G.729
Encyclopedia
G.729 is an audio data compression algorithm for voice that compresses digital voice in packets of 10 milliseconds duration. It is officially described as Coding of speech at 8 kbit/s using conjugate-structure algebraic code-excited linear prediction (CS-ACELP).

Because of its low bandwidth requirements, G.729 is mostly used in Voice over Internet Protocol (VoIP) applications where bandwidth must be conserved. Standard G.729 operates at a bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

 of 8 kbit/s, but there are extensions, which provide rates of 6.4 kbit/s (Annex D, F, H, I, C+) and 11.8 kbit/s (Annex E, G, H, I, C+) for worse and better speech quality, respectively.

G.729 has been extended with various features, commonly designated as G.729a and G.729b.

Dual-tone multi-frequency signaling (DTMF), fax
Fax
Fax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...

 transmissions, and high-quality audio cannot be transported reliably with this codec
Codec
A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...

. DTMF requires the use of the RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals as specified in RFC 2833.

G.729 Annexes

G.729 Annexes
Functionality - A B C D E F G H I C+ J
Low complexity X X
Fixed-point X X X X X X X X X X
Floating-point X X
8 kbit/s X X X X X X X X X X X X
6.4 kbit/s X X X X X
11.8 kbit/s X X X X X
DTX
Discontinuous Transmission
Discontinuous transmission is a means by which a mobile telephone is temporarily shut off or muted while the phone lacks a voice input.-Misconception:...

X X X X X
Embedded variable bit rate, wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....

X

G.729 Annex A

G.729a is a compatible extension of G.729, but requires less computational power. This lower complexity, however, bears the cost of marginally reduced speech quality.

G.729a was developed by a consortium of organizations: France Telecom, Mitsubishi Electric Corporation, Nippon Telegraph and Telephone Corporation (NTT), and Université de Sherbrooke.

The features of G.729a are:
  • Sampling frequency 8 kHz/16-bit (80 samples for 10 ms frames)
  • Fixed bit rate (8 kbit/s 10 ms frames)
  • Fixed frame size (10 bytes for 10 ms frame)
  • Algorithmic delay is 15 ms per frame, with 5 ms look-ahead delay
  • G.729a is a hybrid speech coder which uses Algebraic Code Excited Linear Prediction (ACELP)
  • The complexity of the algorithm is rated at 15, using a relative scale where G.711
    G.711
    G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972. Its formal name is Pulse code modulation of voice frequencies. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can also...

     is 1 and G.723.1
    G.723.1
    G.723.1 is an audio codec for voice that compresses voice audio in 30 ms frames. An algorithmic look-ahead of 7.5 ms duration means that total algorithmic delay is 37.5 ms...

     is 25.
  • PSQM
    PSQM
    PSQM is a computational and modeling algorithm defined in ITU Recommendation ITU-T P.861 that objectively evaluates and quantifies voice quality of voice-band speech codecs....

     testing under ideal conditions yields Mean Opinion Score
    Mean Opinion Score
    The Mean Opinion Score test has been used for decades in telephony networks to obtain the human user's view of the quality of the network. In multimedia especially when codecs are used to compress the bandwidth requirement , the mean opinion score ...

    s of 4.04 for G.729a, compared to 4.45 for G.711
    G.711
    G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972. Its formal name is Pulse code modulation of voice frequencies. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can also...

     (u-law)
  • PSQM testing under network stress yields Mean Opinion Scores of 3.51 for G.729a, compared to 4.13 for G.711
    G.711
    G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972. Its formal name is Pulse code modulation of voice frequencies. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can also...

     (u-law)

G.729 Annex B

G.729 has been extended in Annex B (G.729b) which provides a silence
Silence
Silence is the relative or total lack of audible sound. By analogy, the word silence may also refer to any absence of communication, even in media other than speech....

 compression method that enables a voice activity detection
Voice activity detection
Voice activity detection , also known as speech activity detection or speech detection, is a technique used in speech processing in which the presence or absence of human speech is detected.. The main uses of VAD are in speech coding and speech recognition...

 (VAD) module. It is used to detect voice activity in the signal. It also includes a discontinuous transmission
Discontinuous Transmission
Discontinuous transmission is a means by which a mobile telephone is temporarily shut off or muted while the phone lacks a voice input.-Misconception:...

 (DTX) module which decides on updating the background noise
Ambient noise level
In atmospheric sounding and noise pollution, ambient noise level is the background sound pressure level at a given location, normally specified as a reference level to study a new intrusive sound source.Ambient sound levels are often measured in order to map sound conditions over a...

 parameters for non speech (noisy frames). It uses 2-byte Silence Insertion Descriptor (SID) frames transmitted to initiate comfort noise
Comfort noise
Comfort noise is synthetic background noise used in radio and wireless communications to fill the artificial silence in a transmission resulting from voice activity detection or from the audio clarity of modern digital lines....

 generation (CNG). If transmission is stopped, and the link goes quiet because of no speech, the receiving side may assume that the link has been cut. By inserting comfort noise, analog hiss is simulated digitally during silence to assure the receiver that the link is active and operational.

Other extensions

Recently, G.729 has been extended (with Annex J) 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
G.729.1
G.729.1 is an 8-32 kbit/s embedded speech and audio codec providing bitstream interoperability with G.729, G.729 Annex A and G.729 Annex B. Its official name is G.729-based embedded variable bit rate codec: An 8-32 kbit/s scalable wideband coder bitstream interoperable with G.729.This codec has...

. The G.729.1 codec is hierarchically organized: Its bit rate and the obtained quality are adjustable by simple bitstream truncation.

Licensing

G.729 includes patents
Software patent
Software patent does not have a universally accepted definition. One definition suggested by the Foundation for a Free Information Infrastructure is that a software patent is a "patent on any performance of a computer realised by means of a computer program".In 2005, the European Patent Office...

 from several companies and is licensed by Sipro Lab Telecom. Sipro Lab Telecom is the authorized Intellectual Property Licensing Administrator for G.729 technology and patent pool
Patent pool
In patent law, a patent pool is a consortium of at least two companies agreeing to cross-license patents relating to a particular technology. The creation of a patent pool can save patentees and licensees time and money, and, in case of blocking patents, it may also be the only reasonable method...

. In a number of countries, the use of G.729 may require a license fee and/or royalty fee.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK