| 单词 | LD-CELP (Low Delay Code Excited Linear Prediction) |
| 释义 | LD-CELP (Low Delay Code Excited Linear Prediction) A voice compression algorithm defined in ITU-T G.728, and used in voice over frame relay (VoFR) and voice over Internet Protocol (VoIP). LD-CELP is geared to a rate of 16 kbps, although bit rates as low as 12.8 kbps can be achieved.The low level of delay suggested by the designation is due to the fact LD-CELP accumulates only 5 PCM samples, representing 625µs of a voice stream, in a buffer. A key element of CELP and its variants is the construction and maintenance of a codebook, which comprises binary descriptions of sets of voice samples. CELP employs silence suppression to remove periods of silence and redundancy from the data set, and normalizes the volume level. LD-CELP compares the resulting data set to a set of candidate shapes in the codebook, selects the shape that most closely match the actual data. LD-CELP then transmits the index number of the selected code description and the average loudness level of the set of samples. Every 625µs, the code is sent across the network in a block of 10 bits, yielding a data rate of 16 kbps, which is a compression ratio of 4:1, compared with toll quality PCM voice over the public switched telephone network (PSTN) at 64 kbps. At the receiving end of the transmission, the transmitted code is compared to the codebook, the PCM signal is reconstructed, and, eventually, the analog signal is reconstructed. As compared to CELP, the more frequent transmission of the shorter data blocks yields lower levels of delay through faster processing by the digital signal processors (DSPs), and the compression technique yields more efficient use of bandwidth. LD-CELP yields quality that generally is considered to be on a par with Adaptive Differential Pulse Code Modulation (ADPCM). See also ADPCM, algorithm, analog, binary, buffer, CELP, circuit switching, compression, CS-ACELP, DSP, PCM, PSTN, silence suppression, and toll quality. |
| 随便看 |
|
科学参考收录了5291条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。