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

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a digital signal encoding apparatus for encoding input digital signals.

2. Prior Art

As a technique of high efficiency encoding of voice signals, an audio signal for example, are supplied as is supplied as an input digital signals signal to an input terminal 1 of the digital signal encoding apparatus. These voice signals are This audio signal is first supplied to band-pass filters (BPFs) 11 to 14. These BPF filters divide the frequency range of the voice signals audio signal into a plurality of frequency bands so that the bandwidth will become broader for the higher frequency bands so as to suit the frequency discriminating capability of the human auditory sense. Low-pass filters are built in the BPFs 11 to 14 so that the signals are shifted towards the low frequency sides downwards in frequency by amounts corresponding to the central center frequencies of the pass bands of the BPFs 11 to 14.

The voice signals, audio signal, thus divided into plural frequency bands and shifted to the lower frequency sides downwards in frequency by the BPFs 11 to 14, are is divided into frequency bands B1, B2, B3 and B4 by the BPFs 11, 12, 13 and 14, as shown in FIG. 3. These frequency bands B1 to B4 are selected so that the bandwidths will be the broader, the higher the frequencies, as mentioned previously.

The signals of the respective frequency bands are quantized by quantizers 41 to 44. During such quantization, the frequency characteristics of the frequency components of in the respective bands are detected by spectrum analysis circuits 21 to 24, respectively; and quantization is controlled as a function of the detected output. That is, with the present encoding apparatus, the numbers of allocated bits at the time of quantization are determined on the basis of the results of the signal spectral analyses for the respective frequency bands, and quantization at by the quantizers 41 to 44 is performed on the basis of the so determined numbers of bit allocation.

Thus the signals of the respective frequency bands from the BPFs 11 to 14 are transmitted to spectrum analysis circuits 21 to 24, respectively, where spectral analyses for the refractive respective frequency bands are performed. The results of the analyses are transmitted to bit allocation numbers number decision circuits 31 to 34 which allocate the number of the bits at the time of quantization, so that the bit allocation numbers are determined at by the circuits 31 to 34 on the basis of the results of the analyses. Quantization at by the quantizers 41 to 44 are is performed on the basis of the so determined bit allocation numbers. Quantization The quantized outputs of the quantizers 41 to 44 are synthesized by a multiplexer 6 so as to be outputted at an output terminal 7 of the digital signal encoding apparatus of the present embodiment.

It is noted that, in quantizing the voice signals audio signal previously divided into plural frequency bands to suit the frequency analysis capability of the human auditory sense, since the bandwidths of the respective frequency bands differ from one frequency band to another, the block sizes of the spectral analyses, that is the widths along the time axis of the analytic blocks, will differ from one frequency band to another for the same assumed precision in definition of the analyses along time axis of the frequency bands, with the result that bands. As a result, the efficiency of spectral analyses, and hence the quantization efficiency, are is lowered. Since it is thought in general that the constant amplitude domain of the low frequency range signal lower frequency signals is longer and that of the high frequency range signal higher frequency signals is shorter, an efficient coding taking such into account this difference in the length of the constant amplitude domain cannot be realized.

With this in view, the temporal analytic accuracy, that is, the analytic accuracy along the time axis, is selected to be higher and lower for the high and low frequency range, respectively, for realizing a more efficient quantization. In other words, the durations of the spectral analyses are selected to be shorter and longer for the high and low frequency ranges, respectively.

That is, for in the spectral analyses performed by the spectral analysis circuits 21 to 24, the period of the analyses, which is the detection time interval or the time width as a unit of the analyses along the time axis, is selected to be the longer, the lower the frequency. Selection of the detection time intervals for the spectral analyses as a function of the frequencies may be made on the basis of each of the clock signals obtained upon by dividing the clock frequency of the clock signals signal contained in the voice signals. audio signal.

