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. Note: This article is about audio data compression, which reduces the data rate of digital audio signals. ... Dual-tone multi-frequency (DTMF), also known as Touch Tone® is used for telephone signaling over the line in the voice frequency band to the call switching center. ... Codec is a portmanteau of coder/decoder, which describes a device or program capable of performing transformations on a data stream or signal. ... G.711 is an ITU-T standard for audio companding. ...
G.729 is mostly used in Voice over IP (VoIP) 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. Voice over IP (also called VoIP, IP Telephony, and Internet telephony) refers to technology that enables routing of voice conversations over the Internet or any other IP network. ...
The annex B of G729 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 communcation 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.
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