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JP2009021843

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DESCRIPTION JP2009021843
The present invention provides an acoustic signal processing apparatus and an acoustic signal
processing method capable of increasing the volume without increasing the output voltage even
in a small speaker. An acoustic signal processing apparatus for processing an input acoustic
signal to be reproduced by a speaker, which generates harmonics of a bass component equal to
or lower than a predetermined bass cutoff frequency included in the input acoustic signal To
generate an overtone synthetic sound signal in which overtones are synthesized. Then, an output
sound signal is generated in which a bass component lower than the bass cutoff frequency and a
treble component higher than the predetermined treble cutoff frequency are blocked from the
overtone synthetic acoustic signal. Also, the bass cutoff frequency and the treble cutoff frequency
are set according to the output characteristics of the speaker. [Selected figure] Figure 1
Acoustic signal processing apparatus and acoustic signal processing method
[0001]
The present invention relates to an acoustic signal processing apparatus and an acoustic signal
processing method for processing an input acoustic signal to be reproduced by a speaker.
[0002]
In mobile phones and the like, there is a demand for miniaturizing the size of the device, and
there is a need to miniaturize a speaker incorporated in the device.
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1
However, small speakers have a problem that bass can not be reproduced sufficiently. In order to
solve this problem, it has been practiced to reproduce the bass by playing overtones of the bass
instead of the bass which can not be sufficiently reproduced by a small speaker. If you can hear
sounds that contain harmonics of sounds of a certain frequency (sounds that are integral
multiples of a certain frequency), humans contain sounds of a certain frequency, even if they do
not contain sounds of a certain frequency. It is known as a missing fundamental phenomenon
that sounds like Therefore, by playing overtones of the bass instead of the bass, the bass that is
not actually played can be heard to be played.
[0003]
Patent Document 1 describes a device that controls the directivity of sound reproduced from a
speaker by using harmonics of bass instead of bass whose directional control is difficult. In this
apparatus, fast Fourier transform processing is performed on the acoustic signal reproduced by
the speaker to detect the fundamental frequency of the acoustic signal. Then, the harmonic
overtone of the detected fundamental frequency is emphasized and reproduced from the speaker.
[0004]
Further, Patent Document 2 describes an apparatus capable of easily recognizing a bass by
adding odd-order harmonics of an acoustic signal reproduced by a speaker to the acoustic signal.
In this apparatus, fast Fourier transform processing and modulation processing are performed on
an acoustic signal reproduced by a speaker to generate odd harmonic components of the
acoustic signal. Then, the generated odd harmonic components are added to the sound signal and
reproduced from the speaker. JP, 2006-222670, A JP, 2004-51225, A
[0005]
In the device described in Patent Document 1 described above, the directivity of the sound
reproduced from the speaker is controlled by using harmonics of the bass instead of the bass
whose directivity is difficult to control. This device is used to control the directivity of sound
reproduced from a large-sized speaker, and is not applied to a small-sized speaker which can not
sufficiently reproduce bass. In the device described in Patent Document 2, odd-order harmonics
are generated by performing fast Fourier transform processing on an acoustic signal. Then, by
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2
adding the generated odd harmonics to the acoustic signal, it is possible to easily recognize the
bass. However, this device can not increase the volume of the sound reproduced from the
speaker without increasing the output power. Further, in the apparatuses described in Patent
Document 1 and Patent Document 2, since the fast Fourier transform processing is performed,
the processing becomes enormous.
[0006]
The present invention has been made in view of the above-described points, and an object
thereof is to provide an acoustic signal processing apparatus and an acoustic signal processing
method capable of increasing the volume without increasing the output voltage even in a small
speaker.
[0007]
An acoustic signal processing apparatus according to the present invention is an acoustic signal
processing apparatus that processes an input acoustic signal to be reproduced by a speaker, and
generates harmonics of a bass component equal to or lower than a predetermined bass cutoff
frequency included in the input acoustic signal. A harmonics generation means, a synthesis
means for generating a harmonics synthetic acoustic signal obtained by synthesizing harmonics
with an input acoustic signal, and an output obtained by cutting off a bass component below a
bass cutoff frequency and a high tone component above a predetermined treble cutoff frequency
from the harmonics synthesis acoustic signal It is characterized by comprising filter means for
generating an acoustic signal, and cutoff frequency setting means for setting a bass cutoff
frequency and a treble cutoff frequency according to the output characteristic of the speaker.
[0008]
The acoustic signal processing method according to the present invention is an acoustic signal
processing method for processing an input acoustic signal to be reproduced by a speaker, and
generates a harmonic of a bass component equal to or lower than a predetermined bass cutoff
frequency included in the input acoustic signal. A harmonics generation step, a synthesis step for
generating a harmonics synthesis acoustic signal obtained by synthesizing harmonics with an
input acoustic signal, and an output obtained by cutting off a bass component below the bass
cutoff frequency and a treble component above a predetermined treble cutoff frequency from the
harmonics synthesis acoustic signal It has a filter step of generating an acoustic signal, and a
cutoff frequency setting step of setting a bass cutoff frequency and a treble cutoff frequency
according to the output characteristic of the speaker.
