WO2007029796A1

WO2007029796A1 - Band extending device, band extending method, band extending program

Info

Publication number: WO2007029796A1
Application number: PCT/JP2006/317795
Authority: WO
Inventors: Mitsuya Komamura; Takashi Mitsuhashi
Original assignee: Pioneer Corporation; Techexperts Incorporation
Priority date: 2005-09-08
Filing date: 2006-09-01
Publication date: 2007-03-15
Also published as: JPWO2007029796A1; JP4627548B2

Abstract

There is disclosed a band extending device generating a high-quality band extending signal without using a non-linear processing. The band extending device includes a baseband processing unit, an extended band processing unit, and a mixing unit. The baseband processing unit supplies a baseband signal limited to a predetermined frequency band. The extended band processing unit includes a spectrum reversing unit for reversing the spectrum of the band signal obtained from an input signal, an up-sampler for subjecting the reversed signal to up-sampling, and a band pass filter for subjecting the output of the up-sampler to filtering so as to generate, as an extended band component, a frequency band component having a frequency substantially identical to the frequency of the high frequency end of the frequency band of the baseband signal as a low band end. The mixing unit mixes the baseband signal with the extended band component.

Description

Bandwidth expansion device, bandwidth expansion method, and bandwidth expansion program

TECHNICAL FIELD The present invention relates to a band extension that extends the frequency band of a digital signal such as an audio signal.

Zhang technology. Background Art A number of band expansion techniques have been proposed for expanding the frequency band of digital signals such as band-limited audio signals and compression-coded signals to generate high-quality wideband signals. Such band expansion technology, for example, expands the frequency band of audio signals in a narrow telephone band to reproduce high-quality audio signals, or compresses with a compression method such as MP 3 (PEG-1 Audio Layer 3) This can be applied to the case where the band of the encoded low quality audio signal is expanded to reproduce a signal having a high sound range. A technique using nonlinear processing is known as a technique for extending the bandwidth of an audio signal. For example, in the band expansion technology using nonlinear processing disclosed in the patent document (International Publication No. WO00 / 0 0 7 6 9), the oversampling type low-pass filter is used as the original audio signal. Filters to attenuate components above the sampling frequency f S of approximately 12 or more. Next, the nonlinear processing circuit generates a harmonic component by applying nonlinear processing to the output of the oversampling mouth-and-mouth pass-fill, and outputs a digital 'audio signal containing this harmonic component. To do. In addition, a high pass filter filters the digital audio signal to generate a high frequency component, ie, an extended band component. This high-frequency component is added to the output of the oversampling low-pass filter, thereby generating a signal with an expanded frequency band. However, since the nonlinear processing circuit performs non-linear processing, it generates not only harmonic components but also cross modulation components such as chord components and difference sound components of a plurality of frequency components. There is a problem that it is a component unrelated to the frequency component of the original signal and degrades the signal quality. ,-Non-patent literature (H. Yasukawa, “Spectrum Broadening of Telephone Band Signals Using Multirate Processing for Speech Quality Enhancement,” IEICE Transactions on

Fundamentals Electronics, Communications and Computer Sciences, Vol.

E78-A, No. 8, pp. 996-998, 1995.) is known. FIG. 1 is a diagram schematically showing the configuration of the bandwidth extension device 100 disclosed in this non-patent document. This band extension device 100 is composed of an up sam- pler 10 1, a high-pass filter (HPF) 1 0 2 A, a shaping filter 1 0 3 A, a level adjuster 1 0 4 A, a low-pass filter ( LPF) 1 0 2 B, delay unit 1 0 3 B, level adjuster 1 0 4 B and adder 1 0 5

Upsampler 1◦1 upsamples the input signal at twice the rate. For example, if upsampling is performed on an input signal with the frequency spectrum (ω: angular frequency) shown in Fig. 2A at a double rate, the upsampling signal with the frequency spectrum shown in Fig. 2 Generated. Low pass filter 1 0 2 B generates a baseband component by filtering the up-sampling signal supplied from the up-sampler 10 1. The base spanned component is delayed by the delay unit 1 0 3 B, level-adjusted by the level adjuster 1 0 4 B, and then supplied to the adder 1 0 5. For example, if a low-pass filter with a passband of I ω) <ττΖ 2 1 0 2 フィルタリング filters the upsampling signal shown in Fig. 2 を, the spectrum shown in Fig. The baseband component possessed is obtained. On the other hand, the high-pass filter 10 2 Α filters the up-sampling signal supplied from the up-sampler 1 0 1 to generate an extended band component. This extended band component is shaped by the shaping filter 10 3 A, level-adjusted by the level adjuster 1 0 4 A, and then supplied to the adder 1 0 5. The adder 1 0 5 generates a band extension signal by adding the extension band component supplied from the level adjuster 1 0 4 A to the baseband component supplied from the level adjuster 1 0 4 B. Become. For example, if a high-pass filter with a passband of I ω I> ττΖ 2 1 0 2 Α filters the upsampling signal shown in Fig. 2 Β, the spectrum shown in Fig. 2D An extended band component having is obtained. When this extended band component and the baseband component of FIG. 2C are added, a band extended signal having the spectrum shown in FIG. 2E is generated.

However, as shown in Fig. 2E, the band extension signal includes an extension band component whose spectrum is inverted with respect to the spectrum of the base band component, so that the baseband component and the frequency are ω = ± ττ / 2. There is a problem that the extended band component is not smoothly connected. Since the spectrum of the extended band component is inverted with respect to the spectrum of the base band component, the level adjusters 1 0 4 Α and 1 0 4 Β There is also a problem that it is difficult to adjust each level of the component and the extended band component to an appropriate level. Therefore, it is difficult to generate a high-quality, natural sound quality band extension signal with the technology of the above non-patent document.

Disclosure of the invention

In view of the above, an object of the present invention is to provide a bandwidth extension device, a bandwidth extension method, and a bandwidth extension program that can generate a high-quality bandwidth extension signal without using nonlinear processing.

The band extending apparatus according to the first aspect of the present invention extends the frequency band of an input signal. The band extension apparatus performs baseband processing on the input signal, generates a baseband signal limited to a predetermined frequency band by filtering the upsampled signal, and the input band. An extension band processing unit that generates an extension band component from a force signal; and a mixing unit that mixes the baseband signal with the extension band component. The extension band processing unit includes the input signal or the input signal. A spectrum inversion unit that inverts the spectrum of the band signal obtained from the above to generate an inverted signal, an upsampling unit that performs a cap sampling on the inverted signal, and a filter that filters the output of the upsampler as described above. The component of the frequency band whose lower end is the same frequency as the frequency of the upper end of the frequency band of the baseband signal And a band pass filter generated as an extended band component.

