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DESCRIPTION JP2008085417

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DESCRIPTION JP2008085417
An object of the present invention is to enable voice enhancement of a desired band while
preventing distortion of output sound of a small speaker such as a mobile phone. A drive circuit
is configured to drive a speaker in accordance with an audio signal from an equalizer unit. The
response frequency characteristics of the equalizer unit are, as shown in FIG. 3, a peak portion M
for increasing the gain of the frequency band to be emphasized, and a first valley portion V for
decreasing the gain near the lower limit of the frequency band. It has valleys V for reducing the
gain near the upper limit of the frequency band. Since the gain of the frequency band to be
emphasized is increased and the gain is lowered near the lower limit and the upper limit of the
frequency band, it is possible to emphasize voice in the frequency band while preventing
distortion of the output sound. [Selected figure] Figure 3
Speaker voice enhancement device
[0001]
The present invention relates to a speaker voice emphasizing device suitable for making it easy
to hear the voice of a small speaker such as a mobile phone.
[0002]
In general, the speaker of the mobile phone is not good at particularly low frequency
characteristics due to its small size and the like.
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In FIG. 5, the sound pressure level frequency characteristic is indicated by a broken line Sa for a
small speaker of a conventional mobile phone as an example. According to this frequency
characteristic, the sound pressure level gradually decreases in the low band from around 1000
Hz. For this reason, the sense of loudness is poor particularly for male voice quality.
[0003]
Conventionally, as a method of adjusting the frequency characteristic of the speaker sound, it is
known to provide a parametric equalizer at the front stage of the speaker drive circuit and
appropriately set the parameter (for example, see Patent Document 1). FIG. 6 shows settable
parameters for an example of a conventional parametric equalizer. In this example, three types of
parameters, "frequency", "boost amount" and "bandwidth Q" can be set.
[0004]
When adjusting the frequency characteristic using such a parametric equalizer, the boost amount
is often increased in the frequency band where the sound pressure level is decreasing. JP 2001197585 A
[0005]
According to the above-described prior art, when the boost amount is set to be increased, the
output sound is distorted (clipped) because the input sound volume is increased for the speaker.
Therefore, it is conceivable to lower the overall level so as not to distort (do not clip), but in this
case, the effect is halved because it is the same as lowering the sound volume to be heard.
[0006]
An object of the present invention is to provide a novel speaker speech emphasizing device
capable of emphasizing speech of a desired band while preventing distortion of output sound.
[0007]
A speaker voice emphasizing device according to the present invention comprises: a speaker; an
equalizer unit that receives an audio signal; and a drive circuit that drives the speaker according
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to the audio signal output from the equalizer unit. The response frequency characteristic has a
peak for increasing the gain of the frequency band to be emphasized, and first and second valleys
for decreasing the gain near the lower limit and the upper limit of the frequency band,
respectively. It is characterized by
[0008]
According to the speaker voice emphasizing device of the present invention, since the response
frequency characteristic of the equalizer section has a peak portion for increasing the gain of the
frequency band to be emphasized, the voice can be emphasized in the frequency band.
In addition, since the response frequency characteristics of the equalizer section have the first
and second valley portions for lowering the gains near the lower limit and the upper limit of the
frequency band to be emphasized, the overall total volume almost changes. The distortion of the
output sound can be prevented.
[0009]
In the speaker voice emphasizing device according to the present invention, assuming that the
area of the peak is Sm and the areas of the first and second valleys are S1 and S2, respectively,
the height of the peak is such that Sm S S1 + S2. The depths of the first and second valleys, the
bandwidths of the peaks, and the bandwidths of the first and second valleys may be set.
In this way, since the peaks become dominant, the voice in the band corresponding to the peaks
can be reliably emphasized.
[0010]
According to the present invention, since the gain of the frequency band to be emphasized in the
equalizer section is increased and the gain is decreased near the lower limit and the upper limit
of the frequency band, the distortion of the output sound is prevented while the sound in the
frequency band Can be emphasized.
