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JP2002095096

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2002095096
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
vehicle-mounted sound reproducing apparatus.
[0002]
2. Description of the Related Art When music or the like is reproduced by a sound reproduction
apparatus, it is said that the ideal height of a sound image to be reproduced is the height of the
listener's eyes. For this reason, the speakers are generally installed at the height of the listener's
eyes.
[0003]
However, in the on-vehicle sound reproducing apparatus, the speaker is a listener (a driver or a
passenger of a vehicle. That is, it is difficult to install at the eye level of the passenger, and as
shown in FIG. 12A, the speaker is often installed below the front door of the vehicle or below the
rear door. Therefore, the reproduced sound is heard from below, and the sound image is localized
below the eyes of the listener.
[0004]
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1
In order to avoid such a problem, as shown in FIG. 12A, there is a method of installing a speaker
for high frequency reproduction with a small aperture in front of the listener. However, in this
method, the reproduced sound is separated and heard because the output position of the
reproduced sound is different between the high band and the low band.
[0005]
Also, it is known that sound tends to be absorbed more as it is higher. Therefore, if a speaker is
installed in the lower part of the vehicle compartment, the high region is absorbed by the seat
and the interior, and the reproduction sound output from the sound reproduction apparatus and
the sound actually heard by the listener are different. I will.
[0006]
Further, in order to cope with the above situation, it is effective to actually measure the transfer
function in the vehicle compartment and to correct the reproduced sound according to this
transfer function. A high performance digital signal processor is needed. And, since such digital
signal processing devices are quite expensive, it is difficult to use them for consumer sound
reproduction devices.
[0007]
Furthermore, if the reproduced sound is corrected according to the transfer function, the high
frequency band tends to be emphasized in general, and when the volume level is increased, the
user may feel discomfort.
[0008]
Furthermore, when viewed as an acoustic space, the cabin is quite narrow, and this affects the
reproduced sound, and the reproduced sound that the listener actually listens to is a reproduced
sound lacking in a sense of spread and a sense of depth. .
[0009]
The present invention is intended to solve the above problems.
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2
[0010]
Therefore, in the present invention, the input digital audio signals XL (Z) and XR (Z) of the left
and right channels are YL (Z) · GLL (Z) + YR. (Z) · GLR (Z) = XL (Z) · FLL (Z) + XR (Z) · FLR (Z) YR
(Z) · GLL (Z) + YL (Z) · GLR (Z) = XR (Z) FLL (Z) + XL (Z) FLR (Z) where FLL (Z): from the speakers
of the first left and right channels located in front of the listener in the vehicle compartment to
the left ear and the right ear of the listener Head-related transfer function FLR (Z): Head-related
transfer function GLL (Z) from the first left and right channel speakers to the right and left ears
of the listener: second located in front of and below the listener Transfer function GLR (Z) from
the left and right channel speakers to the left and right ears of the listener: from the second left
and right channel speakers, the right ear and the right ear of the listener A sound image position
correction circuit which converts digital audio signals YL (Z) and YR (Z) represented by a headrelated transfer function to the ear and outputs them, and delays the output signals YL (Z) and
YR (Z) A reflected sound signal forming circuit for forming a signal of a reflected sound, a pair of
adding circuits for adding the signal of the reflected sound to the output signals YL (Z) and YR
(Z), and a pair of adding circuits Hp (Z) = (FLL (Z) + FLR (Z)) / (GLL (Z) + GLR (Z)) Hm (Z) = (FLL
(H) (H). In the case of Z) -FLR (Z) / (GLL (Z) -GLR (Z)), the sound image position correction circuit
adds and subtracts the input digital audio signals XL (Z) and XR (Z). First and second digital
filters having transfer characteristics of a first adder circuit and a subtractor circuit, and the
above Hp (Z) and Hm (Z), to which an output signal of the above first adder circuit and a
subtractor circuit is supplied And these first A second addition circuit and a subtraction circuit
that adds and subtracts each output signal of the second digital filter and the second digital filter
to form the output signals YL (Z) and YR (Z); the first subtraction circuit and the first And a level
control circuit connected in series to the second digital filter in a signal line between the second
addition circuit and the subtraction circuit, and the second addition circuit and the subtraction
circuit are provided by the level control circuit. A vehicle-mounted audio reproduction apparatus
in which the level of the supplied difference signal is controlled and the analog signal output
from the D / A converter circuit is supplied to the speakers of the second left and right channels.
It is.
Therefore, a virtual speaker is disposed in front of the listener, and the sound field and the sound
image are reproduced by this virtual speaker.
[0011]
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3
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Outline of In-Vehicle Sound
Reproducing Apparatus FIG. 1 shows an embodiment of an in-vehicle sound reproducing
apparatus according to the present invention.
That is, as a source of digital audio data, for example, a player 1 of CD or MD is provided, and the
digital audio data output from the player 1 is supplied to the input selector circuit 4.
[0012]
For example, an FM tuner 2 is provided as a source of the analog audio signal, and the analog
audio signal output from the tuner 2 is supplied to an A / D converter circuit 3 and A / D
converted into digital audio data. , And the digital audio data is supplied to the selector circuit 4.