Thus, in the present embodiment, the clock signal components in the voice signals in the audio signal supplied to the input terminal 1 are is separated in a clock circuit 2. The so separated clock signals CK are signal CK is sequentially transmitted through 1/2 frequency dividers 3, 4 and 5 to produce frequency-divided clock signals signal (1/2) CK, divided to one half the original clock frequency CK, frequency-divided clock signals signal (1/4) CK, divided to one-fourth the original clock frequency CK and frequency-divided clock signals signal (1/8) CK, divided to one-eighth the original clock frequency CK. Of the so-produced clock signals, the clock signals CK are signal CK is transmitted to a spectrum analysis circuit 24 and a bit allocation number decision circuit 34, the frequency-divided clock signals signal (1/2) CK are is transmitted to a spectrum analysis circuit 23 and a bit allocation number decision circuit 33, the frequency-divided clock signals (1/4) CK are signal (1/4) CK is transmitted to a spectrum analysis circuit 22 and a bit allocation number decision circuit 32 and the frequency-divided clock signals (1/8) CK are signal (1/8) CK is transmitted to a spectrum analysis circuit 21 and a bit allocation number decision circuit 31.

Hence Consequently, the detection time duration of the spectral analyses, that is, the unit time width for the analyses, becomes is a maximum at the spectrum analysis circuit 21, while it becomes is progressively shorter at the spectrum analysis circuits 22 and 23, becoming and is shortest at the spectrum analysis circuit 24.

By changing the detection time intervals for spectral analyses in this manner, it becomes possible to realize perform efficient spectral analyses and hence efficient quantization at the time of quantizing the voice signals audio signal divided into a plurality of frequency bands to suit the frequency analysis capability of the human auditory sense. With the detection time interval thus changed, the spectrum for each frequency band may be thought to be constant in each block of the band, so that the values of the spectrum analyses for the long-time block may be used in the lower frequency range in substitution for the short-time spectral waveform.

Meanwhile, the The division ratio of the frequency range need not necessarily be inversely proportionate proportional to the time durations for spectrum analyses, that is the time durations bearing the ratios of 8:4:2:1 to the frequency period of the clock signals CK. However, the relative magnitude of the division ratio is preferably selected in the above described manner. Such relative magnitude is in keeping with the direction in which the block size of the spectral analyses, that is the width of the analytic block along the time axis, may be made the same, so that the efficiency is not lowered.

Although the bit allocation numbers for quantization are determined in the above embodiment by the spectral analyses, the bit allocation numbers for quantization may also be determined using the floating coefficients for of a so-called block floating operation.

FIG. 4 shows a portion of the digital signal encoding apparatus of the present embodiment responsible for only one frequency band.

In this figure, voice signals the audio signal at an input terminal 1 are is passed through a band-pass filter (BPF) 50 where the signals of components of the audio signal in a predetermined frequency band are taken out extracted as a block which is then transmitted to a maximum value detection circuit 51 adapted for detecting the maximum value data of the samples in the block. In this maximum value detection circuit 51, the maximum value data sample in the block is detected, and the floating coefficient for the block floating operation is found on the basis of the maximum value data sample.

In detecting the floating coefficient, if the same degree of accuracy is used for the temporal analyses of the respective frequency bands, the efficiency of detection of the floating coefficients and hence the quantization efficiency tends to be lowered, while it is not possible to perform efficient encoding in accordance with the constant-amplitude domains.

Thus the maximum value detection circuit 51 is fed with the frequency-divided clock signals shown in FIG. 2 and the precision of definition along the time axis of the floating coefficient or the analysis time interval of the floating coefficient is determined on the basis of these frequency-divided clock signals. That is, in the present embodiment, the precision of definition along the time axis is selected to be higher and lower for the high and low frequencies, respectively, for realizing more efficient quantization.

The floating coefficients, for which the time intervals for analyses have been determined in this manner, are transmitted to a normalization circuit 52. The aforementioned block data are of samples is also supplied to the normalization circuit 52, so that the block data are of samples is processed in the normalization circuit 52 by block floating on the basis of the above mentioned floating coefficients, and the blocks thus processed by block floating are quantized subsequently.

