JP2002366178A - Method and device for band expansion of audio signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device which can improve the reproduced sound of an audio signal and the reproduced sound of a compressed audio signal, specially and reproduce sound quality of a high pitch range, and expand an audio signal comfortable to the human ears, and expands the band of the audio signal. SOLUTION: A digital signal processing circuit interposed between an input terminal T1 and an output terminal T2 comprises a maximum frequency detecting circuit 1, an adder 2, a spectrum analyzing circuit 3, and a multiplier 11. An expanded signal generating circuit 5 is equipped with a nonlinear processing circuit 21, a high-pass filter 22, a dither signal generating circuit 23, a high-pass filter 24, an adder 25, and a 1/f characteristic filter 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to improve the reproduction sound of an audio signal in an audio device and the reproduction sound of a compressed audio signal, particularly the reproduction sound quality of a high sound range, and reproduce a comfortable audio signal for human ears. The present invention relates to a method and apparatus for extending the bandwidth of a possible audio signal, and more particularly to a method and apparatus for extending the bandwidth of an input audio signal by digitally processing the input audio signal.

[0002]

2. Description of the Related Art For analog audio reproduction signals,
As a prior art audio signal reproducing device for adding a signal having a spectrum whose frequency exceeds the upper limit of the reproduction frequency band or the upper limit of the audible frequency band,
It is disclosed in Japanese Patent Publication No. 1997-36585. FIG. 1 shows the configuration of the audio signal reproducing apparatus.
6 is shown. 16, the audio signal reproducing apparatus includes a buffer amplifier 91, a filter circuit 92, an amplifier 93, a detection circuit 94, a time constant circuit 95, a noise generator 96, a filter circuit 97, a multiplier 98, , And an adder 99.

First, an audio signal is input from an input terminal T1 to a buffer amplifier 91 and then divided into two, and one of the divided audio signals is directly input to an adder 99. The other audio signal divided into two is a filter circuit 9 which is a high-pass filter or a band-pass filter.
2 is input. The filter circuit 92 band-filters and passes only a signal of a specific band in the input audio signal, and then outputs the signal to the amplifier 93. Amplifier 93
Amplifies the input audio signal to a predetermined appropriate level, and outputs the amplified signal to a detection circuit 94 having a time constant circuit 95. The detection circuit 94 detects an envelope level of the input audio signal by performing, for example, envelope detection on the audio signal, and adds a level signal indicating the detected envelope level to the original audio signal. Is output to the multiplier 98 as a level control signal for adjusting the level of.

On the other hand, a noise component generated by a noise generator 96 is input to a filter circuit 97 which is a high-pass filter or a band-pass filter, and
7 passes a noise component in a frequency band of 20 kHz or more and outputs the same to the multiplier 98. The multiplier 98 multiplies the input noise component by the level control signal from the detection circuit 94 to generate a noise component having a level proportional to the level indicated by the level control signal, and outputs the noise component to the adder 99. .

Further, the adder 99 includes a buffer amplifier 9
The noise component from the multiplier 98 is added to the original audio signal from 1 to generate an audio signal to which the noise component has been added and output from the output terminal T2. Here, by selecting the time constant of the time constant circuit 95 to a predetermined value, the noise component generated by the noise generator 96 is adapted to human audibility characteristics, and the sound quality improvement effect of the audio signal is enhanced.

[0006]

As described above,
The high frequency range is expanded by adding random noise proportional to the output level of the high frequency range of the original audio signal to the original audio signal. However, the above-described conventional audio signal reproducing apparatus has the following problems. (1) Since the spectral structure of the high frequency signal of the noise component to be added is different from that of the tone signal, there was a sense of incongruity in sound quality. (2) Further, since the conventional audio signal reproducing apparatus is constituted by an analog circuit, there are the following problems. That is, variations in device performance occur due to variations in components constituting the analog circuit and temperature characteristics, and sound quality degradation occurs each time an audio signal passes through the analog circuit. In addition, if the accuracy of the filter circuit is improved, the circuit scale is increased, which leads to an increase in manufacturing cost. (3) Further, even when a signal having a single spectrum such as a sine wave is input, a random noise component is added, so that the measurement of the signal characteristics results in a significantly deteriorated signal characteristic.

An object of the present invention is to solve the above problems,
It is an object of the present invention to provide a method and an apparatus for extending a band of an audio signal, which have no sound quality discomfort or deterioration, hardly causes a variation in device performance, and has a low manufacturing cost as compared with the related art. .

Another object of the present invention is to solve the above-mentioned problems, and to provide a method of extending the band of an audio signal in which a signal deterioration measurement result does not occur in the measurement of signal characteristics even when a sine wave signal is input. It is intended to provide a device.

[0009]

According to a first aspect of the present invention, a spectrum intensity of a predetermined band of a digital audio signal of a first band having a predetermined highest frequency is calculated, and the calculated spectrum intensity is calculated. Outputting a signal indicating the intensity; and generating an extension signal having a frequency component of a second band higher than the first band.
Controlling the level of the extension signal according to the signal indicating the calculated spectrum intensity; detecting the highest frequency with respect to the digital audio signal of the first band; And adding the extension signal whose level has been controlled to the digital audio signal of the first band, and outputting a digital audio signal as a result of the addition. is there.

According to a second aspect of the present invention, in the audio signal band extending method according to the first aspect, the step of detecting the highest frequency obtains information on the highest frequency of the digital audio signal of the first band. Steps and
Controlling the step of generating the extension signal in consideration of auditory characteristics from the information of the highest frequency.

According to a third aspect of the present invention, in the audio signal band extending method according to the first aspect, the step of detecting the highest frequency obtains information on the highest frequency of the digital audio signal of the first band. Steps and
Controlling the level of the extension signal in consideration of the auditory characteristics from the information of the highest frequency.

According to a fourth aspect of the present invention, in the method of the first aspect, the step of detecting the highest frequency obtains information on the highest frequency of the digital audio signal of the first band. Steps and
Controlling the step of outputting the signal indicating the calculated spectrum intensity in consideration of the auditory characteristics from the information of the highest frequency.

According to a fifth aspect of the present invention, in the audio signal band extending method according to the first aspect, the step of detecting the highest frequency obtains information on the highest frequency of the digital audio signal of the first band. Steps and
Two to three of the steps of generating the extension signal, controlling the level of the extension signal, and outputting the signal indicating the calculated spectrum intensity
And controlling the two steps in consideration of the auditory characteristics from the information of the highest frequency.

According to a sixth aspect of the present invention, in the audio signal band extending method according to the first aspect, the step of detecting the highest frequency includes the step of detecting information of the highest frequency of the digital audio signal of the first band by a predetermined frequency. , The step of generating the extension signal, the step of controlling the level of the extension signal, and the step of outputting the signal indicating the calculated spectrum intensity. And controlling the three steps in a predetermined cycle from the information of the highest frequency in consideration of the auditory characteristics.

According to a seventh aspect of the present invention, in the band expansion method for an audio signal according to any one of the second to sixth aspects, the step of obtaining the information of the highest frequency comprises the step of obtaining the digital audio of the first band. The method includes a step of obtaining information on the highest frequency from the specification information (header information) of the signal.

According to an eighth aspect of the present invention, in the band expansion method for an audio signal according to any one of the second to sixth aspects, the step of obtaining the highest frequency information includes the step of obtaining the digital audio signal of the first band. And analyzing the frequency spectrum to obtain information on the highest frequency.

