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JP2002171588

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2002171588
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
signal interpolation apparatus and a signal interpolation method for improving the spectral
distribution of a signal.
[0002]
2. Description of the Related Art Recently, distribution of data in the MP3 (MPEG1 audio layer 3)
format and supply of music by methods such as FM (Frequency Modulation) broadcasting and
television sound multiplex broadcasting have become popular. In these techniques, in order to
avoid an increase in the amount of data due to an excessively wide band and an increase in the
occupied bandwidth, frequency components of about 15 kHz or more are generally removed
from music to be supplied.
[0003]
As described above, music etc. in which frequency components above a certain value have been
removed usually have poor sound quality. Therefore, it is conceivable to add a signal instead of
the removed frequency component. As a method for this purpose, the method disclosed in
Japanese Patent Laid-Open No. 7-93900, the method disclosed in Japanese Patent Laid-Open No.
6-85607, and Japanese Patent Application No. 2000 filed by the applicant of the present
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application. There is a method disclosed in -178569.
[0004]
The method disclosed in JP-A-7-93900 causes distortion by multiplying an output audio signal
obtained by low-pass filtering a PCM digital audio signal by a signal including an absolute value
component of the output signal. It is a method of making it
[0005]
The method disclosed in Japanese Patent Laid-Open No. 6-85607 extracts a tone color
component in which a fundamental sound and a harmonic sound exist as a pair from an original
audio signal, and uses the extracted tone color component to generate a high frequency band
higher than the band of the original audio signal. This is a method of predicting the overtone
component of and extrapolating to the original audio signal.
[0006]
The method disclosed in Japanese Patent Application No. 2000-178569 filed by the applicant of
the present application divides the spectrum of the PCM signal into a plurality of bands, and one
spectral component of a pair of strongly correlated bands is the original PCM. In addition to the
spectrum of the signal, it is a technique of generating a PCM signal having the spectrum after the
spectral components have been added.
[0007]
However, the audio signal reproduction apparatus disclosed in JP-A-7-93900 only generates
harmonics by distorting the waveform of the output audio signal using an absolute value circuit
or the like. It is not known whether this harmonic can approximate what is contained in the
original audio signal.
[0008]
In addition, when the method of Japanese Patent Laid-Open No. 6-85607 is applied to an original
audio signal obtained by limiting the band of the original voice etc., it is not possible to predict
and extrapolate a harmonic component for a tonal component of a pure tone. Also, with regard to
the tonal component from which the overtone component has been removed as a result of the
band limitation, the removed overtone component can not be estimated and extrapolated.
[0009]
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In this respect, in the frequency interpolator of Japanese Patent Application No. 2000-178569,
since the added spectral component can be regarded as a harmonic component of a part of the
original signal, if the original signal is a band-limited signal, The signal having the spectrum after
the addition of the spectral component is close to the original signal before the band limitation.
[0010]
However, in the method of Japanese Patent Application No. 2000-178569, by dividing the
spectrum of the original signal into bands, of the waveform of the signal represented by the
separated spectrum, the portion immediately before or just after the waveform rises is Distortion
called pre-echo is added.
When the original signal represents speech, the band occupied by the pre-echo generally
corresponds to a portion close to the upper limit (for example, 10 kHz or more) of the band
occupied by the original speech.
For this reason, the speech represented by the signal having the spectrum after the addition of
the spectral component is a distorted high-frequency portion of the speech represented by the
original signal.
[0011]
The present invention has been made in view of the above situation, and it is a signal
interpolation for restoring a signal close to an original signal with less distortion from a
modulated wave obtained using a signal in which the band of the original signal is limited. It is an
object to provide an apparatus and a signal interpolation method.
Another object of the present invention is to provide a signal interpolation apparatus and a signal
interpolation method for restoring an audio signal with high sound quality.
[0012]
SUMMARY OF THE INVENTION In order to achieve the above object, a signal interpolation
apparatus according to a first aspect of the present invention extracts a component in a first
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band of an interpolated signal to be interpolated. And a frequency conversion unit that generates
an interpolation component by frequency converting a filter in the first band extracted by the
filter into a second band higher in frequency than the band occupied by the interpolated signal
And an addition unit that generates an output signal representing a sum of the interpolated
signal and the component for interpolation generated by the frequency conversion unit.