[0013]
Then, in the selector circuit 4, one set of digital audio data supplied thereto is selected, and the
selected digital audio data is supplied to the digital correction circuit 5.
Although the details of the digital correction circuit 5 will be described later, the digital
correction circuit 5 is composed of, for example, a DSP, and positions the sound image
reproduced by the speaker at the ideal position.
-Gives a sense of spaciousness and depth to the playback sound. -Correct the frequency
characteristics etc. And so on.
[0014]
The corrected digital audio data is supplied to a D / A converter circuit 6 where it is D / A
converted into an analog audio signal, and this audio signal is further transmitted through an
attenuator circuit 7 for volume control. It is supplied to the speakers 9L and 9R of the left and
right channels through the output amplifier 8.
[0015]
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4
In this case, the speakers 9L and 9R are arranged (or can be arranged) in the position of FIG.
12A, for example.
That is, assuming that a front seat listener is a target, the speakers 9L and 9R are respectively
disposed below the left and right front doors of the vehicle.
[0016]
A microcomputer 11 is provided for system control, and when the operation key (operation
switch) 12 is operated, the player 1, the tuner 2, the selector circuit 4 or the attenuator circuit 7
can It is controlled by the computer 11, and a source, a volume, etc. are changed.
[0017]
Therefore, reproduced sound such as CD, MD or broadcast is output from the speakers 9L and
9R.
At this time, even if the speakers 9L and 9R are at the position shown in FIG. 12A, the sound
image formed by the reproduced sound is positioned at the height of, for example, the eye of the
listener by correction processing of the digital correction circuit 5. become. Further, even in a
narrow vehicle interior, the reproduction sound is rich in a sense of wideness and depth.
Furthermore, the influence of the frequency characteristic specific to the cabin is also corrected.
[0018]
[Digital Correction Circuit 5] The digital correction circuit 5 performs various corrections as
described above. Therefore, as shown equivalently, as shown in FIG. A sound image position
correction circuit 52 and a depth feeling correction circuit 53 are provided.
[0019]
In this case, the frequency characteristic correction circuit 51 corrects the change of the
frequency characteristic and the disturbance of the frequency characteristic peculiar to the cabin
due to the provision of the sound image position correction circuit 52, and finally supplies them
to the speakers 9L and 9R. Audio signal to have an appropriate frequency characteristic.
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5
Further, the sound image position correction circuit 52 corrects the position of the sound image
and also corrects the sense of spread. Furthermore, the depth feeling correction circuit 53
corrects the feeling of depth by the reflected sound signal.
[0020]
Each of these correction circuits 51 to 53 will be described below. Note that the correction
circuits 52, 53, and 51 will be described in the order of convenience for description.
[0021]
[Sound Image Position Correction Circuit 52] The sound image position correction circuit 52 first
corrects digital audio data so that the sound image is positioned at the height of the listener's
eyes. It is realized by using a transfer function taking into account the auditory characteristics up
to the eardrum of the listener, that is, HRTFs.
[0022]
The head related transfer function can generally be measured as follows.
That is, (a) a speaker and a dummy head in the shape of a human head are arranged in a
predetermined positional relationship. (A) As the test signal, an impulse signal that becomes flat
in the frequency axis when Fourier transformed is input to the speaker. The test signal may be a
signal having an impulse function such as a time-stretched pulse signal. (C) Measure the impulse
response in the artificial ear of the dummy head. It is a head related transfer function when this
impulse response is in the positional relationship of (a) term.
[0023]
Therefore, when using the head-related transfer function in the apparatus of FIGS. 1 and 2, (A) as
shown in FIG. 12A, it is possible to use a human as the front seat of a standard vehicle or a
typical vehicle. Place a dummy head DM in the shape of a head. (B) Place the speaker at an actual
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6
speaker position, for example, and calculate the head related transfer function at this time. (C) A
speaker is placed at a position where an ideal sound field is to be realized, for example, a position
on the dashboard, and a head transfer function at this time is obtained.
[0024]
The sound image position correction circuit 52 corrects digital audio data based on the head
transfer functions of the items (B) and (C). As described above, the sound image position
correction circuit 52 corrects the data. The sound image by the speakers 9L and 9R mounted at
the door position of the front seat is corrected to the position of the sound image by the speaker
in the ideal position.
[0025]
First, it is assumed that the head-related transfer function HRTF measured and analyzed
according to the above-mentioned items (A) to (C) is as follows, as also shown in FIG.
[0026]
FLTF (Z): from the left channel speaker to the left ear HRTFFLR (Z): 〃 right ear 〃FRL (Z): from
the right channel speaker to the left ear HRTFFRR (Z) : 〃 right ear 〃 GLL (Z): position of left
channel speaker to left ear HRTFGLR (Z): 〃 right ear 〃 GRL (Z): position of right channel
speaker to left ear HRTFGRR ( Z): 〃 right ear 〃 However, in this case, as mentioned above, the
position of is an ideal sound field or the position of a speaker that realizes a sound image, and the
position of is a speaker that is actually installed The position is 9L or 9R.
Also, each head transfer function is represented by a complex number.