[0009]
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3
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings.
[0010]
FIG. 1 shows an embodiment of an acoustic signal processing apparatus according to the present
invention.
The acoustic signal processing device 1 processes an input acoustic signal to be reproduced by
the speaker 2.
The input acoustic signal subjected to signal processing by the acoustic signal processing device
1 is input to the speaker 2 and reproduced.
The speaker 2 is, for example, a speaker mounted on a portable device such as a mobile phone,
and can be a speaker of various types such as a dynamic type, a capacitor type, and a
piezoelectric type.
[0011]
The input acoustic signal input to the acoustic signal processing device 1 is input to the overtone
generation means 11 and the synthesis means 12.
The harmonics generation means 11 generates harmonics of a bass component equal to or lower
than a predetermined bass cutoff frequency included in the input sound signal. The value of the
bass cutoff frequency is set according to the output characteristic of the speaker 2. As a method
of generating harmonics of a bass component, a bass component having a bass cutoff frequency
or lower extracted from an input acoustic signal by a low pass filter, and a full-wave rectification
of the extracted bass component can be used. The characteristics of the harmonics to be
generated (the harmonics and their levels) are set according to the output characteristics of the
speaker 2. The synthesizing means 12 generates a harmonic overtone synthesized acoustic signal
obtained by synthesizing the overtones generated by the overtone generation means 11 with the
input acoustic signal.
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[0012]
The equalizer 13 generates an output acoustic signal obtained by blocking (including
attenuating) a bass component below the bass cutoff frequency and a treble component above
the treble cutoff frequency from the overtone synthetic acoustic signal. The values of the bass
cutoff frequency and the treble cutoff frequency are set according to the output characteristics of
the speaker 2. The equalizer 13 corresponds to the filter means. The auto gain controller 14
amplifies the output sound signal with a predetermined gain. The value of the gain of the auto
gain controller 14 is set according to the output characteristic of the speaker 2. The gain of the
auto gain controller 14 may have a frequency dependent characteristic so as to change according
to the frequency of the output acoustic signal, or may have a constant value independently of the
frequency of the output acoustic signal. The auto gain controller 14 corresponds to an
amplification means. The volume control unit 15 changes the output sound signal amplified by
the auto gain controller 14 to the set volume and outputs it to the speaker 2.
[0013]
The control unit 16 controls the overtone generation unit 11, the equalizer 13, and the auto gain
controller 14. The control unit 16 sets, for example, the bass cutoff frequency, the treble cutoff
frequency, the characteristics of the generated harmonics, and the gain of the auto gain
controller 14 in accordance with the setting map shown in FIG. The bass cutoff frequency, the
treble cutoff frequency, the characteristics of the harmonics and the gain of the auto gain
controller 14 are determined by the output characteristics of the speaker 2. The bass cutoff
frequency, the treble cutoff frequency, the characteristics of harmonics and the maximum output
of the speaker are described in the setting map of FIG. 2 for each speaker. The values of the bass
cutoff frequency, the treble cutoff frequency, the characteristics of the harmonics and the
maximum output of the speaker described in the setting map of FIG. 2 are determined according
to the output characteristics of the speaker. FIG. 3 shows the frequencies included in the input
acoustic signal and the frequencies reproducible by the speaker 2. The solid line indicates the
frequency included in the input acoustic signal, and the dotted line indicates the frequency that
can be reproduced by the speaker 2. As shown in FIG. 3, the range of frequencies that can be
reproduced by the speaker 2 is a narrower range than the range of frequencies included in the
input acoustic signal. The value of the bass cutoff frequency described in the setting map of FIG.
2 is set to the lower limit frequency of the frequency range where the speaker 2 can sufficiently
perform reproduction, for example, the value of f0 of FIG. 3. The high frequency cutoff frequency
is set to the upper limit frequency of the frequency range in which the speaker 2 can sufficiently
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perform reproduction, for example, the value of f1 in FIG. The order of the harmonics to be
generated is determined such that the frequency of the harmonics to be generated is included in
the frequency range in which the speaker 2 can sufficiently perform reproduction, for example,
the frequency range between f0 and f1 in FIG. 3 . The level of each harmonic order is determined
so that the sound quality of the sound reproduced from the speaker is appropriate. The gain of
the auto gain controller 14 is set so that the volume of the amplified output acoustic signal does
not exceed the maximum output of the speaker 2. The gain of the auto gain controller 14 may be
set to change according to the frequency of the output acoustic signal. The control unit 16
corresponds to the cutoff frequency setting means. The setting map shown in FIG. 2 is stored in a
memory (not shown) built in the acoustic signal processing device 1.
