Variable-Rate CELP Based on Subband Flatness - Speech and Audio Processing, IEEE Transactions on
نویسندگان
چکیده
Code-excited linear prediction (CELP) is the predominant methodology for communications quality speech coding below 8 kbps, and several variable-rate CELP schemes have been discussed in the literature, including QCELP, the variable-rate wideband digital cellular mobile radio speech coding standard specified in IS-95. A key component of these speech coders is the detection and classification of speech activity, and several cues for rate variation have been studied, such as measuring short-term speech energy, deciding whether the speech is voiced or unvoiced, or making more sophisticated phonetic classifications. We present a new method for rate variation based on a measure of subband spectral flatness, called spectral entropy. Spectral entropy is a normalized indicator of the texture of the input spectrum and is thus less dependent on speech and background noise energy variations. We present some results on the use of spectral entropy for voice activity detection across subbands and then evaluate using spectral entropy for deriving mode and rate allocation cues for a variable-rate CELP coder operating at an average rate of 2 kbps. To achieve communications quality speech at this rate, we develop a new split-band vector quantization (VQ) technique for representing the line spectral pairs and a multiple codebook approach for efficiently quantizing the coefficients of a three-tap pitch predictor, called lag-indexed VQ.
منابع مشابه
Markov model-based phoneme class partitioning for improved constrained iterative speech enhancement
171 A. Benyassine and H. Abut, “Mixture excitations and finite-state CELP speech coders,” in Proc. IEEE ICASSP., Mar. 1992, pp. 1-345-1-348. P. Krmn and B. S. Atal, “Strategies for improving the performance of CELP coders at low bit rates,” in Proc. IEEE ICASSP, Apr. 1988, pp. 151-154. P. moon and B. S. Atal, “On the use of pitch predictors with high temporal resolution,” IEEE Truns. Acoust., S...
متن کاملA Perceptually Based Embedded Subband Speech Coder - Speech and Audio Processing, IEEE Transactions on
A new scheme for robust, high-quality, embedded speech coding based on subband decomposition and perceptually optimized bit allocation and prioritization is presented. An infinte impulse response (IIR) quadrature mirror filterbank (QMF) performs subband decomposition. A perceptual model, computed using subband spectral analysis, optimizes the coder’s perceptual quality. Dynamic bit allocation a...
متن کاملAdaptive forward-backward quantizer for low bit rate high-quality speech coding
A novel variable rate linear predictive coding (LPC) parameter quantization scheme is proposed in which linear prediction is done by using either the current (forward LPC) or previously decoded (backward LPC) speech blocks. The proposed LPC quantization scheme was integrated into the FS1016 Federal Standard CELP coder. Signi cant LPC bit rate reduction is achieved without compromising the decod...
متن کاملA New Algorithm for Voice Activity Detection Based on Wavelet Packets (RESEARCH NOTE)
Speech constitutes much of the communicated information; most other perceived audio signals do not carry nearly as much information. Indeed, much of the non-speech signals maybe classified as ‘noise’ in human communication. The process of separating conversational speech and noise is termed voice activity detection (VAD). This paper describes a new approach to VAD which is based on the Wavelet ...
متن کامل