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JP2004135023

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DESCRIPTION JP2004135023
The present invention relates to an optimum sound image setting by a rear speaker and a
response to head movement. A correction process based on a head acoustic transfer function is
performed on an acoustic signal output from a speaker installed in a rear space of a listener. The
sound signal is localized in a predetermined direction, such as the space in front of the listening
position, by using the sound signal that has been made. Further, it is suitable while detecting the
positional relationship between the speaker and the head of the listener for correction
processing. Choose a head acoustic transfer function. [Selected figure] Figure 1
Acoustic output device, acoustic output system, acoustic output method
The present invention relates to an audio output device capable of localizing a virtual sound
image in an arbitrary space in an AV playback device (audio / visual playback device), a
multimedia playback device, etc. , An acoustic output system, and an acoustic output method. 2.
Description of the Related Art In recent years, in the field of audio / video and multimedia, audio
and video reproduction with a sense of three-dimensionality and presence is desired, and
hardware corresponding to this is actively developed. There is. In particular, in sound
reproduction, an acoustic signal can be heard from the side, the rear, the upper side, or the lower
side without arranging the speaker in the direction of the side, the rear side, the upper side, the
lower side, or a combination of these. Attention has been focused on sound reproducing devices
that cause virtual sound images to be localized. In addition, in sound image control, a technique
for interactively controlling sound image localization is also attracting attention. Generally, in a
stereo sound system conventionally used, a plurality of speakers are used to control the position
of a sound image to give a sense of presence to the listener's hearing. However, in a conventional
speaker system in which speakers are provided at the left and right of the front of the listener, a
sound image can be generated only between the two speakers. Furthermore, when headphones
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are used, a specific phenomenon (in-head localization) in which a sound image can be generated
in the head occurs, and the listener is often tired. On the other hand, with the development of
hardware such as acoustic signal processing technology and DSP (Digital Signal Processor), even
in a system in which left and right speakers are installed in front of a listener, sound image
localization to an arbitrary position in front of the listener is It came to be done. In addition, in a
system using headphones, an attempt has been made to localize the sound image outside the
head. Conventionally, as an acoustic signal processing technique for localizing a sound image by
speaker reproduction of two channels, a technique using convolution of a head acoustic transfer
function in a time domain and crosstalk cancellation is known. In the acoustic signal processing
technology for localizing a sound image, calculation relating to sound image localization is
performed using a head acoustic transfer function that means the transfer characteristic of sound
from the front sound source to the ear of the listener. FIG. 9 is a block diagram showing an
example of a conventional sound reproducing apparatus that controls sound image localization.
In FIG. 9, acoustic signals of L and R channels are inputted to the acoustic signal input unit 31.
The input acoustic signals of L and R channels are respectively converted into digital acoustic
signals by the A / D converter 32, and are input to the digital filter 33.
Then, after being processed by the digital filter 33, it is converted into an analog sound signal by
the D / A converter 34, and is supplied to the speaker 36 of L and R channels via the amplifier
35. The speakers 36 are speakers disposed on the left and right of the front of the listener. In the
sound reproducing apparatus, a sound image localization controller 37 is connected to the digital
filter 33 in order to control the position of the sound image. When an arbitrary predetermined
sound image position is input by the sound image localization controller 37, the digital filter 33
sets each signal of the two channels output from the A / D converter 32 to the sound image
position set by the sound image localization controller 37. Fold in the corresponding coefficient.
Then, the convoluted acoustic signal is amplified by the amplifier 35, and the acoustic signal is
reproduced by the speakers 37 installed on the front left and right of the listener. By performing
such acoustic signal processing, it becomes possible to control the sound image position at any
position on the left and right in front of the listener. Further, in the above-described crosstalk
cancellation technology, it is possible to localize the sound image to the outside of the speaker by
mixing the sounds in antiphase. For example, in FIG. 10, an acoustic signal of sound pressure E is
emitted from a sound image at a virtual position, and the acoustic signal gives sound pressures
yL and yR to the left and right ears of the listener, respectively. The head acoustic transfer
function from the virtual sound image to the left ear is denoted by TL (Z), and the head sound
transfer function from the virtual sound image to the right ear is denoted by TR (Z). When the
relationship between the virtual sound image and yL and yR is expressed using the head acoustic
transfer functions TL (Z) and TR (Z), yL = TL (Z) × E (Equation 1) yR = TR (Z) × E (Equation 2) In
order to localize the sound image to the virtual position in FIG. 10 (the position outside the actual
left and right speakers), the digital filter 33 in FIG. 9 can be obtained by the above (Equation 1)
(Equation 2) The sound signal is corrected by convolution processing so that the sound pressures
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yR and yL are from the virtual sound image. Furthermore, the sound from the front left and right
speakers actually installed to the listener is canceled. That is, the virtual sound image as shown in
FIG. 10 can be created by canceling the sound reaching the right ear from the left speaker and
the sound reaching the left ear from the right speaker (these are referred to as crosstalk
sound ). Specifically, using TL (Z), TR (Z) and the head acoustic transfer function from the actual
speaker to the ear, a direction including the two directional localization filters with common
inputs to determine the direction of the sound image The acoustic image is localized at the virtual
position in FIG. 10 through the acoustic signal in the crosstalk canceller, which comprises a
localizer and a filter having a filter characteristic for removing the influence of crosstalk sound.
