Method and apparatus for encoding audio signals divided into a plurality of frequency bands

Abstract

This invention relates to a digital signal encoding apparatus in which the .[.width of the range in.]. .Iadd.digital signal is divided into frequency components in plural frequency bands and the bandwidth of the frequency bands is .Iaddend.selected to be wider for .[.the.]. higher .[.frequency range.]. .Iadd.frequencies .Iaddend.of the digital .[.signals divided into a plurality of regions.]. .Iadd.signal .Iaddend.and in which the encoded signals are synthesized for the respective .[.ranges.]. .Iadd.frequency bands .Iaddend.wherein encoding is controlled as a function of the output detecting the characteristics of the .Iadd.frequency .Iaddend.components .[.of.]. .Iadd.in .Iaddend.the .[.divided.]. frequency .Iadd.bands .Iaddend.and the detection time interval is selected to be longer for the lower frequency .Iadd.bands .Iaddend.to enable more efficient encoding to be performed as a function of the properties of input digital signals.

What is claimed is: 
     
       1. A digital signal encoding method of the type in which .Iadd.an .Iaddend.input digital .[.signals are.]. .Iadd.signal is .Iaddend.divided into .Iadd.frequency components in .Iaddend.a plurality of frequency bands which are so set that the .Iadd.frequency .Iaddend.bands with higher frequencies will have broader bandwidths, and in which encoded signals are synthesized and outputted for each of the frequency bands, wherein the improvement resides in the steps of: detecting by spectral analyses properties of the frequency components of the frequency bands, .[.with the period of.]. the spectral analyses.[.,.]. .Iadd.having a .Iaddend..[.which is the.]. detection time interval .[.or the time width as a unit of the analyses along the time axis, being.]. selected to be longer for lower frequencies, and generating a corresponding detection output signal; and   controlling the synthesizing and encoding as a function of the detection output signal.   
     
     
       2. The digital signal encoding method according to claim 1.Iadd., .Iaddend.wherein the input digital .[.signals have.]. .Iadd.signal has .Iaddend.a given sampling rate determined by a .Iadd.sampling rate .Iaddend.clock signal.Iadd., .Iaddend.and.Iadd., .Iaddend.in the step of detecting the properties of the frequency components.Iadd., .Iaddend..[.the frequency of.]. clock signals used in the spectral .[.analysis.]. .Iadd.analyses .Iaddend.are derived from the sampling rate clock signal and .[.are.]. .Iadd.have frequencies .Iaddend.selected to be lower for lower frequency bands. 
     
     
       3. A high efficiency digital .[.data.]. .Iadd.signal .Iaddend.encoding method.Iadd., .Iaddend.comprising the steps of: dividing .Iadd.an .Iaddend.input digital .[.data.]. .Iadd.signal .Iaddend.into a plurality of bands .[.so that the.]. .Iadd.having progressive broader .Iaddend.bandwidths thereof .[.will become progressively broader.]. for higher frequency bands;   forming a plurality of blocks, each consisting of a plurality of samples of the divided input digital .[.data,.]. .Iadd.signal, .Iaddend.for each band; and   performing .Iadd.an .Iaddend.orthogonal transformation of each block of the bands to generate coefficient data.   
     
     
       4. The method according to claim 3.Iadd., .Iaddend.wherein the block in which the orthogonal transformation is performed is composed of the same .[.numbers of.]. .Iadd.number .Iaddend.the sample.Iadd.s .Iaddend..[.data for.]. .Iadd.of the divided input signal in .Iaddend.the respective bands. 
     
