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JPH0984200

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DESCRIPTION JPH0984200
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio reproducing circuit for a television receiver, and more specifically, in addition to the
present situation where speakers are provided on the left and right of the screen of the television
receiver, Alternatively, by arranging a center channel speaker at the bottom and reproducing it as
a three-speaker system, the speech serif, the clarity of the announcement, and the center
localization are improved, and the service area of the listener is expanded and the sense of
presence is enhanced. Therefore, the present invention relates to an audio reproduction circuit
for a television receiver which applies a surround processing circuit.
[0002]
2. Description of the Related Art In a conventional television receiver, speakers for reproducing
audio L and R signals are disposed on the left and right of the set, and various surround
processing circuits are inserted into the speakers to realize audio reproduction for realizing
expansion of a sound field. Although it has been performed, by applying the surround processing,
human voices such as speeches and announcements lack in clarity and there is a drawback that
the broadcast content becomes difficult to hear. In addition, human voice is a signal that should
be localized at the center of the set, but there are many L and R in-phase signals even if surround
processing is not performed. However, in order to reproduce the in-phase signal from the left and
right speakers of the set, the sound image is There was a drawback that it spreads out and
localization is blurred. In particular, when playing back a television by plurals, except when
listening at the center position of the television, people located on the left and right are localized
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so that even the in-phase signal can be heard from the near speaker and from the listening point
An interference phenomenon occurs due to the difference in distance to the left and right
speakers, and a valley of sound pressure frequency characteristics is generated in the midrange,
and there is a drawback that the sound is heard as if it is muffled and difficult to hear.
[0003]
There is a Dolby Prologic Surround system as one of the ways to compensate for this
shortcoming. In this case, in addition to the left and right speakers, a center channel speaker is
disposed in the front and a surround channel speaker is disposed in the rear, and input audio L
and R signals are formed into four channels of L, R, C and S. It is a system which drives the
above-mentioned predetermined speaker through the circuit to separate.
[0004]
However, as an audio reproduction system of a television receiver, there are also many problems
such as a significant increase in cost of the circuit and an installation place of a surround channel
speaker. As an audio reproduction circuit for a television receiver that solves this problem, for
example, the configuration of FIG. 7 has been proposed (Japanese Patent Application Laid-Open
No. 3-236691).
[0005]
An example of the audio reproduction circuit for a television receiver will be described below
with reference to FIG. In FIG. 7, reference numeral 30 is a volume adjuster for controlling the
volume of Lt and Rt signals, 31 is a matrix surround circuit, 32 is a subtractor for extracting a
(Lt-Rt) difference component, and 33 is an amplifier for amplifying the difference component. 34
is an adder that adds the Lt signal and the amplified difference component, 35 is a subtractor
that subtracts the Rt signal and the amplified difference component, 36 is an adder that adds the
surround processed Lt and Rt signals, 37 is Band-pass filter (hereinafter referred to as BPF) for
extracting frequency band of human voice, 38 is an amplifier for amplifying human voice
extracted by BPF, 39 is a mode switch for variably controlling gain, 40 is surround processing Is
a subtractor for removing the frequency band of gain-controlled human voice from the extracted
Lt1 signal, 41 is a subtracter for removing gain-controlled human voice frequency band from the
surround processed Rt1 signal , 17 are power amplifiers for driving L channel speakers, 18 is a
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power amplifier for driving center channel speakers, 19 is a power amplifier for driving R
channel speakers, 20 is an L channel speaker, 21 is a center channel speaker, 22 is an R channel
speaker .
[0006]
The operation of the sound reproducing circuit for television receiver configured as described
above will be described. The input audio Lt and Rt signals are adjusted in volume level by the
volume adjuster 30, and then input to the matrix surround circuit 31. The matrix surround
circuit 31 performs a calculation of (Lt−Rt) in a subtractor 32 that extracts the difference
component between the Lt signal and the Rt signal, and extracts a surround signal component.
Generally, the Lt and Rt signals to be input are mixed by the following equation.
[0007]
Lt = L + 0.7C + 0.7S (1) Rt = R + 0.7C-0.7S (2) where L is a left signal component, C is a center
signal component, R is a right signal component, and S is a surround signal component A
coefficient of 0.7 means -3 dB, and the sign of the S signal indicates an antiphase.