For example, although the above-mentioned techniques relating to sound image localization are
known, the following can be mentioned as documents showing the techniques relating to sound
image localization. [Patent Document 1] Japanese Patent Application Laid-Open No. 10-224900
However, in the conventional sound reproducing apparatus as described above, in order to install
the speaker in the space in front of the listener In many cases, it was not possible to mount the
speakers at the positions required to create an ideal sound field and sound image for the listener.
For example, in the case of a listener who is seated on a seat and views an image on a display, it
is necessary to mount a speaker in a place that does not prevent viewing, and the installation
location of the speaker is restricted. Therefore, in some cases, the speaker must be installed at an
undesireable location in front of the listener, and the sound image is free in any space from the
position of the listener, for example, in the side or back of the listener, or up and down. It was not
possible to position it freely. Therefore, the present applicant has previously made a sound
reproducing apparatus capable of obtaining natural sound image localization in any space using
a speaker installed in the space behind the listener in Japanese Patent Application 2001-246360
as prior art. Provided. According to the present invention, a virtual sound source can be disposed
at a place where attachment is not possible originally, and it can be perceived that a reproduced
sound is output from this virtual sound source, so an ideal sound field for a listener And can
produce sound images. However, in this sound reproducing apparatus, when the head of the
listener moves during reproduction, it is difficult to obtain a sufficient sense of sound image
localization because the optimal head sound transfer function can not be applied. SUMMARY OF
THE INVENTION The present invention has been made in view of such problems, and a natural
sound image localization in any space is made using a speaker installed in the space behind the
listener. An object of the present invention is to realize a sound reproducing device that can be
obtained, and at the same time to obtain sound image stability in response to the movement of
the listener's head. Therefore, the sound output device of the present invention is a sound output
device for supplying sound output signals of a plurality of channels to speakers of a plurality of
channels installed in a space behind a listening position of a listener. Correction filter means for
performing correction processing based on a head acoustic transfer function so that sound image
localization is performed in a predetermined direction space with respect to the listening position
with respect to each sound digital input signal; Sound signal output means for supplying a
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channel signal to the speakers of the plurality of channels as sound output signals, sensor means
for detecting the positional relationship between the position of the speaker and the head
position of the listener, and Control means for selecting a head acoustic transfer function in
accordance with the detection result of step I will prepare.
In this case, it is assumed that the predetermined direction space in which sound image
localization is performed is a space in front of the listening position. The control means may
further include operation means for variably instructing a predetermined direction space for
sound image localization, and the control means selects a head acoustic transfer function
according to the detection result of the sensor means and the operation information of the
operation means. Control the correction processing of the correction filter means. The sound
output system according to the present invention comprises the sound output device configured
as described above and a plurality of channels of speakers installed in the space behind the
listening position of the listener. According to the sound output method of the present invention,
when supplying sound output signals of a plurality of channels to speakers of a plurality of
channels installed in a space behind a listening position of a listener, the position of the speakers
and the listening The positional relationship with the head position of the person is detected, the
head sound transfer function is selected according to the detection result, and sound image
localization is made in a predetermined direction space with respect to the listening position for
each sound digital input signal of plural channels. A correction process is performed based on
the selected head acoustic transfer function so that the signals of the plurality of channels
subjected to the correction process are supplied as sound output signals to the speakers of the
plurality of channels. According to such an embodiment of the present invention, listening can be
performed by using an acoustic signal output from a speaker installed in a space behind the
listener as an acoustic signal subjected to correction processing based on a head acoustic
transfer function. The sound image is localized at a predetermined direction position such as a
space in front of the position. Furthermore, a stable sound image localization state is obtained by
selecting an appropriate head acoustic transfer function while detecting the position of the
listener's head in real time. Note that the rear space of the listener includes the right and left ears
of the listener, and in a plane parallel to the central axis of the listener's human body, the plane
includes the plane and is divided by the plane. It means one space that includes the listener's
back of the head. The head acoustic transfer function is a function representing a transfer system
from the sound source to one of the human ears (tympanic membrane), and reflects reflection,
diffraction, resonance, and the like of the head, auricle, shoulders, and the like. This head
acoustic transfer function can be determined by measurement. Also, each head acoustic transfer
function is represented by a complex number. BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, sound reproducing apparatuses according to first and second embodiments of the
present invention will be described in detail with reference to the drawings. First Embodiment
FIG. 1 shows a configuration of a sound reproducing apparatus according to a first embodiment.
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This sound reproducing apparatus includes an audio digital signal input unit 1, a correction filter
unit 2, an audio digital signal output unit 3, a D / A converter 4, an output amplifier 5, left and
right speakers 6 (left channel speaker 6L, right channel speaker 6R) , CPU 11, storage unit 13,
and infrared sensor 17 are configured. The audio digital signal input unit 1 receives, as a source
of digital audio data, digital audio data of L and R 2 channels output from a playback apparatus
for AV media such as CD / MD / DVD, for example. Alternatively, as a source of analog audio
signals, for example, an analog audio signal output from an FM tuner or the like is converted into
digital audio data by an A / D converter (not shown), and the digital audio data is converted to
audio digital signal input unit 1 It may be supplied to Digital acoustic data of the L and R
channels supplied to the audio digital signal input unit 1 is supplied to the correction filter unit 2
and predetermined correction processing is performed. Although the details of the correction
filter unit 2 will be described later, this correction filter unit 2 is positioned at the target position
(the position of the virtual sound image 9 in FIG. 1) of the sound image reproduced by the left
channel and right channel speakers 6L and 6R. Digital sound data is corrected as it comes.
