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JP2002315091

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DESCRIPTION JP2002315091
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aurally
corrects poor bass reproduction defects caused by the high cutoff frequency of the low
frequency side when reproducing an audio signal using small speakers, headphones, etc. Bass
compensation apparatus for realizing the reproduction of heavy bass.
[0002]
2. Description of the Related Art The frequency band of an audio signal input from a sound
source is usually wider than the reproducible frequency band of a speaker. Therefore, in order to
faithfully reproduce an audio signal input from a sound source, it is necessary to provide a
speaker whose reproducible frequency band is as wide as possible. The width of the reproducible
frequency band of the speaker has its own specific range depending on the size, structure, etc. of
the speaker, but in general, the lower the cutoff frequency becomes, the lower the size of the
speaker becomes. The reproduction characteristics of the sound range tend to deteriorate.
[0003]
However, speakers or headphones used in devices requiring portability such as notebook
computers and portable audio playback devices, compact audio systems with a space-saving
concept, or car audio systems installed in limited spaces such as automobile interiors Because of
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the limitations of the installation location, etc., it is desirable that the size and weight be as small
as possible. Therefore, the reproduction characteristic of the bass region is sacrificed at the cost,
and it has become impossible for the user to complain that the reproduction of the bass region is
insufficient.
[0004]
In order to solve the above-mentioned problems, a conventional sound device incorporates a bass
enhancement circuit that compensates for low frequency components. FIG. 4 is a block diagram
showing a configuration example of a conventional bass amplifier circuit. Japanese Patent
Application Laid-Open No. 8-237800, etc. discloses and proposes a bass enhancement circuit
having the above configuration.
[0005]
As shown in this figure, the conventional bass amplifier circuit adds an L-channel component LIN
and an R-channel component RIN of the input audio signal to the adder 30; First low-pass filter
31 (hereinafter referred to as first LPF 31) for extracting only the components, full-wave rectifier
32 for full-wave rectification of output signal A 'of first LPF 31, and second-order from output
signal B' of full-wave rectifier 32 A second low pass filter 33 (hereinafter referred to as a second
LPF 33) for extracting only harmonics, an amplifier 34 for amplifying an output signal C 'of the
second LPF 33, an output signal D' of the amplifier 34 is an L channel component LIN of the
audio signal And R channel component RIN, there are provided adders 35 and 36 for generating
an L channel component LOUT for output and an R channel component ROUT.
[0006]
FIG. 5 is a time chart showing one waveform example of the output signals A ', B' and D '.
As shown in the figure, when an audio signal is input to the bass enhancement circuit having the
above configuration, the output signal D 'has a waveform that is twice the frequency of the
output signal A'.
[0007]
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Certainly, in the bass amplifier circuit having the above configuration, low frequency components
below the reproduction limit of the speaker are shifted to a frequency band one octave higher to
restore the original audio signal. be able to. Therefore, since the low frequency component which
has conventionally been lacking is compensated, more powerful bass reproduction can be
realized.
[0008]
However, as also shown in FIG. 5, the above-described bass enhancement operation is normally
performed only during the period in which the second LPF 33 is in the steady state, and
immediately after the voice signal is input, or In the transition period immediately after the input
of the signal is terminated, an unnecessary direct current component due to the transient
phenomenon may be superimposed on the output signal D ′, and an unpleasant noise may be
generated from the speaker.
[0009]
Further, since the conventional bass amplifier circuit having the above configuration is not
provided with any means for removing low frequency components below the reproduction limit
of the speaker from the input audio signal, unnecessary vibration occurs in the speaker. There
was also a fear that the reproduced sound would be distorted.
[0010]
SUMMARY OF THE INVENTION In view of the above problems, the present invention acoustically
corrects and corrects poor bass reproduction defects caused by the high cutoff frequency of the
low frequency side when reproducing an audio signal using a small speaker, headphones, etc. It
is an object of the present invention to provide a bass compensation device capable of realizing
rich and rich bass reproduction.
[0011]
In order to achieve the above object, a bass compensation apparatus according to the present
invention comprises high-frequency removing means for removing high-frequency components
of an audio signal input from a sound source; And a high pass means for selectively passing only
high frequency components of the audio signal, and an absolute value circuit for full wave
rectification of the output signal of the high pass removing means. And a band limiting means for
selectively passing only a predetermined frequency band component from an output signal of the
absolute value circuit, and an amplifying means for amplifying an output signal of the band
limiting means.
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[0012]
DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment of the bass
compensation device according to the present invention will be described.
FIG. 1 is a block diagram showing a first embodiment of the bass compensation device according
to the present invention.