[0013]
According to such a signal interpolation apparatus, the frequency-converted component of the
signal to be interpolated is added to the signal to be interpolated, and the band is expanded.
Since the added component can be regarded as a harmonic component of a portion of the
interpolated signal, if the interpolated signal is a band-limited signal, the interpolated signal after
the band expansion is band-limited. Close to the original signal before the
Moreover, such a signal interpolation device does not perform processing for decomposing the
spectrum into bands.
Therefore, if the interpolated signal represents an audio signal, the audio signal is restored with
low distortion and high sound quality by restoring the audio signal using the interpolated signal
after the band expansion.
[0014]
If the upper limit of the first band is substantially equal to the upper limit of the distribution of
the spectrum of the signal to be interpolated, the component added to the signal to be
interpolated is particularly the harmonic component of a portion of the signal to be interpolated.
There is a high probability of being able to approximate well.
Therefore, the interpolated signal after the band expansion is closer to the original signal before
the band restriction.
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[0015]
If the lower limit of the second band is substantially equal to the upper limit of the distribution of
the spectrum of the interpolated signal, the spectrum of the component added to the interpolated
signal is the spectrum of the interpolated signal, and the high frequency side And adjacent ones
without gaps. Therefore, the interpolated signal after the band expansion is closer to the original
signal before the band restriction.
[0016]
The filter includes means for changing the range of the first band in response to an instruction
supplied to the filter, and the frequency converter is configured to change the second in response
to the instruction supplied to the filter. A means for changing the range of the band may be
provided. In this case, the signal interpolation device acquires, for example, the interpolated
signal, identifies the upper limit of the acquired spectrum of the interpolated signal, and the first
and second ones based on the identified result. The range of the band is determined, and an
instruction to set the range of the first band to the range determined by itself is supplied to the
filter, and the range determined by the range of the second band is determined to the frequency
conversion unit. The range of the first and second bands is self-optimized by providing spectrum
analysis means for supplying an instruction to
[0017]
The signal interpolation apparatus extracts envelope information representing an envelope of the
spectrum of the signal to be interpolated, acquires the component for interpolation generated by
the frequency conversion unit, and the acquired spectrum intensity of the component for
interpolation is The interpolation component may be filtered so as to be substantially equal to
the intensity represented by the envelope indicated by the envelope information, and the
equalizing unit may be supplied to the addition unit. In this case, the addition unit may generate
an output signal representing the sum of the interpolated signal and the component for
interpolation filtered by the equalizing unit. By having such a configuration, the signal
interpolation device adds the component to be added to the signal to be interpolated to the signal
to be interpolated in accordance with the envelope of the spectrum of the signal to be
interpolated. Therefore, the interpolated signal after the band expansion is closer to the original
signal before the band restriction.
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[0018]
The addition unit includes a delay unit that delays the interpolated signal so as to be substantially
in phase with the interpolation component, and represents a sum of the interpolation component
and the interpolated signal delayed by the delay unit. If the output signal is to be generated, the
adder accurately extends the band of the interpolated signal even if any one of the filter and the
frequency converter generates a delay of the signal.
[0019]
In the signal interpolation method according to the second aspect of the present invention, a
component in a first band is extracted from among interpolated signals to be interpolated, and
the extracted component in the first band is Generating a component for interpolation by
performing frequency conversion to a second band higher than the band occupied by the signal
to be interpolated, and generating an output signal representing a sum of the signal to be
interpolated and the component for interpolation It is characterized by
[0020]
According to such a signal interpolation method, the frequency-converted component of the
signal to be interpolated is added to the signal to be interpolated, and the band is expanded.
Since the added component can be regarded as a harmonic component of a portion of the
interpolated signal, if the interpolated signal is a band-limited signal, the interpolated signal after
the band expansion is band-limited. Close to the original signal before the
Also, such signal interpolation methods do not include the step of decomposing the spectrum
into bands. Therefore, if the interpolated signal represents an audio signal, the audio signal is
restored with low distortion and high sound quality by restoring the audio signal using the
interpolated signal after the band expansion.
