Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
1998-04-15
2001-08-14
Zele, Krista (Department: 2748)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704S226000
Reexamination Certificate
active
06275796
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optimal coding of a speech signal, and more particularly, to an apparatus for quantizing spectral envelope and a method therefor with noise robustness for optimally coding the speech signal, under all the environments in which channel errors are not generated and channel errors are generated, and a method therefor.
2. Description of the Related Art
Standardization of speech encoders is proceeding in the US, Japan, and Europe. Most encoders according to the standardization divide speech into a spectral envelope and an excite signal, quantize them, and transfer corresponding bit streams. Therefore, a method of designing a quantizer in which a spectrum envelope is represented by the minimum number of bits is essential. In order to represent the spectral envelope, a linear predictive coding (LPC) is extracted from the speech. In order to efficiently quantize the spectral envelope, the LPC coefficients are converted into line spectrum frequencies (LSFs).
Paliwal and Atal provided a split-vector quantizer (SVQ) in order to quantize the LSFs (refer to “Efficient Vector Quantization of LPC Parameters at 24 bits/frame.” IEEE Trans, Speech, audio processing. Vol.1, no.1, pp.3-14, January 1993.). In this method, satisfactory performance is obtained from 24 bits/frame by dividing tenth order LSFs into two or three sub-vectors and separately quantizing the sub-vectors.
Meanwhile, a predictive split-vector quantizer (PSVQ) using an interframe correlation for improving the performance of the SVQ was provided in ITU-T Recommendation G.723.1.
However, this method has a shortcoming in that when a channel error is generated, the error affects the next frame. In order to prevent the error from affecting the next frame, de Marca provided a method of alternately using the SVQ and the PSVQ in odd and even frames. However, this method has lower performance than the PSVQ when no channel error is generated.
SUMMARY OF THE INVENTION
To solve the above problem(s), it is an objective of the present invention to provide an apparatus for quantizing a spectral envelope with noise robustness, which shows a satisfactory performance under a clean environment or a background noise environment when no channel error is generated and under a channel noise environment when a channel error is generated, by efficiently preventing the influence of the channel error from spreading so that the channel error affects only several frames, and a method therefor.
It is another objective of the present invention to provide an apparatus for quantizing the spectral envelope with noise robustness, which shows a satisfactory performance under various background noise environments, and a method therefor.
Accordingly, to achieve the first objective, there is provided a spectral envelope quantizing apparatus with noise robustness for representing a spectral envelope of speech by a minimum number of bits for the optimal coding of a speech signal, comprising a line spectrum frequencies (LSFs) input portion for converting linear predictive coding coefficients extracted from the speech into Nth order line spectrum frequencies coefficients and inputting the coefficients as the LSFs of a current frame, a linked split-vector quantizing portion for dividing the LSFs into a predetermined number of linked sub-vectors and quantizing the sub-vectors, a predictive linked split-vector quantizing portion for obtaining the difference between the LSFs and the LSFs of a previous frame and vector-quantizing the difference, and an error selector for comparing the error values of the LSFs quantized in the linked split-vector quantizing portion and the predictive linked split-vector quantizing portion, selecting the codebook index of the quantized LSFs having the smaller error value, and outputting the selected codebook index together with a mode bit.
Also, there is provided a spectral envelope quantizing method with noise robustness for representing a spectral envelope of speech by a minimum number of bits for the optimal coding of a speech signal, comprising the steps of inputting the LSFs of a current frame, dividing the LSFs into a predetermined number of linked sub-vectors and linked split-vector-quantizing the sub-vectors and, at the same time, obtaining the difference between the LSFs and the LSFs of a previous frame and predictive linked split-vector-quantizing the difference, comparing the error values of the linked split-vector quantized LSFs with those of the predictive split-vector quantized LSFs, and selecting the codebook index of the quantized LSFs having the smaller error value and outputting the selected codebook index together with a mode bit.
To achieve the second objective, there is provided a spectral envelope quantizing apparatus with noise robustness for representing a spectral envelope of speech by a minimum number of bits for the optimal coding of a speech signal, comprising an LSFs input portion for converting linear predictive coding coefficients extracted from the speech into Nth order LSF coefficients and inputting the coefficients as the LSFs of a current frame, a clean environment quantizing portion for dividing the LSFs into a predetermined number of linked sub-vectors and vector-quantizing the sub-vectors under a clean speech environment, a babble noise quantizing portion for dividing the LSFs into the predetermined number of linked sub-vectors and vector-quantizing the sub-vectors under a babble noise environment, a car noise quantizing portion for dividing the LSFs into the predetermined number of linked sub-vectors and vector-quantizing the sub-vectors under a car noise environment, a predictive linked split-vector quantizing portion for obtaining the difference between the LSFs and the LSFs of a previous frame and vector-quantizing the difference under all the environments, and an error selector for comparing the error values of the LSFs quantized in the clean environment quantizing portion, the babble noise quantizing portion, the car noise quantizing portion, and the predictive linked split-vector quantizing portion to each other, selecting the codebook index of the quantized LSF having the smallest error value, and outputting the selected codebook index together with a mode bit.
Also, there is provided a spectral envelope quantizing method with noise robustness for representing the spectral envelope of speech by a minimum number of bits for the optimal coding of a speech signal, comprising the steps of inputting the LSFs of a current frame, dividing the LSFs into a predetermined number of linked sub-vectors and linked split-vector-quantizing the sub-vectors through codebooks trained under a clean speech environment, a babble noise environment, and a car noise environment and, at the same time, obtaining a difference between the LSFs and the LSFs of a previous frame through codebooks trained under all the circumstances and predictive split-vector-quantizing the sub-vectors, comparing the error values of the linked split-vector quantized LSFs with those of the predictive split-vector quantized LSFs, and selecting the codebook index of the quantized LSF having the smallest error value and outputting the selected codebook index together with a mode bit.
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Cho Yong-duk
Kim Hong-kook
Kim Moo-young
Burns Doane Swecker & Mathis L.L.P.
Opsasnick Michael N.
Samsung Electronics Co,. Ltd.
Zele Krista
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