Apparatus for quantizing spectral envelope including error selector for selecting a codebook index of a quantized LSF having a smaller error value and method therefor

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.

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.

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.