with long term prediction (LTP) whic:h are based on a modelIn this paper we propose a split-band encoding scheme for 16kbit/s wideband speech coding (50-7000 Hz), using 2 unequal subbands from 0-6 kHz and from 6-7 kHz. This approach was motivated by experimental evaluation of the signal bandwidth of speech frames. The higher subband is simply represented by white noise with adjustment of the short term energy. For the lower subband code-excited linear prediction (CELP) is used. By informal listening tests the speech quality was rated higher than the speech quality of the CCITT G.722 wideband codec operating at 48kbit/s.

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 f o r unvoiced or silent f m m e s 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 dijferent 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 ccdec operating at 48 kbit/s.

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This paper proposes a Wideband-CELP-Coding scheme (bandwidth 7kHz) at 24 kbit/s. The codec introduces a delay of just 10 ms. This fulfills the requirements of a possible codec candidate for wideband speech coding within DECT or video applications [I]. The analysis-by-synthesis structure of the proposed Wideband-CELP-Codec includes an alternative LPC analysis concept, where the autocorrelation function is calculated recursively [2]. This special LPC scheme provides an improved speech quality and a reduction of computational complexity in comparison to conventional algorithms for the LPC analysis. In addition a stochastic sparse codebook with extremely low computational effort is presented, comparable to the one presented in [12] resulting in a neglectable amount of storage. The CCITT G.722 standard was applied as reference codec, in order to compare the new coding scheme in terms of subjective quality. With the proposed Wideband-CELP a speech quality is achieved, which is equivalent to the reference codec op erating at 56 kbit/s.