[0027]
Furthermore, XL (Z): input audio signal on the left channel (audio signal before correction) XR
(Z): right 〃 ()) YL (Z): output audio signal on the left channel (audio signal after correction) ) YR
(Z): Right 〃 ()).
[0028]
Then, in order to reduce the amount of data processing in the sound image position correction
circuit 52, the head related transfer function is "symmetrical", that is, FLL (Z) = FRR (Z) (1) ) FLR
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(Z) = FRL (Z) (2) GLL (Z) = GRR (Z) (3) GLR (Z) = GRL (Z) (assuming that (4) holds Thus, the sound
image position correction circuit 52 is configured.
[0029]
For this reason, it is desirable that the dummy head DM be installed at the center of the front seat
in the vehicle compartment or at the center of the vehicle interior when measuring the headrelated transfer function.
This also reduces the seat-to-seat correction difference and allows for a correction effect on any
seat.
[0030]
Then, under the assumption of the equations (1) to (4), the following equations (5) and (6) should
be satisfied in order to correct the sound being emitted from the speaker at the position Just do
it.
That is, YL (Z) · GLL (Z) + YR (Z) · GLR (Z) = XL (Z) · FLL (Z) + XR (Z) · FLR (Z) (5) YR (Z) · GLL (Z) +
YL (Z) · GLR (Z) = XR (Z) · FLL (Z) + XL (Z) · FLR (Z) (6) where Hp (Z) and Hm (Z) Hp (Z) = (FLL (Z)
+ FLR (Z)) / (GLL (Z) + GLR (Z)) (7) Hm (Z) = (FLL (Z)-FLR (Z)) / (GLL (Z)-GLR (Z)) ... When it
defines as (8), YL (Z) and YR (Z) are YL (Z) = Hp (Z) (XL (Z). + XR (Z) / 2 + Hm (Z) (XL (Z)-XR (Z))
2 ... (9) YR (Z) = Hp (Z) (XL (Z) + XR (Z)) / 2-Hm (Z) (XL (Z)-XR (Z)) / 2 ... (10).
[0031]
Also, it is known that the difference component of the stereo music signal strongly influences the
sense of spread and the sense of stereo.
The second term of the equations (9) and (10) is the difference component of the stereo signal.
Therefore, by controlling the level of the second term, it is possible to control the sense of spatial
spread.
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[0032]
Then, when the coefficient k is multiplied as a parameter for controlling the sense of spread to
the second term of the equations (9) and (10), the equations (9) and (10) are as follows: YL (Z) =
Hp (Z) (XL (Z) + XR (Z)) / 2 + k.Hm (Z) (XL (Z) -XR (Z)) / 2 (11) YR (Z) = Hp (Z) (XL (Z) + XR (Z)) /
2-kHm (Z) (XL (Z) -XR (Z)) / 2 (12) In the equations (11) and (12), when the coefficient k is
increased, the difference component of the second term is emphasized, and hence the sense of
expansion of the reproduction sound field is enhanced.
[0033]
According to the equations (11) and (12), the sound image position correction circuit 52
comprises the filter of the characteristics represented by the equations (7) and (8), the level
control circuit, the addition circuit and the subtraction circuit. And can be configured.
[0034]
Therefore, the sound image position correction circuit 52 can be configured, for example, as
shown in FIG.
That is, digital audio data from the frequency characteristic correction circuit 51 to be described
later is used as the input signals XL (Z) and XR (Z) of the sound image position correction circuit
52, and the output signals thereof are the signals YL (Z) and YR (Z). It becomes.
[0035]
Then, the input signals XL (Z) and XR (Z) are supplied to the adder circuit 521A and the
subtractor circuit 521B, and the sum signal (XL (Z) + XR (Z)) and the difference signal (XL (Z)XR). (Z)) is formed, and the sum signal is supplied to the filter circuit 523A. Also, the difference
signal is supplied to the level control circuit 522 and level control corresponding to the
coefficient k in the equations (11) and (12) is performed and then supplied to the filter circuit
523B.
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[0036]
In this case, the filter circuits 523A and 523B are, for example, of the 70th-order FIR type and
have the transfer characteristics shown by the equations (7) and (8). The output signals of the
filter circuits 523A and 523B are supplied to the adding circuit 524A and the subtracting circuit
524B at a predetermined ratio to form output signals YL (Z) and YR (Z), and these signals YL (Z),
YR (Z) is supplied to the D / A converter circuit 6 through the depth feeling correction circuit 53.
[0037]
Therefore, even if the speakers 9L and 9R are mounted at the door position of the front seat, it is
possible to reproduce a sound image equivalent to that when the speakers 9L and 9R are
disposed at the ideal position.
[0038]
(A) Control of sense of spread As described above, since the difference component of the left and
right channels of the music signal strongly influences the sense of stereo and sense of the spread
of the reproduced sound, the sound image position correction of FIG. The circuit 52 is provided
with a level control circuit 522, and the level of the difference component is controlled
corresponding to the coefficient k.
Therefore, according to the sound image position correction circuit 52, it is possible to control
and emphasize the spatial spread of the reproduced sound.