Since the block floating also is preferably performed in the constant-amplitude signal domain, domain of the signal, the time interval of the floating coefficient for the constant-amplitude signal domain is selected to be longer for the low frequency range where the constant-amplitude domain is longer for realizing efficient block floating.

That is, in the above described first embodiment of the digital signal encoding apparatus of the present invention, encoding is controlled in accordance with the detection output of the characteristics of the components of the frequency bands, while the detection time interval is selected to be longer for the lower frequencies, with the result that the detection efficiency is not lowered and hence efficient encoding suited to the nature of the input digital signals may be achieved.

A second embodiment of the present invention will be hereinafter explained by referring to FIG. 5, et seq.

FIG. 5 shows diagrammatically a typical construction of a high efficiency encoding apparatus for digital data according to the second embodiment.

Referring to FIG. 5, the high efficiency encoding apparatus for digital data a digital signal according to the present embodiment is constituted by a filter bank 104, made up of mirror filters, such as quadrature mirror filters, as the frequency division filters, orthogonal transform circuits 105₁ to 105₅ for performing an orthogonal transform, that is a transform of the time axis into the digital signal on the time axis to the frequency axis, such as fast Fourier transform, and a bit allocation number decision circuit 106 for determining the bit numbers allocated to the respective frequency bands.

To the input terminal 101 are supplied is supplied a 0 to 16 kHz input digital data signal obtained upon sampling audio signals an audio signal with a sampling frequency fs=32 kHz. These input data are The input digital signal is transmitted to the filter bank 104, by means of which the input data are input digital signal is divided into a plurality n of, herein five, frequency bands so that the bandwidths become that have bandwidths that are broader for towards higher frequencies. Thus the input digital data are signal is divided roughly into five channels, that is a channel CH1 with the frequency band of 0 to 1 kHz, a channel CH2 with the frequency band of 1 to 2 kHz, a channel CH3 with the frequency band of 2 to 4 kHz, a channel CH4 with the frequency band of 4 to 8 kHz and a channel CH5 with the frequency band of 8 to 16 kHz, as shown in FIG. 6. Such frequency division in which the bandwidth becomes broader for is broader towards higher frequencies is a frequency division technique taking human auditory characteristics into account, similarly similar to the so-called critical band. The critical band, which takes the human auditory characteristics into account, means the band occupied by a narrow band noise masking a pure tone or sound, wherein the noise has the same amplitude as and encompassing the level or encompasses the pitch of the pure tone or sound, wherein, the higher the frequency, the broader becomes the bandwidth of the critical band. For each of these five channels, blocks each consisting of a plurality of samples, samples of the input digital signal, that is a unit time block, are formed by the orthogonal transform circuits 105₁ to 105₅ and orthogonal transform, such as a fast Fourier transform, is performed for on each unit time block of each channel to produce coefficient data by as a result of the orthogonal transform, such as the FFT coefficient data for FFT. The coefficient data of the respective channels are transmitted to the bit allocation number decision circuit 106, where the bit allocation number data for the respective channels are formed determined and the coefficient data for the respective channels are quantized. The encoder output is outputted at an output terminal 102, while the bit allocation number data are outputted at an output terminal 103.

In this manner, by constituting the unit time blocks from channel data signals having broader bandwidths for higher frequencies, the number of samples in the unit time block becomes smaller for is smaller in the low frequency channels of narrower bandwidths, while becoming larger for bandwidths than in the high frequency channels or broader bandwidths. In other words, the frequency resolution becomes lower and higher for the low and high frequency regions, respectively. By performing orthogonal transformation of each of the time blocks of the respective channels, the coefficient data by resulting from the orthogonal transformation may be obtained at in each channel over the full frequency range at an equal interval on the frequency axis, so that the same high frequency resolution may be realized at both the high and low frequency sides high and low frequencies.

