G.729 is a

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narrow-band

vocoder A vocoder (, a portmanteau of ''voice'' and ''encoder'') is a category of speech coding that analyzes and synthesizes the human voice signal for audio data compression, multiplexing, voice encryption or voice transformation. The vocoder ...

-based

audio data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressi ...

algorithm using a frame length of 10 milliseconds. It is officially described as ''Coding of speech at 8 kbit/s using code-excited linear prediction''

speech coding Speech coding is an application of data compression of digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic d ...

(CS-ACELP), and was introduced in 1996. The wide-band extension of G.729 is called

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 code ...

, which equals G.729 Annex J. Because of its low bandwidth requirements, G.729 is mostly used in

voice over Internet Protocol Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

(VoIP) applications when bandwidth must be conserved. Standard G.729 operates at a

bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction ...

of 8 kbit/s, but extensions 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: * G.729: This is the original codec using a high-complexity algorithm. * G.729A or Annex A: This version has a medium complexity, and is compatible with G.729. It provides a slightly lower voice quality. * G.729B or Annex B: This version extends G.729 with silence suppression, and is not compatible with the previous versions. * G.729AB: This version extends G.729A with silence suppression, and is only compatible with G.729B. *

or Annex J: This version extends G.729A and B with scalable variable encoding using hierarchical enhancement layers. It provides support for

wideband In communications, a system is wideband when the message bandwidth significantly exceeds the coherence bandwidth of the channel. Some communication links have such a high data rate that they are forced to use a wide bandwidth; other links ma ...

speech and audio, using

modified discrete cosine transform The modified discrete cosine transform (MDCT) is a transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where ...

(MDCT) coding.

Dual-tone multi-frequency signaling Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed ...

(DTMF), fax transmissions, and high-quality audio cannot be transported reliably with this

codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or ...

. DTMF requires the use of the named telephony events in the RTP payload for DTMF digits, telephony tones, and telephony signals as specified in RFC 4733.

G.729 annexes

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 Télécom Orange S.A. (), formerly France Télécom S.A. (stylized as france telecom) is a French multinational corporation, multinational telecommunications corporation. It has 266 million customers worldwide and employs 89,000 people in France, and 5 ...

, Mitsubishi Electric Corporation, Nippon Telegraph and Telephone Corporation (NTT). 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 (80 bits) 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 is 1 and

G.723.1 G.723.1 is an audio codec for voice that compresses voice audio in frames. An algorithmic look-ahead of duration means that total algorithmic delay is . Its official name is ''Dual rate speech coder for multimedia communications transmitting at ...

is 25. * PSQM testing under ideal conditions yields

mean opinion score Mean opinion score (MOS) is a measure used in the domain of Quality of Experience and telecommunications engineering, representing overall quality of a stimulus or system. It is the arithmetic mean over all individual "values on a predefined scale t ...

s of 4.04 for G.729a, compared to 4.45 for G.711 (μ-law) * PSQM testing under network stress yields mean opinion scores of 3.51 for G.729a, compared to 4.13 for G.711 (μ-law) Some VoIP phones incorrectly use the description "G729a/8000" in SDP (e.g. this affects some Cisco and Linksys phones). This is incorrect as G729a is an alternative method of encoding the audio, but still generates data decodable by either G729 or G729a - i.e. there is no difference in terms of codec negotiation. Since the SDP RFC allows static payload types to be overridden by the textual rtpmap description this can cause problems calling from these phones to endpoints adhering to the RFC unless the codec is renamed in their settings since they will not recognise 'G729a' as 'G729' without a specific workaround in place for the bug.

G.729 Annex B

G.729 has been extended in Annex B (G.729b) which provides a

silence Silence is the absence of ambient audible sound, the emission of sounds of such low intensity that they do not draw attention to themselves, or the state of having ceased to produce sounds; this latter sense can be extended to apply to the c ...

compression method that enables a voice activity detection (VAD) module. It is used to detect voice activity in the signal. It also includes a discontinuous transmission (DTX) module which decides on updating the background noise parameters for non speech (noisy frames). It uses 2-byte Silence Insertion Descriptor (SID) frames transmitted to initiate comfort noise generation (CNG). If transmission is stopped, and the link goes quiet because of no speech, the receiving side might 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.