[0014]
Next, the operation of the acoustic signal processing device 1 will be described. Here, it is
assumed that the input acoustic signal input to the acoustic signal processing device 1 is as
shown by the solid line in FIG. Also, it is assumed that the frequencies that can be reproduced by
the speaker 2 connected to the acoustic signal processing device 1 are as shown by the dotted
line in FIG. In addition, according to the output characteristic of the speaker 2 connected to the
acoustic signal processing apparatus 1, suppose that the setting map as shown in FIG. 2 is preset.
[0015]
The input sound signal is input to the overtone generation means 11 and the synthesis means
12. The overtone generation means 11 generates an overtone of a bass component equal to or
lower than a predetermined bass cutoff frequency included in the input acoustic signal. The bass
cutoff frequency is set to a value according to the output characteristic of the speaker 2 in
accordance with the setting map shown in FIG. Here, it is assumed that “200 Hz” in the
“speaker A” row of the setting map shown in FIG. 2 is set as the bass cutoff frequency. Note
that "200 Hz" of the bass cutoff frequency corresponds to f0 in FIG. Further, as the order of the
harmonics to be generated, a value according to the output characteristic of the speaker 2 is set
according to the setting map shown in FIG. Here, it is assumed that "2" and "3" of the line of
"speaker A" in the setting map shown in FIG. 2 are set as the harmonic order. Further, it is
assumed that “3” is set as the level corresponding to the harmonic order “2” and “1” is
set as the level corresponding to the harmonic order “3”. In this case, as the overtone, a sound
having a frequency twice as high as the frequency of the bass component and a frequency three
times as high as that of the bass component is generated. Also, a harmonic is generated so that
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6
the ratio of the level of the sound having a frequency twice that of the bass component to the
sound having a frequency three times that of the bass component is "3: 1". The overtone
generation means 11 generates a sound having a frequency twice as high as and a frequency
three times as high as that of the bass component below the bass cutoff frequency f0 (200 Hz)
included in the input acoustic signal. An example of overtones generated at this time is shown in
FIG. The generated harmonics are included in the range of f0 to f1, which is a frequency range in
which the speaker 2 can sufficiently perform reproduction. The synthesis means 12 synthesizes
the overtones generated by the overtone generation means 11 with the input sound signal to
generate a overtone synthetic sound signal. An example of a harmonic overtone synthetic
acoustic signal obtained by synthesizing harmonics with an input acoustic signal is shown in FIG.
[0016]
The overtone synthetic acoustic signal synthesized by the synthesis means 12 is input to the
equalizer 13. Then, the equalizer 13 generates an output acoustic signal in which a bass
component lower than the bass cutoff frequency and a treble component higher than the treble
cutoff frequency are blocked from the overtone synthetic acoustic signal. The bass cutoff
frequency and the treble cutoff frequency are set in accordance with the output characteristic of
the speaker 2 in accordance with the setting map shown in FIG. Here, it is assumed that “200
Hz” in the “speaker A” row of the setting map shown in FIG. 2 is set as the bass cutoff
frequency. Further, it is assumed that “15000 Hz” in the “speaker A” row of the setting map
shown in FIG. 2 is set as the high sound cutoff frequency. Note that "200 Hz" of the bass cutoff
frequency corresponds to f0 in FIG. 3, and "15000 Hz" of the high-tone cutoff frequency
corresponds to f1 in FIG. The equalizer 13 generates an output acoustic signal by blocking the
bass component below the bass cutoff frequency f0 (200 Hz) and the high tone component
above the high cutoff frequency f1 (15000 Hz) from the overtone synthetic acoustic signal. An
example of an output acoustic signal obtained by blocking the bass component lower than the
bass cutoff frequency f0 (200 Hz) and the high-tone component higher than the high cutoff
frequency f1 (15000 Hz) from the harmonic overtone synthetic audio signal shown in FIG. 5 is
shown in FIG. The output sound signal does not include a bass component below the bass cutoff
frequency f0 (200 Hz) which can not be reproduced sufficiently by the speaker 2 and a high-tone
component above the treble cutoff frequency f1 (15000 Hz).
[0017]
The output sound signal is input to the auto gain controller 14 and amplified by a predetermined
gain. The gain of the auto gain controller 14 is set to a value according to the output
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characteristic of the speaker 2 in accordance with the setting map shown in FIG. The value of the
gain of the auto gain controller 14 is set so that the volume of the output acoustic signal
amplified by the auto gain controller 14 does not exceed the maximum output of the speaker 2
shown in the setting map of FIG. The output sound signal amplified by the auto gain controller
14 is changed to the volume set by the volume control unit 15 and then reproduced by the
speaker 2.