If the human auditory characteristics are considered, while the frequency resolution power needs to be high in the low frequency range, it at lower frequencies, but need not be so high in the high frequency range at higher frequencies. For this reason, with the present embodiments, the unit time block in on which the orthogonal transform is performed is composed of the same number of sample data for samples in each band or channel. In other words, the unit time block has different block lengths from one channel to another, in such a manner that the low range has frequency channels have a longer block length and the high range has frequency channels have a shorter block length. That is, the power of a high frequency resolution is maintained at a higher value for the lower frequency range while it is set lower frequencies while the frequency resolution is reduced so as not to be higher than is necessary for the higher frequency range at higher frequencies and the power of temporal resolution is set to be high for the higher frequency range at higher frequencies.

It is noted that, with the present embodiment, the blocks with the same number of samples are subjected to orthogonal transform for the orthogonal transform in channels CH1 to CH5, so that the same number of coefficient data, such as 6-point (pt) coefficient data may be obtained in the respective channels. In this case, the channel block length is 32 ms for channel CH1, 32 ms for channel CH2, 16 ms for channel CH3, 1 ms for channel CH4 and 4 ms for channel CH5. If the fast Fourier transform is performed by way of as the aforementioned orthogonal transform, the amount of processing is 64 log₂ 64 for channels CH1 and CH2, 64 log₂ 64×2 for channel CH3, 64 log₂ 64×4 for channel CH4 and 64 log₂ 64×8 for channel CH5, in the example of FIG. 6. In case of the fast Fourier transform for the full frequency range, the amount of processing is 1024 log₂ 1024=1024×10 for the sampling frequency fs=32 kHz and the coefficient data is 1024 pt for the block length equal to 32 ms.

With the above described construction of the present embodiment, a high power of frequency resolution may be obtained at the low frequency range lower frequencies which is critical for the human auditory sense, while the requirement for a the higher temporal resolution necessary with for transient signals rich in high frequency components as shown in FIG. 9 may also be satisfied. The filter bank, the orthogonal transform circuits or and the like may be those used conventionally so that the construction may be simplified and reduced in costs and the delay time in each circuit of the apparatus may be diminished.

FIG. 7 shows the concrete practical construction of the filter bank 104. In this figure, the 0 to 16 kHz input digital data signal with the sampling frequency fs=32 kHz is supplied to an input terminal 140 of the filter bank 104. These This input digital data are signal is first supplied to a filter QMF filter 141 where the 0 to 16 kHz input digital data are divided into 0 to 8 kHz output data and 8 to 16 kHz output data, of which the 8 to 16 kHz output data are supplied to a low range conversion circuit 145₅. The 8 to 16 kHz data undergo down-sampling in the low range conversion circuit 145₅ to generate 0 to 8 kHz data, which are outputted at output terminal 149₅. The 0 to 8 kHz output from QMF 141 is transmitted to a filter QMF 142, where it is similarly divided into a 4 to 9 kHz output transmitted to a low range conversion circuit 145₄ and a 0 to 4 kHz output transmitted to a QMF 143. The 0 to 4 kHz data signal, converted into the base band data, are a base band signal is obtained at the low range conversion circuit 145₄ so as to be outputted at output terminal 149₄. Similarly, a 0 to 2 kHz output and a 2 to 4 kHz output are produced at filter QMF filter 143, while a 0 to 1 kHz output and a 1 to 2 kHz output are produced at filter QMF filter 144, so as to be converted into low range signals in low range conversion circuits 145₃ to 145₁ before being outputted at output terminals 149₃ to 149₁. These outputs are transmitted via channels CH1 to CH5 to the orthogonal transform circuits 105₁ to 105₅, meanwhile, the 105₅. The low frequency conversion circuit 145₁ may be omitted if so desired.

FIG. 8 shows the construction of a decoder. In this figure, the above mentioned encoder output is supplied to an input terminal 122, while the above mentioned bit allocation number information is supplied to an input terminal 123. These data signals are supplied to a channel information generator 126 where the data of signal from the encoder output are restored into is dequantized to restore the coefficient data of the respective channels on the basis of the bit allocation number information. These restored coefficient data are transmitted to inverse orthogonal conversion circuits 125₁ to 125₅ where an inverse operation inverse to that in the orthogonal conversion circuits 105₁ to 105₅ is performed to produce data in which in which the coefficient data on the frequency axis is converted into samples of a signal on the time axis. The data of samples the respective channels on the time axis are decoded by a synthesis filter 124 before being outputted as the decoder output signal at output terminal 121.