The invention of claim 9 of the present application is directed to claims 1, 2,
In the method of any one of claims 5, 6, 7, and 8, the step of generating the extension signal has a non-linear input / output characteristic, and is adapted for the digital audio signal of the first band. Generating a digital signal of a harmonic component of the digital audio signal by performing nonlinear processing by performing a nonlinear process to generate a digital signal of a harmonic component of the digital audio signal; High-pass filtering a frequency component corresponding to the auditory characteristic from the information of the highest frequency of the audio signal, and outputting the filtered signal as an extension signal.

The invention of claim 10 of the present application relates to claim 1,
In the band extending method for an audio signal according to any one of 2, 5, 6, 7, and 8, the step of generating the extended signal includes the step of generating a dither signal having a predetermined probability distribution with respect to an amplitude level. Filtering the frequency components corresponding to the auditory characteristics from the highest frequency information of the digital audio signal of the first band in the dither signal, and outputting the filtered signal as an extension signal; It is characterized by including.

The invention of claim 11 of the present application is directed to claim 1,
2. The method of expanding a band of an audio signal according to any one of 2, 5, 6, 7, and 8, wherein the step of generating the expanded signal has a non-linear input / output characteristic and the digital audio signal of the first band. By performing nonlinear processing on the digital audio signal to distort the digital audio signal,
Generating a digital signal of a harmonic component of the digital audio signal; and estimating a frequency component corresponding to a hearing characteristic from information of a highest frequency of the digital audio signal of the first band among the digital signals of the harmonic component. Performing a band-pass filtering and outputting the filtered signal as an extension signal; generating a dither signal having a predetermined probability distribution with respect to an amplitude level; Filtering the frequency component corresponding to the auditory characteristic from the information of the highest frequency of the digital audio signal, and outputting the filtered signal; and adding the two high-pass filtered signals. And outputting a signal of the addition result as an extension signal.

The invention of claim 12 of the present application is directed to claim 1,
In the audio signal band extension method according to any one of 9, 10, and 11, before the step of controlling the level, one of the predetermined 1 / f characteristics and 1 / f ² characteristics is filtered. And low-pass filtering the extension signal.

The invention of claim 13 of the present application is directed to claim 10,
In the audio signal band extending method according to any one of items 11 and 12, the step of generating the dither signal includes:
By adding a plurality of steps for generating pseudo-noise sequence noise signals independent of each other and the plurality of pseudo-noise sequence noise signals, one of a Gaussian distribution and a bell-shaped distribution is obtained for the amplitude level. Generating a dither signal as a result of addition having a probability density and outputting it as an extension signal.

The invention of claim 14 of the present application is directed to claims 1 to 1
3. In the band expanding method for an audio signal according to any one of the items 3, the spectrum intensities of a plurality of predetermined bands in the digital audio signal in the first band are calculated, and the spectrum intensities of the calculated bands are calculated based on the calculated spectrum intensities. Determining whether or not the digital audio signal has a single spectrum, and if the digital audio signal is determined not to have a single spectrum, outputting the extended signal while outputting the digital audio signal. Switching the signal so as not to output the extended signal when it is determined that the signal has a single spectrum.

According to a fifteenth aspect of the present invention, a spectrum intensity of a predetermined band of a digital audio signal of a first band having a predetermined highest frequency is calculated, and a signal indicating the calculated spectrum intensity is output. First spectrum analysis means for performing the operation, an extension signal generation means for generating an extension signal having a frequency component of a second band higher than the first band, and a calculation output from the first spectrum analysis means Level control means for controlling the level of the extension signal according to the signal indicating the spectrum intensity,
A maximum frequency detecting means for detecting the highest frequency with respect to the digital audio signal of the first band and controlling each section according to the highest frequency; and an extension signal controlled by the level control means, First adding means for adding a digital audio signal to the digital audio signal and outputting a digital audio signal as a result of the addition.

According to a sixteenth aspect of the present invention, in the audio signal band extending apparatus of the fifteenth aspect, the maximum frequency detecting means obtains information on a maximum frequency of the digital audio signal of the first band. An acquisition means and a control means for controlling the extension signal generating means in consideration of the auditory characteristics from the information of the highest frequency.

According to a seventeenth aspect of the present invention, in the audio signal band extending apparatus of the fifteenth aspect, the maximum frequency detecting means obtains information on a maximum frequency of the digital audio signal of the first band. And a control means for controlling the level control means in consideration of auditory characteristics from the information of the highest frequency.

According to an eighteenth aspect of the present invention, in the audio signal band extending apparatus according to the fifteenth aspect, the highest frequency detecting means obtains information on the highest frequency of the digital audio signal of the first band. An acquisition means, and a control means for controlling the first spectrum analysis means in consideration of auditory characteristics from the information on the highest frequency.

According to a nineteenth aspect of the present invention, in the audio signal band extending apparatus according to the fifteenth aspect, the maximum frequency detecting means obtains information on a maximum frequency of the digital audio signal of the first band. Obtaining means, the extended signal generating means, the level control means,
Control means for controlling two or three of the first spectrum analysis means from the information of the highest frequency in consideration of auditory characteristics.

According to a twentieth aspect of the present invention, in the audio signal band extending apparatus of the fifteenth aspect, the maximum frequency detecting means transmits information of a maximum frequency of the digital audio signal of the first band to a predetermined period. , The extended signal generating means, the level control means, and one of the first spectrum analyzing means.
Control means for controlling one to two or three means in a predetermined cycle from the information of the highest frequency in consideration of the auditory characteristics.

The invention of claim 21 of the present application is directed to claims 16 to
20. In the audio signal band extending apparatus according to any one of the above items 20, the frequency information obtaining means obtains information of a highest frequency from signal specification information (header information) of the digital audio signal of the first band. It is characterized by having means for performing.

The invention of claim 22 of the present application is directed to claims 16 to
21. The audio signal band extending apparatus according to any one of the items 20, wherein the frequency information obtaining means includes means for analyzing a frequency spectrum of the digital audio signal of the first band to obtain information of a highest frequency. It is characterized by the following.

The invention according to claim 23 of the present application is based on claim 15,
16. The audio signal band extending apparatus according to any one of 16, 19, 20, 21, and 22, wherein the extended signal generating means has a non-linear input / output characteristic, and is adapted for the digital audio signal of the first band. By performing nonlinear processing to distort the digital audio signal,
Non-linear processing means for generating a digital signal of a harmonic component of the digital audio signal; and information on the highest frequency of the digital audio signal of the first band among the digital signals of the harmonic component output from the non-linear processing means. A first high-pass filter that performs high-pass filtering of a frequency component corresponding to an auditory characteristic and outputs the filtered signal as an extension signal.

The invention of claim 24 of the present application is directed to claim 15,
16. The audio signal band extending apparatus according to any one of 16, 19, 20, 21, and 22, wherein the extended signal generating means generates a dither signal having a predetermined probability distribution with respect to an amplitude level. A high-pass filtering of a frequency component corresponding to an auditory characteristic from information of a highest frequency of the digital audio signal of the first band in the dither signal, and outputting the filtered signal as an extension signal. 2 high-pass filters.

