Topic
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.
Papers published on a yearly basis
Papers
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20 Jun 1999TL;DR: MPEG-4 parametric speech coding, harmonic vector excitation coding (HVXC) algorithm, is described, showing that the proposed coding method at 2.0 kbps provides significantly better quality than that of FS1016 CELP at 4.8 kbps.
Abstract: MPEG-4 parametric speech coding, harmonic vector excitation coding (HVXC) algorithm, is described. New features of the coder includes a quantizer scheme capable of generating 2.0 and 4.0 kbps scalable bit-streams, where 2.0 kbps decoding is possible using a subset of 4.0 kbps bit-stream. Time scale modification of speech is also possible without changing pitch nor phoneme for fast and slow playback mode. Listening tests show that the proposed coding method at 2.0 kbps provides significantly better quality than that of FS1016 CELP at 4.8 kbps. In October 1998, the HVXC coder was adopted to the Final Draft International Standard (FDIS) of MPEG-4 standardization.
13 citations
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30 Jun 2000TL;DR: In this paper, a bi-directional pitch enhancement system for speech coding systems is proposed, which employs forward pitch enhancement and backward pitch enhancement to maintain a high perceptual quality in reproduced speech.
Abstract: A bi-directional pitch enhancement system for speech coding systems. As speech data applications continue to operate in areas having intrinsic bandwidth limitations, the perceptual quality of reproduced speech data in typical speech coding systems suffers significantly. The present invention employs forward pitch enhancement and backward pitch enhancement to maintain a high perceptual quality in reproduced speech. If desired, the backward pitch enhancement is generated using the forward pitch enhancement itself with the backward pitch enhancement being a mirror image of the forward pitch enhancement that was previously generated. Alternatively, in other embodiments of the invention, the backward pitch enhancement is generated independent of the forward pitch enhancement. The backward pitch enhancement is usually performed on the fixed codebook in code excited linear prediction (CELP) or is performed as post-processing in the decoder.
13 citations
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23 May 1989TL;DR: The objective of the described work is to constrain the algorithmic delay of an analysis-by-synthesis coder to be 2.5 ms while maintaining the bit rate at approximately 13 kb/s, which has been shown to be adequate for the Pan European Digital Mobile Radio System.
Abstract: The objective of the described work is to constrain the algorithmic delay of an analysis-by-synthesis coder to be 2.5 ms while maintaining the bit rate at approximately 13 kb/s, which has been shown to be adequate for the Pan European Digital Mobile Radio System. For applications which do not incorporate some redundancy for error-protection purposes, the bit rate of the speech coder increased to 16 kb/s, while the delay was reduced to as little as 2 ms. >
13 citations
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26 Sep 1995TL;DR: In this paper, an extension to the analysis-by-synthesis (AbS) loop used in code excited linear predictive (CELP) speech codecs is considered.
Abstract: In this paper extensions to the analysis-by-synthesis (AbS) loop used in code excited linear predictive (CELP) speech codecs are considered. Methods for updating the short-term synthesis filter once the excitation parameters have been determined are examined. We show that significant improvements can be achieved by updating the synthesis filter, similar to those obtained using the well known methods of interpolation and bandwidth expansion. However our proposed method of update avoids the increase in the delay of a codec that is usually associated with interpolation. Furthermore the traditional sequential method of determining the adaptive and fixed codebook parameters is examined and compared to an exhaustive search of both codebooks. Three sub-optimum techniques are proposed for improving the performance of the codebook search while maintaining a reasonable level of complexity. The most complex of these increases the codec complexity by only about 40% but provides 80% of the maximum possible 1.1 dB segmental SNR improvement associated with an exhaustive codebook search.
13 citations
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01 Jan 1991TL;DR: The rapidly increasing demand for cellular telephone services is providing the motivation to decrease the bit rate even further — down to 4 kb/s and lower.
Abstract: In recent years, rapid progress has been made in producing high quality speech at low bit rates [1–10]. The introduction of Multi-Pulse Linear Predictive Coding (MPLPC) in 1982 [1] and Code-Excited Linear Prediction (CELP) in 1984 [2,3] led to research in a new class of analysis-by-synthesis speech coders [4–6] that enabled us to encode high quality speech at bit rates as low as 4.8 kb/s [7,8]. The success of these coders has stimulated much interest in using the low bit rate speech coding technology for practical applications. Already, a new speech coding standard [11–12] has been adopted for cellular telephone service in Europe, and similar efforts are under way in North America. A standard based on CELP coding has been proposed by the United States Government for secure telephone, mobile satellite, and land mobile applications [8]. The rapidly increasing demand for cellular telephone services is providing the motivation to decrease the bit rate even further — down to 4 kb/s and lower.
13 citations