[0039]
However, in general, when the level of the difference component is increased to emphasize the
sense of spread, it seems that the volume level is increased. Therefore, in the sound image
position correction circuit 52 of FIG. 2, as shown in FIG. 1, when the level of the difference
component is controlled by the level control circuit 522, at the same time the analog audio signal
is The level is corrected, and the volume of the playback sound is corrected.
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[0040]
Therefore, according to the reproducing apparatus of FIG. 1, the position of the sound image is
corrected to the height of the eyes, and a sufficient sense of expansion can be obtained, or the
sense of expansion can also be emphasized.
[0041]
[Simplification of Sound Image Position Correction Circuit 52] FIG. 6 shows an example of
measurement of an impulse response, and this figure shows a speaker to a front seat disposed at
the left door position of the front seat of the vehicle. It is a measurement result of the impulse
response to the left ear of the dummy head DM arrange | positioned in the center.
[0042]
And, as is clear from this measurement result, a large peak or dip is generated in the impulse
response.
Then, if these peaks and dips are applied to the sound image position correction circuit 52 as
they are, the order of the filter circuits 523A and 523B increases, and a large-scale processing
becomes necessary.
[0043]
Therefore, in the following, a method of simplifying the sound image position correcting circuit
52 by simplifying the filter circuits 523A and 523B will be described.
[0044]
(A) Averaging on the frequency axis For example, in the measurement result of FIG. 6, by taking
the amplitude average on the frequency axis, sharp peaks and tips are removed, and the overall
tendency of the impulse response is used. .
For example, in the case of the measurement result of FIG. 6, the characteristics of the curves A
and B of FIG. 7 are obtained by averaging the amplitudes, and the filter circuits 523A and 523B
are configured according to the characteristics of the curves A and B.
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[0045]
(B) Data flattening FIGS. 8 and 9 show other measurement examples of the impulse response, and
FIG. 8 shows the front left side from the speaker disposed at the left door position of the front
seat of the vehicle. As a result of the measurement of the impulse response to the left ear of the
dummy head DM disposed in the seat, FIG. 9 shows the left of the dummy head DM disposed in
the front right seat from the speaker disposed at the left door position of the front seat of the
vehicle. It is a measurement result of the impulse response to the ear.
[0046]
As is clear from these measurement results and the measurement results shown in FIG. 6, in
general, in the frequency band of 1 kHz or less, the amplitude characteristics tend to be largely
different depending on the measurement points in the vehicle compartment.
This is because the cabin is a closed space and is due to the influence of resonance (standing
wave) in the cabin.
Therefore, correcting such low frequency components limits the listening position. Also, in order
to correct low-pass components, the order of the filter must be sufficiently large.
[0047]
Therefore, no correction is made for the frequency band below 1 kHz. That is, as shown by the
straight line C in FIG. 7, an amplitude of 1 kHz or less flattens the response at its average level.
Then, the filter circuits 523A and 523B are configured in accordance with the characteristics of
the straight line C and the curve B.
[0048]
(C) As a method of reducing the order of the minimum phased filter, there is a method called
minimum phased.
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12
[0049]
Therefore, when performing the calculations of the equations (7) and (8), minimum phase
conversion is performed for each calculation of the numerator and denominator, and then
division is performed to eliminate the order of the filter circuits 523A and 523B.
[0050]
Further, when performing the calculations of the equations (7) and (8), if the minimum phase is
performed on the result of the division of the numerator / denominator, the order of the filter
circuits 523A and 523B is further reduced. Can.
[0051]
However, according to experiments, it is better to correct the sound image by performing the
minimum phase processing for each calculation of the numerator and the denominator and then
performing division than performing the minimum phase processing for the result of performing
the division of the numerator / denominator. The results were good.
[0052]
By implementing the above items (a) to (c), the order of the filter circuits 523A and 523B can be
reduced, and as a result, the sound image position correction circuit 52 can be simplified.
[0053]
[Dense Sense Correction Circuit 53] Generally, when simulating the reflected sound from a wall
or ceiling in a room or a hole, it is possible to give a sense of depth to the reproduced sound.
Therefore, the sense of depth correction circuit 53 adds the signal of the reflected sound to the
signal of the direct sound (original signal) to give a sense of depth, and is configured as shown in
FIG. 3, for example. .
[0054]
That is, since the output signals (digital audio data) YL (Z) and YR (Z) of the sound image position
correction circuit 52 correspond to direct sound, these signals YL (Z) and YR (Z) are added
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13
together. It is supplied to the D / A converter circuit 6 through the circuits 531L and 531R.
Further, the signals YL (Z) and YR (Z) are supplied to processing circuits 532L, 532R to 537L,
537R described later to form predetermined reflected sound signals, and the signals of the
reflected sounds are added to the addition circuits 531L and 531R. Supplied to
[0055]
Therefore, in the addition circuits 531L and 531R, the signal of the reflected sound is added to
the signal of the direct sound, and the output signal is supplied to the D / A converter circuit 6,
so that the reflected sound is added to the direct sound. It will be.
Therefore, it is possible to obtain a reproduced sound rich in depth.
[0056]
(B) As to the blurring of the sound image of vocals As described above, by adding the reflected
sound to the direct sound, it is possible to give a sense of depth to the reproduced sound.