Further, the correction filter unit 2 is controlled based on real-time detection information of the
position of the head of the listener by the infrared sensor 17, and is configured to always execute
optimum correction processing. The digital acoustic data corrected by the correction filter unit 2
is supplied to the D / A converter 4 through the acoustic digital signal output unit 3 and
converted into analog acoustic signals of L and R channels. Then, the analog audio signal is
supplied to the speakers 6L and 6R of the left and right channels through attenuator circuit
processing for adjusting the volume and power amplifier processing in the output amplifier unit
5. The speakers 6 L, 6 R are disposed in the rear space of the listener 8. The rear space includes
the left and right ears of the listener 8 and in a plane 10 parallel to the central axis of the
listener's human body, the plane 10 includes the plane 10 and the space in two spaces divided by
the plane 10 It means one space including the back of the listener 8. For example, as shown in
FIG. 2, the speakers 6L and 6R disposed in the rear space are disposed at the position of the
headrest of the seat 14 (or can be disposed at the position of the headrest).
That is, assuming that a listener who is seated on the seat 14 is a target, the speakers 6L and 6R
are disposed at the left and right positions on the headrest or in the headrest in this manner,
thereby being disposed in the rear space of the listener 8. It will be Then, sound signals such as
CD, MD, DVD or broadcast are output from the speakers 6L, 6R, and the sound image formed by
the sound signals is such that the speakers 6L, 6R are at the position of the headrest in FIG. Also
by the correction processing of the correction filter unit 2, the virtual sound image 9 is
positioned, for example, in front of the listener 8. For example, as shown in FIG. 2, when the
display device 15 is disposed in front and the user is seated to view an image, the position of the
virtual sound image 9 can be made about the position of the display device 15. In FIG. 1 and FIG.
2, the speakers 12 L and 12 R as virtual sound sources are shown. The virtual sound source
mentioned here is a speaker that realizes an ideal sound field or sound image, but is not actually
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installed in space, that is, the speakers 12L and 12R are speakers that do not exist. On the other
hand, assuming that speakers actually installed are called real sound sources, the speakers 6L
and 6R are real sound sources. An appropriate arrangement position of the speakers 6 L, 6 R in
the rear space is shown in FIGS. 3 and 4. FIG. 3 is a top view showing the horizontal direction of
the rear space. As shown in FIG. 3, the back space includes plane 10 and includes all space from
plane 10 to the back of the listener. Therefore, the speakers 6L and 6R are disposed at arbitrary
positions in the rear space. In addition, as shown in FIG. 3, regarding the straight line connecting
the arrangement position of the speakers 6L and 6R to the left and right ears 7L and 7R of the
listener 8, the orthographic projection angle formed with the plane 10 is the angle θ1. Let the
orthogonal projection angle formed with the central axis J of 6R be an angle θ2. In this case, it is
desirable that the angle θ1 and the angle θ2 be 0 ° ≦ θ1 ≦ 90 ° −30 ° ≦ θ2 ≦ + 30 °
(however, the counterclockwise direction is defined as +). By arranging the speakers 6L and 6R
so that the angles θ1 and θ2 satisfy the above conditions, the sound image formed by the
acoustic signals from the speakers 6L and 6R is more effectively corrected by the correction filter
unit 2 The virtual sound image 9 is located, for example, in front of the listener 8. FIG. 4 is a side
view showing the vertical direction of the rear space. As shown in FIG. 4, the back space includes
the plane 10 and includes all the space from the plane 10 to the back of the listener.
Therefore, the speakers 6L and 6R are disposed at arbitrary positions in the rear space. In
addition, as shown in FIG. 4, the straight line connecting the left and right ears 7L and 7R of the
listener 8 from the arrangement position of the speakers 6L and 6R includes the ears on the left
and right of the listener and is perpendicular to the plane 10 Let the orthogonal projection angle
formed with the plane 16 orthogonal to the surface 16 be an angle θ3, and the orthogonal
projection angle formed with the central axes J of the speakers 6L, 6R be an angle θ4. In this
case, it is desirable that the angles θ3 and θ4 be −90 ° ≦ θ3 ≦ 90 ° −30 ° ≦ θ4 ≦ +
30 ° (however, the counterclockwise direction is defined as +). By arranging the speakers 6L
and 6R so that the angles θ3 and θ4 satisfy the above conditions, the sound image formed by
the acoustic signals from the speakers 6L and 6R is more effectively corrected by the correction
filter unit 2 The virtual sound image 9 is located, for example, in front of the listener 8. Further,
in the sound reproducing apparatus of the present embodiment, as shown in FIG. 1, an infrared
sensor 17 is provided. This infrared sensor is a sensor that detects the positional relationship
between the speakers 6L and 6R and the head of the listener 8, specifically, the distance. For
example, as shown in FIG. 2, the infrared sensor is disposed at the center of the headrest of the
seat 14 or the like to detect the positional relationship between the positions of the speakers 6L,
6R and the head of the listener 8 seated on the seat 14. The infrared sensor 17 can detect the
distance of the head of the listener 8 from the positions of the speakers 6L and 6R as the above
positional relationship by being configured to include at least an infrared light emitting unit and
an infrared light receiving unit. The light emitting unit and the light receiving unit may be
separately configured, or may be integrally configured such as a photo coupler. FIGS. 5A, 5 B,
and 5 C show an example of the positional relationship detected by the infrared sensor 17, that
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is, the distance d. As illustrated, even when the listener 8 is seated on the seat 14, the distance d
between the head position and the positions of the speakers 6L and 6R varies depending on the
posture of the listener 8. The infrared sensor 17 detects this distance d, and supplies this
detection information to the CPU 11 shown in FIG. By arranging a plurality of infrared sensors
17 in the height direction, the height position of the head of the listener 8 who is seated can be
detected along with the distance d (horizontal distance). it can. For example, as shown in FIGS. 5
(d) and 5 (e), the height position of the head is largely different depending on whether the
listener 8 is an adult or a child.