     
       5. A high efficiency encoding method of the type in which .Iadd.an .Iaddend.input digital .[.data are.]. signal is converted into data on .[.the.]. .Iadd.a .Iaddend.frequency axis to produce data divided according to predetermined frequency bands, the data of the respective .Iadd.frequency .Iaddend.bands are formed into blocks by selecting .[.the.]. band-widths .Iadd.of the blocks .Iaddend.to be broader .[.for the high frequency ranges.]. .Iadd.at higher frequencies .Iaddend.to compute .[.the.]. floating coefficients for the respective blocks, a floating operation .[.for.]. .Iadd.on .Iaddend.the respective blocks is performed .[.with.]. .Iadd.using .Iaddend.the floating coefficients, and the floating coefficients are quantized, wherein the improvement resides in that: in the step of forming the data .[.of.]. .Iadd.in .Iaddend.the respective .Iadd.frequency .Iaddend.bands into blocks, the number of the data in each block .[.are.]. .Iadd.is .Iaddend.selected to be approximately equal; and   in the step of quantizing the floating coefficients, the floating coefficients .[.for the high frequency ranges.]. are quantized in such a manner that .[.the numbers of.]. .Iadd.progressively fewer .Iaddend.bits are .[.progressively smaller for.]. .Iadd.allocated to .Iaddend.the floating coefficients of .[.the higher frequency ranges..]. .Iadd.the frequency bands at higher frequencies. .Iaddend.   
     
     
       6. A digital signal encoding apparatus of the type including means for dividing .Iadd.an .Iaddend.input digital .[.signals.]. .Iadd.signal .Iaddend.into .Iadd.frequency components in .Iaddend.a plurality of frequency bands which are so set that the .Iadd.frequency .Iaddend.bands with higher frequencies will have broader bandwidths.Iadd., .Iaddend.and means for synthesizing and outputting encoded signals for each of the frequency bands, wherein the improvement comprises: means for detecting by spectral analyses properties of the frequency components of the frequency bands, .[.with the period of.]. the spectral analyses.[., which is the.]. .Iadd.having a .Iaddend.detection time interval .[.or the time width as a unit of the analyses along the time axis, being.]. selected to be longer for lower frequencies, and generating a corresponding detection output signal; and   means for controlling the synthesizing and encoding as a function of the detection output signal.   
     
     
       7. The digital signal encoding apparatus according to claim 6.Iadd., .Iaddend.wherein the input digital signals have a given sampling rate determined by a .Iadd.sampling rate .Iaddend.clock signal.Iadd., .Iaddend.and the means for detecting includes means for deriving.Iadd., .Iaddend..[.clock signals.]. from the sampling rate clock signal .[.and the frequency of these.]. .Iadd.clock signals for use in the spectral analyses, the .Iaddend.clock signals .[.used in the spectral analysis are.]. .Iadd.having frequencies .Iaddend.selected to be lower for lower frequency bands. 
     
     
       8. A high efficiency digital .[.data.]. .Iadd.signal .Iaddend.encoding apparatus.Iadd., .Iaddend.comprising: means for dividing .Iadd.an .Iaddend.input digital .[.data.]. .Iadd.signal .Iaddend.into a plurality of bands .[.so that the.]. .Iadd.having progressive broader .Iaddend.bandwidths .[.thereof will become progressively broader.]. for higher frequency bands;   means for forming a plurality of blocks, each consisting of a plurality of samples of the divided input digital .[.data,.]. .Iadd.signal, .Iaddend.for each band; and   means for performing .Iadd.an .Iaddend.orthogonal transformation of each block of the bands to generate coefficient data.   
     
     
       9. The apparatus according to claim 8.Iadd., .Iaddend.wherein the block in which the orthogonal transformation is performed is composed of the same .[.numbers.]. .Iadd.number .Iaddend.of the .[.sample data for.]. .Iadd.samples of the divided input digital signal in .Iaddend.the respective bands. 
     
     
       10. A high efficiency encoding apparatus of the type which includes means for converting .Iadd.an .Iaddend.input digital .[.data.]. .Iadd.signal .Iaddend.into data on .[.the.]. .Iadd.a .Iaddend.frequency axis to produce data divided according to predetermined frequency bands, means for forming the data .[.of.]. .Iadd.in .Iaddend.the respective .Iadd.frequency .Iaddend.bands into blocks by selecting .[.the.]. bandwidths .Iadd.of the blocks .Iaddend.to be broader .[.for the high frequency ranges.]. .Iadd.at higher frequencies .Iaddend.to compute .[.the.]. floating coefficients for the respective blocks, means for performing a floating operation .[.for.]. .Iadd.on .Iaddend.the respective blocks .[.with.]. .Iadd.using .Iaddend.the floating coefficients, and means for quantizing the floating coefficients, wherein the improvement .[.comprises:.]. .Iadd.resides in that: .Iaddend. .[.that.]. the means for forming the data .[.of.]. .Iadd.in .Iaddend.the respective bands into blocks selects the number of the data in each block to be approximately equal; and   the means for quantizing the floating coefficients quantizes the floating coefficients .[.for the high frequency ranges.]. in such a manner that .[.the numbers of.]. .Iadd.progressively fewer .Iaddend.bits are .[.progressively smaller for.]. .Iadd.allocated to .Iaddend.the floating coefficients of the .[.higher frequency ranges..]. .Iadd.frequency bands at higher frequencies. .Iaddend.   
     