However, just adding a delayed sound to the direct sound as a reflected sound may reduce the
effect of the sense of depth or blur the sound image of the music vocal.
[0057]
Therefore, in the correction circuit 53 of FIG. 3, the signal of the reflected sound is formed as
follows.
That is, the output signals YL (Z) and YR (Z) of the sound image position correction circuit 52 are
supplied to the band attenuation filters 532L and 532R. The filters 532L and 532R are for
limiting the vocal component in the music signal to prevent blurring of the sound image of the
vocal when the signal of the reflected sound is added to the signal of the direct sound.
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[0058]
Therefore, the filters 532L and 532R are, for example, of the second-order IIR type, and their
characteristics are: center frequency: attenuation at 500 Hz to 3 kHz (800 Hz) center frequency:
6 dB to 30 dB (19 dB) Q at the center frequency: 1.0 to 3.0 (2.0) (the optimum value in
parentheses).
[0059]
(C) If the filters 532L and 532R are provided for level compensation of the reflected sound
signal, the energy of the signal decreases.
Therefore, the output signals of the filters 532L and 532R are supplied to the addition circuits
533L and 532R, and the difference signal (XL (Z)-XR (Z)) output from the subtraction circuit
521B of the sound image position correction circuit 52 is added. Attenuation-compensated
signals are extracted from the adder circuits 533L and 533R, which are supplied to the circuits
533L and 533R.
[0060]
At this time, the difference signal supplied from subtraction circuit 521B to addition circuits
533L and 533R is set to a level smaller by, for example, 6 dB than the signal supplied from
addition filters 532L and 532R to addition circuits 533L and 533R. .
[0061]
(C) Low-pitched bass When the reflected sound contains a low-frequency component, the lowfrequency sound is noisy, which is undesirable for hearing.
Therefore, the output signals of the addition circuits 533L and 533R are supplied to the high
pass filters 534L and 534R, and low-frequency components that are undesirable for the sense of
hearing are removed. The filters 534L and 534R are, for example, of the second-order IIR type,
and their characteristics are Q: 0.7071 (0.7071) at a cutoff frequency: 50 Hz to 400 Hz (200 Hz)
center frequency (in parentheses) Is the optimal value).
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[0062]
(D) Improvement of the sense of depth According to experiments, when the sound quality of the
reflected sound is changed and a sound localized at another position is added as the reflected
sound, the sense of depth is effective.
[0063]
Then, the output signals of the filters 534L and 534R are supplied to the high-frequency
enhancement filters 535L and 535R, and the sound quality is changed.
The filters 535L and 535R are, for example, of the second-order IIR type, and their
characteristics are such that the boost frequency at the turnover frequency: 800 Hz to 2 kHz
high band: 3 dB to 8 dB.
[0064]
(E) When the filters 535L and 535R are provided for the correction of the high frequency band,
the high frequency band tends to be emphasized more than necessary. Therefore, the output
signals of the filters 535L and 535R are supplied to the low pass filters 536L and 536R, and the
high frequency is suppressed. The filters 536L and 536R are, for example, of the second-order
IIR type, and the characteristics thereof are Q: 0.7071 (0.7071) at a cutoff frequency of 2 kHz to
10 kHz (3 kHz) center frequency (in parentheses) Is the optimal value).
[0065]
(F) The target reflected sound signal can be obtained by delaying the output signals of the filters
536L and 536R for simulating the reflected sound. Therefore, the output signals of the filters
536L and 536R are supplied to the reflected sound signal forming circuits 537L and 537R. In
the case of FIG. 3, each of the forming circuits 537L and 537R is a delay circuit 5371 having
three taps, coefficient circuits 5372 to 5374 to which tap outputs of the delay circuit 5371 are
supplied, and outputs of these coefficient circuits And an adder circuit 5375 for adding the
signals.
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[0066]
In this case, assuming that one sample period τ of digital audio data is τ = 1 / 44.1 kHz, in the
forming circuit 537 L, for example, the delay time at the first tap of the delay circuit 5371 is 840
τ ( 552τ) 〃 second 〃: 2800τ (1840τ) 〃 third 〃: coefficient (gain) of coefficient circuit
5372 of coefficient circuit 5372: coefficient (gain) of coefficient circuit 5373: coefficient of 14
dB coefficient circuit 5372 (gain) : -14 dB (the value in parentheses is the optimum value).
Further, in forming circuit 537R, for example, the delay time at the first tap of delay circuit 5371:
770τ (506τ) 〃 second 〃: 2800τ (1840τ) 〃 third 〃: 3360τ (2208τ) Gain): coefficient of
-18 dB coefficient circuit 5373 (gain): coefficient of 14 dB coefficient circuit 5372 (gain): -14 dB
(the values in parentheses are optimum values).
[0067]
Therefore, from the adding circuits 5375 and 5375, a signal of a reflected sound whose
frequency characteristic is properly corrected is output. Therefore, the signals of the reflected
sound output from the adding circuits 5375 and 5375 are supplied to the adding circuits 531L
and 531R as described above, and are added to the direct sound signals YL (Z) and YR (Z).