The invention of claim 25 of the present application is directed to claim 15,
16. The audio signal band extending apparatus according to any one of 16, 19, 20, 21, and 22, wherein the extended signal generating means has a non-linear input / output characteristic, and is adapted for the digital audio signal of the first band. By performing nonlinear processing to distort the digital audio signal,
Non-linear processing means for generating a digital signal of a harmonic component of the digital audio signal; and information on the highest frequency of the digital audio signal of the first band among the digital signals of the harmonic component output from the non-linear processing means. A first high-pass filter for high-pass filtering a frequency component corresponding to an auditory characteristic and outputting a filtered signal, and a dither for generating a dither signal having a predetermined probability distribution with respect to an amplitude level A signal generating means for performing high-pass filtering of a frequency component corresponding to an auditory characteristic from information on a highest frequency of the digital audio signal of the first band in the dither signal, and outputting a filtered signal; 2 high-pass filter, a signal output from the first high-pass filter, and a signal output from the second high-pass filter are added. It is characterized in that a second adding means for outputting a signal of addition result as an extension signal.

According to a twenty-sixth aspect of the present invention, in the audio signal band extending device according to the fifteenth or twenty- ^{third aspect,} the audio signal band extending device has one of a predetermined 1 / f characteristic and a 1 / f ² characteristic, A low-pass filter for low-pass filtering the extended signal and outputting the low-pass filtered signal to the level control means.

According to a twenty-seventh aspect of the present invention, in the audio signal band extending device according to the twenty-fourth or twenty-fifth aspect, the audio signal band extending device has one of a predetermined 1 / f characteristic and a 1 / f ² characteristic. A low-pass filter for low-pass filtering the extended signal and outputting the low-pass filtered signal to the level control means.

The invention of claim 28 of the present application relates to claim 24,
28. The audio signal band extending apparatus according to any one of 25 and 27, wherein the dither signal generating means includes a plurality of noise signal generating circuits each generating a pseudo noise sequence noise signal independent of each other; By adding a plurality of pseudo-noise sequence noise signals generated in the past, a dither signal of an addition result having a probability density of one of a Gaussian distribution and a bell-shaped distribution with respect to the amplitude level is generated. And a third adding means for outputting the signal as an extension signal.

The invention of claim 29 of the present application is directed to claims 15 to
28. The audio signal band extending apparatus according to any one of 28, wherein the spectrum intensities of a plurality of predetermined bands in the digital audio signal of the first band are calculated,
Second spectrum analysis means for determining whether or not the digital audio signal has a single spectrum based on the calculated spectrum intensities of the plurality of bands;
When it is determined by the spectrum analysis means that the digital audio signal is not a single spectrum,
A switch for outputting the extended signal to the first adding means and, when it is determined that the digital audio signal has a single spectrum, not to output the extended signal to the first adding means; Means are further provided.

[0038]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a block diagram showing a configuration of an audio signal band extending apparatus according to a first preferred embodiment of the present invention. The audio signal band extending apparatus according to the first preferred embodiment is a digital signal processing circuit inserted between an input terminal T1 and an output terminal T2, and includes a maximum frequency detection circuit 1, an adder 2, , A spectrum analysis circuit 3, a level control circuit 4, an extension signal generation circuit 5, and a multiplier 11. The highest frequency detection circuit 1 includes a frequency information analyzer 12 and a control circuit 13. The spectrum analysis circuit 3
For example, as shown in FIG. 2, it is configured to include an FFT circuit 27, a data selection circuit 28, and a weighting addition circuit 29. The extension signal generating circuit 5 includes a nonlinear processing circuit 21, a high-pass filter 22, a dither signal generating circuit 23, a high-pass filter 24, an adder 25,
An f-characteristic filter 26 is provided.

In FIG. 1, a digital audio signal is input via an input terminal T1. This digital audio signal is, for example, a signal reproduced from a compact disk (CD) or an MP3 (MPEG2-layer).
3) It is a compressed signal. At this time, the signal has a sampling frequency fs = 44.1 kHz and a word length = 16.
This is a signal having bits. The input digital audio signal is divided into a maximum frequency detection circuit 1 and a spectrum analysis circuit 3
And input to the nonlinear processing circuit 21 of the extension signal generation circuit 5.

The nonlinear processing circuit 21 has nonlinear input / output characteristics, and performs nonlinear processing on an input digital audio signal to distort the digital audio signal to generate a harmonic component. The digital audio signal having the component is output to the digital high-pass filter 22. The nonlinear processing circuit 21 includes, for example, an absolute value calculation circuit 31 and a DC offset removal circuit 32 as shown in FIG. Here, the DC offset removing circuit 32 includes a subtractor 33, an averaging circuit 34, and a 乗 算 multiplier 35.

The absolute value calculation circuit 31 performs a nonlinear process such as a full-wave rectification process on the input digital audio signal, and then applies the digital audio signal after the nonlinear process to the subtractor of the DC offset removal circuit 32. 33 and an averaging circuit 34. Absolute value calculation circuit 3
1 outputs a signal having a positive amplitude as it is,
A signal having a negative amplitude is converted into a positive amplitude having the same absolute value as the negative amplitude and output. Therefore, a harmonic component is generated when a signal having a negative amplitude is turned back to the positive side with a zero level as a boundary. Next, the averaging circuit 34
Is configured to include a low-pass filter having a cutoff frequency that is very low as compared with the sampling frequency fs, for example, about 0.0001 fs, and has a predetermined time period (for example, sufficiently longer than the sampling period Ts). A time average of the amplitude of the input digital audio signal is calculated for the time period), and a digital signal having the time average is output to the 乗 算 multiplier 35. And
The 乗 算 multiplier 35 multiplies the input digital signal by １ ／ and outputs a digital signal having a value of the multiplication result to the subtracter 33 as a digital signal indicating a DC offset amount. Further, the subtracter 33 removes the DC offset by subtracting the digital signal output from the 乗 算 multiplier 35 from the digital audio signal output from the absolute value calculation circuit 31.

Here, the digital signal input through the input terminal T1 is a signal based on zero level,
Although the output digital signal from each circuit in FIG. 1 and the digital signal from the output terminal T2 also need to be based on zero level, the input digital signal to the nonlinear processing circuit 21 is a signal based on zero level. However, since the absolute value is converted to a positive level by the absolute value calculation circuit 31 for performing the nonlinear processing, a DC offset occurs. Therefore, an average value is calculated by the averaging circuit 34 with respect to the output digital signal from the absolute value calculation circuit 31, and half of the average value is subtracted from the output digital signal from the absolute value calculation circuit 31. Removes the DC offset.

Then, the digital signal including the harmonic component generated by the nonlinear processing circuit 21 with reference to the level of the input digital audio signal is input to the digital high-pass filter 22, as shown in FIG. The digital high-pass filter 22 high-pass filters only high-frequency components determined from the highest frequency of the input digital audio signal in consideration of the audibility characteristics, and performs adder 25.
Output to Detection of the highest frequency and determination of the high-pass band will be described later.

The dither signal generating circuit 23 shown in FIG. 1 has a frequency band of 0 to fs / 2 and generates a digital audio signal having a random amplitude level with respect to the time axis. It generates a dither signal generated uncorrelated with the digital audio signal input via the digital audio signal, and outputs it to the digital high-pass filter 24. Next, the digital high-pass filter 24 high-pass filters only the high-frequency components determined in consideration of the perceptual characteristics from the highest frequency of the input digital audio signal from the input dither signal, and outputs the high-frequency components to the adder 25. Output. As described above, the detection of the highest frequency and the determination of the high-pass band will be described later.