The band extending method according to the second aspect of the present invention extends the frequency band of the input signal. In this band extension method, (a) upsampling is performed on the input signal, and fill-up ringing is performed on the upsampled signal. Generating a baseband signal limited to a frequency band; (b) generating an extension band component from the input signal; and (c) mixing the extension band component with the baseband signal; The step (b) includes: (b 1 1) generating an inverted signal by inverting the spectrum of the input signal or a band signal obtained from the input signal, and (b-2) (B-3) Applying up-sampling to the inverted signal up-sampled in step (b_2), and applying the fill-up to the inverted signal up-sampled in step (b_2). Generating, as the extension band component, a frequency band component having a frequency that is substantially the same as the end frequency as a low frequency end.

The bandwidth extension program according to the third aspect of the present invention causes a processor to execute bandwidth extension processing for extending the frequency bandwidth of an input signal. The band extension processing includes baseband processing for generating a baseband signal limited to a predetermined frequency band by performing upsampling on the input signal and filtering the upsampled signal, and the input An extension band process for generating an extension band component from a signal, and a mixing process for mixing the extension band component with the base spanned signal, wherein the extension band process is obtained from the input signal or the input signal. Spectral inversion processing that inverts the spectrum of the band signal to generate an inverted signal, up-sampling processing that performs up-sampling on the inverted signal, and filtering the output of the up-sampler results in the baseband. The component of the frequency band that has the same frequency as the low frequency end of the high frequency end of the signal frequency band. Serial includes a filter processing for generating as an extended band component, a.

Brief Description of Drawings Fig. 1 is a diagram schematically showing the configuration of a conventional bandwidth extension device.

2A to 2E are diagrams schematically showing a frequency spectrum for explaining a conventional band extension method.

FIG. 3 is a functional block diagram schematically showing the configuration of the bandwidth extension apparatus according to the first embodiment of the present invention.

4A to 4C are diagrams schematically showing a frequency spectrum for explaining the band expansion method of the first embodiment.

FIG. 5A to FIG. 5E are diagrams schematically showing a frequency spectrum for explaining the band expansion method of the first embodiment.

6A and 6B are diagrams schematically showing a frequency spectrum for explaining the bandwidth extension method of the first embodiment.

7A and 7B are diagrams showing the frequency spectrum of the band extension signal generated according to the band extension method of the first embodiment and the frequency spectrum of the original signal, and FIG. FIG. 5 is a diagram showing a frequency spectrum for explaining another example of a method for calculating a mixing coefficient,

FIG. 9 is a diagram for explaining still another example of the calculation method of the mixing coefficient, and FIG. 10 is a functional block diagram schematically showing the configuration of the bandwidth extension apparatus according to the second embodiment of the present invention. And

FIGS. 11-8 to 11D are diagrams schematically showing a frequency spectrum for explaining the bandwidth expansion method of the second embodiment.

FIGS. 12A and 12B are diagrams schematically showing a frequency spectrum for explaining the bandwidth expansion method of the second embodiment. FIG. 13 is a functional block diagram schematically showing the configuration of the bandwidth extension apparatus according to the third embodiment of the present invention.

FIGS. 14A to 14F are diagrams schematically showing a frequency spectrum for explaining the band extending method of the third embodiment.

FIG. 15 is a functional block diagram schematically showing the configuration of the bandwidth extension apparatus according to the fourth embodiment of the present invention.

FIG. 16 is a diagram schematically showing the configuration of the mixing unit used in the bandwidth extension apparatus of the fourth embodiment.

FIGS. 17-8 to 17D are diagrams schematically showing frequency vectors for explaining the bandwidth extension method of the fourth embodiment,

FIGS. 18A to 18G are diagrams schematically showing a frequency spectrum for explaining the band expansion method of the fourth embodiment.

19A to 19C are diagrams showing various application examples.

BEST MODE FOR CARRYING OUT THE INVENTION

This application is based on Japanese Patent Application No. 2005-260541 and is incorporated herein by reference.

Various embodiments according to the present invention will be described below.

1. First example

FIG. 3 is a functional block diagram schematically showing the configuration of the bandwidth extension apparatus 1 of the first embodiment according to the present invention. The bandwidth expansion device 1 includes a baseband processing unit 10, a coefficient determination unit 20, an expansion bandwidth processing unit 30, and a mixing unit 40. The baseband processing unit 10 performs upsampling on the sequence of the input signal X (n) (n is an integer) A baseband signal x _L (n) limited to a predetermined frequency band is generated by filtering the upsampled signal sequence. The input signal X (n) is a digital signal such as an audio signal.

The basepand processing unit 10 includes an upsampler 11, a low-pass filter (LPF) 12, and a delay device 13. Upsampler 1 1 generates a sequence of upsampled signals xu (n) by upsampling the sequence of input signals X (n) at a rate N times (N is an integer greater than or equal to 2), ie a factor of N . The low-pass filter 12 has a pass band of I ω I <π / Ν (ω is the angular frequency), and the filter sequence is applied to the sequence of the up-sampling signal xu (n). A sequence of filter signals x _L (n) limited to the frequency band of π ΖΝ is generated. Delay device 13 delays filter signal x _L (n) by a predetermined delay time and outputs the delayed signal as a baseband signal. Figures 4A to 4C illustrate the frequency spectrum when N is "2". Given the input signal X (n) shown in Figure 4A, the upsampler 1 1 upsamples the input signal X (n) at a double rate, or a factor of 2, and An upsampling signal x _u (n) having a frequency spectrum shown in FIG. The low-pass filter 12 filters the upsampling signal xu (n) in Fig. 4B to generate a filter signal (n) limited to the frequency band of πΖ2 to 10 Tt / 2. .

On the other hand, the extended band processing unit 30 has a function of generating an extended band component z _B (n) from the sequence of the input signal X (n). The extended band processing unit 30 includes a high-pass filter (HPF) 31, a down sampler 32, a spectrum inversion unit 33, and an up sampler. 34 and a band pass filter (BPF) 35. The high-pass filter 31 has a pass band (second frequency band) of I ω Ι> ττΖ2, and filters the sequence of the input signal X (η) to generate a sequence of the filter signal ΧΗ (η) . The downsampler 32 then downsamples the sequence of fill signals x _H (n) at a rate of 2 or a factor of 2 and converts the downsampled signal or sequence of band signals x _D (n). Generate. Figures 5A to 5B illustrate frequency spectra. When the input signal X (n) shown in Fig. 4A is supplied, the high-pass filter 31 with a pass band of I ω I> ττΖ 2 is a filter with the frequency spectrum shown in Fig. 5Α. An evening signal x _H (n) is generated. The downsampler 32 also performs downsampling on the filter signal x _H (n) at a rate of 1/2, that is, a factor of 2, so that the downsampling signal x having the frequency spectrum shown in FIG. _D (n) is generated.