In this case, even if the horizontal distance d between the speakers 6L and 6R and the head is the
same, if the height position of the head is different between a child and an adult, the actual
distance from the speakers 6L and 6R to the head is Will be different. Therefore, if a plurality of
infrared sensors 17 are arranged in the height direction so that the height of the head, ie, the
distance h in the vertical direction between the speakers 6L and 6R and the head can also be
detected as shown in FIG. The positional relationship between the speakers 6L and 6R and the
head can be detected more accurately in response to the listeners 8 of various heights / seat
heights. Although not shown in the drawings, it is conceivable that the head of the listener 8 may
be displaced to the left or right in the sheet 14, so a plurality of infrared sensors 17 are disposed
in the lateral direction of the backrest of the sheet 14 It is also preferable to be able to detect a
deviation (distance) of the image. Although the infrared sensor 17 is disposed at the center of the
headrest of the seat 14 in this example, the infrared sensor 17 may be disposed at any location.
Moreover, it is not restricted to an infrared sensor. That is, any configuration can be used as long
as it can detect at least the positional relationship (at least distance) between the speakers 6L and
6R disposed in the rear space and the head of the listener 8, and the configuration and the
arrangement position thereof are not limited. For example, when it is set as the sound
reproduction system in a car, you may arrange at a headrest of a driver's seat, and may arrange
at a ceiling, a side wall part, etc. in a car. The CPU 11 in FIG. 1 constantly monitors the detection
information from the infrared sensor 17, that is, the positional relationship between the speakers
6L and 6R and the head of the listener 8. In addition, in the storage unit 13, a head acoustic
transfer function measured in advance in various positional relationships is stored as a database.
The head acoustic transfer function is a function representing a transfer system from the sound
source to one of the human ears (tympanic membrane), and reflects reflection, diffraction,
resonance, and the like of the head, auricle, shoulders, and the like. This head acoustic transfer
function can be determined by measurement. Also, each head acoustic transfer function is
represented by a complex number. When the CPU 11 determines the positional relationship
(distance) based on the detection information from the infrared sensor 17, the CPU 11 searches a
database in the storage unit 13 based on the positional relationship, and transmits head acoustics
according to the positional relationship. Get a function Then, the acquired head acoustic transfer
function (or a correction parameter value calculated from the head sound transfer function) is
supplied to the correction filter unit 2, and parameters for correction processing (transfer
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characteristics Hp (Z), Hm (described later) Set Z)).
That is, in the present embodiment, the reproduced sound from the speakers 6 L and 6 R
disposed in the rear space is localized in the virtual sound image 9 in the front space by the
correction processing by the correction filter unit 2 as described above. Although the parameters
of correction processing are variably controlled in real time according to the positional
relationship between the speakers 6 L and 6 R and the head of the listener 8, the virtual sound
image 9 is obtained regardless of the movement of the listener 8 posture, etc. It stabilizes the
localization state of The correction process using the head acoustic transfer function will be
described below. First, a method of measuring the head acoustic transfer function will be
described. As described above, the correction filter unit 2 corrects the digital sound signal so that
the sound image is located in an arbitrary space, but this correction is a head that also takes into
consideration the auditory characteristics from the speaker to the eardrum of the listener. It is
realized by using a partial acoustic transfer function. This head acoustic transfer function can
generally be measured as follows. (A) A speaker and a dummy head in the shape of a human
head are arranged. (B) As a test signal, an impulse signal which 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 acoustic transfer function when this impulse
response is in the positional relationship of the above (a). Therefore, for example, in the sound
reproducing apparatus of this example in which the speakers 6 L and 6 R are disposed on the
sheet 14 as shown in FIG. 2, when using the head acoustic transfer function, (A) a standard sheet
or Place a dummy head in the shape of a human head on a typical seat. (B) The speakers are
arranged at the actual speaker positions, for example, the positions of the speakers 6L and 6R, ie,
the position of the headrest of the seat 14, and the head acoustic transfer function in the case
where the speakers 6L and 6R are present is determined. (C) Heads when there are speakers at
positions where the virtual sound source is to be realized, for example, the positions of the virtual
speakers 12L and 12R, that is, the left and right of the display 15 of FIG. Find the acoustic
transfer function. In this way, it is possible to measure the head acoustic transfer function for
correcting the position of the sound image by the correction filter unit 2. That is, the correction
filter unit 2 corrects the digital sound signal on the basis of the head sound transfer function of
(B) and (C), and as described above, the headrest of the seat 14 is corrected by this data
correction. The sound image by the attached speakers 6L, 6R is corrected to the position of the
sound image by the speakers 12L, 12R at the position of the virtual sound source.