Specifically, the dither signal generation circuit 23
For example, it is configured as shown in FIG. 4, the dither signal generation circuit 23 includes a plurality of N pseudo noise sequence noise signal generation circuits (hereinafter referred to as PN sequence noise signal generation circuits) 40-n (n = 1, 2,..., N); Adder 4
1, a DC offset removal constant signal generator 43, and a subtractor 44. Here, each PN-sequence noise signal generation circuit 40-n generates a pseudo-noise signal having a uniform random amplitude level, which is an M-sequence noise signal, having an initial value independent of each other, for example. 4
Output to 1. Next, the adder 41 adds a plurality of N pseudo noise signals output from the plurality of PN sequence noise signal generation circuits 40-1 to 40-N, and outputs a pseudo noise signal resulting from the addition to the subtractor 44. . On the other hand, the DC offset removal constant signal generator 43 outputs a DC offset removal constant signal that is the sum of the time average values of the pseudo noise signals from the plurality of N PN sequence noise signal generation circuits 40-1 to 40-N. It is generated and output to the subtractor 44. Then, the subtracter 44 generates and outputs a dither signal having no DC offset by subtracting the DC offset removing constant signal from the sum of the pseudo noise signals.

Here, each PN sequence noise signal generating circuit 4
0-n (n = 1, 2,..., N) is 3 as shown in FIG.
2-bit shift register 51 and exclusive OR gate 5
2, a clock signal generator 53, and an initial value data generator 54. In the 32-bit shift register 51, different initial values are set from the initial value data generator 54 for each of the PN sequence noise signal generating circuits 40-n, and then based on the clock signal generated by the clock signal generator 53. And the 32-bit shift register 51
Counts one bit at a time so as to shift data from the least significant bit (LSB) to the most significant bit (MSB). 32
32-bit data (0 to 0) of the bit shift register 51
Includes 31st bit data. ), One-bit data of the most significant bit (MSB; 31st bit) and its 3 bits
The 1-bit data of the bit is the exclusive OR gate 5
The exclusive OR gate 52 inputs the 1-bit data of the result of the exclusive OR operation based on the clock signal from the clock signal generator 53 to the least significant bit (32-bit shift register 51) of the 32-bit shift register 51. LSB). The lower 8 bits of the 32-bit shift register 51
The bit data is output as a PN sequence noise signal. By configuring the PN sequence noise signal generation circuit 40-n in this manner, each PN sequence noise signal generation circuit 4
The PN sequence noise signals output from 0-n become 8-bit PN sequence noise signals independent of each other.

In the example of FIG. 5, each PN sequence noise signal generation circuit 40-n is configured as described above in order to generate 8-bit PN sequence noise signals independent of each other. However, the present invention is not limited to this and may be configured as follows. (1) PN taken out of 32-bit shift register 51
The bit positions of the 8 bits of the series noise signal are made different from each other. That is, the PN sequence noise signal generation circuit 40-1
Extracts a PN sequence noise signal of 8 bits from the least significant 8 bits, a PN sequence noise signal generation circuit 40-2 extracts a PN sequence noise signal from 8 bits immediately above the least significant 8 bits, and so on. Take out the signal. (2) Instead of this, the bit position of the 32-bit shift register 51 for extracting 1-bit data to be input to the exclusive OR gate 52 is set to each PN sequence noise signal generation circuit 4
Different from each other at 0-n. (3) Or the example of FIG. 5 and the modification of the above (1),
At least two of the modifications of the above (2) are combined.

Then, by adding a plurality of PN sequence noises independent of each other, a PN sequence noise signal having a probability density with respect to the amplitude level is generated as shown in FIG. 6, FIG. 7, and FIG. Can be. For example, when n = 1, a white noise signal having a probability density of a uniform distribution with respect to the amplitude level can be generated as shown in FIG. When n = 12, if the central limit theorem is used, each PN sequence from the PN sequence noise signal generation circuit 40-n that generates 12 uniform random numbers because the Gaussian distribution has a variance of 1/12. By adding the noise signals, a Gaussian noise signal having a Gaussian probability density with respect to the amplitude level can be generally generated as shown in FIG. Further, when n = 3, as shown in FIG. 7, a Bell distribution having a probability distribution of a bell-shaped distribution or a bell-shaped distribution with respect to the amplitude level, which is close to the Gaussian distribution and slightly larger than the Gaussian distribution. Type (bell-shaped) noise signal can be generated. As described above, the circuits of FIGS. 4 and 5 are configured to generate, for example, the noise signal of FIG.
With a small-scale circuit, a dither signal close to a natural sound or musical sound signal can be generated.

Returning to FIG. 1, the adder 25 of the extension signal generating circuit 5 includes the digital signal of the band-limited harmonic component from the high-pass filter 22 and the band-limited digital signal from the high-pass filter 24. And the resulting digital signal is added to a 1 / f characteristic filter 2.
6 to the multiplier 11 of the level control circuit 4.
Here, as shown in FIG. 9, the 1 / f characteristic filter 26 is higher than the band B1 from the frequency 0 to fs / 6.
In the band B2 from the frequency fs / 6 to fs / 2,
This is a so-called 1 / f characteristic low-pass filter having an attenuation characteristic having a slope of 6 dB / oct.

The insertion position of the 1 / f characteristic filter 26 is not limited to the embodiment shown in FIG.
6 may be inserted between the high-pass filter 22 and the adder 25 as well as between the high-pass filter 22 and the adder 25. Also, the 1 / f characteristic filter 26
May be inserted only between the high-pass filter 22 and the adder 25, or may be inserted only between the high-pass filter 24 and the adder 25. Further, instead of the 1 / f characteristic filter 26, a 1 / f ² characteristic filter having the attenuation characteristic of FIG. 10 may be provided. Here, as shown in FIG. 10, the 1 / f ² characteristic filter has a frequency fs / 6 to fs / 2 higher than a band B1 from frequency 0 to fs / 6.
This is a low-pass filter having a so-called 1 / f ² characteristic having an attenuation characteristic having a slope of −12 dB / oct in a band B2 up to the band B2.

On the other hand, the spectrum analysis circuit 3 calculates the spectrum intensity of a predetermined band determined from the highest frequency of the digital audio signal input to the input terminal T1 in consideration of the perceptual characteristics, and calculates the calculated spectrum intensity. The output signal is output to the multiplier 11 of the level control circuit 4. FIG.
The FFT circuit 27 of the spectrum analysis circuit 3 shown in FIG.
By performing a fast Fourier transform process on the input digital audio signal using the T operation method, for example, if the frequency resolution number is 1024, 204
Based on the data for each 8Ts, a total of 1024 spectral intensities for each frequency fs / 1024 are calculated and output to the data selection circuit 28. Next, the data selection circuit 28
, Based on the input spectrum intensity for each frequency fs / 1024, for example, selectively extracts the data of the spectrum intensity corresponding to the band of the frequency fs / 10 to fs / 2 and outputs the data to the weighting addition circuit 29. Further, the weighting addition circuit 29 applies a predetermined weighting coefficient to the extracted spectral intensity data from the highest frequency of the digital audio signal input to the input terminal T1 for each data in consideration of the audibility characteristics. To calculate the spectrum intensity of the band of the frequency fs / 10 to fs / 2 of the input digital audio signal, and output the signal indicating the spectrum intensity of the operation result to the multiplier 11 of the level control circuit 4. Output to Highest frequency detection,
The determination of the band for calculating the spectrum intensity and the weighting coefficient will be described later.

