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.

Stability Analysis of Speech Synthesis Filter of CELP-Based AMR-WB Codec

Abstract: The speech codec analyzes the speech using A(z) (analysis filter) and synthesizes back at decoder side using linear prediction coefficients (LPC). These LP coefficients are sensitive and cannot be sent directly in a transmission channel. A small corruption in LPC values during transmission destroys the synthesized speech at the decoder side. We have presented new results on the stability and sensitivity of LPC based on changes in speech input pitch length, sign bit, and LPC values during transmission (or for any other reason) consecutively and simultaneously. Present analysis will help to add varying dynamic range to LSF coding. For this each individual LPC need to be related to each LSF. All the speech inputs considered in this study are voiced speech, which has been separated manually. For a specific order, we analyzed the numbers of LPC which are more responsible for increase in prediction error at decoder side when they are corrupted by noise. Present analysis provides the reference for number of bits required for quantization of LPC or line spectral pairs (LSF).

Packet loss concealment using piggybacking for speech over IP network services

Abstract: This paper addresses a packet loss concealment method (PLC) based on piggybacking to improve speech quality degradation caused by packet losses for code excited linear predictive (CELP) type coders. We applied our proposed scheme to the standard ITU-T G.729 Conjugate-Structure Algebraic CELP (CS-CELP) speech coder to evaluate its performance. The average spectral distortion (Avg. SD), the perceptual evaluation of speech quality (PESQ) and enhanced modified bark spectral distortion (EMBSD) tests under a variety of packet loss rates prove that the proposed PLC based piggybacking is better than the concealment method embedded in the ITU-T G.729 for speakers (female and male). The performance measures confirm that our PLC method based piggybacking is superior than the one embedded in the standard ITU-T G.729.

Bitrate Scalability for Multi-Pulse Based Code Excited Linear Prediction Speech Coder

Abstract: Problem statement: The bitrate scalability is an important functionality that is defined in the Moving Picture Expert Group (MPEG-4) requirements. Since the traffic in a communication network varies with time, the capability of varying the bitrate of a speech coder is needed. Approach: This study proposes an approach to vary the bitrate by using a bitrate scalable tool which is attached with the core section of Multi-Pulse based Code Excited Linear Predictive (MP-CELP) coder. The bitrates scalable tool employs multi-stage excitation coding based on an embedded-coding approach. The multi-pulse excitation codebook at each stage is adaptively produced depending on the selected excitation signal at the previous stage. Results: The experimental results show that the speech quality of the proposed coder with the bitrate scalable tools is improved above the speech quality of the conventional coder. Conclusion: From the study, the proposed approach gives a tool to improve the speech compression and can also support a variety of coder bitrates.

Single and double frame quantization of LSF parameters using noise feedback coding

Abstract: We present a scheme for single frame (20 msec) and double frame (40 msec) quantization of line spectral frequency (LSF) parameters in a code-excited linear prediction (CELP) speech coder using noise feedback coding. To improve the performance, an appropriate lattice structure is used as the quantizer in the noise feedback loop. We also consider a switched structure based on using either a double frame quantizer or two single frame quantizers for two subsequent frames where an extra bit is used to specify the choice offering a lower distortion. Numerical results are presented showing an excellent performance with very low complexity.

Waveform Interpolation in Speech Coding

Abstract: In waveform coders, the quantized values of the transmitted parameters are selected on the basis of a fidelity criterion comparing the original and reconstructed speech signals. An important class of waveform coders is formed by the analysis-by- synthesis coders [1], which include code-excited linear prediction (CELP). In these coders, a multitude of trial reconstructed signals is generated for a large selection of quantization levels of the coder parameters. The fidelity criterion is then used to select a good set of quantization levels for the parameters.