JP2002132297

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DESCRIPTION JP2002132297
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
waveform correction apparatus and a waveform correction method, and more particularly to a
waveform correction apparatus and a waveform correction method for correcting the waveform
of a signal representing speech.
[0002]
2. Description of the Related Art In order to efficiently transmit or record voice data representing
voice, techniques for compressing voice data have become widespread in recent years. As a
method of compression, for example, methods such as MP3 (MPEG1 audio layer 3) and AAC
(Advanced Audio Coding) are known.
[0003]
However, when the voice is reproduced by using the decompressed compressed audio data, the
waveform of the audio obtained by the reproduction contains distortion, and this distortion is the
distortion of the audio. It is the cause of deterioration. For example, a distortion called pre-echo is
added to a portion of an audio waveform obtained by reproduction of compressed audio data
immediately before or after the original audio waveform rises. In general, the band occupied by
pre-echo corresponds to a portion close to the upper limit (for example, 10 kHz or more) of the
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band occupied by the original voice. For this reason, the sound obtained by reproduction is
obtained by distorting the high frequency part of the original sound. Then, simply limiting the
band of the audio obtained by reproducing the audio data, the components included in the
original audio are removed together with this distortion, and it is not possible to prevent the
deterioration of the audio.
[0004]
In addition to the distortion caused by the compression of the audio data, unnecessary
components such as noise are added to the audio obtained by reproducing the audio data to
cause deterioration of the audio.
[0005]
The present invention has been made in view of the above circumstances, and it is an object of
the present invention to provide a waveform correction apparatus and a waveform correction
method for selectively removing distortion of audio obtained by reproduction of compressed
audio data. Do.
Another object of the present invention is to provide a waveform correction apparatus and a
waveform correction method for removing unnecessary components from voice obtained by
reproducing voice data.
[0006]
SUMMARY OF THE INVENTION In order to achieve the above object, according to a first aspect
of the present invention, there is provided a waveform correction apparatus comprising: a first
band component occupying a first band among input signals supplied from the outside; A first
filter for extracting the first band component, first determination means for determining whether
or not the amplitude of the first band component exceeds a first predetermined value, and the
amplitude of the first band component is second A second determination unit that determines
whether the length of time below a predetermined value has reached a predetermined value; and
the amplitude of the first band component has exceeded the first predetermined value. Until the
second determining means determines that the length of time during which the amplitude of the
first band component falls below the second predetermined value reaches a predetermined value
after the determining means determines A period during which the input signal is output, and a
period excluding the period during which the second band of the input signal is occupied;
Comprising a second filter for extracting and outputting band component, and characterized in
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that.
[0007]
According to such a waveform correction device, when the amplitude of the first band
component exceeds the first predetermined value due to the rising or falling of the input signal,
the second filter cancels the band limitation, and the input signal The second filter narrows the
passband to the second band when the amplitude of the first band component falls below the
second predetermined value for a predetermined time or more due to the substantially
interruption.
Therefore, if distortion due to compression of audio data is added immediately before the rise
and fall of the input signal and exists outside the second band, this distortion is selectively
removed. In addition, unnecessary components other than this distortion are also removed by the
second filter if they are outside the second band. Since the period during which the second filter
cancels the band limitation is a period during which the amplitude of the input signal is large, the
influence of unnecessary components on the sound quality is small.
[0008]
When a band occupied by distortion caused by compression of audio data corresponds to a
portion close to the upper limit of bands occupied by the original audio, the first band is a band
on the higher frequency side than a predetermined first frequency. If the second band is a band
lower than the predetermined second frequency, this distortion can be efficiently removed by
appropriately setting the first and second frequencies. .
[0009]
Further, according to a second aspect of the present invention, there is provided a waveform
correction device comprising: a first filter for extracting a first band component occupying a first
band among input signals supplied from the outside; A second filter for extracting a second band
component occupying a second band; first determining means for determining whether or not
the amplitude of the first band component exceeds a first predetermined value; A second
determination means for determining whether or not the length of time during which the
amplitude of the second band component falls below the second predetermined value reaches a
predetermined value, and the amplitude of the first band component When the length of time
during which the amplitude of the first band component falls below the second predetermined
value reaches a predetermined value after the first judging means judges that the first
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predetermined value is exceeded The input signal is output during a period until the second
determination means makes a determination, and the input signal is output during the period
excluding the period And a third filter for extracting and outputting a third band component
occupying a third band of the signal, and wherein the.