Spectrum inverter 33 inverts the spectrum of the down-sampling signal x _D (n) to generate an inverted signal z _D (n). As will be explained below using mathematical formulas, “spectrum inversion” means that the frequency spectrum of a signal is shifted by an angular frequency of 7T. Since the signal obtained by inverting the polarity of every other downsampling signal x _D (n) becomes the inverted signal z _D (n), the signal between the down sampling signal x _D (n) and the inverted signal z _D (n) Is expressed by the following equation (1).

z _D (n) = x _D (n) x (one I) "

(1) where j is the imaginary unit (j ² = — 1), and L is the number of Fourier transform samples and is a positive integer. Therefore, the discrete Fourier transform Z _D (k) of the inverted signal z _D (n) is developed as follows. Z _D (k) = ^ z _D (n) exp (-; * 2 ^ r½ / L)

L-l

= ^ x _D (n) exp (-jn π) exp (-j 2π1σι / L)

Therefore, when X _D (k) is the discrete Fourier transform of the downsampled signal x _D (n), the following equation (2) holds.

According to Equation (2), Z _D (k) is obtained by shifting X _D (k) by LZ2 point, that is, angular frequency 7C in the frequency domain. Therefore, “spectrum inversion” means that the frequency spectrum of the signal is shifted by the angular frequency π.

Next, referring to FIG. 3, the upsampler 34 performs upsampling on the series of the inverted signal z _D (n) at a rate of 2 ×, that is, a factor of 2 ×, so that the upsampled signal z _u (n) Generate a series. Furthermore, the bandpass filter evening 35 has a passband of 2 τι / (2 XN) <I ωI <3 兀 no (2 XN), and fills the sequence of the upsampling signal zu (n). To generate a sequence of extended band components z _B (n). The frequency at the low band end (low band side end) of the band of this extended band component z _B (n) is approximately equal to the frequency at the high band edge (high band side end) of the band of the baseband signal x _L (n). The filter characteristics of the bandpass filter 35 (passband Zone, stopband and cut-off frequency). In this example, the frequency of the low band end of the extended band component z _B (n) is approximately ± 2 πΖ (2 ΧΝ), and the frequency of the high band end of the baseband signal x _L (n) is also π Since the frequency is / Ν, both frequencies are almost the same.

Fig. 5 C to Fig. 5 例示 illustrate frequency spectra when Ν is “2”. At this time, the spectrum inversion unit 33 inverts the spectrum of the downsampling signal x _D (n) shown in FIG. 5 to generate an inverted signal z _D (n) having the spectrum shown in FIG. 5C. Also, the upsampler 34 upsamples the inverted signal z _D (n) at a rate of 4 times, that is, a factor of 4, and generates the up sampled signal zu (n) having the spectrum shown in Fig. 5D. Generate. The bandpass filter 35 with a passband of 2 πΖ4 <I ω | <3 4 applies an extended band with the spectrum shown in Fig. 5E by filtering the upsampling signal zu (n). A fill signal z _B (n) consisting of components is generated. In this case, the frequency band 7TZ2 at the high end of the band of baseband signal x _L (n) shown in Fig. 4C is the frequency ± ττΖ of the low band end of the extended band component ζ _Β (η) in Fig. 5 Matches 2.

The baseband signal x _L (n) and the extended band component z _B (n) are mixed by the mixing unit 40. The coefficient determination unit 20 is a processing block that calculates the frequency spectrum of the input signal X (n) and determines the mixing coefficient to be multiplied by the extension band component z _B (n) based on the frequency spectrum. The coefficient determination unit 20 includes an FFT unit (fast Fourier transform unit) 21, a spectrum calculation unit 22, and a coefficient calculation unit 23. The FFT unit 21 calculates a signal sequence in the frequency domain by performing a fast Fourier transform on the sequence of the input signal X (n). In addition, the spectrum calculation unit 22 calculates the frequency spectrum of the input signal X (n) based on the frequency domain signal sequence supplied from the FFT unit 21. The coefficient calculation unit 23 calculates a linear or non-linear regression curve in the range of% / 2 to redundant frequency based on the frequency spectrum calculated by the spectrum calculation unit 22, and uses this regression curve. Thus, the mixing coefficient can be calculated. Specifically, a linear regression line expressed by a linear function may be used as the regression curve.

In the case of the first embodiment, components in the frequency band (second frequency band ττΖ 2 to 兀) as shown in FIG. 5A are extracted from the input signal X (n), and these components are down-sampled and scanned. By applying spectrum inversion, upsampling and filtering, an extended band component ζ _Β (η) as shown in Fig. 5 生成 is generated. Therefore, the mixing coefficient C (η) is equal to or lower than the frequency ω = ττ at the high end relative to the spectrum value L _A of the regression curve at the frequency ω = ττΖ 2 at or near the low end. It is given by the ratio L _B ZL _A of the spectral value L _B of the regression curve at nearby points.

FIG 6 A is a diagram illustrating the frequency spectrum of the input signal X (n) and the regression curve L _R. Based on the spectrum curve C _s , the regression curve L _{R in} the frequency range of πΖ2 π is calculated. Since this frequency spectrum is expressed in decibels (dB), when the amplitude at the point of ω = π / 2 is expressed in VB as the amplitude at the point of VA ω = ττ, the mixing coefficient C (η) is , C (η) L _B ZL _A L _B = 10 ( ^VB2 WL _A = 10 ^{(VA / 20} is given.

The mixing unit 40 includes a multiplier 41 and an adder 42. The multiplier 41 multiplies the mixing coefficient C (n) supplied from the coefficient determination unit 20 by the extension band component z _B (n), and the adder 42 supplies the multiplication result from the baseband processing unit 10. Supplied Add to baseband signal. As a result of the addition, a band extension signal y (n) is generated. Figure 6B shows the frequency spectrum of the band extension signal y (n) when N is “2”. This band extension signal y (n) is a signal obtained by mixing the baseband signal x _L (n) of FIG. 4C with the extension band component z _B (n) of FIG. 5E.

Fig. 7A is a graph illustrating the measured value of the frequency spectrum (horizontal axis: Hz) of the original signal when the sampling frequency fs is 1 1025 Hz, and Fig. 7B is the band extension of the first embodiment. 5 is a graph illustrating the measured value of the frequency spectrum of the band extension signal obtained as a result of extending the frequency band of the original signal using the device 1. Figure 7B shows that the baseband signal and the extended band component are smoothly connected.