[0021]
If the upper limit of the first band is substantially equal to the upper limit of the distribution of
the spectrum of the signal to be interpolated, the component added to the signal to be
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interpolated is particularly the harmonic component of a portion of the signal to be interpolated.
There is a high probability of being able to approximate well. Therefore, the interpolated signal
after the band expansion is closer to the original signal before the band restriction.
[0022]
If the lower limit of the second band is substantially equal to the upper limit of the distribution of
the spectrum of the interpolated signal, the spectrum of the component added to the interpolated
signal is the spectrum of the interpolated signal, and the high frequency side And adjacent ones
without gaps. Therefore, the interpolated signal after the band expansion is closer to the original
signal before the band restriction.
[0023]
The interpolated signal is acquired, the upper limit of the acquired distribution of the spectrum
of the interpolated signal is identified, the ranges of the first and second bands are determined
based on the identified result, and according to the determination result, If the ranges of the first
and second bands are to be changed, the ranges of the first and second bands are automatically
optimized.
[0024]
The envelope information representing the envelope of the spectrum of the interpolated signal is
extracted, and the interpolation is performed such that the intensity of the spectrum of the
component for interpolation is substantially equal to the intensity represented by the envelope
indicated by the envelope information. Components may be filtered to generate an output signal
representing the sum of the interpolated signal and the filtered component for interpolation.
By doing this, the component to be added to the interpolated signal is added to the interpolated
signal along the envelope of the spectrum of the interpolated signal. Therefore, the interpolated
signal after the band expansion is closer to the original signal before the band restriction.
[0025]
Assuming that the interpolated signal is delayed so as to be substantially in phase with the
interpolation component, and the output signal representing the sum of the interpolation
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component and the delayed interpolated signal is generated. Even when a signal delay occurs in
the process of extracting the component in the band of and the process of generating the
component for interpolation, the band expansion of the interpolated signal is accurately
performed.
[0026]
A computer-readable recording medium according to a third aspect of the present invention is a
computer-readable recording medium, comprising: a filter for extracting a component in a first
band from among interpolated signals to be interpolated; A frequency converter configured to
generate an interpolation component by frequency converting a component in the first band into
a second band on a higher frequency side than a band occupied by the interpolated signal; the
interpolated signal, and A program for functioning as an addition unit that generates an output
signal representing a sum with the component for interpolation generated by a frequency
conversion unit is recorded.
[0027]
A computer that executes a program recorded on such a recording medium extends the band of
the signal to be interpolated by adding, to the signal to be interpolated, a component of the signal
to be interpolated whose frequency has been converted.
Since the added component can be regarded as a harmonic component of a portion of the
interpolated signal, if the interpolated signal is a band-limited signal, the interpolated signal after
the band expansion is band-limited. Close to the original signal before the
Also, such a computer does not perform the process of decomposing the spectrum into bands.
Therefore, if the interpolated signal represents an audio signal, the audio signal is restored with
low distortion and high sound quality by restoring the audio signal using the interpolated signal
after the band expansion.
[0028]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A signal interpolation apparatus
according to an embodiment of the present invention will be described below by taking a high
frequency signal interpolator as an example with reference to the drawings.
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[0029]
FIG. 1 is a diagram showing the configuration of a high frequency signal interpolator according
to the embodiment of the present invention.
As illustrated, the high-frequency signal interpolator includes a variable BPF (band pass filter) 1,
a delay unit 2, a spectrum analysis unit 3, a variable frequency oscillation unit 4, a mixing unit 5,
and a variable HPF (high pass). A filter 6) and an adder 7 are provided.
[0030]
The variable BPF 1 is supplied with a signal (input signal) to be subjected to spectrum
interpolation by the high-frequency signal interpolator, and the input signal supplied to the
variable BPF 1 is supplied from the spectrum analysis unit 3 to the first signal described later.
The components in the passband having the center frequency and bandwidth specified by the
control signal are passed to the mixing unit 5 to substantially block other components.
[0031]
The input signal is a signal representing voice or the like.
The spectral distribution of the voice or the like represented by the input signal corresponds to,
for example, the original voice or the like from which frequency components of a predetermined
value or more (for example, 14 kHz or more) have been removed.