[0010]
According to such a waveform correction device, when the amplitude of the first band
component exceeds the first predetermined value due to the rising or falling of the input signal,
the third filter cancels the band limitation, and the input signal The third filter narrows the
passband to the third band when the amplitude of the second band component falls below the
second predetermined value for a predetermined time or more due to substantially interruption.
Therefore, if distortion due to compression of audio data is added immediately before the rise
and fall of the input signal and exists outside the third band, this distortion is selectively
removed.
In addition, unnecessary components other than this distortion are also removed by the third
filter if they are outside the third band. Since the period during which the third filter cancels the
band limitation is a period during which the amplitude of the input signal is large, the influence
of unnecessary components on the sound quality is small.
[0011]
Further, in the waveform correction method according to the third aspect of the present
invention, a first band component occupying a first band in an input signal supplied from the
outside is extracted, and the amplitude of the first band component is It is determined whether or
not a predetermined value of 1 has been exceeded, and it is determined whether or not the
length of time during which the amplitude of the first band component has fallen below a second
predetermined value has reached a predetermined value, After it is determined that the
amplitude of one band component exceeds the first predetermined value, the length of time for
which the amplitude of the first band component falls below the second predetermined value
reaches a predetermined value. The input signal is output during a period until it is determined
that the second band component of the input signal occupying a second band is extracted and
output.
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[0012]
According to such a waveform correction method, when the amplitude of the first band
component exceeds the first predetermined value due to the rising or falling of the input signal,
the entire band of the input signal is output, and the input signal is substantially reduced. When
the amplitude of the first band component falls below the second predetermined value for a
predetermined time or more due to the interruption, the output component of the input signal is
limited to the component in the second band.
Therefore, if distortion due to compression of audio data is added immediately before the rise
and fall of the input signal and exists outside the second band, this distortion is selectively
removed. In addition, unnecessary components other than this distortion are also removed if they
are outside the second band. Since the period in which the band limitation is canceled is a period
in which the amplitude of the input signal is large, the influence of unnecessary components on
the sound quality is small.
[0013]
A computer-readable recording medium according to a fourth aspect of the present invention is a
computer-readable recording medium according to the first aspect, which comprises a computer
for extracting a first band component occupying a first band from an externally supplied input
signal First determining means for determining whether or not the amplitude of the first band
component exceeds a first predetermined value; and a length of time during which the amplitude
of the first band component falls below a second predetermined value And a second
determination unit that determines whether the value of the first band component has reached a
predetermined value, and the first determination unit determines that the amplitude of the first
band component exceeds the first predetermined value. And outputting the input signal during a
period until the second determining unit determines that the length of time when the amplitude
of the first band component falls below the second predetermined value reaches a predetermined
value. A second band occupying a second band of the input signal during a period other than the
period A second filter which divides extracted and output, a program for functioning in and
characterized by recording.
[0014]
When the amplitude of the first band component exceeds the first predetermined value due to
the rising or falling of the input signal, the computer recorded on such a recording medium
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cancels the band limitation of the signal to be output, and the input signal When the amplitude of
the first band component falls below the second predetermined value for a predetermined time
or more due to substantially interruption, the band of the signal to be output is narrowed to the
second band.
Therefore, if distortion due to compression of audio data is added immediately before the rise
and fall of the input signal and exists outside the second band, this distortion is selectively
removed. In addition, unnecessary components other than this distortion are also removed by the
second filter if they are outside the second band. Since the period during which the second filter
cancels the band limitation is a period during which the amplitude of the input signal is large, the
influence of unnecessary components on the sound quality is small.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION A waveform correction apparatus and a
waveform correction method according to an embodiment of the present invention will be
described below with reference to the drawings, taking a waveform corrector as an example.
[0016]
FIG. 1 is a diagram showing the configuration of a waveform corrector according to the
embodiment of the present invention.
As shown in the figure, the waveform corrector includes a high pass unit 1, a low pass unit 2, an
edge detection unit 3, a high pass signal detection unit 4, reference voltage sources 5 and 6, and
a time measurement unit. 7 and a control unit 8.
[0017]
The high pass unit 1 includes a high pass filter or the like, and is externally supplied with an
audio signal (hereinafter referred to as an input signal ) whose waveform is to be corrected.
Then, among the input signals supplied to itself, a component whose frequency exceeds a
predetermined value (hereinafter referred to as high frequency component ) is supplied to
the edge detection unit 3 and the high frequency signal detection unit 4 and other components
are Substantially shut off. The input signal is, for example, an audio signal obtained by
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decompressing audio data representing audio compressed using a method such as MP3 (MPEG1
audio layer 3) or AAC (Advanced Audio Coding).
