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.

Low-delay CELP and tree coders: comparison and performance improvements

Abstract: A stochastic tree coder based on the (M,L) search algorithm suggested by V. Iyengar and P. Kabal (1988) and a low-day CELP (code-excited linear prediction) coder proposed by J.H. Chen (1989) are considered. The individual components (predictors, gain adaptation, excitation coding) of the two coders are analyzed. The performances of the two types of coders are compared. The two coders have comparable performance at 16 kb/s under clean channel conditions. Methods to improve the performance of the coders, particularly with a view to bringing the bit rate to below 16 kb/s, are studied. Suggestions for improving the performance include an improved high-order predictor (applicable to both coders), and training of the excitation dictionary as well as a better gain adaptation strategy for the tree coder. >

A simulation tool for introducing algebraic celp (ACELP) coding concepts in a DSP course

Abstract: This paper presents an educational tool 1 for introducing Code Excited Linear Prediction (CELP) coding concepts in senior undergraduate and graduate DSP-related courses The tool consists of a user-friendly graphical interface along with a complete MATLAB 2 realization of all aspects of the Algebraic CELP G729 algorithm [2] This simulation software is accompanied by a series of computer experiments and exercises that can be used to provide hands-on training to class participants The exercises designed based on the simulation tool may be used by instructors in a class setting to demonstrate key signal processing concepts associated with the processing of telephone-based speech The MATLAB ACELP tool is being used in Arizona State University undergraduate DSP courses as well as in a graduate course on speech coding and in a continuing education short course Evaluation of the tool and the exercises is being performed by an educational software assessment specialist In the last ten years we have witnessed a series of breakthroughs in speech coding followed by several standardization efforts [1] Most of the standardized algorithms are based on CELP coders Although speech coding researchers and practitioners are well aware of the fundamental ideas used in CELP, students do not get much of an opportunity in courses to study these algorithms A software simulation tool, implementing the ACELP algorithm has been developed for the purpose of introducing speech coding and the associated signal processing concepts to both undergraduate and graduate students We choose an Algebraic Code Excited Linear Prediction (ACELP) algorithm as a basis for this educational tool because of the wide proliferation of algebraic codebooks in cellular standards The algorithm was coded in a modular manner and in its entirety using MATLAB The tool is based on a user-friendly graphical user interface (GUI) that allows the student to study and verify through graphics the various aspects of the algorithm such as: the LP analysis, the open-loop pitch search, the adaptive codebook search (pitch search), the fixed codebook search, and the bit allocation patterns We choose MATLAB as the implementation platform because it allows the user to easily understand the complex parts of the algorithm whose function is not

Celp-Based speech coding for fine grain scalability by altering sub-frame pitch-pulse

Abstract: Methods and systems for providing a CELP-based speech coding with fine grain scalability include a parameter encoder that generates a basic bit-stream from LPC coefficients for a frame, pitch-related information for all the sub-frames obtained by searching an adaptive codebook, and first pulse-related information for even sub-frames obtained by searching a fixed codebook. The parameter encoder also generates enhancement bits, which are preceded by the basic bit-stream, from second pulse-related information for odd sub-frames. The quality of synthesized speech is improved on a basis of one additional odd sub-frame pulse, as more of the second pulse-related information in the enhancement bits is received by a decoder.

Analysis-by-synthesis multimode harmonic speech coding at 4 kb/s

Abstract: This paper presents a 4 kb/s analysis-by-synthesis multimode harmonic coder (AbS-MHC). Novel features of this coder include a signal modification technique that allows time-domain analysis-by-synthesis parameter estimation in a sinusoidal coding framework, and a frequency-domain transition speech model with improved parameter estimation and quantization schemes. An efficient quantization scheme for harmonic magnitudes based on weighted non-square transform vector quantization (WNSTVQ) is also used. Subjective quality tests indicate that the 4 kb/s AbS-MHC coder outperforms the 5.3 kb/s G.723.1 standard CELP coder and produces speech quality very similar to the 6.3 kb/s G.723.1 coder.

Decoder Initializing Technique for Improving Frame-Erasure Resilience of a CELP Speech Codec

Abstract: The authors present and evaluate a technique for synchronizing the internal states of a code-excited-linear-prediction (CELP) encoder and decoder after the occurrence of frame erasure. The designed technique, called ldquoduplicated transmission (DT),rdquo uses some redundant information for realizing synchronization. The encoder performs encoding processes twice and sends two codes for each frame. One code is encoded by an encoder that is initialized. The code is used in cases where the previous frame is erased. An onset detector is combined with the DT technique to select the frames to which the DT should be applied. Subjective test results suggest that, by introducing DT selectively, the number of DT frames is reducible by about 80% without degrading the subjective quality. Results demonstrate that synchronization of the internal states is effective in cases of erasure of onset. The DT technique requires no additional algorithmic delay. For that reason, it would a better choice for particular applications for which the delay has a significant impact.