In forming determining the bit allocation information for each channel in the bit allocation number decision circuit 106 of FIG. 5, the allowable signal noise level is set calculated and the masking effect is taken into consideration at this time so that the allowable noise level will be higher for the higher band frequency for the same energy value for determining the allocation bit number for each band. The masking effect means both the masking effect for signals on the time axis and that for signals on the frequency axis. That is, by such according to the masking effect, any noise in the masked signals, if any, may that is masked by a signal will not be heard. Hence, in the actual audio signals, any noises in the masked noise masked by signals on the frequency axis are allowable noises is allowable noise, so that, during quantization of the audio coefficient data, it becomes possible to diminish the number of the allocated bits corresponding to the allowable noise level.

In the above described second embodiment of the high efficiency encoder for digital data, an input digital signal, the input digital data are signal is divided into a plurality of bands so that the bandwidth will become broader for the higher frequency range, that have bandwidths that are broader towards higher frequencies, blocks each consisting of a plurality of samples are formed for each band and orthogonal transform is performed for each of the blocks so as to produce the coefficient data to realize encoding with a higher frequency resolution power. The orthogonal transform block consists of the same number of sample data for samples in each band, so that a high power of the high frequency resolution required for the lower frequency range frequencies may be realized, while the requirement for a high power of temporal resolution for transient signals rich in high frequency components may also be satisfied.

In this manner a highly efficient encoding consistent with the human auditory characteristics may be achieved. The construction for implementing the encoder of the present embodiment may be simple and inexpensive since the components may be those used conventionally.

A third embodiment of the present invention will be hereinafter explained by referring to FIG. 11 showing, as a typical example of high efficiency encoding, a high efficiency encoder in which the above mentioned adaptive transform coding is applied.

In FIG. 11, the input digital data are signal is transmitted via input terminal 201 to a block forming circuit 211 where they are it is formed into blocks at of a predetermined time interval duration before being transmitted to a fast Fourier transform (FFT) circuit 212. In this FFT circuit 212, the data in the form of unit time blocks unit time blocks of the input digital signal are converted into coefficient data on the frequency axis. Assuming that the FFT operation for 2048 samples is to be performed, the FFT coefficient data expressed by the phase angle of 1023 points and the amplitude point of 1025 points (or the imaginary number part of 1023 points and the real number part of 1025 points), may be found. These FFT coefficient data are transmitted to critical band separation circuits 213₁ to 213₂5 where they are divided into, for example 25 critical bands so as to be formed into blocks.

Since the band or block width of the critical bands becomes progressively broader for the higher frequency range, towards higher frequencies, the number of samples in one block becomes larger for the higher frequency range than for the lower frequency range coefficient data in each band is larger at higher frequencies than at lower frequencies. In such case, the efficiency of block floating for the higher frequency range, applied to the higher-frequency bands, which will be explained subsequently, becomes lower. is reduced.

Thus, with the present embodiment, an approximately equal number of samples of the coefficient data of in the respective bands are collected and arranged into a block form. That is, the numbers of coefficient data in the blocks are approximately equal. For example, sample N coefficient data (FFT coefficient data) are collected along the frequency axis into one block. Referring to the signal path downstream of the critical band separation circuit 213₁, samples N coefficient data (one block) are outputted from the critical band separating circuit 213₁. This block is transmitted to the normalization circuit 214₁, while also being transmitted to a floating coefficient computing circuit 217₁. In the computing circuit 217₁, the floating coefficient is computed and transmitted to the normalization circuit 214₁, where the floating operation for the block is performed with the use of the floating coefficient for normalization. The output of the normalization circuit 214₁ is transmitted to the quantization circuit 251₁ for quantizing the normalized block. The quantization is performed on the basis of the bit number information from a bit allocation number decision circuit 219 determining the number of the bits allocated to the respective critical bands. The output from the quantizer 215₁ is supplied to a synthesizer 216. The floating coefficient is quantized in a floating coefficient quantization (FC quantization) circuit 218₁, with a predetermined number of bits c for each block as a unit, before being transmitted to the synthesizer multiplexer 216. The quantization outputs from the block and the quantization output of the floating coefficient are synthesized in the synthesizer multiplexed in the multiplexer 216 so as to be outputted at an output terminal 202.