As described above, the band extending apparatus 1 of the first embodiment inverts the spectrum of the band signal x _D (n) obtained by down-sampling the band signal x _H (n) whose frequency band is limited. . Further, the bandwidth extension device 1 up-samples the inverted signal z _D (n) and filters the up-sampled signal zu (n) so that the frequency of the baseband signal x _L (n) is obtained. frequency [pi / New substantially the same frequency of the high frequency end of the band and to generate a component of extension band zeta to a low pass end beta (eta), such extension band component zeta _beta (eta) is a baseband signal x Mixed with _L (n). Since such a band extension device 1 inverts the spectrum of the band signal x _D (n), compared to the conventional technology that does not perform spectrum inversion, the extension band component z _B (n) and the baseband signal The connectivity with X! _ (N) is improved and the quality of the output signal y (n) can be improved.

Furthermore, the bandwidth extension device 1 is based on the frequency spectrum of the input signal X (n). Since the mixing coefficient C (n) to be multiplied by the extended band component z _B (n) is calculated, the extended band component can be smoothly connected to the baseband signal and has a high-quality and natural frequency spectrum. The band extension signal y (n) can be generated. Next, another example of the method for calculating the mixing coefficient C (n) will be described. Narrowband This calculation method, which includes a first average of the scan Bae spectrum values at a plurality of points in the narrow band [Delta] [omega _Alpha including the frequency ω = ττΖ2 the low frequency end and the <L _A>, the frequency omega == high frequency end The second average L _B > of the spectral values at multiple points in Δω _算出 is calculated, and then the ratio between the first average L _A > and the second average L _B > is the mixing coefficient C (n). 1 is calculated. FIG. 8 is a graph illustrating a frequency spectrum for explaining the calculation method. Such case, narrowband [Delta] [omega first average rather VA> spectral values in _Alpha, second average in our Kerusupe vector value to a narrow band [Delta] [omega _beta <VB> and is calculated. Since the frequency spectrum is expressed in decibels (dB), the mixing coefficient C (n) is C (n) = <L _B > / <L _A >, <L _B > = 10 ( ^{<VB> / 20} ), <L _A > = 10 ( ^{<VA> / 20} ),

If the above calculation method is used, the coefficient calculation unit 23 does not require a regression curve of the frequency spectrum, so the mixing coefficient C (n) can be calculated with a small amount of computation, and low power consumption is also realized. it can.

Further, another method for calculating the mixing coefficient C (n) will be described with reference to FIG. FIG. 9 is a functional block diagram schematically showing a configuration of a coefficient determination unit 20D that replaces the coefficient determination unit 20 shown in FIG. The coefficient determination unit 20D includes band pass filters (BP F) 24A and 24B, square sum calculation units 25 A and 25 B, and a coefficient calculation unit 26. One band-pass filter 24 A has a low-frequency end frequency n? Only the specified narrow band including the pass band, and the other band pass filter (BP F) 24 B has only a predetermined narrow band including the frequency ω == π at the high band end as a pass band. The square sum calculators 25 Α and 25 繰り返し repeatedly calculate the square sums <Α ² > and <Β ² > of the outputs of the bandpass filters 24 Α and 24 Β, respectively, every predetermined sampling period Τ. For example, if the series of output values of the bandpass filter 24 A is A 1, A 2, A 3,…, the sum of squares A ² > is (Al) ² + (A2) ² + (A3) ² + ... Then, the coefficient calculation unit 26 calculates the square root value of the ratio of the sum of squares (<8 ² ><8 ² » ⁽¹ is the mixing coefficient C (n).

The coefficient determination unit 20D does not require a Fourier transform and a frequency spectrum, and the bandpass filters 24 A and 24B do not necessarily have to be configured with an FIR filter (finite-length impulse response filter). It can be configured with an IIR filter (infinite length impulse response filter) with a small number of taps. Therefore, the coefficient determination unit 20D can calculate the mixing coefficient C (n) with a smaller amount of computation than the coefficient determination unit 20 of FIG. 3, and can realize low power consumption.

2. Second embodiment

Next, a band extending apparatus and a band extending method according to the second embodiment of the present invention will be described. FIG. 10 is a functional block diagram schematically showing the configuration of the band extending apparatus 2 of the second embodiment. It should be noted that the components denoted by the same reference numerals in FIG. 10 and FIG. 3 are assumed to have the same function or the same configuration, and detailed description thereof is omitted.

Referring to FIG. 10, the bandwidth expansion device 2 of the second embodiment includes a baseband processing unit 10, a coefficient determination unit 2 OA, and an expansion bandwidth processing unit 3 OA. As described above, the baseband processing unit 10 performs upsampling on the sequence of the input signal X (n), and performs filtering on the upsampled signal sequence. The baseband signal x _L (n) limited to the frequency band of is generated.

The extension band processing unit 3 OA has a function of generating an extension band component z _H (n) from the sequence of the input signal X (n). The extended band processing unit 3 OA includes a spectrum inversion unit 33, an upsampler 36, and a band pass filter 37. The spectrum inversion unit 33 inverts the spectrum of the input signal X (n) to generate an inverted signal z (n). Upsampler 36 has an inverted signal Z at a rate N times or a factor of N

The sequence of (n) is upsampled to generate a sequence of upsampled signal zu (n). The band pass filter 37 has a pass band of π / Ν <I ω I <2 TCZN, and the filter signal z which is an extended band component by filtering the sequence of the upsampling signal zu (n). Generate a sequence of _B (n). This extended band component z _B (n) is supplied to the mixing unit 40.

FIG. 1 18 to FIG. 11 1D illustrate frequency spectra when N is “2”. In such a case, when the input signal X (n) shown in FIG. 11A is supplied, the spectrum inversion unit 33 inverts the spectrum of the input signal X (n), and the result shown in FIG. Generate an inverted signal z (n) with the frequency spectrum to be controlled. The upsampler 36 performs upsampling on the series of the inverted signal z (n) at twice the rate, that is, a factor of 2, and the upsampling signal zu (n ) Is generated. In addition, the band pass filter 37 has a pass band of π / l <\ ω \ <、, and generates an extended band component ζ _Β (η) having a frequency spectrum shown in FIG. _11D .

On the other hand, the coefficient determining unit 20 Α has an FFT unit 21, a spectrum calculating unit 22, and a coefficient calculating unit 23 Α. The coefficient calculation unit 23 A is calculated by the spectrum calculation unit 22 Based on the obtained frequency spectrum, a linear or non-linear regression curve can be calculated in the frequency range of 0 to 7 mm, and the mixing coefficient can be calculated using this regression curve. Specifically, a linear regression line expressed by a linear function may be used as the regression curve.

