G.728 LD- CELP also refers to a described by the ITU- T codec for compression of speech for use in telephony and IP telephony area. The peculiarity of G.728 is its extremely low latency of five samples. At a sampling rate of 8 kHz, this corresponds to a time delay of 0.625 ms. Therefore the algorithm is Code Excited Linear Prediction also referred to as LD-CELP for low delay and is based on the CELP compression algorithm.
Compression in the encoder the PCM voice signal with 64 kbit / s is converted into a serial bit stream at 16 kbit / s. The decoder is generated from the encoded data stream is a PCM speech signal. The compression factor of four is clearly delimited in the process. The PCM speech signal can usually be present with non-linear Abtastkennlinie by the processes μ -law or A-law, as in the telephony field.
The linear prediction as a basis function is achieved by a 50th order LPC filter. For the implementation of the entire process, which is in floating point or fixed-point arithmetic is available, a digital signal processor with a computing power of around 30 MIPS per channel is required.