G.729 Annex J (G.729.1)

G.729 Annex J, maintained by

, provides support for

speech and audio. Introduced in 2006, it defines variable bit-rate wideband enhancement using up to 12 hierarchical layers. The core layer is an 8 kbit/s G.729 bitstream, the second layer is a 4 kbit/s

narrowband Narrowband signals are signals that occupy a narrow range of frequencies or that have a small fractional bandwidth. In the audio spectrum, narrowband sounds are sounds that occupy a narrow range of frequencies. In telephony, narrowband is usua ...

enhancement layer, and the third 2 kibt/s layer is a bandwidth enhancement layer. Further layers provide wideband enhancement in 2 kbit/s steps. The G.729.1 uses three-stage coding: embedded code-excited linear prediction (CELP) coding of the lower band, parametric coding of the higher band by Time-Domain Bandwidth Extension (TDBWE), and enhancement of the full band by a predictive

transform coding Transform coding is a type of data compression for "natural" data like audio signals or photographic images. The transformation is typically lossless (perfectly reversible) on its own but is used to enable better (more targeted) quantization, ...

algorithm called

time-domain aliasing cancellation The modified discrete cosine transform (MDCT) is a transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where su ...

(TDAC), also known as

(MDCT) coding. Bit rate and the obtained quality are adjustable by simple bitstream truncation.

Licensing

As of January 1, 2017, the patent terms of most licensed

patents A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...

under the G.729 Consortium have expired, the remaining unexpired patents are usable on a

basis. G.729 includes patents from several companies which were until the expiry licensed by Sipro Lab Telecom, the authorized Intellectual Property Licensing Administrator for G.729 technology and

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 ...

Past patent litigation

AIM IP LLC, a

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based in

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, CA filed 17

patent infringement Patent infringement is the commission of a prohibited act with respect to a patented invention without permission from the patent holder. Permission may typically be granted in the form of a license. The definition of patent infringement may v ...

lawsuits in the Central District Courts of California accusing 22 different companies, including,

Cisco Systems Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...

Polycom Poly, formerly Polycom, a part of HP Inc., is an American multinational corporation that develops video, voice and content collaboration and communication technology. Polycom was co-founded in 1990 by Brian L Hinman and Jeffrey Rodman. In 2018 ...

and others of infringing U.S. Patent No. 5,920,853. The '853 patent was filed at the

United States Patent and Trademark Office The United States Patent and Trademark Office (USPTO) is an agency in the U.S. Department of Commerce that serves as the national patent office and trademark registration authority for the United States. The USPTO's headquarters are in Alex ...

in 1996 by

Rockwell International Rockwell International was a major American manufacturing conglomerate involved in aircraft, the space industry, defense and commercial electronics, components in the automotive industry, printing presses, avionics and industrial products. R ...

. The inventors listed on the '853 patent are Benyassine Adil, Su Huan-Yu and Shlomot Eyal. In 2000, the '853 patent was assigned by

to Conexant Systems, an American-based software developer and fabless semiconductor company, which began as a division of Rockwell before being spun-off as its own

public company A public company is a company whose ownership is organized via shares of stock which are intended to be freely traded on a stock exchange or in over-the-counter markets. A public (publicly traded) company can be listed on a stock exchange ( ...

. In 2010, the '853 patent was sold by Conexant Systems to AIM IP LLC, a

based in

. The '853 patent contains patent claims which cover lookup tables used in G.729. The patent has since expired and is no longer in force due to its

patent term The term of a patent is the maximum time during which it can be maintained in force. It is usually expressed in a number of years either starting from the filing date of the patent application or from the date of grant of the patent. In most patent ...

expiring.

RTP payload type

G.729 is assigned the static payload type 18 for RTP by

IANA The Internet Assigned Numbers Authority (IANA) is a standards organization that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System (DNS), media types, and other Interne ...

. The rtpmap parameter description for this payload type is "G729/8000". Both G.729a and G.729b use the same rtpmap description as G.729. G.729a and G.729b are indicated using annexb=no or annexb=yes, respectively. G.729 Annex B (G.729b) is the default in absence of parameter ''annexb'' in the Session Description Protocol.

References

External links

ITU-T Recommendation G.729
- technical specification.
G.729 Error Recovery for Internet Telephony

Sipro Lab Telecom (administers the patent pools for G.723.1 and G.729)

Voiceage's G.729 implementation
{{Compression formats Audio codecs Speech codecs ITU-T recommendations ITU-T G Series Recommendations