Then, based on the signal indicating the spectrum intensity from the spectrum analysis circuit 3, the level control circuit 4 uses the sum signal of the band-limited harmonic component signal and the dither signal from the 1 / f characteristic filter 26. Controls the signal level of an extension signal. Here, the level control circuit 4
As shown in FIG. 1, the multiplication unit 11 is configured by a multiplier 11, multiplies the extension signal from the extension signal generation circuit 5 by a predetermined coefficient, and outputs a signal of the multiplication result to the adder 2. This coefficient is determined from the highest frequency of the digital audio signal input to the input terminal T1 together with the signal indicating the spectrum intensity in consideration of the audibility characteristics. That is, the level control circuit 4 determines the frequency fs / 10 of the input digital audio signal.
When the spectrum intensity at fs / 2 is large, 1 /
It operates so as to increase the signal level from the f-characteristic filter 26. When the spectrum intensity of the input digital audio signal at frequencies fs / 10 to fs / 2 is small, the signal level from the 1 / f-characteristic filter 26 is reduced. To work. Highest frequency detection, multiplier 1
The determination of the coefficient relating to 1 will be described later.

Further, the adder 2 adds the digital audio signal input via the input terminal T1 and the sum signal of the digital signal of the harmonic component and the dither signal from the level control circuit 4, and outputs the added signal to the output terminal T2. Output via.

On the other hand, the frequency information analyzer 12 of the highest frequency detection circuit 1 extracts the highest frequency information from the specification information (header information) of the signal included in the digital audio signal input via the input terminal T1. . The header information includes, for example, the sampling frequency, the number of channels of the digital audio signal, the number of bit rates, etc., in addition to the maximum reproduction frequency of the digital audio signal. It is paired with a musical tone digital signal. Further, as means for detecting the highest frequency information of the digital audio signal input via the input terminal T1, a configuration in which the digital audio signal is converted into a frequency domain by using an FFT circuit to obtain the highest frequency from the magnitude of the spectrum intensity. It may be. Next, the control circuit 13
Are based on the highest frequency information obtained by the frequency information analyzer 12, the bands of a plurality of digital high-pass filters 22 and 24 prepared in advance in consideration of the auditory characteristics, and the bands selected by the data selection circuit 28. , And a control signal for determining an optimum value from the weighting coefficient of the weighting addition circuit 29 and the coefficient value of the multiplier 11,
The signal is transmitted to the extension signal generation circuit 5 and the level control circuit 4.

Here, FIG. 11 shows a perceptual curve of a free-field plane wave according to Robinson-Daddson as a typical auditory sense characteristic (cited document: Auditory and Psychoacoustic Corona). The numerical value attached to the curve is the level of the loudness of the sound, 1 kHz.
A value equal to the sound pressure level of the pure tone is written, and all points on each curve sound the same regardless of the frequency of the pure tone. MAF is the minimum audible limit. Based on this, the spectrum intensity of the input digital audio signal and the spectrum intensity of the band to be extended are balanced. Specifically, when the highest frequency of the input digital audio signal is 12 kHz and the band for calculating the spectrum intensity is around 6 kHz, the spectrum intensity for expanding the band of 12 kHz or more is determined by the input digital audio signal. 3-5d than spectral intensity
It would be good if it was about B lower.

As described above, according to the first preferred embodiment of the present invention, the digital audio signal has the same spectral structure as that of the tone signal in the frequency band or more that the input digital audio signal has (that is, the dither signal). The generation frequency is approximately Gaussian distribution or bell distribution, which has a generation mechanism similar to that of natural sound.) Generates harmonic components and dither signals, and generates them according to the high-frequency spectrum intensity of the input digital audio signal. By adding the digital signal of the higher harmonic component and the dither signal to the input digital audio signal, it is possible to easily generate a digital audio signal having an extended audio band in proportion to the prior art.

Also, since the maximum frequency of the input digital audio signal can be detected and the band can be expanded in consideration of the audibility characteristics, it can be applied to various digital audio signals having different reproduction bands without any unnatural feeling. It can be a tone.

Further, since the signal processing in the audio signal band extending apparatus of the present embodiment is all digital signal processing, there is no performance variation due to the variation of the components constituting the circuit and the temperature characteristics. In addition, the sound quality does not deteriorate every time the audio signal passes through the circuit. Further, even if the accuracy of the filter included is pursued, the circuit scale is not increased as compared with the analog circuit configuration, and the manufacturing cost is not increased.

In this embodiment, the signal of the harmonic component is generated by the nonlinear processing circuit 21 without limiting the band of the input digital audio signal. A signal whose band has been limited by the high-pass filter may be input to the nonlinear processing circuit 21 to generate a signal of a harmonic component.

Although the absolute value calculation circuit 51 is used as a full-wave rectification circuit in FIG. 5 to configure the nonlinear processing circuit 21, the present invention is not limited to this.
Alternatively, a half-wave rectifier circuit that outputs only the positive portion of the input digital audio signal and outputs the negative portion of the input digital audio signal as zero level may be used.

The control circuit 13 is based on the highest frequency information obtained by the frequency information analyzer 12 and takes into account the audibility of the digital high-pass filter 2 prepared in advance.
A control signal for determining an optimum value from among the 2, 2 and 24 bands, the band selected by the data selection circuit 28, the weighting coefficient of the weighting addition circuit 29, and the coefficient value of the multiplier 11, is converted into a spectrum analysis circuit. 3. Although the control signal is transmitted to the extension band generation circuit 5 and the level control circuit 4, the control signal may be transmitted to any one or two of the spectrum analysis circuit 3, the extension band generation circuit 5 and the level control circuit 4. Good.

The highest frequency detecting circuit 1 is, for example,
The operation may be performed at a predetermined cycle for each frame unit of the input digital audio signal.

(Embodiment 2) FIG. 12 is a block diagram showing a configuration of an audio signal band extending apparatus according to a second preferred embodiment of the present invention. In FIG. 12, the same components as those in FIG.
A detailed description thereof will be omitted. The audio signal band extending apparatus according to the second preferred embodiment differs from the audio signal band extending apparatus of FIG. 1 in the following points. (1) Instead of the level control circuit 4, a level control circuit 4a including a smoothing circuit 14 and a multiplier 11 is provided. (2) It further includes a spectrum analysis circuit 6 and a switch 7. Hereinafter, the above difference will be described in detail. A predetermined band is determined from the highest frequency of the digital audio signal input to the input terminal T1 of the frequency fs / 10 to fs / 2 output from the spectrum analysis circuit 3 in FIG. Then, the smoothing circuit 14 performs an envelope detection process, a time integration process, or a low-pass filter process on the signal indicating the spectrum intensity. Thereafter, by multiplying the processed signal by the extension signal output from the extension signal generation circuit 5, the level control in the level control circuit 4a becomes slower in time.

FIG. 13 shows the spectrum analysis circuit 6 of FIG.
FIG. 2 is a block diagram showing an internal configuration of the device. The spectrum analysis circuit 6 includes a high-pass filter 61 as shown in FIG.
, An absolute value calculation circuit 62, a low-pass filter 63,
A subtractor 64, a low-pass filter 65, an absolute value calculation circuit 66, a low-pass filter 67, and a determination circuit 68 are provided. 13, the digital audio signal input via the input terminal T1 in FIG. 12 is input to a high-pass filter 61 and a subtractor 64. The high-pass filter 61 performs high-pass filtering from the low-pass filtered digital audio signal so as to pass only a band component having a frequency of fs / 10 to fs / 2, and subjects the signal to an absolute value calculation circuit. 62 and a low-pass filter 63 that performs time integration. As a result, the spectrum intensity yah of the input digital audio signal in the frequency band fs / 10 to fs / 2 is calculated, and a signal indicating the spectrum intensity yah is output to the determination circuit 68.