[0008]
That is, the difference component is extracted by the subtracter 32 by subtracting the above
equations (1) and (2), Lt−Rt = (LR) + 1.4S (3), and L, R A level 1.4 times (3 dB) higher than that
of the signal component can be extracted, and the center signal component C, which is an inphase component, disappears.
When the difference component extracted by the subtractor 32 is amplified by the amplifier 33
(amplification degree: a), and the Lt signal whose volume is adjusted by the adder 34 is added,
Lt1 = (L + 0.7C + 0.7S) + a When (LR) + 1.4a · S (4) is obtained and the difference component is
subtracted from the Rt signal whose volume is adjusted by the subtractor 35, Rt1 = (R +
0.7C−0.7S) −a · (LR) − Obtain 1.4a · S (5). The adder 36 is configured to add the equations (4)
and (5), and Ct = L + R + 1.4C (6) when calculated. The surround signal component S disappears,
and the center signal component C is L and R. A level 1.4 times (3 dB) higher than the signal
component can be extracted. The BPF 37 extracts frequency components from 400 Hz to 5 KHz
as a frequency band of human voice, which is gain controlled by the mode switch 39 and
reproduced through the power amplifier 18 by the center channel speaker 21. The signals of the
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voice band gain controlled by the mode switch 39 are subtracted from the Lt1 and Rt1 signals
through the subtractors 40 and 41, except for the reproduction from the left and right speakers.
The Lt1 and Rt1 signals from which the voice band is subtracted are reproduced from the L
channel speaker and the R channel speaker through the power amplifiers 17 and 18,
respectively. The mode switcher 39 changes the gain of the voice of the extracted person by
setting the mode by the mode of the program (narration, music, theater).
[0009]
However, in the above-mentioned conventional configuration, when the voice of the person
localized at the center is cut off at a low frequency of 400 Hz, the voice becomes dull and dull.
Also, if the high frequency component is also cut off at 5 KHz or more, the clarity is lost. That is,
it is the voice of the human being that is primarily localized at the center, and although it is an
important technical task to reproduce it clearly, we define 400 Hz to 5 KHz as the voice of the
human, and only human voice It is unreasonable in the place which tries to take out from the
center speaker. There is also an instrument for center localization, and it is easier to hear the inphase monaural signal if it is output from the center channel speaker. Further, in the case of the
conventional configuration, the sound image gathers in the vicinity of the center of the television
receiver, and there is a problem that the feeling of spreading disappears. That is, when the
human voice is subtracted from equation (4) as C, the output Ls of the L channel speaker is
obtained, and when calculated, Ls = (1 + a) La.R + 2.1a.S (7), and similarly The R channel speaker
output Rs obtains Rs = (1 + a) Ra.L-2.1a.S (8), but the meaning of the equations (7) and (8) means
that the level of the surround signal component S becomes high and L , R-channel speakers are
only output in reverse phase, and the sound field does not become a factor to expand.
[0010]
Moreover, not only L signal components but also R signal components in reverse phase are
output to the L channel speaker side, but this is also not a factor for the sound field to spread,
and it is another effect to the extent that localization is blurred. It does not.
[0011]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems,
and is a simple circuit configuration, low cost, and sound for television receiver that balances the
expansion of sound field, the goodness of center localization, and the clearness of human voice. It
aims at providing a reproduction circuit.
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[0012]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an audio
reproducing circuit for a television receiver according to the present invention adds L channel
signal and R channel signal of input audio to extract an in-phase component. A first adder, a high
pass filter (hereinafter referred to as HPF) for extracting only the middle high frequency
component of the extracted and extracted in-phase components, and a level adjustment for the
middle high frequency component extracted by the HPF And a first power amplifier provided in
series with the first power amplifier for power amplification and driving a center channel speaker
provided at the upper or lower center of the television receiver with the first power amplifier; A
first low pass filter (hereinafter referred to as an LPF) for extracting low frequency components
of the in-phase components is provided downstream of the adder, and a first amplifier for
amplifying the output of the first LPF. A second adder downstream of a subtractor for extracting
a difference signal of L channel signal and R channel signal of input voice, a phase shifter for
delaying the phase of the difference signal extracted by the subtractor, and a high band By
means of the second adder, through an attenuator comprising in series a second LPF for blocking
the output and a second amplifier for amplifying the output of the second LPF, and an attenuator
for attenuating the output of the second amplifier, A third adder for looping the phase delay
signal and adding the phase delay signal that is the output of the second amplifier, and the L
channel signal that is input and the low frequency component that is the output of the first
amplifier; A second volume regulator is provided in series to adjust the level of the third adder
output, and a second power amplifier for power amplification is provided in series, and an L
channel speaker installed on the left side of the television receiver is the second one. Driven by a
power amplifier A phase delay signal passing through a phase inverter for inverting the output
phase of the second amplifier, and a fourth adder for adding the input R channel signal and the
output of the first amplifier, A third volume regulator for level adjustment of the adder output of
4 and a third power amplifier for power amplification are provided in series, and the third power
amplifier for driving an R channel speaker installed on the right of the television receiver And
consists of.
