Code-excited linear prediction

About: Code-excited linear prediction is a research topic. Over the lifetime, 2025 publications have been published within this topic receiving 28633 citations. The topic is also known as: CELP.

Scalable Speech Coding for IP Networks: Beyond iLBC

Abstract: High quality speech at low bit rates makes code excited linear prediction (CELP) the dominant choice for a narrowband coding technique despite the susceptibility to packet loss. One of the few techniques which received attention after the introduction of CELP coding technique is the internet low bitrate codec (iLBC) because of inherent high robustness to packet loss. Addition of rate flexibility and scalability makes the iLBC an attractive choice for voice communication over IP networks. In this paper, performance improvement schemes of multi-rate iLBC and its scalable structure are proposed, and the proposed codec enhanced from the previous work is re-designed based on the subjective listening quality instead of the objective quality. In particular, perceptual weighting and the modified discrete cosine transform (MDCT) with short overlap in weighted signal domain are employed along with the improved packet loss concealment (PLC) algorithm. The subjective evaluation results show that the speech quality of the proposed codec is equivalent to that of state-of-the-art codec, G.718, under both a clean channel condition and lossy channel conditions. This result is significant considering that development of the proposed codec is still in early stage.

A backward adaptive 8 kbit/s speech coder using conditional pitch prediction

Abstract: The authors present a high-quality 8-kb/s speech coder with an algorithmic delay of 2.875 ms. The proposed coder is based on the backward-adaptive CELP (code-excited linear prediction) coder. It uses two new techniques to improve the quality. One is conditional pitch prediction, where the pitch period is selected from the candidates pruned by backward pitch analysis. The other is a switchover of the synthesis filter, where one of two sets of filter coefficients for the random excitation is selected. Experiments show that the quality of the proposed coder is superior to that of a 6-b mu -law pulse-code modulation (PCM) coder. In particular, the quality of female speech coding is equivalent to that of a 7-b PCM. >

Pitch synchronous multi-band (PSMB) speech coding

Abstract: A novel speech coding algorithm, named pitch synchronous multiband (PSMB), is proposed. It uses the multiband excitation (MBE) model to generate a representative pitch-cycle waveform (PCW) for each frame. The representative PCW of a frame is encoded by two out of three codebooks depending upon whether the frame is related or unrelated to the previous frame. The new speech coder introduces a pitch-period-based coding feature. The PSMB coder operating at 4 kbps outperforms the Inmarsat 4.15 kbps IMBE coder by a clear margin. It is also found to be slightly better than the FS1016 4.8 kbps code excited linear predictive (CELP) coder in terms of perceptual quality. Fast search algorithms for the three codebooks used in PSMB are also developed.

Adaptive code excited predictive coding

Abstract: A novel way to use the code excited linear prediction (CELP) concept that decreases the processing load while keeping the same speech quality is discussed. Rather than performing individual weighting of each candidate sequence, a global implementation of the perceptual weighting function at the codebook level is proposed. As a result, the analysis-by-synthesis procedure does not require the processing of all the candidate sequences through the synthesis and weighting filters; the complexity requirement of the algorithm is therefore much reduced. The concept is carried out with an adaptive codebook. Two fixed-point implementations of the adaptive CELP (ACELP) algorithm are reported: a 7.2 kb/s block coder (7 MIPS), and a 12 kb/s low-delay coder (11 MIPS). Both coders have been rated to provide the same quality as the 13 kb/s block coder adopted by the GSM for the European cellular telephone. >