Method and apparatus for low bit rate encoding and decoding

Abstract

An apparatus and method of low bit rate encoding and reproducing. The method includes transforming input audio signals in a time domain into spectral signals in a frequency domain, extracting important-spectrum components from the spectral signals in the frequency domain, and quantizing the important-spectrum components, extracting residual-spectrum components other than the important-spectrum components from the spectral signals in the frequency domain, and calculating and quantizing a noise level of the residual-spectrum components, and encoding the quantized important-spectrum components and the quantized noise level losslessly, and outputting encoded bitstreams.

What is claimed is: 
     
       1. A method of low bit rate encoding comprising:
 transforming input audio signals in a time domain into spectral signals in a frequency domain;   extracting spectrum components from the spectral signals in the frequency domain, and quantizing the spectrum components based on a psychoacoustic analysis of the spectral signals;   extracting residual-spectrum components other than the spectrum components from the spectral signals in the frequency domain, and calculating and quantizing a noise level corresponding to noise components of the residual-spectrum components based on the psychoacoustic analysis of the spectral signals; and   encoding the quantized spectrum components and the quantized noise level losslessly, without the noise components, and outputting encoded bitstreams.   
     
     
       2. The method of  claim 1 , wherein the quantizing of the spectrum components based on the psychoacoustic analysis of the spectral signals comprises:
 modeling the audio signal in the time domain in a context of human perceptual auditory characteristics, prior to extracting the spectrum components from the spectral signal in the frequency domain, and quantizing the spectrum components,   wherein a perceptually important component is selected using the modelling result, and the spectrum components and noise level are quantized up to the number of bits assigned according to the encoding bit-assignment information.   
     
     
       3. The method of  claim 1 , wherein the extracted spectrum components are obtained by zeroing a predetermined range of spectrum components around the spectrum components. 
     
     
       4. The method of  claim 1 , wherein the extracting residual-spectrum components other than the spectrum components from the spectral signal in the frequency domain, and calculating and quantizing a noise level of the residual-spectrum components comprises:
 extracting residual-spectrum components other than the spectrum components from the spectral signal in the frequency domain;   dividing the residual-spectrum components into sub-bands, and calculating noise levels for a magnitude of a noise of each of the sub-bands; and   quantizing the calculated noise levels.   
     
     
       5. The method of  claim 4 , wherein the magnitude of the noise is obtained by estimating an extent of the noise according to a linear expectation analysis. 
     
     
       6. The method of  claim 4 , wherein the noise level, aNoise, is calculated by:
   aNoise=√{square root over (Energy/nCountFreq)}×dNoise×α, and
   wherein Energy is the energy of the sub-band, nCountFreq is a number of non-zero spectrum components, dNoise is a calculated magnitude of the noise for the sub-band, and α is a perceptual weight constant determined by noise characteristics.   
     
     
       7. An apparatus for low bit rate encoding, comprising:
 a spectrum component processing unit that extracts spectrum components from a spectral signal in a frequency domain and quantizes the spectrum components;   a psychoacoustic modeling unit performing a psychoacoustic analysis of the spectral signals;   a noise component processing unit that extracts residual-spectrum components other than the spectrum components from the spectral signal in the frequency domain, and calculates and quantizes noise levels corresponding to noise components of the residual-spectrum components based on the psychoacoustic analysis performed by the psychoacoustic modeling unit; and   a lossless encoding unit that losslessly encodes the spectrum components and the noise level, without the noise components and outputs encoded bitstreams.   
     
     
       8. The apparatus of  claim 7 , further comprising:
 the psychoacoustic modeling unit that models an input audio signal in a time domain by human perceptual auditory characteristics, and calculates encoding bit-assignment information,   wherein the spectrum component processing unit and the noise component processing unit quantize the spectrum components and the noise level, respectively, up to the number of bits assigned according to the encoding bit-assignment information.   
     
     
       9. The apparatus of  claim 7 , wherein the noise component processing unit comprises:
 a residual-spectrum component extracting unit that extracts residual-spectrum components other than the spectrum components from the spectral signal in the frequency domain;   a noise level calculation unit that divides the residual-spectrum components into sub-bands, and calculates noise levels for magnitudes of noise of the sub-bands; and   a noise level quantizing unit that quantizes the noise level.   
     
