G.718
Encyclopedia
G.718 is an ITU-T
recommendation embedded scalable speech and audio codec
providing high quality narrowband (250 Hz to 3.5 kHz) speech over the lower bit rates and high quality wideband (50 Hz to 7 kHz) speech over the complete range of bit rates. In addition, G.718 is designed to be highly robust to frame erasures, thereby enhancing the speech quality when used in internet protocol
(IP) transport applications on fixed, wireless and mobile networks. Despite its embedded nature, the codec also performs well with both narrowband and wideband generic audio signals.
The codec has an embedded scalable structure, enabling maximum flexibility in the transport of voice packets through IP networks of today and in future media-aware networks. In addition, the embedded structure of G.718 will easily allow the codec to be extended to provide a superwideband (50 Hz to 14 kHz) and stereo capability through additional layers which are currently under development in ITU-T
Study Group 16. The bitstream may be truncated at the decoder side or by any component of the communication system to instantaneously adjust the bit rate to the desired value without the need for out-of-band signalling. The encoder produces an embedded bitstream structured in five layers corresponding to the five available bit rates: 8, 12, 16, 24 & 32 kbit/s.
The G.718 encoder can accept wideband sampled signals at 16 kHz, or narrowband signals sampled at either 16 or 8 kHz. Similarly, the decoder output can be 16 kHz wideband, in addition to 16 or 8 kHz narrowband. Input signals sampled at 16 kHz, but with bandwidth limited to narrowband, are detected by the encoder.
The output of the G.718 codec is capable of operating with a bandwidth of 50 Hz to 4 kHz at 8 and 12 kbit/s and 50 Hz to 7 kHz from 8 to 32 kbit/s.
The high quality codec core represents a significant advance in quality over currently available codecs, providing 8 kbit/s wideband clean speech quality equivalent to G.722.2 at 12.65 kbit/s whilst the 8 kbit/s narrowband codec operating mode provides clean speech quality equivalent to G.729
Annex E at 11.8 kbit/s.
The codec operates on 20 ms frames and has a maximum algorithmic delay of 42.875 ms for wideband input and wideband output signals. The maximum algorithmic delay for narrowband input and narrowband output signals is 43.875 ms. The codec may also be employed in a low-delay mode when the encoder and decoder maximum bit rates are set to 12 kbit/s. In this case the maximum algorithmic delay is reduced by 10 ms.
The codec also incorporates an alternate coding mode, with a minimum bit rate of 12.65 kbit/s, which is bitstream interoperable with ITU-T
Recommendation G.722.2, 3GPP
AMR-WB
and 3GPP2 VMR-WB
mobile wideband speech coding standards. This option replaces Layer 1 and Layer 2, and the layers 3-5 are similar to the default option with the exception that in Layer 3 few bits are used to compensate for the extra bits of the 12.65 kbit/s core. The decoder is further able to decode all other G.722.2 operating modes. G.718 also includes discontinuous transmission
mode (DTX) and comfort noise
generation (CNG) algorithms that enable bandwidth savings during inactive periods. An integrated noise reduction algorithm can be used provided that the communication session is limited to 12 kbit/s.
The underlying algorithm is based on a two-stage coding structure: the lower two layers are based on Code-Excited Linear Prediction (CELP) coding of the band (50-6400 Hz) where the core layer takes advantage of signal-classification to use optimized coding modes for each frame. The higher layers encode the weighted error signal from the lower layers using overlap-add modified discrete cosine transform
(MDCT) transform coding. Several technologies are used to encode the MDCT coefficients to maximize performance for both speech and music.
G.718 was developed in ITU-T
Study Group 16 as part of an open consortium of 9 organizations; Motorola
, Nokia
, Ericsson
, Texas Instruments
, VoiceAge Corporation, Panasonic
, Huawei
, France Telecom
, Qualcomm
.
G.718 is officially described as Frame error robust narrowband and wideband embedded variable bit-rate coding of speech and audio from 8-32 kbit/s.
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
recommendation embedded scalable speech and audio codec
Audio codec
All codecs are devices or computer programs capable of coding or decoding a digital data stream or signal.The term audio codec has two meanings depending on the context:...
providing high quality narrowband (250 Hz to 3.5 kHz) speech over the lower bit rates and high quality wideband (50 Hz to 7 kHz) speech over the complete range of bit rates. In addition, G.718 is designed to be highly robust to frame erasures, thereby enhancing the speech quality when used in internet protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) transport applications on fixed, wireless and mobile networks. Despite its embedded nature, the codec also performs well with both narrowband and wideband generic audio signals.