[0018]
The low pass section 2 is constituted by a low pass filter, an analog switch, etc., and the same
input signal as that supplied to the high pass section 1 is externally supplied in parallel with the
high pass section 1. . Further, a control signal described later supplied from the control unit 8 is
supplied. Then, when the control signal instructs to turn on the low pass unit 2, the low pass unit
2 is a component having a frequency equal to or less than a predetermined value in the supplied
input signal (hereinafter referred to as
The low frequency component (referred to as low
frequency component ) is output as the output signal of this waveform corrector, and
substantially blocks other components. In addition, the noise outside the band including the low
frequency component is also substantially blocked. On the other hand, when the control signal
instructs to turn off the low-pass unit 2, the supplied input signal is output as it is as an output
signal of the waveform corrector. Note that the input signal may contain a component that does
not belong to either the high frequency component or the low frequency component.
[0019]
The edge detection unit 3 includes an absolute value circuit, a comparator, and the like, and is
supplied with a high frequency component from the high frequency pass unit 1 and generates
the first reference voltage from the first reference voltage source 5. It is supplied with voltage.
Then, a predetermined reset signal is supplied to the control unit 8 in a period in which the high
frequency component is higher than the first reference voltage, and the supply of the reset signal
is stopped in another period.
[0020]
The reference voltage source 5 is composed of, for example, a shunt regulator or a zener diode.
The value of the first reference voltage is such that the edge detection unit 3 starts supply of the
reset signal when the absolute value of the input signal supplied to the high pass unit 1 and the
low pass unit 2 reaches a certain level. It is chosen as a good value.
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[0021]
The high frequency band signal detection unit 4 includes a detection unit, a comparator, and the
like. The high frequency band component is supplied from the high frequency band passage unit
1 and the second reference voltage source 6 generates a second reference voltage. A reference
voltage is supplied. Then, while the high frequency component is higher than the second
reference voltage, the high frequency detection signal of the predetermined level is supplied to
the time measuring unit 7, and the high frequency detection signal is supplied during the other
periods. Stop.
[0022]
The reference voltage source 6 may have, for example, substantially the same configuration as
the reference voltage source 5 except that a second reference voltage is generated instead of the
first reference voltage. The value of the second reference voltage is, for example, chosen to be
equal to the minimum value of the value intended as the amplitude of the normal input signal.
[0023]
The time measurement unit 7 includes a crystal oscillator, a counter unit, a gate unit, and the like,
and continuously determines whether the high frequency detection signal is supplied from the
high frequency signal detection unit 4 or not. Then, a predetermined set signal is supplied to the
control unit 8 during a period from when it is determined that the signal is supplied until a
predetermined time (hereinafter, referred to as "time T") elapses. Stop.
[0024]
The control unit 8 is composed of an RS flip-flop unit or the like, and is low during a period from
when the edge detection unit 3 starts supply of the reset signal until when the time measurement
unit 7 starts supply of the set signal. The band pass unit 2 is supplied with a control signal
instructing to turn off the low band pass unit. On the other hand, during the other period, the
control signal for instructing to turn on the low pass unit is supplied to the low pass unit 2.
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[0025]
In a period (for example, a period from time t0 to time t1 shown in FIG. 2) in which a state where
the input signal is not supplied to the high pass unit 1 and the low pass unit 2 of this waveform
correction unit continues for more than time T. The control unit 8 of the waveform corrector
supplies a control signal instructing to turn on the low pass unit 2 to the low pass unit 2 and the
low pass unit 2 is turned on. Therefore, even if the low pass part 2 (and the high pass part 1) is
supplied with noise outside the band to which the low pass component belongs, this noise is not
output from this waveform corrector.
[0026]
Next, when the input signal starts to be supplied to the high pass unit 1 and the low pass unit 2
(time t1), the edge detection unit 3 supplies a reset signal to the control unit 8. As a result, the
control unit 8 supplies a control signal instructing to turn off the low pass unit 2 to the low pass
unit 2 and the low pass unit 2 is turned off. Therefore, the waveform corrector outputs the input
signal as it is as the output signal. On the other hand, the high frequency band signal detection
unit 4 supplies the high frequency detection signal to the time measurement unit 7.
[0027]
Then, as a result of the instantaneous value of the input signal continuing a constant steady
value, the amplitude of the high frequency component falls below a predetermined level, and the
output of the high frequency detection signal ceases (time t2 shown in FIG. 2). When time T
passes further from time t (time t3 shown in FIG. 2), the time measuring unit 7 supplies a set
signal to the control unit 8. As a result, the control unit 8 supplies a control signal instructing to
turn on the low pass unit 2 to the low pass unit 2 and the low pass unit 2 is turned on. Therefore,
the waveform corrector outputs the low frequency component of the input signal as an output
signal and blocks the other components.