It is noted that, for maintaining the efficiency of the block floating operation at the higher frequency range higher frequencies and achieving effective bit allocation which takes human auditory characteristics into account, the FC quantization circuit is adapted to perform quantization with or a number of bits which is the lesser less the higher the frequency of the floating coefficient. That is, with the present high efficiency encoding apparatus, k blocks each consisting of N consecutive samples coefficient data are generated from each band for the high frequency range having at higher frequencies where the bands have a broader band width and a large number of samples, include a larger number of coefficient data, wherein k denotes a natural number which differs from one band to another. Taking an the output of the critical band separating circuit 213₂5 of the high frequency range as an example, the output of the critical band separating circuit 213₂5 is transmitted to k sub-band forming circuits 221₂5,1 to 221₂5,k from which the blocks are consisting of N consecutive samples coefficient data are generated. These blocks are processed by the normalization circuits 214₂5,1 to 214₂5,k, floating coefficient computing circuits 217₂5,1 to 217₂5,k, quantization circuits 215₂5,1 to 215₂5,k and by the FC quantization circuits 218₂5,1 to 218₂5,k, similar to those downstream of the critical band separating circuits 214₂5,1 to 214₂5,k before being transmitted to the synthesize 216.

At this time, in In the FC quantization circuits 218₂5,1 to 218₂5,k, the floating coefficients have been quantized on the block-by-block basis are quantized block-by-block with the number of bits r lesser which is less than the predetermined number of bits c at used by the FC quantization circuit 218, (c>r). Meanwhile, the The numbers of samples N of coefficient data N in the respective bands blocks are provided so as to be uniform to some extent.

As shown for example in FIG. 12, a predetermined number of bits r lesser r, which is less than the predetermined number of bits c for the lower range used in the lower frequency bands, such as band B₁, B₂, . . . among the critical bands B1 to B25, are is provided to k sub-bands sb₂5,1 1 to sb₂5,1 k in a higher range each of the k sub-bands sb₂5,1 to sb₂5,k in a higher frequency band such as band B25, and quantization is performed with the number of bits r. The predetermined numbers of the bits may for example be 6 for the bands B1 and B2 and 4 for band B25, that is, four bits for each of the sub-bands sb 25, 1 to sb 25₁ k, as shown in brackets sb₂5,1 to sb₂5,k, as shown in parentheses in the drawing. Although not shown, 6 bits, 5 bits and 4 bits may be provided to bands B1 to B5, B6 to B15 and bands B16 to B25, respectively. In determining the numbers of floating coefficient quantization bits, the number of the bits may be adjusted with the data taking the signal dispersion in the block taken into consideration. In this case, the numbers of allocation bits for the floating coefficients are decreased for the blocks with larger dispersion.

With the above described third embodiment, since the predetermined number of bits are provided to the sub-bands of the high frequency range higher-frequency sub-bands at the time of quantization of the floating coefficients, it does not occur that coefficients the numbers of the bits of the floating coefficients per sample one of the coefficient data in the frequency band in the high frequency range be higher frequency bands is not decreased drastically as compared to the numbers of the bits for the low frequency range, lower frequency bands, even in cases wherein the band or block width is enlarged for the high frequency range, at higher frequencies, such as in the above mentioned critical bands, so that it becomes possible to prevent the effect efficiency of the block floating in the high frequency range at higher frequencies from being lowered. On the other hand, the floating coefficients of the higher frequency range at higher frequencies are quantized with the smaller number of the bits, a smaller number of bits so that bits may be used more efficiently at the high frequency region where the larger number of the bits in higher frequencies where a larger number of bits is not required in view as a result of the human auditory characteristics.

