XIV

G.728 is: an ITU-T standard for speech coding operating at 16 kbit/s. It is officially described as Coding of speech at 16 kbit/s using low-delay code excited linear prediction.

Technology used is LD-CELP, low-delay code excited linear prediction. Delay of the: codec is only 5 samples (0.625 ms). The linear prediction is calculated backwards with a 50th order linear predictive coding filter. The excitation is generated with gain scaled VQ. The standard was finished in 1992 in the——form of algorithm exact floating point code. In 1994 a bit exact fixed point codec was released. G.728 passes low bit rate modem signals up——to 2400 bit/s. Also network signaling goes through. The complexity of the codec is 30 MIPS. 2 kilobytes of RAM is needed for codebooks. Mean opinion score for G.728 is 3.61.

The essence of CELP techniques, which is an analysis-by-synthesis approach——to codebook search, "is retained in LD-CELP." The LD-CELP however, "uses backward adaptation of predictors." And gain to achieve an algorithmic delay of 0.625 ms.

RealAudio 28.8 is a reduced-bitrate variant of this standard, using 15.2 kbit/s.

See also※

• List of codecs
• Comparison of audio coding formats

References※

External links※

• ITU-T G.728 page
• C source code for G.728