[0028]
In addition, when the input signal falls rapidly (time t4), the edge detection unit 3 supplies a reset
signal to the control unit 8, and as a result, the low pass unit 2 is turned off. Therefore, the
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waveform corrector outputs the input signal as the output signal as it is until the low-pass unit 2
is turned on again after time t4.
[0029]
By performing the above-described operation, the waveform corrector passes the input signal
without band limitation to the input signal in a period from the rise or fall of the input signal to
the passage of time T. On the other hand, in the other period, band limitation is applied to the
input signal, and the low band component of the input signal is allowed to pass, and the
component excluding the low band component is removed.
[0030]
The configuration of the waveform corrector is not limited to that described above. For example,
the low pass section 2 may be configured to amplify a signal output by itself, or perform an
arbitrary process on this signal and then output it as an output signal. Further, the range of the
band occupied by the signal supplied by the high pass unit 1 to the edge detection unit 3 and the
high pass signal detection unit 4 is arbitrary, so that the high pass unit 1 is an arbitrary band
instead of the high pass filter. A filter having characteristics may be provided. In addition, the
range of the band occupied by the output signal output by the low-pass unit 2 in the state where
the low-pass unit 2 is on is also arbitrary. Therefore, the low-pass unit 2 may be replaced by any
low pass filter. A filter having band characteristics may be provided.
[0031]
Further, the components of the input signal supplied to the edge detection unit 3 and the high
frequency signal detection unit 4 may have different frequency characteristics. Therefore, for
example, as shown in FIG. 3, this waveform corrector is a band pass unit 1A for blocking
components different in band from each other among the signals supplied thereto instead of the
high pass unit 1 in the configuration of FIG. And 1B. Then, the band pass units 1A and 1B receive
the supply of input signals from the outside, and the band pass unit 1A supplies the edge
detection unit 3 with a component (first band component) excluding the component blocked by
itself in the input signal. The band pass unit 1B may supply the high frequency signal detection
unit 4 with components (second band components) other than the components blocked by itself
in the input signal. In addition, parts other than the point mentioned above among the structures
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of FIG. 3 should just be substantially the same as the structure of FIG.
[0032]
Further, all or part of the high pass unit 1, the low pass unit 2, the edge detection unit 3, the high
pass signal detection unit 4, the reference voltage source 5, the reference voltage source 6, the
time measurement unit 7 and the control unit 8 May be composed of a DSP (Digital Signal
Processor) or a CPU (Central Processing Unit).
[0033]
Further, the input signal, the high band signal, the low band signal or the output signal may be
composed of data representing an instantaneous value of the strength of the signal in digital
form.
In addition, the set signal, the reset signal or the high frequency detection signal may also be
composed of data in digital format. When the high band signal is composed of data in digital
form, the reference voltage source 5 or 6 does not have to actually generate the first or second
reference voltage, and data representing the first or second reference voltage You just need to
generate Then, the edge detection unit 3 or the high frequency signal detection unit 4 generates
a reset signal or high frequency based on the value of the high frequency signal composed of the
data in digital format and the value of the data representing the first or second reference voltage.
A detection signal may be generated.
[0034]
Although the embodiments of the present invention have been described above, the waveform
correction 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, the high pass unit 1,
the low pass unit 2, the edge detection unit 3, the high pass signal detection unit 4, the reference
voltage sources 5 and 6, and the time measurement unit 7 described above. By installing the
program from a medium (CD-ROM, floppy (registered trademark) disk or the like) storing a
program for executing the operation with the control unit 8, a waveform corrector configured to
execute the above-mentioned processing is configured. be able to.
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[0035]
Also, for example, this program may be posted on a bulletin board (BBS) of a communication line,
and this may be distributed via the communication line, and the carrier wave is modulated by a
signal representing this program, and the obtained modulated wave is A device that transmits
and receives this modulated wave may demodulate the modulated wave to restore this program.
The above-described processing can be executed by activating these programs and executing
them under the control of the OS in the same manner as other application programs.
[0036]
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.
[0037]
As described above, according to the present invention, a waveform correction device and a
waveform correction method for selectively removing distortion of sound obtained by
reproduction of compressed sound data are realized. . Further, according to the present
invention, a waveform correction device and a waveform correction method for removing
unnecessary components from voice obtained by reproducing voice data are realized.
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