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Improvements to the Analysis-by-Synthesis Loop in CELP Codecs

Woodard, J. and Hanzo, L. (1995) Improvements to the Analysis-by-Synthesis Loop in CELP Codecs At of the IEE RRAS'95, United Kingdom. 26 - 28 Sep 1995. , pp. 114-118.

Record type: Conference or Workshop Item (Other)


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 1.1dB segmental SNR improvement associated with an exhaustive codebook search.

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Published date: September 1995
Additional Information: Conf. Public. No. 415 Event Dates: 26-28 September 1995 Organisation: IEE Address: Bath, UK
Venue - Dates: of the IEE RRAS'95, United Kingdom, 1995-09-26 - 1995-09-28
Organisations: Southampton Wireless Group


Local EPrints ID: 258129
PURE UUID: c66ce72b-1f56-46b0-a8fd-37ea57a5f91e

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Date deposited: 30 Jul 2003
Last modified: 18 Jul 2017 09:34

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Author: J. Woodard
Author: L. Hanzo

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