Difference between revisions 106703697 and 106703698 on dewiki

'''G.718''' is an [[ITU-T]] standard 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 (contracted; show full)
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 
performance improvementadvance 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]], [http://www.voiceage.com VoiceAge Corporation]<ref>[http://www.voiceage.com/trademarks.php Trademarks<!-- Bot generated title -->]</ref>, [[Panasonic]], [[Huawei]], [[France Telecom]], [[Qualcomm]].

== See also ==
* [[G.711]] (a-law and mu-law/u-law)
* G.718
* [[G.719]]
* [[G.722]]
* [[G.722.1]]
* [[G.722.2]]
* [[G.723]]
* [[G.723.1]]
* [[G.726]]
* [[G.728]]
* [[G.729]]
* [[G.729a]]
* [[List of codecs]]

== External links ==
* [http://www.itu.int/rec/T-REC-G.718/en Official ITU-T G.718 standard]

{{Compression Formats}}

[[Category:Audio codecs]]
[[Category:Speech codecs]]
[[Category:ITU-T recommendations]]

{{telecomm-stub}}