In the case of the second embodiment, by applying upsampling and filtering to the components of the entire frequency band of the input signal X (η), an extended band component ζ _Β (η) as shown in Fig. 11 D is generated. Is done. Therefore, the mixing coefficient C (η) is equal to the low end frequency ω = 0 of the frequency band of the input signal X (η) or the spectral value L _A of the regression curve at a point near it. Is given by the ratio L _B / L _A of the spectral value L _B of the regression curve at or near the frequency ω = ττ.

Figure 12A is a diagram you illustrate a frequency spectrum and regression curve L _R of the input signal X (n). Of the spectrum curve C _s , the regression curve L _{R in} the 0 to redundant frequency range is calculated. Since this frequency spectrum is expressed in decibels (dB), when the amplitude at the point of ω = 0 is expressed as VA and the amplitude at the point of ω = ττ is expressed as VB, the mixing coefficient C (η) is C ( n) = L _B ZL _A , L _B = 10 ^ ^{/ 20} ), L _A = 10 ( ^{VA / 20} ).

Note that the mixing coefficient C (n) may be calculated by applying the calculation methods shown in FIGS. 8 and 9 instead of the calculation method of the coefficient determining unit 20A. In such a case, the calculation method shown in FIGS. 8 and 9 may be applied by setting the frequency at the low end to ω = 0 and the frequency at the high end to ω = π.

In the mixing unit 40, the multiplier 41 multiplies the extension coefficient band component z _B (n) by the mixing coefficient C (n) supplied from the coefficient determining unit 2OA, and the adder 42 This is added to the baseband signal supplied from the baseband processing unit 10. As a result of the addition, a band extension signal y (n) is generated. Figure 12B shows the frequency spectrum of the band extension signal y (n) when N = 2. This band extension signal y (n) is a signal obtained by mixing the baseband signal with the extension band component z _B (n) of FIG. 11D. As described above, the band extending apparatus 2 of the second embodiment inverts the spectrum of the input signal X (n), up-samples the inverted signal z (n), and performs the up-sampled signal zu (n) Is applied to the baseband signal (n) to generate an extended band component ζ _Β (η) with the same frequency as the high frequency ττΖΝ of the baseband signal (n). Such an extended band component ζ _Β (η) is mixed with the base spanned signal x _L (n). Since such a band extension device 2 inverts the spectrum of the input signal X (n), compared to the conventional technique that does not perform spectrum inversion, the extension band component z _B (n) and the baseband The connectivity with the signal x _L (n) is improved, and the quality of the output signal y (n) can be improved.

Furthermore, since the band extension device 2 calculates the mixing coefficient C (n) to be multiplied by the extension band component z _B. (N) based on the frequency spectrum of the input signal X (n), the band extension device 2 It can be smoothly connected to the baseband signal, and it is possible to generate a band extension signal y (n) with a high-quality and natural frequency spectrum.

3. Third Example

Next, a bandwidth extension apparatus and a bandwidth extension method according to a third embodiment of the present invention will be described. FIG. 13 is a functional block diagram schematically showing the configuration of the bandwidth extension device 3 of the third exemplary embodiment. It should be noted that the components denoted by the same reference numerals in FIGS. 13 and 3 are assumed to have the same function or the same configuration, and detailed description thereof is omitted. Referring to FIG. 13, the bandwidth expansion device 3 of the third embodiment includes a baseband processing unit 10, a coefficient determination unit 20 B, a first expansion band processing unit 30, and a second expansion band processing unit 50. is doing. As described above, the baseband processing unit 10 performs upsampling on the system of the input signal X (n) and filters the upsampled signal sequence to limit the baseband limited to a predetermined frequency band. A panda signal x _L (n) is generated. The first extension band processing unit 30 has a function of generating a first extension band component z _B (n) from the sequence of the input signal X (n).

The second extension band processing unit 50 includes an upsampler 51 and a band pass filter (BPF) 52. The upsampler 5 1 upsamples the downsampling signal x _D (n) sequence supplied from the downsampler 3 2 of the first extension band processing unit 30 at a rate of 2 XN times, that is, a factor of 2 XN. To generate a sequence of up-sampled signals x _U2 (n). The bandpass filter (BPF) 5 2 has a passband of 3% / (2 XN) <\ ω \ <4% / (2 ΧΝ) and filters the sequence of upsampled signals x _U2 (n) To generate the second extended band component x _B (n).

Figures 14-8 to 14E illustrate frequency spectra for N = 2. When the input signal X (n) having the spectrum shown in Fig. 4A is supplied, the baseband processing unit 10 outputs the baseband signal (n) having the spectrum shown in Fig. 14A. The first extension band processing unit 30 outputs the first extension band component z _B (n) having the spectrum shown in FIG. 14B. The downsampler 3 2 of the first extension band processing unit 30 uses the downsampling signal x _D (n) having the spectrum shown in FIG. 14C as the upsampler 5 1 of the second extension band processing unit 50. To supply. Therefore, The upsampler 51 generates the upsample signal x _U2 (n) having the spectrum shown in FIG. 14D. The band pass filter 52 has a pass band of 3 ττΖ4 <| ω | <π, and outputs the second extension band component X Β (η) having the spectrum shown in FIG.

The coefficient determination unit 20Β has substantially the same configuration and function as the coefficient calculation unit 23 in FIG. 3, and includes a first mixing coefficient C (η) and a second mixing coefficient C (η) ² that is a square value thereof. To the mixing unit 40 部. In the mixing unit 40, the first multiplier 41 乗算 multiplies the first extension band component z _B (n) by the first mixing coefficient C (n) and supplies the multiplication result to the adder 43. The second multiplier 41 B multiplies the second extension band component x _B (n) by the second mixing coefficient C (n) ² and supplies the multiplication result to the adder 43. The adder 43 generates a band extension signal y (n) by adding the multiplication results to the baseband signal supplied from the base processing unit 10. Figure 14F shows the frequency spectrum of the band extension signal y (n) when N = 2. The band extension signal y (n) in Fig. 14F is replaced with the baseband signal x _L (n) in Fig. 14A by the first extension band component z _B (n) in Fig. 14B and the second extension in Fig. 14E. This signal is a mixture of the band components B (n).

As described above, the band extension device 3 of the third embodiment adds the second extension band component x _B (n) to the second extension band component x _B (n) in addition to the configuration of the band extension device 1 (FIG. 3) of the first embodiment. Since the extended band processing unit 50 is provided, it is possible to obtain an output signal y (n) whose frequency band is further expanded.