Here, the case where the audio signal input from the sound source is a stereo signal having an L
channel component and an R channel component will be described as an example.
[0013]
As shown in the figure, the bass compensation device of this embodiment includes a high
frequency band removing circuit 1 for removing high frequency components from the L channel
component LIN of the audio signal input to the terminal a, and a high frequency component from
the L channel component LIN. The subtractor 2 for reducing the output signal A of the area
removal circuit 1, the absolute value circuit 3 for full wave rectification of the output signal A of
the high frequency removal circuit 1, and the output signal B of the absolute value circuit 3 Is
added to the output signal of the subtractor 2 and the added signal is L. The band pass filter 4
(hereinafter referred to as BPF 4) for selectively passing through, the amplifier 5 for amplifying
the output signal C of BPF 4 and the output signal D of the amplifier 5 And an adder 6 that
outputs the channel component LOUT from the terminal c.
[0014]
Further, in the bass compensation device of the present embodiment, a high frequency removal
circuit 7 for removing high frequency components from the R channel component RIN of the
audio signal input to the terminal b, and a high frequency removal circuit 7 from the R channel
component RIN A subtractor 8 for reducing the output signal, an absolute value circuit 9 for fullwave rectifying the output signal of the high-frequency removing circuit 7, a band pass filter 10
for selectively passing only a predetermined frequency band component from the output signal
of the absolute value circuit 9 (Hereinafter referred to as BPF 10), an amplifier 11 for amplifying
the output signal of BPF 10, and an output signal of amplifier 11 added to the output signal of
subtractor 8, and the added signal is output from terminal d as R channel component ROUT And
a vessel 12.
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[0015]
The terminal c and the terminal d described above are connected to a speaker (not shown).
In addition to the speakers, if it is possible to separately provide a speaker dedicated to bass
reproduction, the adders 6 and 12 are not necessarily provided, and the output ends of the
amplifiers 5 and 11 are directly connected to the speaker dedicated to bass reproduction. Just do
it.
[0016]
Next, signal processing in the bass compensation apparatus having the above configuration will
be described with reference to FIGS. 1 and 2. FIG.
FIG. 2 is a time chart showing one waveform example of the output signals A, B and D.
Although only the signal processing of the L channel component is described here, the same
signal processing is performed on the R channel component.
[0017]
The L channel component LIN of the audio signal input from the sound source to the terminal a
is input to the high frequency removal circuit 1 and the subtractor 2 respectively.
The high frequency removal circuit 1 comprises a low pass filter or the like having a
predetermined cutoff frequency, and has a characteristic of passing only frequency components
lower than the cutoff frequency. Here, the main purpose of the high frequency removal circuit 1
is to remove high frequency noise of burst nature inputted to the terminal a. Therefore, the cutoff
frequency of the high frequency removal circuit 1 may be set lower than the frequency band of
high frequency noise. With such a configuration, it is possible to prevent or reduce the
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generation of noise from the speaker by frequency conversion of high frequency noise.
[0018]
In the bass compensation device of the present embodiment, the cutoff frequency of the highfrequency removing circuit 1 is set around the bass cutoff frequency of the speaker. With such a
setting, the high frequency band removing circuit 1 according to this embodiment not only
removes high frequency noise from the L channel component LIN of the audio signal, but also
extracts a low frequency component below the speaker reproduction limit. Will also do.
[0019]
Also, by subtracting the output signal A of the high frequency band removing circuit 1 from the L
channel component LIN by the subtractor 2, low frequency components below the speaker
reproduction limit can be removed from the audio signal input to the speaker. Therefore, it is
possible to solve the conventional problem that the speaker generates unnecessary vibration and
distortion of the reproduced sound. Of course, the same effect can be obtained by providing a
high pass filter instead of the subtractor 2, but this configuration is more advantageous in terms
of circuit scale reduction.
[0020]
The absolute value circuit 3 full-wave rectifies the output signal A of the high-frequency
removing circuit 1. As an example of the absolute value circuit 3, a bridge circuit or the like
formed of a diode can be used. By using such an absolute value circuit 3 to double the frequency
of the bass component, it is possible to realize a user-friendly bass compensation device having
high linearity of input / output characteristics.
[0021]
The BPF 4 selectively passes only a predetermined frequency band component from the output
signal B of the absolute value circuit 3. As described above, the second harmonic is extracted
from the output signal B by providing the band pass filter instead of the low pass filter at the rear
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stage of the absolute value circuit 3 and immediately after the sound signal is input or the input
of the sound signal It is possible to remove an unnecessary direct current component due to a
transient phenomenon immediately after the Therefore, it is possible to realize a bass
compensation device excellent in distortion factor characteristics and transient characteristics.