[0011]
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FIG. 1 shows a circuit configuration of a speaker voice emphasizing device according to an
embodiment of the present invention.
[0012]
The input terminal 10 a of the equalizer unit 10 is supplied with the decoded digital audio signal
a from the mobile phone.
The equalizer unit 10 includes a first signal path from the delay unit 12 to one input end of the
mixer 14, an APF (all pass filter) 16, a low shelving type EQ (equalizer) 18, an HPF (high pass
filter) 20 and And a second signal path leading to the other input end of the mixer 14 via the LPF
(low pass filter) 22.
The digital audio signal a from the input terminal 10a is branched into first and second digital
audio signals a1 and a2, and the first digital audio signal a1 is input to the delay unit 12 and the
second digital audio signal a2 is input to the APF 16; The digital audio signal b transmitted from
the delay unit 12 and the digital audio signal c transmitted from the LPF 22 are appropriately
level-adjusted by the mixer 14 and mixed.
[0013]
The digital audio signal d transmitted from the mixer 14 is converted into an analog audio signal
e by a D / A (digital / analog) converter 24. The amplifier 26 drives the small speaker 28 in
response to the analog audio signal e, and the speaker 28 emits sound.
[0014]
The delay unit 12 applies a predetermined time delay to the digital audio signal a1, and a final
change in phase characteristic is produced according to the applied time delay. The APF 16
passes signals in all frequency ranges, and is used to apply a phase change to each frequency.
The low shelving type EQ 18 is a filter for roughly raising the gain like a shelf with respect to low
frequencies. The HPF 20 is a filter that passes signals of frequencies above the cutoff frequency
and attenuates signals of frequencies below the cutoff frequency. The LPF 22 is a filter that
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passes signals of frequencies below the cutoff frequency and attenuates signals of frequencies
above the cutoff frequency.
[0015]
FIG. 3 shows an example of the response frequency characteristic of the equalizer unit 10. This
response frequency characteristic includes a peak portion M for increasing the gain in a
frequency band to be emphasized (for example, 200 to 700 Hz), and There are valleys V1 and V2
for reducing the gain near the lower limit and near the upper limit, respectively. In order to
obtain such response frequency characteristics, as an example, the cutoff frequency of the HPF
20 is 300 Hz, the cutoff frequency of the LPF 22 is 800 Hz, and the peak frequency of the low
shelving type EQ is 550 Hz. The shape of the characteristic curve is adjusted by appropriately
adjusting the time delay given by the delay unit 12, the phase characteristic of the APF 16, and
the mixing ratio of the signals b and c at the mixer 14.
[0016]
As the response frequency characteristics of the equalizer unit 10, when the area of the peak
portion M (the result of mathematical integration) is Sm, and the areas of the valley portions V1
and V2 are S1 and S2, respectively, then Sm S S1 + S2 It is desirable to set the height of the peak
M, the depth of the valleys V1 and V2, the bandwidth of the peak M, the bandwidth of the valleys
V1 and V2, and the like. When the height of the mountain portion M is increased, the feeling of
emphasis is further increased, and when the bandwidth of the mountain portion M is increased,
the frequency band in which the feeling of emphasis is felt is expanded. The valleys V1 and V2
help to suppress the increase in volume based on the peak M (to keep the overall total volume as
it is).
[0017]
In FIG. 5, a curve Sb indicates the sound pressure level frequency characteristic of the speaker 28
when the response frequency characteristic of the equalizer unit 10 is as shown in FIG.
Comparing the characteristics Sa and Sb, it can be seen that the sound pressure level is improved
(sound is emphasized) in the frequency range of 200 to 700 Hz. Therefore, the loudness of men
in the low range is improved. Further, since the sound pressure level is lowered near the lower
limit and the upper limit of the frequency range of 200 to 700 Hz, it is possible to prevent the
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output sound from being distorted or broken.