     
       10. A computer-readable storage medium encoded with processing instructions for causing a processor to execute a method of low bit rate encoding, the method comprising:
 transforming an input audio signal from the time domain to the frequency domain;   extracting spectrum components from a spectral signal in a frequency domain, and quantizing the spectrum components based on a psychoacoustic analysis of the spectral signals;   extracting residual-spectrum components other than the spectrum components from the spectral signal in the frequency domain, and calculating and quantizing a noise level corresponding to noise components of the residual-spectrum components based on the psychoacoustic analysis of the spectral signals; and   encoding the quantized spectrum components and the quantized noise level losslessly, without the noise components, and outputting encoded bitstreams.   
     
     
       11. A method of low bit rate decoding, comprising:
 decoding input bitstreams into spectral signals losslesslylossless-decoding, performed by at least one processor, a bitstream to obtain quantized spectrum components; 
 dequantizing the quantized spectrum components, of decoded spectral signals, surrounded by spectrum components during an encoding of the input bitstream that were quantized to zero within the encoding; 
 dequantizing a noise level of additional information of the decoded spectral signals and a subband from the bitstream in order to obtain a dequantized noise level; 
 generating a respective noise components component, using the dequantized noise level, for residue each spectrum components component set to zero other than the each spectrum components component set to non-zero; and 
 generating spectral signals in a frequency domain using the dequantizedreplacing each of spectrum components and thecomponents set to zero with its respective noise componentscomponent; and 
 generating a digital audio signal, based on the replacing and the spectrum component set to non-zero of the subband for audio reproduction, 
 wherein in the replacing, a frequency range of spectrum components set to zero around the spectrum component set to non-zero for which their noise components are to be replaced is determined based on a frame length. 
 
     
     
       12. The method of  claim 11 , wherein the dequantizing the noise level of additional information of the decoded spectral signals to generate generating the noise components component, comprises:
 dequantizing the noise level of the additional information of the decoded spectral signals; and 
 generating the respective noise components component from the noise level excluding a predetermined range around the spectrum components. 
 
     
     
       13. An apparatus for low bit rate decoding, comprising:
 a lossless decoding unit implemented by a processor that decodes input bitstreams into spectral signals losslessly lossless-decodes a bitstream to obtain quantized spectrum components; 
 a spectrum component dequantizing unit implemented by the processor that dequantizes the quantized spectrum components, of the decoded spectral signals, surrounded by spectrum components during an encoding of the input bitstream that were quantized to zero within the encoding; 
 a noise component processing unit implemented by the processor that dequantizes a noise level of additional information of the decoded spectral signals a subband from the bitstream in order to obtain a dequantized noise level and generates a respective noise components component using the dequantized noise level, for residue each spectrum components component set to zero other than the each spectrum components component set to non-zero; 
 a spectrum combining unit implemented by the processor that combines replaces each of the dequantized spectrum components and the components set to zero with its respective noise components component to be output as a spectral signals signal in a frequency domain; and 
 a signal generating unit implemented by the processor that generates spectral signals in a time domain from the spectral signals in the frequency domain a digital audio signal, based on the replacing and the spectrum component set to non-zero of the subband for audio reproduction, 
 wherein in the replacing, a frequency range of spectrum components set to zero around the spectrum component set to non-zero for which their noise components are to be replaced is determined based on a frame length. 
 
     
     
       14. The apparatus of  claim 13 , wherein the noise component processing unit comprises:
 a noise level dequantizing unit that dequantizes the noise level of the additional information of the decoded spectral signals; and 
 a noise component generating unit implemented by the processor  that generates components the respective noise component  from the dequantized noise level for a range excluding the range of the spectrum components. 
 
     
     
       15. A non-transitory computer-readable storage medium encoded with processing instructions for causing a processor to execute a method of low bit rate decoding, comprising:
 decoding input bitstreams into spectral signals losslesslylossless-decoding, performed by at least one processor, a bitstream to obtain quantized spectrum components; 
 dequantizing the quantized spectrum components, of decoded spectral signals, surrounded by spectrum components during an encoding of the input bitstream that were quantized to zero within the encoding; 
 dequantizing a noise level of additional information of the decoded spectral signals and a subband from the bitstream in order to obtain a dequantized noise level;  
 generating a respective noise components component, using the dequantized noise level, for each spectrum components component set to zero other than the each spectrum components quantized component set to non-zero; and 
 generating spectral signals in a frequency domain using the dequantizedreplacing each of spectrum components and theset to zero with its respective noise componentscomponent; and 
 generating a digital audio signal, based on the replacing and the spectrum component set to non-zero of the subband for audio reproduction, 
 wherein in the replacing, a frequency range of spectrum components set to zero around the spectrum component set to non-zero for which their noise components are to be replaced is determined based on a frame length.