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G.729 Voice [[codec] audio standard

Complete  Definition

G.729 is an ITU-T algorithm  for voice encoding that  produces an 80-bit voice sample every 10 msec (bit rate  of 8 kbps). The codec  works in blocks of 10 msec and so it is possible to  generate frames of multiple  10 msec duration.

G.729 is an audio data compression algorithm for voice that compresses   voice audio in chunks of 10 milliseconds. Music or tones such as DTMF or fax  tones cannot be transported reliably  with this codec, and thus use G.711 or  out-of-band methods to transport these  signals.

G.729 is mostly used in Voice over IP applications for its low bandwidth   requirement. Standard G.729 operates at 8 kbit/s, but there are extensions,   which provide also 6.4 kbit/s and 11.8 kbit/s rates for marginally worse and   better speech quality respectively. Also very common is G.729a which is   compatible with G.729, but requires less computation. This lower complexity is   not free since speech quality is marginally worsened.

The annex B of G.729 is a silence compression scheme, which has a VAD module which  is used to detect  voice activity, speech or non speech. It also includes a DTX  module which  decides on updating the background noise parameters for non speech  (noisy  frames). These frames which are transmitted to update the background  noise  parameters are called SID frames. A comfort noise generator (CNG) is also  there  because in a communication channel, if transmission is stopped, because  it's not  speech, then the other side may assume that link has been cut. This is  also  taken care of by the annex B standard.

Recently, G.729 has been extended to provide support for wideband speech and   audio coding, i.e., the transmitted acoustic frequency range is extended to 50   Hz - 7 kHz. The respective extension to G.729 is referred to as G.729.1. The   G.729.1 coder is hierarchically organized: Its bit rate and the obtained  quality  are adjustable by simple bitstream truncation.

ITU  G.729 Status

Wikipedia Definition for   G.729

Also See