[0018]
As described above, the acoustic signal processing apparatus 1 according to the embodiment of
the present invention generates harmonics of a bass component equal to or lower than a
predetermined bass cutoff frequency included in the input acoustic signal to be reproduced by
the speaker 2 and inputs the harmonics as input acoustics. A harmonic overtone synthetic sound
signal synthesized into a signal is generated. The equalizer 13 cuts off a bass component below
the bass cutoff frequency and a treble component above the treble cutoff frequency from the
harmonic overtone synthetic audio signal to generate an output acoustic signal. The bass cutoff
frequency is set to the lower limit frequency of the frequency range in which the speaker 2 can
sufficiently perform reproduction. The high sound cutoff frequency is set to the upper limit
frequency of the frequency range in which the speaker 2 can sufficiently perform reproduction.
The generated output sound signal is amplified at a predetermined gain by the auto gain
controller 14 and reproduced by the speaker 2.
[0019]
Since the harmonics of the bass component lower than the predetermined bass cutoff frequency
are synthesized with the input acoustic signal, the bass can be heard by the listener even with a
small speaker which can not reproduce the bass sufficiently. If harmonics of the bass component
are reproduced, even if the bass component is not reproduced, it sounds like the bass component
is reproduced to the human ear. Therefore, even in a small speaker in which the bass component
can not be reproduced sufficiently, the bass component can be reproduced by reproducing the
overtone of the bass component.
[0020]
Further, since the bass component below the bass cutoff frequency and the high-tone component
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above the treble cutoff frequency are cut off from the overtone synthetic acoustic signal obtained
by combining the harmonics of the bass component into the input acoustic signal, the acoustic
signal input to the speaker It does not include bass and treble components that the speaker can
not reproduce sufficiently. By blocking the components of the frequency range that the speaker
can not reproduce sufficiently from the acoustic signal, the amplitude of the acoustic signal can
be reduced, and the power necessary for reproduction can be suppressed. In addition, since the
component of the frequency domain that the speaker can reproduce sufficiently does not change,
the volume heard by the human ear does not change. Therefore, the power required for
reproduction can be reduced without changing the volume heard by the human ear.
[0021]
Furthermore, since the output acoustic signal obtained by blocking the bass component below
the bass cutoff frequency and the treble component above the treble cutoff frequency from the
harmonic overtone synthetic acoustic signal is amplified with a predetermined gain by the auto
gain controller 14, the amplitude of the output acoustic signal is reduced. It can be enlarged and
reproduced from the speaker 2. Therefore, the volume of the sound reproduced from the speaker
2 can be increased.
[0022]
Since the bass cutoff frequency, the treble cutoff frequency, the characteristics of the harmonics
and the values of the gain of the auto gain controller 14 are set according to the output
characteristics of the speaker 2 connected to the acoustic signal processing device 1, the output
characteristics of the connected speaker 2 Can perform signal processing of the input sound
signal according to
[0023]
When the bass cutoff frequency, the treble cutoff frequency, the harmonics characteristic and the
gain of the auto gain controller 14 are set according to the output characteristic of the speaker 2,
as shown in FIG. The memory 21 and the control unit 16 are connected when the acoustic signal
processing apparatus 1 and the speaker 2 are connected, and the control unit 16 connects the
memory 21 to the speaker 2. The output characteristics may be read and set.
[0024]
As described above, according to the acoustic signal processing device of the present invention,
the harmonic component of the bass component is synthesized with the input acoustic signal to
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block the bass component below the bass cutoff frequency and the high-tone component above
the treble cutoff frequency. Therefore, even in a small speaker which can not sufficiently
reproduce bass, the bass component can be reproduced, and the volume reproduced from the
loudspeaker can be increased.
[0025]
It is a block diagram showing an acoustic signal processing device which is an example of the
present invention.
It is a figure which shows the example of the setting map of the acoustic signal processing
apparatus of FIG.
It is a figure which shows the output characteristic of the speaker connected to the acoustic
signal processing apparatus of FIG. 1, and the example of an input acoustic signal.
It is a figure which shows the example of the harmonics produced | generated by the acoustic
signal processing apparatus of FIG. It is a figure which shows the example of the harmonicovertone synthetic | combination acoustic signal produced | generated by the acoustic signal
processing apparatus of FIG. It is a figure which shows the example of the output acoustic signal
produced | generated by the acoustic signal processing apparatus of FIG. It is a block diagram
which shows the modification of the acoustic signal processing apparatus of FIG.
Explanation of sign
[0026]
DESCRIPTION OF SYMBOLS 1 acoustic signal processing apparatus 11 harmonics production |
generation means 12 synthetic | combination means 13 equalizer 14 auto gain controller 15
volume control part 16 control part 2 speaker
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