Claims

1. A digital signal encoding method of the type in which an input digital signals are signal is divided into frequency components in 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 by spectral analyses properties of the frequency components of the frequency bands, with the period of the spectral analyses, having a 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, wherein the input digital signals have signal has a given sampling rate determined by a sampling rate clock signal, and, in the step of detecting the properties of the frequency components, the frequency of clock signals used in the spectral analysis analyses are derived from the sampling rate clock signal and are have frequencies selected to be lower for lower frequency bands.

3. A high efficiency digital data signal encoding method, comprising the steps of:

dividing an input digital data signal into a plurality of bands so that the having progressive broader 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, signal, for each band; and

performing an orthogonal transformation of each block of the bands to generate coefficient data.

4. The method according to claim 3, wherein the block in which the orthogonal transformation is performed is composed of the same numbers of number the samples data for of the divided input signal in the respective bands.

5. A high efficiency encoding method of the type in which an input digital data are signal is converted into data on the a frequency axis to produce data divided according to predetermined frequency bands, the data of the respective frequency bands are formed into blocks by selecting the band-widths of the blocks to be broader for the high frequency ranges at higher frequencies to compute the floating coefficients for the respective blocks, a floating operation for on the respective blocks is performed with using the floating coefficients, and the floating coefficients are quantized, wherein the improvement resides in that:

in the step of forming the data of in the respective frequency bands into blocks, the number of the data in each block are is 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 progressively fewer bits are progressively smaller for allocated to the floating coefficients of the higher frequency ranges. the frequency bands at higher frequencies.

6. A digital signal encoding apparatus of the type including means for dividing an input digital signals signal into frequency components in a plurality of frequency bands which are so set that the frequency bands with higher frequencies will have broader bandwidths, 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 having a 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, wherein the input digital signals have a given sampling rate determined by a sampling rate clock signal, and the means for detecting includes means for deriving, clock signals from the sampling rate clock signal and the frequency of these clock signals for use in the spectral analyses, the clock signals used in the spectral analysis are having frequencies selected to be lower for lower frequency bands.

8. A high efficiency digital data signal encoding apparatus, comprising:

means for dividing an input digital data signal into a plurality of bands so that the having progressive broader 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, signal, for each band; and

means for performing an orthogonal transformation of each block of the bands to generate coefficient data.

9. The apparatus according to claim 8, wherein the block in which the orthogonal transformation is performed is composed of the same numbers number of the sample data for samples of the divided input digital signal in the respective bands.

10. A high efficiency encoding apparatus of the type which includes means for converting an input digital data signal into data on the a frequency axis to produce data divided according to predetermined frequency bands, means for forming the data of in the respective frequency bands into blocks by selecting the bandwidths of the blocks to be broader for the high frequency ranges at higher frequencies to compute the floating coefficients for the respective blocks, means for performing a floating operation for on the respective blocks with using the floating coefficients, and means for quantizing the floating coefficients, wherein the improvement comprises: resides in that:

that the means for forming the data of in 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 progressively fewer bits are progressively smaller for allocated to the floating coefficients of the higher frequency ranges. frequency bands at higher frequencies.

11. A digital signal encoding method of the type in which an input digital signals are signal is divided into frequency components in 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 in the frequency bands, with the time duration of this detection of the properties of the frequency components being having a time duration 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, and wherein the frequency of clock signals used in the spectral analysis step is have frequencies selected to be lower for the clock signals for lower the frequency bands with lower frequencies; 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 an input digital signals signal into frequency components a plurality of frequency bands which are so set that the frequency bands with higher frequencies will have broader bandwidths, 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 in the frequency bands, with the time duration of this detection of the frequency components being having a time duration 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, and wherein the frequency of clock signals used in the spectral analysis means is have frequencies selected to be lower for the clock signals for lower the frequency bands with lower frequencies; and

means for controlling the synthesizing and encoding as a function of the detection output signal.

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.

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. 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. 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. 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. 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. 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. 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.

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.

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. 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. 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. 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. 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.