The codec has an embedded scalable structure, enabling maximum flexibility in the transport of voice packets through IP networks of today and in future media-aware networks. In addition, the embedded structure of G.718 will easily allow the codec to be extended to provide a superwideband (50 Hz to 14 kHz) and stereo capability through additional layers which are currently under development in ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
Study Group 16. The bitstream may be truncated at the decoder side or by any component of the communication system to instantaneously adjust the bit rate to the desired value without the need for out-of-band signalling. The encoder produces an embedded bitstream structured in five layers corresponding to the five available bit rates: 8, 12, 16, 24 & 32 kbit/s.
The G.718 encoder can accept wideband sampled signals at 16 kHz, or narrowband signals sampled at either 16 or 8 kHz. Similarly, the decoder output can be 16 kHz wideband, in addition to 16 or 8 kHz narrowband. Input signals sampled at 16 kHz, but with bandwidth limited to narrowband, are detected by the encoder.
The output of the G.718 codec is capable of operating with a bandwidth of 50 Hz to 4 kHz at 8 and 12 kbit/s and 50 Hz to 7 kHz from 8 to 32 kbit/s.
The high quality codec core represents a significant advance in quality over currently available codecs, providing 8 kbit/s wideband clean speech quality equivalent to G.722.2 at 12.65 kbit/s whilst the 8 kbit/s narrowband codec operating mode provides clean speech quality equivalent to G.729
G.729
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 .Because of its low bandwidth requirements,...
Annex E at 11.8 kbit/s.
The codec operates on 20 ms frames and has a maximum algorithmic delay of 42.875 ms for wideband input and wideband output signals. The maximum algorithmic delay for narrowband input and narrowband output signals is 43.875 ms. The codec may also be employed in a low-delay mode when the encoder and decoder maximum bit rates are set to 12 kbit/s. In this case the maximum algorithmic delay is reduced by 10 ms.
The codec also incorporates an alternate coding mode, with a minimum bit rate of 12.65 kbit/s, which is bitstream interoperable with ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
Recommendation G.722.2, 3GPP
3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...
AMR-WB
AMR-WB
Adaptive Multi-Rate Wideband is a patented speech coding standard developed based on Adaptive Multi-Rate encoding, using similar methodology as Algebraic Code Excited Linear Prediction...
and 3GPP2 VMR-WB
VMR-WB
Variable-Rate Multimode Wideband is a source-controlled variable-rate multimode codec designed for robust encoding/decoding of wideband/narrowband speech. The operation of VMR-WB is controlled by speech signal characteristics and by traffic condition of the network...
mobile wideband speech coding standards. This option replaces Layer 1 and Layer 2, and the layers 3-5 are similar to the default option with the exception that in Layer 3 few bits are used to compensate for the extra bits of the 12.65 kbit/s core. The decoder is further able to decode all other G.722.2 operating modes. G.718 also includes 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:...
mode (DTX) and 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) algorithms that enable bandwidth savings during inactive periods. An integrated noise reduction algorithm can be used provided that the communication session is limited to 12 kbit/s.
The underlying algorithm is based on a two-stage coding structure: the lower two layers are based on Code-Excited Linear Prediction (CELP) coding of the band (50-6400 Hz) where the core layer takes advantage of signal-classification to use optimized coding modes for each frame. The higher layers encode the weighted error signal from the lower layers using overlap-add modified discrete cosine transform
Modified discrete cosine transform
The modified discrete cosine transform is a Fourier-related transform based on the type-IV discrete cosine transform , with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset,...
(MDCT) transform coding. Several technologies are used to encode the MDCT coefficients to maximize performance for both speech and music.
G.718 was developed in ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
Study Group 16 as part of an open consortium of 9 organizations; Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
, Nokia
Nokia
Nokia Corporation is a Finnish multinational communications corporation that is headquartered in Keilaniemi, Espoo, a city neighbouring Finland's capital Helsinki...
, Ericsson
Ericsson
Ericsson , one of Sweden's largest companies, is a provider of telecommunication and data communication systems, and related services, covering a range of technologies, including especially mobile networks...
, Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
, VoiceAge Corporation, Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
, Huawei
Huawei
Huawei is a Chinese multinational networking and telecommunications equipment and services company headquartered in Shenzhen, Guangdong, China...
, France Telecom
France Télécom
France Telecom S.A. is the main telecommunications company in France, the third-largest in Europe and one of the largest in the world. It currently employs about 180,000 people and has 192.7 million customers worldwide . In 2010 the group had revenue of €45.5 billion...
, Qualcomm
Qualcomm
Qualcomm is an American global telecommunication corporation that designs, manufactures and markets digital wireless telecommunications products and services based on its code division multiple access technology and other technologies. Headquartered in San Diego, CA, USA...
.
G.718 is officially described as Frame error robust narrowband and wideband embedded variable bit-rate coding of speech and audio from 8-32 kbit/s.