[0068]
In this case, the reflected sound signal supplied to the adding circuits 531L and 531R is set to a
level smaller by, for example, 6 dB than the direct sound signals YL (Z) and YR (Z). At this time, if
the signal level of the reflected sound and the delay time in the delay circuits 5371 and 5371 are
made variable, the sense of depth can be changed.
[0069]
[Frequency Characteristic Correction Circuit 51] The frequency characteristic correction circuit
51 is configured, for example, as shown in FIG. 4, and corrects various frequency characteristics
described below to obtain a more appropriate sound image or reproduction sound field. It will be
realized.
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[0070]
(A) Correction of the sound image position described above for the correction of the low
frequency component generally tends to increase the high frequency level.
Therefore, in the correction circuit 51 of FIG. 4, the output signal of the selector 4 is supplied to
the band enhancement filters 511L and 511R, the low range is enhanced, and the frequency
balance of the output sound is corrected.
[0071]
The filters 511L and 511R are, for example, of the second-order IIR type, and their
characteristics are as follows: center frequency: 20 Hz to 120 Hz (62 Hz) boost amount at center
frequency: 2 dB to 18 dB (6.0 dB) Q at the center frequency: 1.0 to 3.0 (1.2) (the optimum value
in parentheses).
[0072]
(B) Reduction of the influence of resonance (standing wave) in the passenger compartment The
inside of the passenger compartment is a sealed space having a complicated shape.
Then, in the enclosed space, a resonance of the sound output from the speaker causes the "invehicle resonance phenomenon" of the standing wave to occur.
[0073]
According to the investigation, the frequency at which the influence of the vehicle interior
resonance phenomenon is most prominent is generally a frequency band of 800 Hz or less,
which causes a "smearing feeling". Therefore, if the output level of the sound in the band of 100
Hz to 800 Hz is lowered, the feeling of stiffness can be reduced without much affecting the
texture of the music signal.
[0074]
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Therefore, in the digital correction circuit 51, the output signals of the filters 511L and 511R are
supplied to the band attenuation filters 512L and 512R to reduce the resonance in the vehicle
compartment.
[0075]
The filters 512L and 512R are, for example, of the second-order IIR type, and their
characteristics are: center frequency: 150 Hz to 600 Hz (300 Hz) attenuation at the center
frequency: 3 dB to 6 dB (3 dB) Q in frequency: 2.0 to 4.0 (3.0) (the value in parentheses is the
optimum value).
[0076]
(C) It has already been described that there is a tendency for the high frequency level to become
higher when the sound image position correction as described above for the adjustment of the
effect linked to the volume control is performed, but as a result, the volume is increased.
Sometimes it causes the problem that the high frequency sounds are heard.
[0077]
Thus, the output signals of the filters 512L and 512R are supplied to variable high-attenuation
filters (shelving filters) 513L and 513R.
Further, the control signal of the attenuation amount of the high frequency band is supplied from
the microcomputer 11 to the filters 513L and 513R.
[0078]
The filters 513L and 513R are, for example, of the first-order IIR type, and the characteristics
thereof are: attenuation frequency: 1 dB to 3 kHz (2.5 kHz) attenuation amount: 0 dB to 12 dB
(The value in parentheses is the optimal value).
[0079]
When the volume adjustment key of the keys 12 is operated, the microcomputer 11 controls the
attenuation amount of the attenuator circuit 7 to adjust the volume of the reproduced sound. At
this time, the volume is increased. The microcomputer 11 simultaneously controls the
attenuation of the high band in the filters 513L and 513R so that the attenuation of the high
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band in the filters 513L and 513R becomes larger as it becomes larger.
[0080]
Therefore, when the volume is high, the high frequency band is suppressed, and appropriate
reproduction can be performed at any volume, and the control thereof can be easily performed.
[0081]
(D) In the Case where the High-Range Dedicated Speaker is Installed Depending on the type of
vehicle, the high-range dedicated speaker may be disposed near the position shown in FIG. 12A.
And when performing the above-mentioned correction | amendment of a sound image position,
since a sound image is correct | amended to a position, even if it provides the speaker only for
such a high region, isolation | separation of a sound image is not carried out.
[0082]
However, if a high frequency dedicated speaker is arranged near the position, more high
frequency bands will reach the listener than when the speaker is only in position, so the high
frequency area is emphasized. It becomes a sound.
[0083]
Therefore, the output signals of the filters 513L and 513R are supplied to high-pass attenuation
filters (shelving filters) 514L and 514R to attenuate the high regions, and the output signals of
the filters 514L and 514R are frequency characteristic correction circuits. This is an output
signal of 51.
[0084]
For this reason, the filters 514L and 514R are configured, for example, as a first-order IIR type,
and the characteristics thereof are: attenuation in the turnover frequency: 3 kHz to 8 kHz (1 kHz)
high region: variable by the user It is said that 0 dB to 12 dB (the value in parentheses is the
optimum value).
[0085]
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It should be noted that when no high frequency dedicated speaker is installed (in the vicinity of
the position), the attenuation in the high frequency band of the filters 514L and 514R may be set
to 0 dB.
[0086]
[Summary] As described above, according to the on-vehicle acoustic reproducing apparatus of
FIGS. 1 to 4, the virtual speaker is disposed at a place where the attachment is impossible
originally, and the reproduced sound from this virtual speaker is obtained. Can be perceived as
being output, so that an ideal vehicle interior sound field and sound image can be created.