[0013]
According to the above configuration, the input L and R signals are added and reproduced by the
center channel speaker, thereby improving the center localization of the in-phase signal.
Above all, the localization of human voices (serifs, announcements, etc.) is improved and can be
heard clearly.
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At the same time, the surround processing circuit with simple phase processing for L and R
difference signals also makes it possible to sense the spread of the sound field, solving the
contradictory issues of good center localization and the spread of the sound field, and wide
service area Audio reproduction for television becomes possible.
[0014]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A sound reproducing circuit for a
television receiver according to an embodiment of the present invention will be described in
detail with reference to FIGS.
[0015]
FIG. 1 is a block diagram of an audio reproduction circuit for a television receiver according to an
embodiment of the present invention.
In FIG. 1, reference numeral 1 is an adder for adding the L channel signal and R channel signal of
the input voice to extract an in-phase signal, 2 an LPF for extracting only a bass region, 3 an
amplifier for performing signal amplification, 4 is an HPF for extracting the middle high band, 5
is a subtractor for extracting the difference signal of L channel and R channel of the input voice,
6 is a phase shifter for delaying the phase, 7 is an LPF for cutting off high band, 8 is a signal An
amplifier for amplification, 9 is an adder for adding the difference signal and the phase-delayed
signal, 10 is an attenuator for attenuating the phase-delayed signal, 11 is a phase for inverting
the phase-delayed signal An inverter, 12 is an adder for adding the input R channel signal, a low
frequency component of the in-phase signal, and a phase-delayed, phase-inverted signal, 13 is an
input L-channel signal, an in-phase signal Low frequency component and phase Adder for adding
the spread signal, 14 is a volume controller for adjusting the R channel signal playback level, 15
is a volume controller for adjusting the center channel signal playback level, 16 is a volume
controller for adjusting the L channel signal playback level 17 is a power amplifier for power
amplifying an R channel signal, 18 is a power amplifier for power amplifying a center channel
signal, 19 is a power amplifier for power amplifying an L channel signal, and 20 is an R channel
speaker for reproducing an R channel signal 21 is a center channel speaker arranged at the
upper or lower center of the television receiver and reproducing a center channel signal, and 22
is an L channel speaker reproducing an L channel signal.
[0016]
The operation of the television receiver audio reproduction circuit configured as described above
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will be described below.
[0017]
FIG. 2 (a) is an explanatory view showing an interference phenomenon of a two-speaker system
equipped with L and R channel speakers in a television receiver, and an in-phase signal
(monaural signal) is reproduced from the L and R channel speakers. FIG. 2 (b) shows an example
of the sound pressure frequency characteristic at this time when the position is shifted laterally
from the center of the television receiver.
[0018]
That is, when shifted to the left and right, a difference occurs in the distance from the listening
point to the L channel speaker and the R channel speaker, and the disturbance of the frequency
characteristic occurs around 500 Hz.
Because of this, it sounds like the midrange is full.
[0019]
On the other hand, FIG. 3A shows the positions of sound images when a plurality of listeners
listen to this monaural signal.
That is, since the listener located at the center of the television receiver in FIG. 3A has the same
sound pressure of the L and R channel speakers, the in-phase center signal is localized at the
center of the television receiver. However, for the listener located at the left, the center signal is
localized slightly to the left.
As described above, in the two-speaker system, the sound quality is degraded, and the service
area is narrow.
[0020]
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Therefore, as shown in the embodiment of FIG. 1, the input Lt and Rt signals are added by the
adder 1 and reproduced from the center channel speaker 21. The amplifier 15 is a volume
controller that adjusts the level, and 18 is a power amplifier for driving the center channel
speaker. The HPF 4 is used to extract middle and high frequency components, and is used to
exclude low frequency components of the in-phase signal extracted by the adder 1.