[0032]
The delay unit 2 is supplied with the same input signal as that supplied to the variable BPF 1 at
the same time as the variable BPF 1. Then, the input signal supplied to itself is delayed and
supplied to the addition unit 7. The length of time for which the delay unit 2 delays the signal is
substantially the length of time that elapses until the component of the signal supplied to the
variable BPF 1 is supplied to the addition unit 7 via the mixing unit 5 and the variable HPF 6.
Shall be equal to Further, the phase of the delayed input signal supplied from the delay unit 2 to
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the addition unit 7 and the phase of the signal supplied from the variable HPF 6 to the addition
unit 7 are between those simultaneously supplied to the addition unit 7 In this case, it is assumed
that they are substantially in phase.
[0033]
The spectrum analysis unit 3 includes, for example, a DSP (Digital Signal Processor), a CPU
(Central Processing Unit), and the like. The spectrum analysis unit 3 is supplied with the same
input signal as that supplied to the variable BPF 1 at the same time as the variable BPF 1. Then,
the supplied input signal is analyzed, and based on the analysis result, a first control signal for
specifying the pass band of the variable BPF 1 and a frequency for specifying the frequency of a
local oscillation signal described later generated by the variable frequency oscillator 4 are
described. 2 and a third control signal specifying the passband of the variable HPF 6. Then, the
generated first control signal is supplied to the variable BPF 1, the second control signal is
supplied to the variable frequency oscillating unit 4, and the third control signal is supplied to
the variable HPF 6. Specifically, the spectrum analysis unit 3 performs the processing described
as (1) to (4) below.
[0034]
(1) First, the spectrum analysis unit 3 Fourier transforms the input signal supplied to itself. Then,
the component with the highest frequency is extracted from the components of the spectrum
obtained as a result of the Fourier transform, and the frequency of the extracted component is
specified as the upper limit value of the band occupied by the input signal.
[0035]
(2) Next, the spectrum analysis unit 3 is added to the input signal by spectrum interpolation
based on the upper limit value of the band occupied by the input signal and the predetermined
value indicating the upper limit of the frequency of the component to be added to the input
signal. Determine the bandwidth occupied by the component.
[0036]
(3) Next, the spectrum analysis unit 3 determines the passbands of the variable BPF 1 and the
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variable HPF 6 and the frequency of the local oscillation signal so as to meet the conditions
shown as (a) to (d) below.
That is, as shown in FIG. 2, (a) the band occupied by the input signal (the band shown as “Bin”
in FIG. 2) is the upper limit frequency of the pass band of the variable BPF 1 (the band shown as
“BA” in FIG. Substantially equal to the upper-limit frequency of (b) the band occupied by the
component added to the input signal by the spectral interpolation, the band width of the
passband of the variable BPF 1 (the band shown as “Badd” in FIG. 2) (C) the frequency of the
local oscillator signal (the frequency shown as “fOSC” in FIG. 2 and herein) is substantially
equal to the difference between the upper and lower limits of the passband of the variable BPF 1.
Equally, (d) The lower limit frequency of the passband of the variable HPF 6 (the band shown as
"BB" in FIG. 2) is the frequency fOSC of the local oscillation signal and the frequency belonging to
the band Badd The passbands of the variable BPF 1 and the variable HPF 6 and the frequency of
the local oscillation signal are determined so that the relationship of being larger than the
maximum value of the absolute value of the difference of
[0037]
That is, the lower limit frequency of the passband of the variable BPF1 is fHL, the upper limit
frequency of the passband of the variable BPF1 is fHH, the upper limit of the band occupied by
the input signal is f0, and the band occupied by the component added to the input signal by
spectrum interpolation Lower limit of fIL, lower limit of the band occupied by the component
added to the input signal by spectral interpolation fIH, bandwidth occupied by the additional
component of the input signal by spectrum interpolation is BW, lower limit of the passband of
the variable HPF 6 Assuming that the frequency is fHPF, the values of fHL, fHH, f0, fIL, fIH, BW,
fHPF and fOSC substantially have the relationships shown in Formula 1 to Formula 3.