[0022]
The amplifier 5 amplifies the output signal C of the BPF 4 to the amplitude level of the output
signal A. The adder 6 adds the output signal D of the amplifier 5 to the output signal of the
subtracter 2 and outputs the addition signal from the terminal c as an L channel component
LOUT. By such a bass compensation operation, it is possible to shift low frequency components
below the reproduction limit of the speaker to a frequency band one octave higher and restore
the original audio signal. Therefore, since it becomes possible to reproduce the low frequency
component which has conventionally been lacking, it is possible to realize more powerful bass
reproduction.
[0023]
Next, a second embodiment of the bass compensation device according to the present invention
will be described. FIG. 3 is a block diagram showing a second embodiment of the bass
compensation device according to the present invention. Note that the bass compensation device
of the present embodiment is configured on the premise that the audio signal input from the
sound source is a stereo signal having an L channel component and an R channel component.
[0024]
As shown in the figure, in the bass compensation device of the present embodiment, a high band
removing circuit 20 for removing high frequency components from the L channel component
LIN of the audio signal input to the terminal a, and a terminal b are input. A high band removing
circuit 21 for removing high frequency components from the R channel component RIN of the
audio signal, a subtractor 22 for subtracting an output signal of the high frequency removing
circuit 20 from the L channel component LIN, and high band removing from the R channel
component RIN A subtractor 23 for subtracting the output signal of the circuit 21, an adder 24
for adding both output signals of the high-frequency removing circuits 20 and 21, an absolute
value circuit 25 for full-wave rectifying an output signal of the adder 24, and an absolute value A
bandpass filter 26 (hereinafter referred to as a BPF 26) for selectively passing only a
predetermined frequency band component from an output signal of the circuit 25; an amplifier
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27 for amplifying an output signal of the BPF 26; The adder 28 adds the power signal to the
output signal of the subtractor 22 and outputs the addition signal as an L channel component
LOUT from the terminal c, and the output signal of the amplifier 27 similarly to the output signal
of the subtractor 23, and the addition signal And an adder 29 that outputs the R channel
component ROUT from the terminal d.
[0025]
The bass compensation operation by the high-frequency removing circuits 20 and 21, the
absolute value circuit 25, the BPF 26, and the amplifier 27 is the same as that of the first
embodiment described above, and thus the detailed description will be omitted.
With such a configuration, the signal system necessary for the bass compensation operation can
be unified, so that the circuit scale can be reduced as compared with the bass compensation
device of the first embodiment described above.
[0026]
As described above, the bass compensation apparatus according to the present invention
comprises high-frequency removing means for removing high-frequency components of an audio
signal input from a sound source, and the high-frequency removing means from the audio signal.
Subtraction means for reducing the output signal of the high-pass filter for selectively passing
only high-frequency components of the audio signal, an absolute value circuit for full-wave
rectifying the output signal of the high-pass filter, and The apparatus comprises a band limiting
means for selectively passing only a predetermined frequency band component from an output
signal, and an amplifying means for amplifying an output signal of the band limiting means.
[0027]
With such a configuration, low frequency components below the reproduction limit of the
speaker can be shifted to a frequency band one octave higher.
Therefore, it is possible to reproduce the low frequency component which has conventionally
been lacking, and to realize more powerful bass reproduction.
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[0028]
Further, by providing a band limiting means at the subsequent stage of the absolute value circuit,
the second harmonic is extracted from the output signal of the absolute value circuit, and
immediately after the audio signal is input or immediately after the input of the audio signal is
completed. The unnecessary DC component due to the transient phenomenon of Therefore, it is
possible to realize a bass compensation device excellent in distortion factor characteristics and
transient characteristics.
[0029]
Furthermore, by subtracting the output signal of the high frequency band removing means from
the original audio signal, low frequency components below the speaker reproduction limit can be
removed from the audio signal input to the speaker. Therefore, it is possible to solve the
conventional problem that the speaker generates unnecessary vibration and distortion of the
reproduced sound. Of course, the same effect can be obtained by providing high-pass means
instead of the subtracting means, but providing the subtracting means is advantageous from the
viewpoint of circuit scale reduction.
[0030]
The bass compensation device according to the present invention may be incorporated into an
acoustic device as a drive system such as a small speaker or headphone. With such a
configuration, even a small speaker with poor bass reproduction capability can perform bass
reproduction, so the bass reproduction capability is large as before, and the size of the speaker is
large. There is no need to Therefore, it can contribute to the miniaturization, weight reduction,
weight reduction, and cost reduction of the acoustic device.
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