On the other hand, the subtracter 64 subtracts the signal after high-pass filtering from the high-pass filter 61 from the digital audio signal input via the input terminal T1, and lowers the signal resulting from the subtraction. By passing the signal through the band-pass filter 65, the components in the frequency band from 0 to fs / 10 are extracted. By passing the extracted components of the frequency band of 0 to fs / 10 through the absolute value calculation circuit 66 and the low-pass filter 67 for performing time integration, the band of the input digital audio signal having the frequency range of 0 to fs / 10 is obtained. Is calculated, and the spectrum intensity yal is calculated.
A signal indicating “al” is output to the determination circuit 68.

The determination circuit 68 determines the spectrum intensity yal of the input digital audio signal at frequencies 0 to fs / 10 and the frequencies fs / 10 to fs / 2.
And the switching of the switch 7 is controlled as follows. (A) when the spectrum intensity yal is equal to or higher than a predetermined threshold level and the spectrum intensity yah is lower than the threshold level, or (b) the spectrum intensity yal
Is below a predetermined threshold level and the spectral intensity ya
When h is greater than or equal to a predetermined threshold level, switch 7
Is switched to the contact b side, and the extension signal from the level control circuit 4 a is not output to the adder 2, but a zero-level signal is output to the adder 2. On the other hand, in cases other than the above (a) and (b), the switch 7 is switched to the contact a side to output the extension signal from the level control circuit 4a to the adder 2.

That is, the input digital audio signal has a spectral intensity not less than a predetermined threshold in each of two bands, a frequency band of 0 to fs / 10 and a frequency band of fs / 10 to fs / 2. , The switch 7 is switched to the contact a side to extend the band of the input digital audio signal. On the other hand, if the spectrum intensity yal is equal to or higher than the predetermined threshold level and the spectrum intensity yah is lower than the predetermined threshold level, there is substantially no band component of the frequency fs / 10 to fs / 2. The switch 7 is switched to the contact b side. If the spectrum intensity yal is less than the predetermined threshold level and the spectrum intensity yah is equal to or higher than the predetermined threshold level, there is no fundamental component but only harmonic components, that is, not a tone but a high frequency unit. The switch 7 is switched to the contact b side when it is determined that the sound is one spectrum or a non-tone sound generated intentionally. Thus, when a single spectrum or a non-tone signal is detected, the switch 7 is controlled so as not to extend the band as shown in FIG. That is, the spectrum of the digital signal output from the audio signal band extending apparatus of the present embodiment is cut off by the spectrum 100 of the highest band in the band B1 of the input digital signal.

In this embodiment, the smoothing circuit 14
When the switch 7 is switched to the contact a side, the extended signal from the extended signal generating circuit 5 is smoothed on the input digital audio signal in terms of spectral characteristics as shown in FIG. Is added to lead to. That is, the spectrum of the digital signal output from the audio signal band extending apparatus of the present embodiment is connected to the spectrum 101 of the highest band in the band B1 of the input digital signal and the spectrum 101 of the lowest band in the band B2. After that, the slope of the spectrum in the band B2 is made the same as the slope of the spectrum in the band B1,
It is continuous.

As described above, according to the second preferred embodiment of the present invention, the same advantages as those of the first preferred embodiment are provided, and the smoothing circuit 14 is provided. Therefore, the extension signal generation circuit 5
Can be added in accordance with the high-band spectral intensity of the input digital audio signal so as to be smoothly connected to the input digital audio signal on the spectral characteristics.

Also, since it has the spectrum analysis circuit 6 and the switch 7, a sine wave having a single spectrum,
When a non-tone signal is input, the switch 7 can be switched to the contact b to control not to add the extension signal, that is, the extension function of the audio band can be stopped. In this case, it is possible to prevent a measurement result in which signal characteristics are significantly deteriorated.

In the preferred embodiment described above, in the extension signal generation circuit 5, the signal of the harmonic component generated by the nonlinear processing circuit 21 and the high-pass filter 22, the dither signal generation circuit 23 and the high-pass filter 24
Is generated by the adder 25 and added by the adder 25 to form an extension signal. However, the present invention is not limited to this, and the extension signal includes the harmonic component signal and the dither signal. May be included.

In the preferred embodiment described above, the spectrum analysis circuit 6 calculates the spectrum intensities of the two bands to determine whether the input digital audio signal is a single spectrum or a non-tone signal. However, the present invention is not limited to this, and the spectrum analysis circuit 6
, The spectrum intensities of a plurality of bands may be calculated to determine whether the input digital audio signal is a single spectrum or a non-tone signal.

In the above preferred embodiment, 1
Although the / f characteristic filter 26 is provided, the present invention is not limited to this and may not be provided.

In the preferred embodiment described above, the audio signal band extending device is constituted by a hardware digital signal processing circuit. However, the present invention is not limited to this. For example, the structure shown in FIG. 1 or FIG. May be realized by a signal processing program, and the signal processing program may be executed by a DSP (Digital Signal Processor).

[0075]

Therefore, according to the first aspect of the present invention,
Since the audio signal band device including the first addition means, the first spectrum analysis means, the level control means, and the extension signal generation means is constituted by a digital signal processing circuit, the performance of the apparatus hardly varies. It is possible to provide a method and an apparatus for extending the band of an audio signal, which is less expensive and has a lower manufacturing cost than the related art.

According to the twelfth, twenty-sixth, and twenty-seventh aspects of the present invention, the addition level of the extension signal is adjusted in accordance with the high-band spectrum intensity of the digital audio signal input from the first spectrum analysis means. Further, since an extended signal passed through a low-pass filter having a 1 / f characteristic or a 1 / f ² characteristic is used, a natural sound close to a tone signal can be obtained without changing the sound quality of the input original digital audio signal. An extended signal having a timbre can be added, and there is no unnaturalness or deterioration in sound quality.

Further, according to the invention of claims 9 to 11 and 23 to 25 of the present application, the digital audio signal has the same spectral structure as that of the tone signal in the band or higher that the digital audio signal has (that is, the frequency of generation of the dither signal is Generates a harmonic component and a dither signal by generating a substantially Gaussian distribution or a bell distribution. The harmonic component and dither signal are generated, and the generated harmonics are generated in accordance with the high frequency spectrum intensity of the input digital audio signal. By adding the digital signal and the dither signal of the wave component to the input digital audio signal, it is possible to easily generate a digital audio signal having an extended audio band in proportion to the related art.

According to the invention of claims 2 to 8 and 16 to 22 of the present application, the maximum frequency of the input digital audio signal is detected or detected at a predetermined cycle, and the band is expanded in consideration of the audibility characteristics. Therefore, it is possible to provide a natural tone with less discomfort with respect to digital audio signals having various reproduction bands or a change in band within an input digital audio signal.

Further, according to the inventions of claims 14, 28 and 29 of the present application, since the second spectrum analyzing means and the switching means are provided, even if a sine wave signal is input, signal deterioration in signal characteristic measurement is prevented. It is possible to provide an audio band extension method and apparatus that does not generate a planning result.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an audio signal band extending apparatus according to a first preferred embodiment of the present invention.

FIG. 2 is a block diagram showing an internal configuration of the spectrum analysis circuit 3 of FIG.

FIG. 3 is a block diagram showing an internal configuration of the nonlinear processing circuit 21 of FIG.