Regarding the measurement of the head acoustic transfer function in the above (B), that is, the
head acoustic transfer function for the speakers 6 L and 6 R and the dummy head, the head
according to the listener's various postures and sitting heights on the seat Measure according to
the position of the unit. That is, while changing the position of the dummy head, the head
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acoustic transfer functions corresponding to each position of the head are measured, and these
are converted into a database as a head sound transfer function corresponding to the head
position. In addition, regarding the measurement of the head acoustic transfer function in the
above (C), that is, for the head sound transfer function for the position where the virtual sound
source is to be realized and the dummy head, set a point to be the virtual sound source position
to set the speaker 12L. Speakers corresponding to 12R are arranged to measure the head
acoustic transfer function, but also in this case, the measurement is performed according to the
position of the listener on the seat and the head position according to the sitting height. Then,
they are put into a database as a head acoustic transfer function according to the head position.
That is, according to the head position of the listener 8 seated on the seat 14, the head sound
transfer function from the speakers 6L and 6R of the real sound source to the listener 8 and the
listening from the speakers 12L and 12R of the virtual sound source The head acoustic transfer
function to the person 8 is database-ized so that it can be selected, and the storage unit 13 stores
such a database. In the example of the first embodiment shown in FIG. 1, the virtual sound image
9 is fixed to the front of the listener 8, but in the case of the second embodiment described later,
the virtual sound image 9 is virtual. The position of the sound image 9 can be variably set
arbitrarily by the listener 8. In that case, for example, as the head sound transfer function from
the virtual sound source speakers 12L and 12R to the listener 8, the measurement of (C) is
performed while changing the positions of the virtual sound source speakers 12L and 12R to
various positions. , Need to be a database. The correction process using the head acoustic
transfer function is performed as follows. First, it is assumed that the head acoustic transfer
function measured and analyzed by the above (A) to (C) is as follows as shown in FIG. FLL (Z):
Head sound transfer function from the left channel speaker 12L of the virtual sound source to
the left ear FLR (Z): Head sound transfer function from the speaker 12L of the left channel of the
virtual sound source to the right ear FRL (Z): Head sound transfer function from the speaker 12R
of the right channel of the virtual sound source to the left ear FRR (Z): Head sound transfer
function from the speaker 12R of the right channel of the virtual sound source to the right ear
GLL (Z): Head sound transfer function GLR (Z) from the speaker 6L of the left channel of the real
sound source to the left ear: Head sound transfer function from the speaker 6L of the left
channel of the real sound source to the right ear GRL (Z): right of the real sound source Head
sound transfer function GRR (Z) from the speaker 6R of the channel to the left ear: Head sound
transfer function from the speaker 6R of the right channel of the real sound source to the right
ear However, as described above, the positions of the virtual sound sources 12L and 12R are the
positions of the speakers that realize the ideal sound field or sound image, and the positions of
the real sound sources 6L and 6R are actually installed. Position of the speaker.
Also, each head acoustic transfer function is represented by a complex number. Further, XL (Z):
acoustic input signal of left channel (acoustic signal before correction) XR (Z): acoustic input
signal of right channel (acoustic signal before correction) YL (Z): acoustic of left channel Output
signal (corrected acoustic signal) YR (Z): An acoustic output signal of the right channel (corrected
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acoustic signal). Here, due to the sound pressure outputted by the actual speakers 6 L, 6 R
disposed behind the listener 8, the left ear 7 L of the listener 8 is YL (Z) · GLL (Z), and YR (Z) The
sound pressure of GRL (Z) is obtained. Similarly, due to the sound pressure output by the actual
speakers 6L and 6R, the sound pressure of the right ear 7R of the listener 8 is YR (Z) · GRR (Z)
and YL (Z) · GLR (Z) Is obtained. On the other hand, assuming that the virtual sound source
speakers 12L and 12R are actually arranged, the left ear 7L of the listener 8 has XL (Z) · FLL (Z),
and XR (Z) · FRL The sound pressure of (Z) is obtained. Similarly, the sound pressure of XR (Z) ·
FRR (Z) and XL (Z) · FLR (Z) is obtained at the right ear 7R of the listener 8 by the sound pressure
output by the speakers 12L and 12R. Be The sound pressure obtained by the left ear 7L and the
right ear 7R by the actual speakers 6L and 6R can be obtained by the left ear 7L and the right
ear 7R when the virtual sound source speakers 12L and 12R are actually arranged. If it becomes
similar to the sound pressure, the speakers 6L and 6R of the actual sound source can form the
same state as the case where the speakers 12L and 12R of the virtual sound source are actually
arranged. That is, YL (Z) · GLL (Z) + YR (Z) · GRL (Z) = XL (Z) · FLL (Z) + XR (Z) · FRL (Z) · · ·
(Expression 3) YR (Z) · GRR (Z) + YL (Z) .GLR (Z) = XR (Z) .FRR (Z) + XL (Z) .FLR (Z) (Equation 4)
may be established. That is, basically, as the correction processing in the correction filter unit 2,
the sound of the left and right channels in which the above (formula 3) (formula 4) holds for the
sound input signals XL (Z) and XR (Z) of the left and right channels If the output signals YL (Z)
and YR (Z) are obtained, the left and right ears 7L and 7R of the listener 8 are virtually detected
by the speakers 12L and 12R of the virtual sound source using the actual speakers 6L and 6R. A
sound image 9 can be formed. Here, in order to reduce the amount of data processing in the
correction filter unit 2, the above-mentioned head acoustic transfer function is symmetrical ,
that is, FLL (Z) = FRR (Z) (Expression 5) FLR (Z) = FRL (Z) (6) GLL (Z) = GRR (Z) (7) GLR (Z) = GRL
(Z) (8) The correction filter unit 2 is configured on the assumption that
In addition, in order to assume left-right symmetry in this way, the installation location of the
dummy head when measuring the head acoustic transfer function is the center of the seat 14, ie,
the middle of the left and right speakers 6L and 6R actually installed. Is desirable. Also, this
makes it possible to reduce the correction error caused by the sheet, and the correction effect
can be expected for any sheet. Then, under the assumption of (Eq. 5) (Eq. 6) (Eq. 7) (Eq. 8), in
order to correct the sound from virtual sound sources 12 L and 12 R, the above (Eq. 3) The
following (Expression 9) (Expression 10) obtained by modifying (Expression 4) may be satisfied.