     
       11. A digital signal encoding method of the type in which .Iadd.an .Iaddend.input digital .[.signals are.]. .Iadd.signal is .Iaddend.divided into .Iadd.frequency components in .Iaddend.a plurality of frequency bands which are so set that the frequency bands with higher frequencies will have broader bandwidths, and in which encoded signals are synthesized and outputted for each of the frequency bands, wherein the improvement resides in the steps of: detecting properties of the frequency components .[.of.]. .Iadd.in .Iaddend.the frequency bands, .[.with the time duration of.]. this detection of the properties of the frequency components .[.being.]. .Iadd.having a time duration .Iaddend.selected to be longer for lower frequencies, and generating a corresponding detection output signal, wherein the step of detecting the properties of the frequency components includes a spectrum analysis step.Iadd., .Iaddend.and wherein .[.the frequency of.]. clock signals used in the spectral analysis step .[.is.]. .Iadd.have frequencies .Iaddend.selected to be lower for .Iadd.the .Iaddend.clock signals for .[.lower.]. .Iadd.the .Iaddend.frequency bands .Iadd.with lower frequencies.Iaddend.; and   controlling the synthesizing and encoding as a function of the detection output signal.   
     
     
       12. A digital signal encoding apparatus of the type including means for dividing .Iadd.an .Iaddend.input digital .[.signals.]. .Iadd.signal .Iaddend.into .Iadd.frequency components .Iaddend.a plurality of frequency bands which are so set that the .Iadd.frequency .Iaddend.bands with higher frequencies will have broader bandwidths.Iadd., .Iaddend.and means for synthesizing and outputting encoded signals for each of the frequency bands, wherein the improvement comprises: means for detecting properties of the frequency components .[.of.]. .Iadd.in .Iaddend.the frequency bands, .[.with the time duration of.]. this detection of the frequency components .[.being.]. .Iadd.having a time duration .Iaddend.selected to be longer for lower frequencies, and generating a corresponding detection output signal, wherein the means for detecting the properties of the frequency components includes a spectrum analysis means.Iadd., .Iaddend.and wherein .[.the frequency of.]. clock signals used in the spectral analysis means .[.is.]. .Iadd.have frequencies .Iaddend.selected to be lower for the clock signals for .[.lower.]. .Iadd.the .Iaddend.frequency bands .Iadd.with lower frequencies.Iaddend.; and   means for controlling the synthesizing and encoding as a function of the detection output signal. .Iadd.   
     
     
       13.  A digital signal encoding method for encoding an input digital signal, the method comprising the steps of: dividing the input digital signal into frequency components in a plurality of frequency bands;   synthesizing and outputting encoded signals for each of the frequency bands;   detecting by spectral analyses properties of the frequency components in the frequency bands, and generating a corresponding detection output signal; and   controlling the synthesizing of the encoded signals as a function of the detection output signal. .Iaddend..Iadd.   
     