4. Fourth example

Next, a band extending apparatus and a band extending method according to the fourth embodiment of the present invention will be described. FIG. 15 is a functional block diagram schematically showing the configuration of the bandwidth extension device 4 of the fourth exemplary embodiment. It should be noted that the components denoted by the same reference numerals in FIG. 15 and FIG. 3 are assumed to have the same function or the same configuration, and detailed description thereof is omitted.

Referring to FIG. 15, the bandwidth extension device 4 of the fourth embodiment includes a baseband processing unit 10, a coefficient determination unit 20 C, a first extension band processing unit 30 C, a second extension band processing unit 50 C and a mixing unit. Has 40C. FIG. 16 schematically shows the configuration of the mixing section 40C. As described above, the baseband processing unit 10 performs upsampling on the sequence of the input signal X (n), and performs filtering on the upsampled signal sequence to limit the baseband to a predetermined frequency band. The signal x _L (n) is generated.

The first extension band processing unit 30C has a function of generating a plurality of first sub-band components..., Z _N-1 as extension band components from the sequence of the input signal X (n). The first extended band processing unit 30C includes a high-pass filter (HPF) 31, a down sam- ber 32, a spectrum inversion unit 33, and an up sam- ber 34, and a plurality of band pass filters each having a different pass band ( BPF) 35 _1; .., 35 _N-1 has a filter bank. The k th (k is an integer from 1 to N—1) band pass filter 35 _k has a pass band of 2 k TCZ (2N) <I ω I <(2 k + 1) κ / (2N) Yes. These band-pass filters 35... 35 _Ν-1 filter the upsampling signal z _u (n) from the upsampler 34 to obtain a plurality of first subband components z, ..., z _N-1 is generated and supplied to the multiplier 44.

On the other hand, the second expansion band processing unit 50C has an upsammbler 51, and each Have a filter bank composed of a plurality of band pass filter (BPF) 52 _1; ..., 52 _N−1 . The kth (k is an integer from 1 to N—1) bandpass filter 52 _k has a passband of (2 k + 1) t / (2N) <I ω I <(2 k + 2)% / (2N) Have. The upsampler 5 1 applies the upsampling signal x _U2 (n) to the series of downsampling signal x _D (n) from downsampler 32 by upsampling by a factor of 2 XN, that is, a factor of 2 XN. Generate a series of The bandpass filter 52 _1; 52 _N-1 applies a filter ring to the sequence of the up-sampling signal x _U2 (n) to obtain a plurality of second subband components X, ..., x _N whose frequency band is limited. ₋₁ is generated and supplied to the multiplication unit 44. Bandpass filter 35 _1? ..., 35 _N-1 filter characteristics and bandpass filter 52 _1; …, 52 _N-1 filter characteristics are the first and second subband components _Z1 , z _N-1 , X ₁₅ ..., x _N-1 are configured to be substantially continuous. Band-pass filter 35 ₁₅ 5 352, 52 ₂ ,…, 35 _N-1 and 52 _N-1 passbands are continuous. As a result, the frequency band of the band extension signal y (n) is not discontinuous and is continuously continuous.

Figures 17A to 17D and 18A to 18G illustrate frequency spectra for N = 4. These frequency spectra are shown only in the 0 to redundant frequency range. — 71: Even in the frequency range of 0 to 0, frequency spectra that are mirror images of the frequency spectrum and the point at ω = 0 (Fig. Not shown) exists. When an input signal X (n) having a spectrum is supplied as shown in Fig. 17 Α, the baseband processing unit 10 generates a spectrum limited in the band from 0 to 兀 4 as shown in Fig. 17B. The baseband signal x _L (n) is output. First expansion In the bandwidth processing unit 30 C, the downsampler 32 outputs a downsampling signal XD (n) having the spectrum shown in FIG. 17 C, and the spectrum inversion unit 33 has the spectrum shown in FIG. Output inverted signal z _D (n) with. In this case, the bandpass filter 35 _1; 35 _2, 35 _3, respectively, and outputs the FIG 18A, I 8B, the first sub-band component having a spectrum shown in Figure _{_{18 C Z1, z 2, z}} 3. On the other hand, the band-pass filter 52 52 _2, 52 _3, respectively, and outputs the Figure 1 8D, FIG. 1 8E, a second sub-band component _X1 having a spectrum shown in FIG. 18 F, ₂₎ x _3. It can be seen that the frequency bands of the first and second subband components z 1, xz ₂ , x ₂ , z ₃ , and x ₃ shown in FIGS. 18A to 18F are continuous. Coefficient determination unit 20 Also generates the same mixing coefficient C as the mixing coefficient C (n) given by the coefficient determination unit 20 in Fig. 3, and calculates the mixing coefficient of C ² , C ³ , ..., C ^2N — ² To do. These mixing coefficient data CDs are supplied to the mixing section 40C.

As illustrated in FIG. 16, the mixing unit 40 C includes first subband component multipliers 4 5 _1; ..., 45 _N−1 and second subband component multipliers 46 _1; ·, With 46 ^. The first sub-band component multipliers 45 ^ 45 ₂ ,..., 45 _N-1 are respectively input to the first sub-band components z _l5 z ₂ _,. _2> ···, 45 _N-1 is given multiplication coefficients C, C ³ , ···, C ^2N — ³ , respectively. On the other hand, the multiplier 46 46 ₂ of the second sub-band components, ..., the 46 _N-1, respectively, the second sub-band component _{x, x 2, ···, x} N-1 inputs and, the multipliers 46 46 _2, · ■ ·, the 46 _N-1, respectively, the multiplication factor ^{^{C 2, C 4, ···,}} C 2N - 2 are given. The adder 43 adds all outputs of the multipliers 45... 45 _N−1 , 46..., 46 _{N−1 to} the baseband signal to generate a band extension signal y (n). As a result, as illustrated in FIG. 18G, an extended band component in which the first subband component and the second subband component are alternately arranged is formed in the frequency spectrum of the band extension signal y (n). Will be.

As described above, in the bandwidth expansion device 4 of the fourth embodiment, the first expansion bandwidth processing unit 30 C and the second expansion bandwidth processing unit 50 C have filter banks 35 to 35 _N-1 and 5 2 ₁₉ . Since it has _N-1 , it is possible to generate a band extension signal y (n) having a high-quality and natural frequency spectrum.