[0018]
FIG. 2 shows a speaker voice emphasizing device according to another embodiment of the
present invention. In this embodiment, the equalizer unit 30 is configured by a series connection
path of PEQs (parametric equalizers) 32, 34, and 36. .
[0019]
The decoded digital audio signal A from the mobile phone is supplied to the input terminal 30 a
of the equalizer unit 30, and this signal A is input to the PEQ 32.
The digital audio signal B transmitted from the PEQ 32 is input to the PEQ 34. The digital audio
signal C transmitted from the PEQ 34 is input to the PEQ 36. The digital audio signal D
transmitted from the PEQ 36 is input to the D / A converter 38 and converted into an analog
audio signal E. The amplifier 40 drives the small speaker 42 in response to the analog audio
signal E, and the speaker 42 emits sound.
[0020]
FIG. 4 shows an example of the response frequency characteristic of the equalizer unit 30. This
response frequency characteristic corresponds to the peak portion M for increasing the gain in
the frequency band to be emphasized (for example, 120 to 800 Hz), and There are valleys V1
and V2 for reducing the gain near the lower limit and near the upper limit, respectively. As an
example, the PEQs 32, 34, and 36 are in charge of forming the valley portion V1, the mountain
portion M, and the valley portion V2, but it is a matter of course that the PEQs 32, 34, and 36
may be in charge of different. Assuming that the area of the peak M is Sm and the areas of the
valleys V1 and V2 are S1 and S2 as described above with reference to FIG. 3, the height of the
peak M and the valleys V1 and V2 are such that SmSS1 + S2. It is desirable to set the depth of the
ridge, the bandwidth of the peak M, the bandwidth of the valleys V1 and V2, and the like.
[0021]
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In the embodiment of FIG. 2, when the response frequency characteristic of the equalizer unit 30
shown in FIG. 4 is used, a sound pressure level frequency characteristic similar to Sb of FIG. 5 is
obtained. Therefore, it is possible to perform low-range speech emphasis while preventing
distortion of the output sound.
[0022]
The present invention is not limited to the embodiments described above, and can be
implemented in various modified forms. For example, the following changes are possible.
[0023]
(1) In the embodiment shown in FIG. 1, the connection order of the APF 16, the low shelving type
EQ 18, the HPF 20 and the LPF 22 is not limited to that shown in the drawing, but the order is
arbitrary as long as they are connected in series.
[0024]
(2) In the embodiment shown in FIG. 1, the HPF 20 and the LPF 22 may be replaced by a band
pass filter having a low cutoff frequency similar to the HPF and a high cutoff frequency similar to
the LPF 22.
[0025]
(3) In the embodiment shown in FIG. 2, the equalizer unit 30 may be configured by a graphic
equalizer.
[0026]
(4) Although the embodiments shown in FIGS. 1 and 2 are in the form of digital signals, the
present invention can also be implemented in the form of analog signals.
When the present invention is implemented in digital signal form, it may be implemented by
software processing using a small computer.
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[0027]
(5) A portable video phone or the like may be used as the mobile phone.
[0028]
It is a block diagram showing a speaker voice emphasis device concerning one embodiment of
this invention.
It is a block diagram which shows the speaker audio | voice emphasis apparatus which concerns
on other embodiment of this invention.
It is a graph which shows the response frequency characteristic of the equalizer part of the
apparatus of FIG.
It is a graph which shows the response frequency characteristic of the equalizer part of the
apparatus of FIG. It is a graph which shows a sound pressure level frequency characteristic about
the speaker of the apparatus of FIG. It is a graph which shows the parameter which can be set
about an example of the conventional parametric equalizer.
Explanation of sign
[0029]
10a, 30a: input terminal, 10, 30: equalizer unit, 12: delay device, 14: mixer, 16: APF (all pass
filter), 18: low shelving type EQ (equalizer), 20: HPF (high pass filter), 22: LPF (low pass filter) 24,
38: D / A converter, 26, 40: amplifier, 28, 42: small speaker, 32, 34, 36: PEQ (parametric
equalizer).
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