[0087]
Therefore, the sound image can be prevented from being localized downward, and the sound
image can be localized at the ideal eye height.
In addition, it is possible to eliminate the problem that occurs when a small high-frequency
reproduction speaker is installed at the upper side, that is, the problem that sounds are separated
and heard, and it is perceived that sound is coming out from one speaker It can be done.
[0088]
Furthermore, by controlling the level of the difference component, it is possible to correct the
spatial spread of the sound field.
In addition, it is possible to make an optimal correction according to the volume level.
Furthermore, by providing the depth feeling correction circuit 53, the reflected sound is included
in the reproduced sound, so that the reproduced sound with a rich sense of depth can be
obtained.
[0089]
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Further, the sound image position correction circuit 52 can be simplified, and the desired
purpose can be achieved even with a DSP with a small processing capacity.
Furthermore, even if the transfer function is measured, optimal correction can be performed even
in any type of vehicle model.
[0090]
Further, by taking an average of a plurality of transfer functions, it is possible to create an
effective correction filter circuit even for a plurality of vehicle types, and therefore, it can also be
spread as a correction filter circuit that does not limit the vehicle type.
[0091]
[Outline of In-Vehicle Sound Reproducing Apparatus (Part 2)] Generally, the left and right
speakers for stereo reproduction are ideally placed in symmetrical positions as viewed from the
listener, and the sound image reproduced by the speakers is It is ideal to locate in front of the
listener.
[0092]
However, in the vehicle-mounted sound reproducing apparatus, as described with reference to
FIG. 12A, the speaker is disposed below the front door for the front seat and below the rear door
for the rear seat, or as shown in FIG. 12B. As shown in the figure, it is often arranged at the
position of the rear tray.
[0093]
Therefore, for example, to the passenger in the seat on the front right side, the reproduction
sound output from the speakers disposed on the front right side first reaches, and thereafter, the
reproduction sound output from the other speakers is Each will arrive late.
Therefore, the passenger hears the reproduced sound out of phase, and it becomes impossible to
obtain a clear sense of localization.
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22
[0094]
Therefore, a part of the vehicle-mounted sound reproducing apparatus is called a "seat position
function" and realizes an optimum reproduction sound field corresponding to the seating
position (seat position) of the passenger. There is something.
[0095]
FIG. 10 shows the case where the present invention is applied to an on-vehicle sound
reproducing apparatus having a seat position function.
That is, the processing units 1 to 9L and 9R are configured in the same manner as the apparatus
of FIG. 1 except for a part of the digital correction circuit 5.
Then, although the details of the digital correction circuit 5 will be described later, digital audio
data of the left and right channels for the rear seat are taken out from the digital correction
circuit 5.
[0096]
The digital audio data has its delay time and frequency characteristics corrected in accordance
with the seat position function, and this digital audio data is supplied to the D / A converter
circuit 6B to be converted into an analog audio signal by D / A conversion. The audio signal is
supplied to the speakers 9LB and 9RB of the left and right channels through the output amplifier
8B through the attenuator circuit 7B for volume control.
In this case, the speakers 9LB and 9RB are disposed, for example, at the position of FIG. 12A or
the position of FIG. 12B.
[0097]
Therefore, the sound image formed by the reproduced sound of the speakers 9L, 9R, 9LB, 9RB is
located at the height of, for example, the eyes of the listener, and has a rich sense of expanse and
depth, etc. When, these effects can be obtained regardless of the sitting position of the listener.
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[0098]
[Digital Correction Circuit 5 (Part 2)] The digital correction circuit 5 is configured, for example, as
shown in FIG. 11 in order to realize the sheet position function.
That is, digital audio data output from the sense of depth correction circuit 53 is supplied to the
D / A converter circuit 6 through the delay circuits 54L and 54R, and D / A converted into an
analog audio signal.
[0099]
Although the low frequency component is not related to the localization of the sound image, the
digital audio data output from the filters 511 L and 511 R is a variable high frequency
attenuation filter (shelving filter) in order to improve the texture of the low frequency region. The
signals are supplied to 515 LB and 515 RB, and the high region is attenuated.
[0100]
In this case, when the filters 515LB and 515RB set the "seat position" somewhere on the front
seat, that is, any one of the front seat, the front seat right and the front seat left, the rear
speakers 9LB and 9RB Is to prevent the sound image from being pulled backward by suppressing
the high-frequency component of the reproduction sound output from.
[0101]
For this reason, the filters 515 LB, 515 RB are, for example, of the first-order IIR type, and their
characteristics are controlled by the turnover frequency: attenuation at 3 kHz high range: the
microcomputer 11.
[0102]
The output signals of the filters 515LB and 515RB are supplied to the D / A converter circuit 6B
through the delay circuits 54LB and 54RB, and D / A converted into an analog audio signal.
[0103]
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The delay circuits 54L, 54R, 54LB, 54RB are for adjusting the phase of the reproduced sound
output from the speakers 9L, 9R, 9LB, 9RB in accordance with the seating position of the
passenger.