FIG. 4 is a block diagram showing an internal configuration of a dither signal generation circuit 23 of FIG.

FIG. 5 is a PN sequence noise signal generation circuit 40-n of FIG. 4;
FIG. 3 is a block diagram showing an internal configuration of (n = 1, 2,..., N).

6 is a PN sequence noise signal generation circuit 40-n of FIG. 5;
9 is a graph showing a function of a probability density with respect to an amplitude level of a white noise signal generated according to an example of (n = 1, 2,..., N).

FIG. 7 is a PN sequence noise signal generation circuit 40-n of FIG. 5;
6 is a graph showing a function of a probability density with respect to an amplitude level of a bell distribution type noise signal generated according to an example of (n = 1, 2,..., N).

8 is a PN sequence noise signal generation circuit 40-n of FIG. 5;
6 is a graph illustrating a function of a probability density with respect to an amplitude level of a Gaussian noise signal generated according to an example of (n = 1, 2,..., N).

FIG. 9 is a spectrum diagram showing a frequency characteristic of the 1 / f characteristic filter 26 of FIG.

FIG. 10 is a spectrum diagram illustrating frequency characteristics of a 1 / f ² characteristic filter that replaces the 1 / f characteristic filter 26 of FIG. 1;

FIG. 11 is a loudness isocurve of a pure tone (Robinson-
FIG.

FIG. 12 is a block diagram showing a configuration of an audio signal band extending apparatus according to a second preferred embodiment of the present invention.

FIG. 13 is a block diagram showing an internal configuration of the spectrum analysis circuit 6 of FIG.

14 is a spectrum diagram showing a spectrum intensity of an input digital signal input to the audio signal band extending apparatus of FIG.

15 is a spectrum diagram showing a spectrum intensity of a digital signal after band expansion by the audio signal band expansion device of FIG. 12;

FIG. 16 is a block diagram showing a configuration of an audio signal band extending device according to the related art.

[Explanation of symbols]

T1 input terminal T2 output terminal 1 highest frequency detection circuit 2 adder 3 spectrum analysis circuit 4 level control circuit 5 extension signal generation circuit 6 spectrum analysis circuit 7 switch 11 multiplier 12 frequency information analyzer 13 control circuit 14 smoothing circuit 21 nonlinear Processing circuit 22 High-pass filter 23 Dither signal generation circuit 24 High-pass filter 25 Adder 26 1 / f characteristic filter 27 FFT circuit 28 Data selection circuit 29 Weighted addition circuit 31 Absolute value calculation circuit 32 DC offset removal circuit 33 Subtractor 34 Averaging circuit 35 1/2 multiplier 40-n (n = 1, 2,..., N) PN sequence noise signal generating circuit 41 Adder 43 DC offset removing constant signal generator 44 Subtractor 51 32-bit shift register 52 Exclusive OR gate 53 Clock signal generation Generator 54 Initial value data generator 61 High-pass filter 62 Absolute value calculation circuit 63 Low-pass filter 64 Subtractor 65 Low-pass filter 66 Absolute value calculation circuit 67 Low-pass filter 68 Judgment circuit 91 Buffer amplifier 92 Filter circuit Reference Signs List 93 amplifier 94 detection circuit 95 time constant circuit 96 noise generator 97 filter circuit 98 multiplier 99 adder 100 spectrum of highest band in band B1 of input digital signal 101 spectrum of lowest band in band B2 102 band B2 Spectral tilt

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kiyotaka Nagai 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (29)