That is, FRR (Z) is replaced by FLL (Z), FRL (Z) by FLR (Z), GRR (Z) by GLL (Z), and GRL (Z) by GLR
(Z), respectively. YL (Z) · GLL (Z) + YR (Z) · GLR (Z) · XLL (Z) · FLL (Z) + XR (Z) · FLR (Z) · · ·
(Expression 9) YR (Z) · GLL ( Z) + YL (Z)-GLR (Z) = XR (Z)-FLL (Z) + XL (Z)-FLR (Z) (Equation 10)
Here, Hp (Z) and Hm (Z) can be expressed as follows: Hp (Z) = (FLL (Z) + FLR (Z)) / (GLL (Z) + GLR
(Z)) (Expression 11) Hm (Z) = (FLL (Z) -FLR (Z)) / (GLL (Z) -GLR (Z)) (Equation 12), the above
(Equation 9) (Equation 10) YL (Z) and YR (Z) are as follows: YL (Z) = Hp (Z) (XL (Z) + XR (Z)) / 2 +
Hm (Z) (XL (Z)-XR (Z)) / 2 (formula 13) YR (Z) = Hp (Z) (XL (Z) + XR (Z)) / 2-Hm (Z) (XL (Z)-XR
(Z)) / 2 · · · (Equation 14) Here, Hp (Z) and Hm (Z) represent the transfer characteristics of the
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first digital filter and the second digital filter incorporated in the correction filter unit 2. Also, it is
known that the difference component of the two-channel stereo sound signal strongly influences
the sense of stereo and the sense of wideness. And "Hm (Z) (XL (Z)-XR (Z)))" of (Formula 13)
(Formula 14) is a difference component of a stereo sound signal. Therefore, by controlling the
level of this Hm (Z) · (XL (Z) −XR (Z)) term, it is possible to control the spatial spread feeling.
Therefore, if the term Hm (Z) · (XL (Z) −XR (Z)) of (Expression 13) (Expression 14) is
multiplied by a coefficient k as a parameter for controlling the sense of spread, Formula 13)
(formula 14) becomes like following (formula 15) (formula 16).
YL (Z) = Hp (Z) (XL (Z) + XR (Z)) / 2 + kHm (Z) (XL (Z) -XR (Z)) / 2 (15) YR (Y) Z) = Hp (Z) (XL (Z)
+ XR (Z)) / 2-k Hm (Z) (XL (Z)-XR (Z)) / 2 (Equation 16) In the equations (15) and (16), when the
coefficient k is increased, the difference component of the term "Hm (Z). (XL (Z) -XR (Z))" is
emphasized, and hence the reproduced sound field Sense of spread is enhanced. Then, as the
correction filter unit 2 of this example, the correction processing shown in the above (Equation
15) (Equation 16) is performed on the sound input signals XL (Z) and XR (Z) of the left and right
channels inputted. Sound output signals YL (Z) and YR (Z) of the left and right channels may be
obtained. By this, the above (formula 9) (formula 10) is satisfied, and the virtual sound image 9
can be formed by the speakers 6L and 6R. Furthermore, it is possible to control the spread of the
reproduction sound field. Therefore, as the correction filter unit 2, the filter of the characteristics
Hp (Z) and Hm (Z) whose characteristics are represented by Equation 11 and Equation 12 and
addition / subtraction in Equation 15 and Equation 16 can be performed. And a level control
circuit for multiplying the coefficient k. The correction filter unit 2 is formed of, for example, a
DSP, and performs correction processing by its arithmetic processing. The processing is as
shown in FIG. 7 in terms of hardware. The acoustic input signals XL (Z) and XR (Z) are supplied
to the subtraction circuit 22 and the addition circuit 21 to form a difference signal and a sum
signal. Then, the difference signal which is the output of the subtraction circuit 22 is supplied to
the level control circuit 24, and level control corresponding to the coefficient k in (Expression
15) (Expression 16) is performed. Then, the difference signal is supplied to the FIR filter circuit
25 of the transfer characteristic Hm (Z) of (Expression 12). Further, the sum signal which is the
output of the addition circuit 21 is supplied to the FIR filter circuit 23 of the transfer
characteristic Hp (Z) of (Expression 11). The output signals of these two FIR filter circuits 23 and
25 are subjected to a predetermined ratio (1/2 multiplication) by the level control circuits 26 and
27 and supplied to the addition circuit 28 and the subtraction circuit 29 to obtain the acoustic
output signal YL ( Z) and YR (Z) are formed. The acoustic output signals YL (Z) and YR (Z) are
supplied to the D / A converter 4 of the next stage through the acoustic digital signal output
circuit 3 as shown in FIG.