[0021]
This is because the in-phase signal also includes a deep bass component, and is for the protection
of the speaker and the clarity of the sound. Usually, human voices are low at frequencies around
200 Hz, and it is known that when played back to frequencies below this, the voice will become
muffled, and conversely, playback from 400 Hz or so will not produce a pleasing sound .
[0022]
Among the in-phase signals extracted in this manner, the position of the sound image when
reproduced from the center channel speaker as a center signal from which the low-frequency
component has been removed is shown in FIG. That is, even when listening from the center
position of the television receiver or from a position shifted from the center, the center signal is
localized as if it is output from the center of the television receiver. In practice, the center signal
is also output from the L and R channel speakers, but since the level is low, it is localized almost
at the center (details will be described later).
[0023]
Of the in-phase signal extracted from the adder 1, only the low band component is extracted by
the LPF 2 and the adder 12 distributes the signal from the R channel speaker side and the adder
13 to reproduce from the L channel speaker.
[0024]
This is because, due to the mechanism of the internal components of the television receiver,
component materials such as a printed circuit board are arranged behind the center channel
speaker, and there is not enough space for arranging a sufficient low-pass reproducible speaker
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For this reason, low-frequency reproduction is impossible, and there is a relatively large space for
low-frequency components, so it is better in terms of mechanism to output with the L and R
channel speakers in the box shape that is currently mainstream.
By the way, since there is no sense of localization in the low range, it may be output anywhere.
[0025]
Next, the operation of the surround circuit will be described. Let Lt and Rt be input L and R
signals, and let Lt and Rt be described again as L signal component, R signal component, C signal
component and S signal component as in the conventional example. Lt = L + 0.7C + 0.7 S (1) Rt =
R + 0.7C-0.7S (2) The output of the subtractor 5 for extracting the difference component between
the input Lt and Rt signals is Lt-Rt = (LR) + 1.4S ( 3)
[0026]
The difference component is phase-delayed by the phase shifter 6 having a one-stage phase
shifter configuration, and amplified by the amplifier 8 through the LPF 7 for blocking high
frequency components. The amplified difference component is attenuated in amplitude by the
attenuator 10, added again by the adder 9, and phase-delayed.
[0027]
This is to obtain the maximum effect in one stage of the phase shifter. The difference component
output from the amplifier 8 is added to the input Lt by the adder 13 and reproduced through the
volume adjuster 16 and the power amplifier 19 by the L channel speaker 22.
[0028]
Similarly, the difference component output from the amplifier 8 is phase-inverted by the phase
inverter 11 and added to the Rt input thereto by the adder 12, and the volume adjuster 14 and
the power amplifier 17 are used to Reproduce.
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[0029]
Here, assuming that the amplification degree of the amplifier 8 for amplifying the difference
component is a and the phase delay is φ, the output signals Ls and Rs of the surround processed
L and R channel speakers are expressed by the following equations.
[0030]
Ls = Lt + a · (Lt−Rt) φ (9) Rs = Lt + a · (Lt−Rt) φ (10) a: amplification degree of the amplifier 8
where (Lt−Rt) φ: phase delay by φ Show what you are doing.
Now, consider the time when only the left component L is input.
That is, in the equation (1) (2), R = C = S = 0, and in the equation (9) (10) Ls = L + a · (L) φ (9)
−1Rs = −a · (L) φ ( 10) -1 and L = sin θ (θ = 2π · f · t: f is frequency), and assuming that the
phase delay amount is φ = 90 °, (9) −1, (10) − Equation 1 is Ls = sin θ + a · sin (θ) φ = sin
θ + a · sin (θ−90 °) = sin θ−a · cos θ (9) −2Rs = −a · (L) φ = −a · Since sin (θ-90 °) = a ·
cos θ (10) −2, this sound is output from the L and R channel speakers respectively. When this
sound is reproduced from the L and R channel speakers respectively, it is analyzed how the
listener hears. This explanatory view is shown in FIG.
[0031]
As an example, consider the case of listening to a 29-inch television receiver at a distance of 2 m.