     
       14.  The digital signal encoding method according to claim 13, wherein: in the step of dividing the input digital signal into a plurality of frequency bands, the input digital signal is divided into frequency bands having broader bandwidths at higher frequencies; and   in the step of detecting properties of the frequency components, the spectral analyses have a detection time selected according to the bandwidth of the respective frequency band. .Iaddend..Iadd.15. The digital signal encoding method according to claim 14, wherein:   the input digital signal has a given sampling rate determined by a sampling-rate clock signal; and   the step of detecting properties of the frequency components includes the step of deriving, from the sampling-rate clock signal, clock signals for use in the spectral analyses. .Iaddend..Iadd.16. The digital signal encoding method according to claim 15, wherein, in the step of deriving clock signals for use in the spectral analyses, the clock signals have frequencies selected according to the bandwidth of the respective frequency band. .Iaddend..Iadd.17. The digital signal encoding method according to claim 15, wherein, in the step of detecting by spectral analyses, the spectral analyses have a detection time selected according to the bandwidth of the respective frequency band. .Iaddend..Iadd.18. The digital signal encoding method according to claim 13, wherein, in the step of dividing the input digital signals into a plurality of frequency bands, the input digital signal is divided into least two frequency bands having equal bandwidths. .Iaddend..Iadd.19. A digital signal encoding method for encoding an input digital signal, the method comprising the steps of:   dividing the input digital signal into a plurality of frequency bands;   forming a plurality of blocks, each consisting of a plurality of samples of the divided input digital signal, for each frequency band; and   performing an orthogonal transformation of each block of the frequency bands to generate coefficient data. .Iaddend..Iadd.20. The digital signal encoding method according to claim 19, wherein the method additionally comprises the ste p of dividing the coefficient data into predetermined frequency blocks having broader bandwidths at higher frequencies.   
     
     
        .Iaddend..Iadd.21.  The digital signal encoding method according to claim 19, wherein, the step of forming a plurality of blocks forms, in one of the frequency bands, blocks consisting of samples equal in number to the samples in the blocks in at least one other of the frequency bands. .Iaddend..Iadd.22. The digital signal encoding method according to claim 19, wherein, in the step of dividing the input digital signal into a plurality of frequency bands, frequency bands with higher frequencies have broader bandwidths. .Iaddend..Iadd.23. The digital signal encoding method according to claim 19, wherein, in the step of dividing the input digital signal into a plurality of frequency bands, at least two of the frequency bands have equal bandwidths. .Iaddend..Iadd.24. A digital signal encoding method for an input digital signal, the method comprising the steps of: converting the input digital signal into coefficient data on a frequency axis;   dividing the coefficient data into predetermined frequency bands;   forming the coefficient data in the respective frequency bands into blocks of approximately equal numbers of coefficient data;   computing a floating coefficient for the each of the blocks;   performing a floating operation on each of the blocks using the respective floating coefficient; and   quantizing the floating coefficients in a manner that allocates progressively fewer quantizing bits to the floating coefficients of the frequency bands at higher frequencies. .Iaddend..Iadd.25. The digital signal encoding method according to claim 24, wherein the step for dividing the coefficient data into predetermined frequency bands divides the coefficient data into predetermined frequency bands having broader bandwidths at hither frequencies. .Iaddend..Iadd.26. The digital signal encoding method according to claim 24, wherein, in the step of forming the coefficient data into blocks, more than one block is formed in a frequency band at a higher frequency. .Iaddend..Iadd.27. A digital signal encoding an apparatus, comprising:   frequency dividing means for dividing an input digital signal into frequency components in a plurality of frequency bands;   means for synthesizing and outputting encoded signals for each of the frequency bands;   means for detecting by spectral analyses properties of the frequency components in the frequency bands, and for generating a corresponding detection output signal; and   means for controlling the means for synthesizing and outputting encoded   
     