[0038]
FHH = fIL = f0 fOSC = (fHH-fHL) = (fIH-fIL) = BW fHPF> max [| fHL-fOSC |, | fHH-fOSC |] (wherein
, Max [α, β] is the larger of two values α and β)
[0039]
(4) Then, using the values of fHH and fHL that satisfy the above conditions (a) to (d), the
spectrum analysis unit 3 uses the center frequency of the passband of the variable BPF 1 (ie,
{(fHH-fHL) And the bandwidth (i.e. the value of (fHH-fHL)) are determined.
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Then, a first control signal is generated that specifies these determined values as the center
frequency and bandwidth value of the passband of the variable BPF 1 and supplies the first
control signal to the variable BPF 1.
Further, a second control signal specifying the value of fOSC satisfying the above conditions (a)
to (d) as the frequency of the local oscillation signal is generated and supplied to the variable
frequency oscillation unit 4. Also, a third control signal is generated that specifies the value of
fHPF that satisfies the conditions (a) to (d) described above as the lower limit frequency of the
passband of the variable HPF 6 and supplies the third control signal to the variable HPF 6. The
high-frequency signal interpolator may use, for example, a predetermined value sufficiently
higher than f0 as the value of fIH.
[0040]
The variable frequency oscillation unit 4 receives the second control signal from the spectrum
analysis unit 3, generates a local oscillation signal composed of a signal of a frequency indicated
by the second control signal, and mixes the generated local oscillation signal. Supply to section 5.
[0041]
The mixing unit 5 is configured of, for example, a multiplication circuit or the like.
The mixing unit 5 mixes the component supplied from the variable BPF 1 with the local
oscillation signal generated by the variable frequency oscillation unit 4 to generate a signal
representing the product of the component passing through the variable BPF 1 and the local
oscillation signal. Supply the generated signal to the variable HPF 6.
[0042]
The signal supplied to the variable HPF 6 by the mixing unit 5 is a component (sum component)
having a frequency corresponding to the sum of the frequency of the component passing
through the variable BPF 1 and the frequency of the local oscillation signal and the frequency
and local oscillation signal of the component passing through the variable BPF 1 And a
component (difference component) having a frequency corresponding to the frequency
difference of
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[0043]
Among the components supplied from the mixing unit 5, the variable HPF 6 passes the
component in the passband whose lower limit is the value indicated by the third control signal
supplied from the spectrum analysis unit 3 and supplies the component to the addition unit 7
And substantially block other components.
[0044]
The spectrum of the sum component supplied to the variable HPF 6 by the mixing unit 5
occupies a band whose upper limit is the frequency (fHL + fOSC) and whose upper limit is the
frequency (fHH + fOSC).
Further, the spectrum of the difference component supplied to the variable HPF 6 by the mixing
unit 5 occupies a band whose upper limit is the smaller value of the frequencies | fHL−fOSC |
and | fHH−fOSC |
On the other hand, the lower limit frequency fHPF of the passband of the variable HPF 6 satisfies
the above-mentioned condition (d) (the condition shown in equation 3). Therefore, the variable
HPF 6 passes the sum component of the signal supplied by the mixing unit 5 and supplies it to
the addition unit 7 to substantially block the difference component.
[0045]
The addition unit 7 generates a signal representing the sum of the delayed input signal supplied
from the delay unit 2 to itself and the component supplied from the variable HPF 6, and outputs
the signal as an output signal of the high-frequency signal interpolator.
[0046]
The output signal is frequency-converted to the input signal so that the components in the
continuous band including the spectrum with the highest frequency among the input signal are
included in the high frequency band adjacent to the upper limit of the band occupied by the
input signal. And the signal obtained by adding it.
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When the input signal is a band limited signal, the component added to the input signal is likely
to be composed of some harmonic components of the input signal before being band limited.
Thus, if the input signal is a band limited signal, the output signal will be close to the input signal
before the band limited.
[0047]
The configuration of the high frequency signal interpolator is not limited to that described above.
For example, a digital signal processor (DSP) or a central processing unit (CPU) performs some or
all of the functions of the variable BPF 1, the delay unit 2, the variable frequency oscillation unit
4, the mixing unit 5, the variable HPF 6, and the addition unit 7. It is also good.
