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Variable Bitrate Wideband Speech Coding Using Perceptually Motivated Thresholds

Authors:
Paulus, J.
Book Title:
Proceedings of IEEE Workshop on Speech Coding (SCW)
Pages:
p.p. 35-36
Address:
Annapolis, Maryland, USA
Date:
Sep. 1995
Language:
English

Abstract

This paper proposes a variable bitrate wideband CELP coding scheme (50-7000 Hz) with a one-way coder-decoder delay of 25 ms only. The bitrate varies between 6.4 kbit/s and 14.8 kbit/s with a mean of 11.2 kbit/s at a voice activity of 95 %. The variation of the bitrate is based on a voiced-unvoiced-silence classification of the speech frame to be encoded. For voiced frames a perceptually based focussed LTP analysis is used, and for unvoiced or silent frames the LTP filter is omitted. Additionally, in adjacent frames with small spectral changes LPC parameters are repeated using an adaptive LPC codebook. For the classification of the different modes a cepstral distance measure, and a new adaptive detector is used. By informal listening tests the speech quality was rated higher than the CCITT G.722 wideband codec operating at 48 kbit/s.

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