[Claims] A step of calculating a spectrum intensity of a predetermined band among digital audio signals of a first band having a predetermined highest frequency, and outputting a signal indicating the calculated spectrum intensity; Generating an extension signal having a frequency component of a second band higher than the band of the above; controlling the level of the extension signal according to the signal indicating the calculated spectrum intensity; Detecting the highest frequency with respect to the digital audio signal of the band, controlling each unit according to the highest frequency, and adding the extended signal whose level is controlled to the digital audio signal of the first band. And outputting a digital audio signal as a result of the addition. 2. The step of detecting the highest frequency includes the step of obtaining information of the highest frequency of the digital audio signal of the first band, and the step of obtaining the extension signal in consideration of hearing characteristics from the information of the highest frequency. Controlling the step of generating an audio signal. 3. The step of detecting the highest frequency includes the step of obtaining information of the highest frequency of the digital audio signal of the first band; Controlling the level of the audio signal. 2. The method of claim 1, further comprising: 4. The step of detecting the highest frequency includes the step of obtaining information of the highest frequency of the digital audio signal of the first band, and the step of calculating the highest frequency by considering the auditory characteristics from the information of the highest frequency. Controlling the step of outputting a signal indicative of the spectrum intensity.
A method for extending a band of an audio signal as described above. 5. The step of detecting the highest frequency includes the step of obtaining information on the highest frequency of the digital audio signal of the first band, the step of generating the extension signal, and controlling the level of the extension signal. And the step of outputting a signal indicating the calculated spectrum intensity.
2. The method according to claim 1, further comprising the step of: controlling one of the steps from the information of the highest frequency in consideration of the auditory characteristics. 6. The step of detecting the highest frequency includes: obtaining information of the highest frequency of the digital audio signal of the first band at a predetermined period; generating the extension signal; One or two of a step of controlling a signal level and a step of outputting a signal indicating the calculated spectrum intensity.
2. The method according to claim 1, further comprising the step of: controlling one to three steps at a predetermined cycle from the information of the highest frequency in consideration of the auditory characteristics. 7. The step of obtaining the information of the highest frequency includes the step of obtaining the information of the highest frequency from the specification information (header information) of the digital audio signal of the first band. Claims 2 to 6
The band expansion method of an audio signal according to any one of the above. 8. The method according to claim 2, wherein the step of obtaining the highest frequency information includes a step of analyzing a frequency spectrum of the digital audio signal of the first band to obtain information of a highest frequency. Any one of ~ 6
The band expansion method of the audio signal described in the paragraph. 9. The step of generating the extension signal has a nonlinear input / output characteristic, and performs nonlinear processing on the digital audio signal of the first band to distort the digital audio signal. Generating a digital signal of a harmonic component of the digital audio signal; and extracting a frequency component corresponding to an auditory characteristic from information on a highest frequency of the digital audio signal of the first band in the digital signal of the harmonic component. And filtering the high-pass filtered signal and outputting the filtered signal as an extended signal. 9. The audio signal according to claim 1, wherein Bandwidth extension method. 10. The step of generating the extension signal, the step of generating a dither signal having a predetermined probability distribution with respect to an amplitude level; and the step of generating a highest frequency of the digital audio signal of the first band among the dither signals. Filtering the frequency component corresponding to the auditory characteristics from the information of the high frequency band and outputting the filtered signal as an extension signal. 9. The bandwidth extension method for an audio signal according to claim 1, wherein: 11. The step of generating the extension signal has a nonlinear input / output characteristic, and performs a nonlinear process on the digital audio signal of the first band to distort the digital audio signal. Generating a digital signal of a harmonic component of the digital audio signal; and extracting a frequency component corresponding to an auditory characteristic from information on a highest frequency of the digital audio signal of the first band in the digital signal of the harmonic component. Performing high-pass filtering and outputting the filtered signal as an extension signal; generating a dither signal having a predetermined probability distribution with respect to an amplitude level; From the information of the highest frequency of the digital audio signal of the band, the frequency component corresponding to the auditory characteristics is high-pass filtered, 4. The method according to claim 1, further comprising: outputting a post-wave signal; and adding the two high-pass filtered signals and outputting a signal resulting from the addition as an extension signal. , 5, 6, 7, and 8. 12. A step of low-pass filtering the extension signal having one of predetermined 1 / f characteristics and 1 / f ² characteristics before the step of controlling the level. 10. The method according to claim 1, further comprising:
12. The method of extending the band of an audio signal according to any one of items 10 and 11. 13. A method for generating a dither signal, comprising the steps of: generating a pseudo noise sequence noise signal which is independent of each other; and adding the plurality of pseudo noise sequence noise signals to an amplitude level. Generating a dither signal as a result of addition having a probability density of one of a Gaussian distribution and a bell-shaped distribution and outputting the dither signal as an extension signal. 3. The band expansion method of an audio signal according to claim 1. 14. Calculating the spectrum intensities of a plurality of predetermined bands among the digital audio signals of the first band, and converting the digital audio signal into a single signal based on the calculated spectrum intensities of the plurality of bands. Determining whether or not the digital audio signal is a spectrum; and, when determining that the digital audio signal is not a single spectrum, outputting the extended signal and determining that the digital audio signal is a single spectrum. The method according to any one of claims 1 to 13, further comprising a step of switching so as not to output the extension signal when the judgment is made. 15. A first spectrum analyzing means for calculating a spectrum intensity of a predetermined band of a digital audio signal of a first band having a predetermined highest frequency and outputting a signal indicating the calculated spectrum intensity. Extension signal generation means for generating an extension signal having a frequency component of a second band higher than the first band; and a signal indicating the calculated spectrum intensity output from the first spectrum analysis means. Level control means for controlling the level of the extension signal, and maximum frequency detection means for detecting the highest frequency for the digital audio signal of the first band and controlling each section according to the highest frequency. Adding the extension signal controlled by the level control means to the digital audio signal of the first band; Band extender of the audio signal, characterized in that it comprises a first adding means for outputting Le audio signal. 16. The maximum frequency detecting means includes: frequency information obtaining means for obtaining information on the highest frequency of the digital audio signal in the first band; and the extension in consideration of hearing characteristics from the information on the highest frequency. 16. The audio signal band extending apparatus according to claim 15, further comprising control means for controlling the signal generating means. 17. The maximum frequency detecting means, comprising: frequency information obtaining means for obtaining information on the highest frequency of the digital audio signal in the first band; and the level information in consideration of a hearing characteristic from the information on the highest frequency. The audio signal band extending apparatus according to claim 15, further comprising control means for controlling the control means. 18. The maximum frequency detecting means, comprising: frequency information obtaining means for obtaining information on the highest frequency of the digital audio signal in the first band; and 16. The audio signal band extending apparatus according to claim 15, further comprising control means for controlling said one spectrum analysis means. 19. The maximum frequency detecting means includes: frequency information obtaining means for obtaining information on the highest frequency of the digital audio signal of the first band; the extension signal generating means; the level control means; 16. The audio signal band expansion according to claim 15, further comprising control means for controlling two or three of the one spectrum analyzing means in consideration of the auditory characteristics from the information of the highest frequency. apparatus. 20. The maximum frequency detecting means, frequency information obtaining means for obtaining information of the highest frequency of the digital audio signal in the first band at a predetermined cycle, the extended signal generating means, and the level control Means, and control means for controlling one to two to three of the first spectrum analysis means at predetermined intervals from the information of the highest frequency in consideration of auditory characteristics. 16. The audio signal band extending apparatus according to claim 15, wherein: 21. The frequency information obtaining means includes means for obtaining information of the highest frequency from the specification information (header information) of the digital audio signal of the first band. Claims 16-2
0. The audio signal band extending apparatus according to any one of 0 to 0. 22. The frequency information obtaining means according to claim 16, further comprising means for analyzing a frequency spectrum of the digital audio signal of the first band and obtaining information of a highest frequency. The audio signal band extending device according to any one of the above items. 23. The extended signal generating means has a non-linear input / output characteristic, and performs non-linear processing on the digital audio signal of the first band to distort the digital audio signal. Non-linear processing means for generating a digital signal of a harmonic component of the digital audio signal; and hearing information from the highest frequency information of the digital audio signal of the first band among the digital signals of the harmonic component output from the non-linear processing means. 20. A first high-pass filter for high-pass filtering a frequency component according to a characteristic and outputting the filtered signal as an extension signal. The audio signal band extending apparatus according to any one of 20, 21, 22. 24. An extended signal generating means, comprising: a dither signal generating means for generating a dither signal having a predetermined probability distribution with respect to an amplitude level; and a maximum of a digital audio signal of the first band among the dither signals. 16. A second high-pass filter that high-pass-filters a frequency component corresponding to the auditory characteristic from frequency information and outputs the filtered signal as an extension signal. , 16,19,20,21,2
3. The band extending apparatus for an audio signal according to any one of 2. 25. The extended signal generating means has a non-linear input / output characteristic, and performs nonlinear processing on the digital audio signal in the first band to distort the digital audio signal, Non-linear processing means for generating a digital signal of a harmonic component of the digital audio signal; and hearing information from the highest frequency information of the digital audio signal of the first band among the digital signals of the harmonic component output from the non-linear processing means. A first high-pass filter for high-pass filtering a frequency component according to the characteristic and outputting a filtered signal; a dither signal for generating a dither signal having a predetermined probability distribution with respect to an amplitude level Generating means for responding to auditory characteristics from information of the highest frequency of the digital audio signal of the first band in the dither signal. A second high-pass filter that performs high-pass filtering of the filtered frequency component and outputs a filtered signal, a signal output from the first high-pass filter, and a second high-pass filter. And a second adding means for adding a signal output from the pass filter and outputting a signal as a result of addition as an extension signal.
The audio signal band extending device according to any one of claims 6, 19, 20, 21, and 22. 26. A low-pass filter having a filter characteristic of one of a predetermined 1 / f characteristic and a 1 / f ² characteristic, and low-pass filtering the extended signal to output to the level control means. The audio signal band extending apparatus according to claim 15 or 23, further comprising a filter. 27. A low-pass filter having a filter characteristic of one of a predetermined 1 / f characteristic and a 1 / f ² characteristic, and low-pass filtering the extended signal to output to the level control means. 26. The audio signal band extending device according to claim 24, further comprising a filter. 28. The dither signal generating means includes: a plurality of noise signal generating circuits each generating a pseudo noise sequence noise signal independent of each other; and a plurality of pseudo noise sequence noises generated by each of the noise generating circuits. A third adding unit that generates a dither signal of an addition result having a probability density of one of a Gaussian distribution and a bell-shaped distribution with respect to the amplitude level by adding the signals, and outputs the dither signal as an extension signal; The audio signal band extending apparatus according to any one of claims 24, 25, and 27, comprising: 29. Calculating the spectrum intensities of a plurality of predetermined bands among the digital audio signals of the first band, and converting the digital audio signal into a single signal based on the calculated spectrum intensities of the plurality of bands. Second spectrum analysis means for determining whether or not the spectrum is a spectrum; and when the second spectrum analysis means determines that the digital audio signal is not a single spectrum, the extension signal is converted to the first signal. While the digital audio signal is determined to have a single spectrum, the extended signal is added to the first signal.
29. The audio signal band extending apparatus according to claim 15, further comprising: switch means for switching so as not to output to the adding means.