     
        signals as a function of the detection output signal. .Iaddend..Iadd.28. The digital signal encoding apparatus according to claim 27, wherein: the frequency dividing means divides the digital input signal into frequency bands having broader bandwidths at higher frequencies; and   the means for detecting detects by spectral analyses having a detection time selected according to the bandwidth of the respective frequency band. .Iadd.29. The digital signal encoding apparatus according to claim 27, wherein:   the input digital signal has a given sampling rate determined by a sampling-rate clock signal; and   the means for detecting includes means for deriving, from the sampling-rate clock signal, clock signals for use in the spectral analyses. .Iaddend..Iadd.30. The digital signal encoding apparatus according to claim 29, wherein the means for deriving clock signals for use in the spectral analyses includes means for selecting frequencies for the clock signals according to the bandwidth of the respective frequency band. .Iaddend..Iadd.31. The digital signal encoding apparatus according to claim 29, wherein the means for detecting detects by spectral analyses having a detection time selected according to the bandwidth of the respective frequency band. .Iaddend..Iadd.32. The digital signal encoding apparatus according to claim 27, wherein the frequency dividing means divides the input digital signal into frequency bands in such a manner that two of the frequency bands have equal bandwidths. .Iaddend..Iadd.33. A digital signal encoding apparatus, comprising:   means for dividing an input digital signal into a plurality of frequency bands;   means for forming a plurality of blocks, each consisting of a plurality of samples of the divided input digital signal, in each frequency band; and   means for performing an orthogonal transformation of each block in each of the frequency bands to generate coefficient data. .Iaddend..Iadd.34. The digital signal encoding apparatus according to claim 33, wherein the means for forming a plurality of blocks forms, in one of the frequency bands, blocks consisting of samples equal in number to the samples in the blocks in at least one other of the frequency bands. .Iaddend..Iadd.35. The digital signal encoding apparatus according to claim 33, wherein the means for dividing the input digital signal into a plurality of frequency bands divides the input digital signal into frequency bands having broader   
     
     
        bandwidths at higher frequencies. .Iaddend..Iadd.36.  The digital signal encoding apparatus according to claim 33, wherein the means for dividing the input digital signal into a plurality of frequency bands divides the input digital signal into frequency bands, at least two of the frequency bands having equal bandwidths. .Iaddend..Iadd.37. A digital signal encoding apparatus, comprising: means for converting an input digital signal into coefficient data on a frequency axis;   means for dividing the coefficient data into predetermined frequency bands;   means for forming the coefficient data in the respective bands into blocks, the numbers of coefficient data in the blocks being selected to be approximately equal;   means for computing a floating coefficient for each of the blocks;   means for performing a floating operation on each of the blocks using the respective floating coefficient, and   means for quantizing the floating coefficients in a manner that allocates progressively fewer quantizing bits to the floating coefficients of frequency bands at the higher frequencies. .Iaddend..Iadd.38. The digital signal encoding apparatus according to claim 37, wherein the means for dividing the coefficient data into predetermined frequency bands divides the coefficient data into predetermined frequency bands having broader bandwidths at higher frequencies. .Iaddend..Iadd.39. The digital signal encoding apparatus according to claim 37, wherein the means for forming the coefficient data into blocks forms more than one block in a frequency band at a higher frequency. .Iaddend..Iadd.40. A digital signal encoding apparatus for encoding an input digital signal, the apparatus comprising:   means for orthogonally transforming the input digital signal to provide data on a frequency axis; and   means for dividing the data into frequency bands having broader bandwidths at higher frequencies. .Iaddend..Iadd.41. The digital signal encoding apparatus according to claim 40, wherein the means for dividing divides the data into frequency bands corresponding to critical bands. .Iaddend..Iadd.42. The digital signal encoding apparatus according to claim 40, additionally comprising:   block forming means for forming the data in the frequency bands into blocks of approximately equal numbers of data, and   means for applying block floating to each block of data.   
     
     
        .Iaddend..Iadd.     The digital signal encoding ap paratus of claim 42, wherein the block forming means includes means for dividing the data in a frequency band into plural blocks, each block corresponding to a sub band obtained by dividing the frequency band in frequency. .Iaddend..Iadd.44. A digital signal encoding method for encoding an input digital signal, the method comprising the steps of: orthogonally transforming the input digital signal to provide data on a frequency axis; and   dividing the data into frequency bands having broader bandwidths at higher frequencies. .Iaddend..Iadd.45. The digital signal encoding method according to claim 44, wherein the step of dividing the data into frequency bands divides the data into frequency bands corresponding to critical bands. .Iaddend..Iadd.46. The digital signal encoding method according to claim 44, additionally comprising the steps of:   forming the data in the frequency bands into blocks of approximately equal numbers of data, and   applying block floating to each block of data. .Iaddend..Iadd.47. The digital signal encoding method according to claim 46, wherein the step of forming the data into blocks includes the step of dividing the data in a high frequency band into plural blocks, each block corresponding to a sub band obtained by dividing the high frequency band in frequency. .Iaddend.