5. Application examples

The band extension apparatuses 1 to 4 of the first to fourth embodiments can be applied to various devices. FIG. 19A to FIG. 19C are diagrams schematically showing an application example of the band extension device 1. FIG. Referring to FIG. 19A, the bandwidth extension device 1 (or bandwidth extension devices 2 to 4) is connected between the audio signal processing unit 60 and the D / A converter (DAC) 61. The audio signal processing unit 60 is a block that performs audio signal processing such as PCM encoding, for example. The band extension device 1 can extend the frequency band of the signal supplied from the audio signal processing unit 60 and supply the band extension signal to the DZA converter 61. In the example of FIG. 19B, the bandwidth extension device 1 (or bandwidth extension devices 2 to 4) is connected between a decoder 62 incorporated in a mobile phone or an optical disk playback device and a DZA converter (DAC) 63. ing. The band extension device 1 can extend the frequency band of the decoded signal supplied from the decoder 62 and supply the band extension signal to the D-no A converter 63.

In the example of Fig. 19C, the bandwidth extension device 1 (or bandwidth extension devices 2 to 4) is connected between a tuner 64 such as an AM tuner or FM tuner, and a DZA converter (DAC) 67. Connected between. The output of the tuner 64 is filtered by a low-pass filter (LPF) 6 5 and converted to 8/0 by an AZD converter (AD C) 6 6. The band extension device 1 extends the frequency band of the digital output of the A / D converter 66 and supplies the band extension signal to the DZA converter 67.

Further, all or a part of the bandwidth extension apparatuses 1 to 4 of the first to fourth embodiments may be realized by hardware, or may be realized by a program executed by a processor such as a CPU. May be.

Claims

The scope of the claims

1. A bandwidth expansion device for expanding the frequency band of an input signal,

A baseband processing unit that performs upsampling on the input signal and fills the upsampled signal to generate a baseband signal limited to a predetermined frequency band; and

An extension band processing unit that generates an extension band component from the input signal;

A mixing unit that mixes the extension band component with the baseband signal, and the extension band processing unit includes:

A spectrum inversion unit that inverts a spectrum of the input signal or a band signal obtained from the input signal to generate an inverted signal;

An upsampling unit for upsampling the inverted signal;

By performing fill-up ringing on the output of the upsampler, a frequency band component having a frequency that is substantially the same as the frequency at the high frequency end of the frequency band of the baseband signal is generated as the expansion band component. Bandpass fill and

A band extending apparatus comprising:

2. The bandwidth extension apparatus according to claim 1,

The spectrum inversion unit inverts the spectrum of the band signal to generate the inverted signal,

The extended bandwidth processing unit

A filter limited to the second frequency band by filtering the input signal. A second bandpass filter that generates an evening signal, and

A band extender comprising: a down sampler for down-sampling the fill signal to obtain the band signal.

3. The band extending apparatus according to claim 2, wherein the downsampler performs the downsampling with two factors.

4. The band extending apparatus according to claim 2 or 3, wherein a frequency spectrum of the input signal and a regression curve of the frequency spectrum are calculated, and the extension band component is multiplied using the regression curve. And a coefficient determination unit that determines a power mixing coefficient, wherein the mixing unit multiplies the extension band component by the mixing coefficient and adds the multiplication result to the baseband signal. .

5. The band extending apparatus according to claim 4, wherein the coefficient determining unit uses the regression curve to calculate a frequency at a frequency at a high frequency end of the second frequency band or a frequency in the vicinity thereof.

Obtaining a first spectral value and a second spectral value at a frequency at or near the lower end of the second frequency band, and obtaining the first and second spectral values. A band extending apparatus for calculating a ratio of spectrum values as the mixing coefficient.

6. The band extending apparatus according to claim 2 or 3, wherein a frequency spectrum of the input signal is calculated, and a coefficient for determining a mixing coefficient to be multiplied by the extended band component using the frequency spectrum. A decision unit; The coefficient determination unit uses the frequency spectrum to reduce the first spectrum value at a frequency at or near the high frequency end of the second frequency band and the low frequency band of the second frequency band. Obtaining a second spectrum value at a frequency at or near the band edge, and calculating a ratio between the first and second spectrum values as the mixing coefficient,

The band expanding device, wherein the mixing unit multiplies the expansion band component by the mixing coefficient and adds the multiplication result to the one spanned signal.

7. The band extending apparatus according to claim 2, wherein a frequency spectrum of the input signal is calculated, and a coefficient for determining a mixing coefficient to be multiplied by the extended band component using the frequency spectrum. A decision unit;

The coefficient determination unit uses the frequency spectrum to calculate a first average of spectrum values in a predetermined narrow band including a frequency at a high frequency end of the second frequency band, and a low value of the second frequency band. Calculating a second average of spectrum values in a predetermined narrow band including a frequency at a band edge, and calculating a ratio of the first and second averages as the mixing coefficient;

The band expanding device, wherein the mixing unit multiplies the tension band component by the mixing coefficient and adds the multiplication result to the base spanned signal.

8. The band extending apparatus according to claim 2, further comprising a coefficient determining unit that determines a mixing coefficient to be multiplied by the extended band component,

The coefficient determination unit A first band pass filter for filtering the input signal having a predetermined narrow band including a frequency at a high end of the second frequency band as a pass band;

A second band pass filter that has a predetermined narrow band including a frequency at a lower end of the second frequency band as a pass band and applies a filter ring to the input signal;

The sum of squares of the output of the first bandpass filter is calculated over a predetermined sample period, and the sum of squares of the output of the second bandpass filter is calculated over the sample period to calculate the sum of squares. An arithmetic unit that calculates a square root value of the ratio of

The mixing unit multiplies the extension band component by the mixing coefficient and adds the multiplication result to the baseband signal.

9. The band extending apparatus according to claim 1, wherein a frequency spectrum of the input signal and a regression curve of the frequency spectrum are calculated, and a mixing coefficient to be multiplied by the extension band component is calculated using the regression curve. A coefficient determination unit for determining,

The spectrum inversion unit inverts the spectrum of the input signal to generate the inverted signal,

The mixing unit multiplies the extension band component by the mixing coefficient and adds the multiplication result to the baseband signal. .

10. The band extending apparatus according to claim 9, wherein the coefficient determination unit uses the regression curve to calculate a first frequency at a frequency at a high frequency end of the frequency band of the input signal or a frequency in the vicinity thereof. The spectral value of 1 and the frequency or frequency at the lower end of the frequency band of the input signal. Obtains a second spectral value at a frequency in the vicinity thereof, and calculates a ratio of the first and second spectral values as the mixing coefficient.