Further, particularly in the present example, as described above, by detecting the position of the
head of the listener from the infrared sensor 17 in real time, the CPU 11 always selects an
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optimal head sound transfer function, and the correction filter unit It is set to 2. That is,
depending on the detection result of the head position of the listener 8, a set of head acoustic
transfer functions FLL (Z), FRR (Z), FLR (Z), FRL (Z), GLL (Z) , GRR (Z), GLR (Z), and GRL (Z) are
selected from the database of the storage unit 13. However, since it is based on the above
(formula 5)-(formula 8), FLL (Z), FLR (Z), GLL (Z), and GLR (Z) are actually selected as one set of
head acoustic transfer functions It should be done. As understood from this, adopting the
assumptions of the above (Equation 5) to (Equation 8) is not only simplification of the calculation
of the correction filter unit 2 but also the database of the storage unit 13 The size can be
reduced, and an effect of realizing simplification of measurement of the head acoustic transfer
function also occurs. The head acoustic transfer functions FLL (Z), FLR (Z), GLL (Z), and GLR (Z)
have characteristics Hp (Z) as shown in (Expression 11) and (Expression 12). And Hm (Z). That is,
the CPU 11 selects a head selected according to the detection result of the infrared sensor 17
with respect to each of the FIR filters (FIR filter circuits 23 and 25 in FIG. 7) of the characteristics
Hp (Z) and Hm (Z) in the correction filter unit 2 Control is performed to set the characteristics Hp
(Z) and Hm (Z) derived from the partial acoustic transfer functions FLL (Z), FLR (Z), GLL (Z) and
GLR (Z). As described above, in the sound reproducing apparatus of this embodiment, even if the
speakers 6L and 6R of the actual sound source are attached to the rear space (for example, the
headrest of the seat 14), the positions of the speakers 12L and 12R as virtual sound sources ( For
example, a sound image equivalent to the case where the speakers are arranged on the left and
right of the display 15 installed in front of the seat 14 can be obtained, and even when the
listener's head shakes or moves, Since the virtual sound source can be appropriately arranged
and the reproduced sound can be perceived as being output from the virtual sound source, an
ideal sound field and sound image can be created without a sense of discomfort for the listener.
Furthermore, since such a sound field can be realized by the speakers 6L and 6R in the rear
space, the speaker arrangement in the front space can be omitted, and the ease and freedom of
the speaker installation can be improved.
This is suitable for installation of the sound reproduction apparatus in various spaces such as
indoors and in a car. In addition, it is possible to prevent the sound image from being localized in
the space inside or behind the listener's head and to localize the sound image in any space. In
addition, it is possible to eliminate the problem that occurs when satellite speakers for small
high-frequency band reproduction are provided side by side, that is, the inconsistency that
sounds are separated and heard, and sound is output from one speaker. It can be perceived. As
described above, the difference component between the left and right channels of the sound
signal strongly influences the sense of stereo and the sense of expansion of the reproduced
sound, but as shown in FIG. A circuit 24 is provided, and the multiplication process of the
coefficient k of the level control circuit 24 can emphasize the spatial spread of the reproduced
sound. Of course, by variably setting, for example, the multiplication coefficient k of the level
control circuit 24 by the CPU 11, the level of the difference component supplied from the
subtraction circuit 23 to the FIR filter circuit 25 in the subsequent stage can be variably
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controlled. It is also possible to adjust and correct the sense of spread and to make an optimal
correction according to the volume level. In the above description, although the head acoustic
transfer function is stored as a database in the storage unit 13 and stored, it is not always
necessary to store the measured head acoustic transfer function itself. That is, characteristics Hp
(Z) and Hm (Z) corresponding to various head position states of the listener 8 are calculated from
the head acoustic transfer function measured in advance, and the transfer characteristics are
controlled by the FIR filter circuits 23 and 25. The values may be stored as a database. Further,
by taking an average of a plurality of head acoustic transfer functions, even when three or more
speaker systems are used, an effective correction filter unit 2 can be created, therefore, the
number of speakers is not limited. It can also be widely applied as the correction filter unit 2
(sound reproduction device). Second Embodiment FIG. 8 shows a sound reproducing apparatus
according to a second embodiment. The configuration shown in FIG. 8 corresponds to the
configuration shown in FIG. 1 to which an operation unit 18 is added. The other configuration is
basically the same as that of FIG. In FIG. 8, the operation unit 18 can be arbitrarily operated by
the listener 8 or the like, and is for changing the position of the virtual sound image 9 arbitrarily.
For example, by operating the operation unit 18, the listener 8 can change the position of the
virtual sound image 9 in the front space, for example, as virtual sound images 9a and 9b.
For this purpose, it is only necessary to variably select a head acoustic transfer function from the
speakers 12L and 12R of the virtual sound source that realizes the position of the virtual sound
image 9 instructed by the operation unit 18. In this case, at the time of measurement of the head
sound transfer function performed in advance, the positions of the speakers 12 L and 12 R of the
virtual sound source are variously selected as the head sound transfer function from the speakers
12 L and 12 R of the virtual sound source to the listener 8. The measurement of (C) described
above is performed while changing to the position, and is made into a database and stored in the
storage unit 13. Then, the CPU 11 measures the head acoustic transfer function (FLL (Z), FLR
measured in the arrangement state of the speakers 12 L and 12 R for positioning at the
instructed virtual sound image 9 according to the operation of the operation unit 18. Select (Z)).