[0048]
In addition, the passbands of the variable BPF 1 and the variable HPF 6 and the frequency of the
local oscillation signal are fixed in advance to a value that matches the above-described
conditions (a) to (d). It is also good. In this case, the high-frequency signal interpolator does not
have to include the spectrum analysis unit 3.
[0049]
Further, the values of fHL, fHH, f0, fIL, fIH, BW, fHPF and fOSC do not necessarily have the
relationships shown in Formula 1 to Formula 3. Thus, for example, the signal added to the input
signal via frequency conversion does not have to include the spectrum of the highest frequency
of the input signal. However, if the signal added to the input signal through frequency conversion
(the component passing through the variable HPF 6) includes the spectrum of the highest
frequency of the input signal, this signal added to the input signal is the input signal It is likely to
be considered as a harmonic component of a part of itself. Thus, if the input signal represents a
band limited audio signal, the output signal will be closer to the input signal before the band is
limited. In addition, when the values of fHL, fHH, f0, fIL, fIH, BW, fHPF and fOSC have the
relationships shown in Formula 1 to Formula 3, the spectrum of the component passing through
the variable HPF 6 is the high frequency spectrum of the input signal. It will be adjacent without
gaps on the side. Thus, if the input signal represents a band limited audio signal, the output
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signal will be closer to the input signal before the band is limited.
[0050]
Further, this high-frequency signal interpolator may determine the intensity of the spectrum of
the component to be added to the input signal by extrapolating it to the envelope of the spectrum
of the input signal. Specifically, for example, this high-frequency signal interpolator further
includes an envelope analysis unit and an equalizer. Among them, the equalizer filters the
component to be supplied to the addition unit 7 by the variable HPF 6 so as to match the
frequency characteristic indicated by the signal supplied thereto, and then supplies the
component to the addition unit 7. On the other hand, the envelope analysis unit performs
processing of regression calculation based on a spectrum obtained as a result of the spectrum
analysis unit 3 Fourier transforming the input signal, thereby specifying a function forming an
envelope of the spectrum of the input signal. Then, based on the specified function and each
value of fIL and fIH determined by the spectrum analysis unit 3, the frequency characteristic of
the output signal in the band where the lower limit frequency is fIL and the upper limit frequency
is fIH is determined and determined It is assumed that a signal indicating the result is supplied to
the above-mentioned equalizer. In this case, the spectrum analysis unit 3 may supply data
representing a spectrum obtained as a result of Fourier transformation of the input signal to the
envelope analysis unit, and the envelope analysis unit may, for example, The value of fIL may be
acquired by acquiring the control signal of 3.
[0051]
Although the embodiment of the present invention has been described above, the signal
interpolation device according to the present invention can be realized using a normal computer
system, not by a dedicated system. For example, in the personal computer or microcomputer, the
variable BPF 1 described above, the delay unit 2, the spectrum analysis unit 3, the variable
frequency oscillation unit 4, the mixing unit 5, the variable HPF 6, the addition unit 7, the
envelope analysis unit And a high-frequency signal interpolator that executes the abovementioned processing by installing the program from a medium (CD-ROM, MO, floppy (registered
trademark) disk, etc.) storing the program for executing the operation of the equalizer. Can be
configured.
[0052]
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Also, for example, the program may be posted on a bulletin board (BBS) of a communication line,
and the program may be distributed via the communication line, and the carrier wave is
modulated by a signal representing the program, and the obtained modulated wave is A device
that transmits and receives this modulated wave may demodulate the modulated wave to restore
the program. Then, the above process can be executed by activating this program and executing
it under the control of the OS in the same manner as other application programs.
[0053]
If the OS shares part of the processing or if the OS constitutes part of one component of the
present invention, the recording medium stores the program excluding that part. May be Also in
this case, in the present invention, the recording medium stores a program for executing each
function or step executed by the computer.
[0054]
As described above, according to the present invention, it is possible to restore a signal close to
the original signal with less distortion from a modulated wave obtained using a signal in which
the band of the original signal is limited. A signal interpolation apparatus and a signal
interpolation method of the present invention are realized. Further, according to the present
invention, a signal interpolation apparatus and a signal interpolation method for restoring an
audio signal with high sound quality are realized.
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