1 1. The band extending apparatus according to claim 1, wherein a frequency spectrum of the input signal is calculated, and a coefficient determination is performed to determine a mixing coefficient to be multiplied by the extended band component using the frequency spectrum. Further comprising

The coefficient determination unit uses the frequency spectrum to set a first spectrum value at a frequency at or near a high frequency end of the frequency band of the input signal and a frequency of the input signal. Obtaining a second spectrum value at a frequency at the lower end of the band or a frequency in the vicinity thereof, and calculating a ratio of the first and second spectrum values as the mixing coefficient,

1 2. The band extension apparatus according to claim 1, wherein a frequency spectrum of the input signal is calculated, and a coefficient determination is performed to determine a mixing coefficient to be multiplied by the extension band component using the frequency spectrum. Further comprising:

The spectrum inversion unit inverts the spectrum of the input signal to generate the inverted signal, The coefficient determination unit uses the frequency spectrum to calculate a first average of spectrum values in a predetermined narrow band including a frequency at a high frequency end of the frequency band of the input signal, and the input signal. The second average of the spectrum values in a predetermined narrow band including the frequency at the lower end of the frequency band is calculated, and the ratio of the first and second averages is calculated as the mixing coefficient. ,

1 3. The band stretching apparatus according to claim 1, further comprising a coefficient determination unit that determines a mixing coefficient to be multiplied by the extended band component,

The coefficient determination unit

A first band pass filter having a predetermined narrow band including a frequency at a high frequency end of the frequency band of the input signal as a pass band and filtering the input signal; and a frequency at a low frequency end of the frequency band of the input signal A second band-pass filter that has a predetermined narrow band including a pass band as a pass band and filters the input signal, and sums the squares of the outputs of the first band-pass filter over a predetermined sample period. And calculating a square sum of the output of the second bandpass filter over the sample period and calculating a square root value of the ratio of the square sum as the mixing coefficient, and

The mixing unit multiplies the extension band component by the mixing coefficient and outputs the multiplication result. A band expanding device characterized by adding to a spanned signal.

1 4. The band extending apparatus according to claim 2 or 3, further comprising a second extension band processing unit that generates a second extension band component from the input signal,

The second extension bandwidth processing unit

An up-sampling unit for up-sampling the band signal supplied from the down-sampling unit included in the extended band processing unit;

By performing filtering on the output of the up-sampler, a band pass that generates a frequency band component having a frequency that is substantially the same as the high-frequency end frequency of the extension band component as the second extension band component is generated. A filter, and

The mixing unit mixes the extension band component and the second extension band component with the baseband signal.

15. The band extending apparatus according to claim 14, wherein a frequency spectrum of the input signal and a regression curve of the frequency spectrum are calculated, and the extended band is calculated using the regression curve. A coefficient determining unit that determines a first mixing coefficient to be multiplied by a component and a second mixing coefficient to be multiplied by the second extension band component;

The mixing unit multiplies the extension band component by the first mixing coefficient and multiplies the second extension band component by the second mixing coefficient and adds the multiplication result to the baseband signal. Bandwidth expansion device.

16. The band extending apparatus according to claim 14, wherein a frequency spectrum of the input signal is obtained. And a coefficient determining unit that determines a first mixing coefficient to be multiplied by the extension band component and a second mixing coefficient to be multiplied by the second extension band component using the frequency spectrum. Prepared,

The mixing unit multiplies the extension band component by the first mixing coefficient and multiplies the second extension band component by the second mixing coefficient and adds the multiplication result to the total spanned signal. A bandwidth extension device.

1 7. The band extending apparatus according to claim 2 or 3, further comprising a second extension band processing unit that generates a second extension band component from the input signal,

The bandpass filter included in the extension band processing unit generates a plurality of first subband components limited to different frequency bands as the extension band components by filtering the output of the upsampler. It is made up of Phil Yubank,

The second extension bandwidth processing unit

An upsampler for upsampling the band signal supplied from the downsampler included in the extended band processing unit;

A filter puncture that generates a plurality of second sub-band components limited to different frequency bands as the second extension band components by filtering the output of the up-sampler, and

The band extending device, wherein the mixing unit mixes the first sub-band component and the second sub-band component with the baseband signal.

1 8. The band extending apparatus according to claim 17, wherein the frequency band of the first subband component and the frequency band of the second subband component are continuous.

19. The band extending apparatus according to claim 17 or 18, wherein a frequency spectrum of the input signal and a regression curve of the frequency spectrum are calculated, and the regression curve is used to calculate the frequency spectrum. A coefficient determination unit for determining a plurality of first mixing coefficients to be multiplied by the first sub-band components and a plurality of second mixing coefficients to be multiplied by the second sub-band components, respectively;

The mixing unit multiplies the first subband component by the first mixing coefficient, and multiplies the second subband component by the second mixing coefficient, and adds the multiplication result to the baseband signal. A bandwidth expansion apparatus characterized by:

20. The band extending apparatus according to claim 17 or 18, wherein a frequency spectrum of the input signal is calculated, and each of the first subband components is calculated using the frequency spectrum. A coefficient determining unit that determines a plurality of first mixing coefficients to be multiplied and a plurality of second mixing coefficients to be multiplied by the second subband component, respectively, and the mixing unit includes the first subband component; A band extending apparatus characterized by multiplying the first mixing coefficient and multiplying the second subband component by the second mixing coefficient, respectively, and adding the multiplication result to the baseband signal.

2 1. A bandwidth expansion method for extending the frequency bandwidth of an input signal, (a) performing upsampling on the input signal and filtering the upsampled signal to generate a baseband signal limited to a predetermined frequency band; and

(b) generating an extended band component from the input signal;

(c) mixing the extension band component with the baseband signal, and

Step (b)

(b-1) inverting the spectrum of the input signal or a band signal obtained from the input signal to generate an inverted signal;

(b-2) performing upsampling on the inverted signal;

(b-3) By applying filtering to the inverted signal up-sampled in step (b-2), the frequency substantially the same as the frequency at the high end of the frequency band of the baseband signal is reduced. Generating a frequency band component as a band edge as the extended band component; and a band extending method comprising:

22. A bandwidth extension program for causing a processor to execute bandwidth extension processing for extending a frequency bandwidth of an input signal,

The bandwidth extension process includes:

Baseband processing for generating a baseband signal limited to a predetermined frequency band by performing upsampling on the input signal and performing fill-up on the upsampled signal;

Extended band processing for generating an extended band component from the input signal; Mixing processing for mixing the tension band component to the baseband signal, and the extension band processing comprises:

A spectrum inversion process for generating an inverted signal by inverting the spectrum of the input signal or a band signal obtained from the input signal;

Up-sampling processing for up-sampling the inverted signal, and a frequency band having a low-frequency end that is substantially the same as the high-frequency end frequency of the baseband signal by filtering the output of the up-sampler And a band expansion program for generating a band component as the expansion band component.