Note that there are a plurality of sets of head acoustic transfer functions (FLL (Z), FLR (Z))
selected according to the operation. This is because a plurality of head sound transfer functions
are measured while changing the head position of the listener 8 in the arrangement state of one
speaker 12L, 12R. For example, when the position of the virtual sound image 9a is instructed,
head acoustics measured a plurality of times by changing the position of the dummy head in the
arrangement state of the speakers 12L and 12R (the positions of 12La and 12Ra) for realizing
the virtual sound image 9a. A transfer function is chosen. In this case, the CPU 11 further selects
the head acoustic transfer functions FLL (Z), FLR (Z), GLL (Z), and GLR (Z) according to the
detection information from the infrared sensor 17. That is, the head position of the present
listener 8 is obtained from the plurality of FLL (Z) and FLR (Z) as the head acoustic transfer
function corresponding to the position of the virtual sound image 9 selected according to the
operation of the operation unit 18 One FLL (Z) and one FLR (Z) are selected, and one GLL (Z) and
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one GLR (Z) are selected as in the first embodiment. Thus, when the head sound transfer
functions FLL (Z), FLR (Z), GLL (Z), and GLR (Z) are selected, the selected head sound transfer
functions FLL (Z), FLR (Z) Controlling the transfer characteristics Hp (Z) and Hm (Z) of the FIR
filter circuits 23 and 25 in the correction filter unit 2 with GLL (Z) and GLR (Z) is the same as in
the first embodiment. . That is, in the case of the second embodiment, the position of the virtual
sound image 9 can be arbitrarily changed, and the position of the virtual sound image is moved
according to the preference of the listener 8, or The position of the virtual sound image 9 can be
adjusted according to the listening environment including the installation space of the playback
device and the arrangement position of the display device 15.
Although the embodiment of the present invention has been described above, further various
modifications can be considered as the present invention. In the above example, the head
position of the listener 8 corresponds to the movement in the front-rear direction and the
difference in the height direction (seat height difference) in real time, but the lateral shift and the
angle state of the head direction It is also conceivable to be able to detect and to select a head
acoustic transfer function accordingly. Of course, the arrangement of the speakers 6 L and 6 R is
not limited to the seat 14 but may be in any form as long as it is arranged in the space behind the
listener 8. Also, in the case of the example arranged in the seat 14, not only the indoor seat and
the seat in the car but also the seat of a train, a ship, an airplane, a theater etc. make the acoustic
experience full of presence in various environments. It can be realized. As can be understood
from the above description, according to the present invention, the correction processing based
on the head acoustic transfer function is performed on the sound signal output from the speaker
installed in the space behind the listener. The sound signal is localized in a predetermined
direction such as the space in front of the listening position, and the head is appropriately
adjusted while detecting the position of the head of the listener for the correction process. The
partial acoustic transfer function is selected. For this reason, even when the listener's head
shakes or moves, the virtual sound source can be appropriately arranged, and it can be perceived
that the reproduced sound is output from this virtual sound source, and the listener Can create
an ideal and stable sound field and sound image without discomfort. In addition, since the
speaker is installed in the space behind the listener, the speaker can be freely placed in any space
from the position of the listener without installing the speaker in an unwilling place in front of
the listener. The sound image can be localized. This eliminates the difficulty with the loudspeaker
arrangement indoors and the like. Further, in the case of displaying an image, there is an
advantage that the arrangement relationship of the speaker with the display device or the screen
can be eliminated. In addition, by reproducing a virtual sound image in an arbitrary space by a
rear speaker, for example, a speaker disposed on a seat, an effective acoustic sensation can be
obtained, and therefore, it can be used as a car, train, ship, airplane, and indoor viewing
applications. The effect is that it is possible to realize effective music appreciation like listening to
live performances and immersive movie appreciation like being in a movie theater.
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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a configuration example of
a sound reproduction device according to a first embodiment of this invention. FIG. 2 is an
explanatory view of a speaker and a sensor disposed on a seat in the embodiment. FIG. 3 is a top
view showing the horizontal direction of the rear space in the sound reproduction device of the
embodiment. FIG. 4 is a side view showing the vertical direction of the rear space in the sound
reproduction device of the embodiment. FIG. 5 is an explanatory diagram of a listener, a real
sound source, a virtual sound source, and a head sound transfer function in the sound
reproduction device according to the embodiment. FIG. 6 is an explanatory view of a positional
relationship between a speaker and a head of a listener in the sound reproduction device
according to the embodiment. FIG. 7 is an explanatory diagram of correction processing of the
sound reproduction device according to the embodiment; FIG. 8 is a block diagram of a
configuration example of a sound reproduction device according to a second embodiment of the
present invention. FIG. 9 is a block diagram showing a configuration example of a conventional
sound reproduction apparatus. FIG. 10 is an explanatory view of radiation of an acoustic signal E
from a virtual sound image. [Description of the code] 1 acoustic digital signal input unit, 2
correction filter unit, 3 acoustic digital signal output unit, 4 D / A converter, 5 output amplifier, 6
L left channel speaker, 6 R right channel speaker, 17 infrared sensor, 18 Operation unit
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