The angle of the L and R channel speakers placed on the television receiver as viewed from the
listener is about 10 °, and the time delay at this time is according to the professional journal
"Hearing and voice" (The Institute of Electronics and Communication Engineers P. 134) And 0.1
ms, and the level difference between the left ear and the right ear is 0.8 (-2 dB). Using this data,
the transfer function EL to the left ear of the listener and the transfer function ER to the right ear
are EL = (sin θ−a · cos θ) + b · a · (cos θ) τ = (sin θ− a · cos θ) + b · a · cos {2πf (t−τ)} (9)
-3 ER = (a · cos θ) + b · (sin θ−a · cos θ) τ = (a · cos θ) + b · sin {2πf (t−τ)} − a · b · cos
{2πf (t−τ)} (10) -3 where b = 0.8 (attenuation coefficient), τ = 0.1 ms (delay time), a: amplifier
8 The degree of amplification of The result of calculating this equation with f = 1 KHz is shown in
FIG. FIG. 5 shows the transfer function of the left ear in the upper part, and the transfer function
of the right ear in the lower part. The middle row is the difference between the left and right
ears.
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[0032]
As can be seen from FIG. 5, according to the surround processing of the present invention, a
high-level sine wave signal is transmitted to the left ear, and conversely, the signal is canceled to
the right ear, and You will hear a low sine wave.
[0033]
This means that when a signal is added only to the L component, it behaves as if there is a sound
source in the direction of the left ear, and a virtual L channel speaker is outside the L channel
speaker of the television receiver with an opening angle of 10 °. It is theoretically different from
the conventional reverse phase reproduction, which means that the sound image is enlarged, and
the localization is simply lost, which means that the sound image is expanded.
[0034]
The same applies to the R component.
By the way, in the conventional example, the phase delay is not inserted, and analysis of the case
where the phase delay is not inserted according to the equations (9) -2 and (10) -2 is as shown in
FIG. The transfer function of is almost the same, and localization is made between L and R
speakers in the television receiver, and the sound image is not enlarged.
[0035]
Also, when only the C signal component is input, as understood from the configuration, the C
component with a coefficient of 0.7 C is output from the center channel speaker at 1.4 C and the
L and R channel speakers, but the 6 dB There is a level difference and it is almost recognized as
center localization.
[0036]
Next, when the surround signal component S is analyzed, the transfer function to both ears is EL
= −ER (11), and is only in reverse phase.
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According to the analysis result, the phase delay may be only 90 °, and can be realized with one
stage phase delay.
However, the phase delay needs to be applied to the entire band, and needs to be set to a low
frequency as much as possible.
[0037]
As described above, according to the present invention, localization of the in-phase signal
localized at the center is improved by adding the L and R signals to be input and reproducing by
the center channel speaker, and in particular, it is possible to The localization of the voices
(serifs, announcements, etc.) is improved and can be heard clearly. At the same time, by using a
surround processing circuit with simple phase processing for L and R difference signals, the
expansion of the sound field is also felt, and the contradictory problems of good localization and
the expansion of the sound field are solved, and more It has the advantages of being realistic,
making it easy to clearly hear human voices, and enabling the reproduction of television sound in
a wide service area. Also, due to the configuration of the television receiver, sufficient low
frequency reproduction can not be expected from the center channel speaker, so the low
frequency output from the L and R channel speakers compensates the sound quality of the inphase signal to sufficiently low frequency. It has the advantage of being able to play back
possible voices.
[0038]
Brief description of the drawings
[0039]
1 is a block diagram of an audio reproducing circuit for a television receiver according to an
embodiment of the present invention.
[0040]
Fig. 2 (a) A diagram showing the television receiver and the listening position
[0041]
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Fig. 3 (a) An illustration of center localization in L and R channel speaker reproduction
[0042]
Fig. 4 Relationship between the positions of the television receiver L and R channel speakers and
the listening position
[0043]
Fig. 5 Explanation of transfer function to the left and right ears of the listener
[0044]
Fig. 6 Transfer function to the left and right ears of the listener in the conventional surround
circuit
[0045]
Fig. 7 A block diagram of a conventional television receiver reproduction circuit
[0046]
Explanation of sign
[0047]
1, 9, 12, 13 Adders 2, 7 Low Pass Filters 3, 8 Amplifiers 4 High Pass Filters 5 Subtractor 6
Phaser 10 Attenuator 11 Phase Invertor 14, 15, 16 Volume Adjusters 17, 18, 19 power amplifier
20 R channel speaker 21 center channel speaker 22 L channel speaker 30 volume adjuster 31
matrix surround circuit 32, 35, 40, 41 subtractor 33, 38 amplifier 34, 36 adder 37 band pass
filter 39 mode switching device
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