729 standard include G.729a and G.729 b.
G.72a is a compatible extension of G.729 that requires less computational power at the expense of slightly lower speech quality. It was initially developed by a consortium of organizations, including France Telecom, Mitsubishi Electric Corporation, Nippon Telegraph and Telephone Corporation (NTT) and Université de Sherbrooke. Its key features include a fixed bit rate and fixed frame size.
G.729b provides silence compression that enables voice activity detection modules, which detect voice activity in signals. It also includes a discontinuous transmission module that decides when to update background noise parameters for lack of speech and use three-byte silence insertion descriptor frames to initiate noise generation. If transmission stops and the link goes quiet due to no speech, the receiving side may assume the transmission has been cut. Analog hiss is simulated digitally by inserting comfort noise during silence to assure the receiver that links are active and operational.
G.729 is also extended to provide support for wideband speech and audio coding.