Further, the delay circuits 54LB and 54RB are configured to convert the reproduction sound
output from the front speakers 9L and 9R to the reproduction sound output from the rear
speakers 9LB and 9RB to the passenger seated in the front seat. In comparison, it is also for
relatively 10 milliseconds to reach 20 milliseconds earlier.
The delay time of these delay circuits 54L to 54RB is controlled by the microcomputer 11.
[0104]
In such a configuration, when a predetermined seating position of the operation keys 12 is
operated to input the seating position of the passenger, the microcomputer 11 causes the high
frequency components in the filters 515LB and 515RB to correspond to the operation. The
attenuation amount and the delay time of the delay circuits 54L to 54RB are controlled.
Therefore, the delay circuits 54L to 54RB can match the phase when the reproduced sound
output from the speakers 9L to 9RB reaches the passenger, and as a result, the localization of the
sound image can be clarified.
[0105]
Further, the high frequency components of the reproduced sound output from the rear speakers
9LB and 9RB are attenuated by the filters 515LB and 515RB, so that the position of the sound
image perceived by the passenger of the front seat is pulled backward. Can be obtained and clear
localization can be obtained from this point as well.
[0106]
Furthermore, the human auditory sense has the property that a preceding sound effect (Heath
effect), that is, a sound that is reached earlier by about 10 ms to 20 ms is emphasized and
perceived, but the delay circuit The reproduction sound output from the front speakers 9L and
9R by 54LB and 54RB is 10 ms to 20 ms relatively ahead of the reproduction sound output from
the rear speakers 9LB and 9RB. The reproduced sound output from 9L and 9R is emphasized,
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and the sound image can be localized forward without reducing the overall volume.
[0107]
In addition, since the low frequency band that does not significantly affect the localization of the
sound image is output from the speakers 9LB and 9RB, the overall sound pressure level does not
decrease, or the thickness of the low frequency band disappears. I have nothing to do.
Further, in the on-vehicle audio system, since the rear speakers are generally larger in diameter
than the front speakers, the performance of the speakers 9LB and 9RB can be sufficiently
obtained for low frequency output.
[0108]
Furthermore, since the reproduced sound output from the front speakers 9L and 9R is
emphasized and perceived because of the preceding sound effect, the signal processing such as
graphic equalizer processing is performed by the convenience of the DSP, etc. , 9R, even if it can
be set only to the signal line of the audio signal supplied, it acts so that the effect is effective to
the whole vehicle interior.
[0109]
[Others] In the above description, the seating position of the passenger is input using the
operation key 12. However, the seating position of the passenger is detected by an infrared
sensor provided in the vehicle compartment or a pressure sensor provided in the seat. It is also
possible to control the filters 515LB and 515RB and the delay circuits 54L to 54RB to
characteristics corresponding to the seating position by the microcomputer 11 according to the
detection output.
[0110]
[List of abbreviations used in this specification] A / D: Analog to Digital CD: Compact Disc D / A:
Digital to Analog DSP: Digital Signal Processor FIR: Finite Impulse Response FM: Frequency
Modulation HRTF: Head Related Transfer Function IIR: Infinite Impulse ResponseMD: Mini DiscQ:
Quality
[0111]
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According to the present invention, even if the mounting position of the speaker is limited, the
sound image can be localized at the ideal eye height.
In addition to being able to obtain a rich sense of spread and a sense of depth, the sense of
spread and the sense of depth can be adjusted according to the preference of the listener.
[0112]
Furthermore, the correction filter circuit can be simplified, and even the DSP with small
processing capacity can achieve the intended purpose.
In addition, as long as the transfer function is measured, optimal correction can be performed on
any type of vehicle.
Furthermore, by taking an average of a plurality of transfer functions, it is possible to create an
effective correction filter circuit even for a plurality of vehicle types, and therefore, it can be
popularized as a correction filter circuit that does not limit the vehicle type.
[0113]
Brief description of the drawings
[0114]
1 is a system diagram showing an embodiment of the present invention.
[0115]
2 is a system diagram showing an embodiment of the present invention.
[0116]
3 is a system diagram showing an embodiment of the present invention.
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[0117]
4 is a system diagram showing an embodiment of the present invention.
[0118]
5 is a plan view for explaining the present invention.
[0119]
6 is a characteristic diagram for explaining the present invention.
[0120]
7 is a characteristic diagram for explaining the present invention.
[0121]
8 is a characteristic diagram for explaining the present invention.
[0122]
9 is a characteristic diagram for explaining the present invention.
[0123]
10 is a system diagram showing another embodiment of the present invention.
[0124]
11 is a system diagram showing another embodiment of the present invention.
[0125]
12 is a diagram for explaining the sound field in the passenger compartment.
[0126]
Explanation of sign
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[0127]
DESCRIPTION OF SYMBOLS 1 ... CD or MD player, 2 ... FM tuner, 3 ... A / D converter circuit, 4 ...
selector, 5 ... digital correction circuit, 6 ... D / A converter circuit, 7 ... attenuator circuit for
volume control, 8 ... Output amplifier 9L and 9R Speaker 11 microcomputer 12 operation key 51
frequency characteristic correction circuit 52 sound image position correction circuit 53 sense of
depth correction circuit
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