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.

Harmonic coding of speech at 4.8 kb/s

Abstract: This paper describes a new speech coding technique which yields improved speech quality over existing 2.4 kb/s LPC vocoders. The method is computationally efficient and operates at a data rate of 4.8 kb/s. Each speech frame is initially classified as voiced or unvoiced. Unvoiced frames are synthesized using a linear predictive coding filter with noise or multipulse excitation. Voiced frames are synthesized using a sum of sinusoids. The frequency of each sinusoid is defined by peaks in the frequency spectrum. A new interpolation technique provides a computationally efficient method of locating the spectral peaks. A real-time, fully quantized version has been implemented in hardware.

A 6 KBPS Regular Pulse CELP Coder for Mobile Radio Communications

Abstract: Low bit rate coding techniques are currently an important topic in speech research, because of the wide range of emerging applications such as narrow band digital speech transmission or voice messaging. In designing a low bit rate speech coder, the main issue is to achieve good quality with low enough complexity to allow for real time implementation. Moreover, in mobile telephony, the coder must also be robust to adverse transmission conditions (background noise, transmission errors...) [1].

LSP parameter interpretation for speech classification

Abstract: This paper describes several methods of interpreting line spectral pair (LSP) parameters such as those generated by CELP and LPC speech coders. Analysis methods are proposed to assist in automatic classification of the phonetic content of an encoded speech signal. In particular, the advantages of analysing the lower bitrate parameters available at a speech coder output rather than the higher bitrate input parameters, are discussed. Comparisons are made with existing parametric measures in terms of both performance and implementation complexity, with a view to maximising classification performance whilst minimising complexity.

Hybrid Scalar/Vector Quantization of Mel-Frequency Cepstral Coefficients for Low Bit-Rate Coding of Speech

Abstract: In this paper, we propose a low bit-rate speech codec based on a hybrid scalar/vector quantization of the mel-frequency cepstral coefficients (MFCCs). We begin by showing that if a high-resolution mel-frequency cepstrum (MFC) is computed, good-quality speech reconstruction is possible from the MFCCs despite the lack of explicit phase information. By evaluating the contribution toward speech quality that individual MFCCs make and applying appropriate quantization, our results show perceptual evaluation of speech quality (PESQ) of the MFCC-based codec matches the state-of-the-art MELPe codec at 600 bps and exceeds the CELP codec at 2000 -- 4000 bps coding rates. The main advantage of the proposed codec is in distributed speech recognition (DSR) since speech features based on MFCCs can be directly obtained from code words thus eliminating additional decode and feature extract stages.

A 4 kb/s hybrid MELP/CELP speech coding candidate for ITU standardization

Abstract: This paper presents an improved 4 kb/s hybrid MELP/CELP speech coder submitted as a candidate for ITU standardization. The coder uses three modes: a high-quality MELP coder for strongly voiced speech frames, an ACELP coder with pitch prediction for weakly voiced frames, and a stochastic CELP coder for unvoiced frames. We present recent enhancements to this coder, both to improve speech quality and to reduce coder complexity. Previous lTU Selection Testing results on an earlier version of this coder showed that it met nearly all requirements for toll-quality speech, more than any other candidate. Our internal testing shows that the current reduced-complexity fixed-point coder maintains this high performance.