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JPH11136790

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DESCRIPTION JPH11136790
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
band emphasizing circuit, and more particularly to a circuit for emphasizing high and low
frequencies of digital signals used in audio and the like.
[0002]
2. Description of the Related Art In an audio system, it is common practice to correct frequency
characteristics or output a reproduced sound with a sense of liveliness by emphasizing low and
high frequencies.
[0003]
In recent years, various types of processing have been performed by digital signal processing
performed using digitized analog signals.
For example, in Japanese Patent Application Laid-Open No. 58-182315, the transfer function of a
digital filter is changed by adjusting the poles and zeros of the transfer function of the cyclic
digital filter using a cyclic digital filter to change the high frequency and low frequency band. It
has been shown to perform emphasis and attenuation.
08-05-2019
1
[0004]
In the above technique, in order to control the poles and zeros of the transfer function, digital
filter coefficients are stored in a plurality of memories, and the filter coefficients are
appropriately selected to obtain arbitrary enhancement and attenuation characteristics.
[0005]
However, in the circuit described above, since the transfer function is uniquely determined by the
filter coefficients stored in the memory, the enhancement / attenuation characteristics are
determined regardless of the level of the input signal. .
Generally speaking, the lower the volume and the higher the frequency is emphasized as the
volume becomes smaller, there is a demand to intensify the degree of band emphasis according
to the input signal level, but the technique to realize this is It did not exist.
[0006]
The present invention has been made in view of such circumstances, and an object thereof is to
provide a band emphasizing circuit capable of changing frequency characteristics according to
an input signal level, for example, as the input signal level is smaller. It is an object of the present
invention to provide a band emphasizing circuit that lifts low frequencies.
[0007]
According to the invention of claim 1, in order to achieve the above object, one or more digital
filters having filtering characteristics defined by filter coefficients are used to enhance or
attenuate predetermined bands. A band emphasizing circuit is provided, characterized in that the
band emphasizing circuit includes a coefficient generation unit that adopts a signal obtained by
processing a digital signal input to the one or more digital filters as the filter coefficient.
[0008]
In the present invention, emphasis means, of course, increasing the amplitude of a predetermined
frequency component, as well as reducing the amplitude of a predetermined frequency
component relatively to a specific frequency component other than the predetermined frequency
component. It also includes increasing the amplitude, and thus also means the natural emphasis
and attenuation.
08-05-2019
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[0009]
The invention according to claim 2 is that, in claim 1, the coefficient generation unit is a unit that
generates a filter coefficient using a signal obtained by adding digital signals input to each of a
plurality of digital filters. It features.
[0010]
Furthermore, in the invention according to claim 3, in any one of claims 1 and 2, the coefficient
generation unit is an absolute value conversion unit that performs absolute value conversion on
one or more digital signals input to the digital filter; It is characterized in that it comprises an
averaging means for averaging the absolute valued signals, and a conversion means for
converting the averaged signals into filter coefficients.
[0011]
The absolute value conversion means may perform absolute value conversion of a signal
obtained by adding digital signals input to each of the plurality of digital filters when performing
absolute value conversion of the plurality of digital signals.
[0012]
In the invention according to claim 4, according to claim 3, the conversion means previously
generates coefficient generation data for generating a filter coefficient such that the frequency
characteristic in the predetermined band becomes predetermined. The magnitude relationship
between storage means defined and stored, coefficient generation data stored in the storage
means, and coefficient generation data corresponding to filter coefficients generated by
processing the digital input signal And selecting means for selecting one of the coefficient
generation data with reference to the reference.
There is a mode in which the selection means selects the larger one of the coefficient generation
data and the mode in which the smaller one is selected.
[0013]
Further, according to the invention of claim 5, there is provided a circuit for emphasizing or
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3
attenuating a predetermined band of a digital signal of two channels by using a digital filter
having a filtering characteristic determined by a filter coefficient, wherein the digital signal of
two channels is Low-pass filter consisting of a pair of high-pass filtering means for performing
predetermined high-pass filtering by inputting each of the above, and a digital filter of variable
filter coefficient connected to each high-pass filtering means in a predetermined connection
mode A pair of low-pass filtering means for performing the pairing, an adding means for adding
the signals of the two channels, an absolute value means for absoluteizing the signal added by
the adding means, and the absolute value means Averaging means for averaging absolute value
signals, and coefficient generation data for generating filter coefficients such that the frequency
characteristic in the predetermined band is predetermined. Selection means for selecting any one
of storage means defined and stored, coefficient generation data stored in the storage means and
signals averaged by the averaging means according to a predetermined rule And.
In this case, the signal selected by the selection means may be processed so as to be the filter
coefficient of the low pass filter means.
[0014]
The connection mode may be serial or parallel, and the predetermined rule for the selection
means to perform the selection operation may be to select any larger signal or to select any
smaller signal. Furthermore, as the frequency characteristic, one that is flat or constant can be
mentioned.
[0015]
More specifically, the following band emphasizing circuit is provided.
That is, a circuit for emphasizing or attenuating a predetermined band of a digital signal of two
channels by using a digital filter having a filtering characteristic determined by a filter
coefficient, wherein each of the digital signals of two channels is input to a predetermined high
band A pair of high-pass filtering means for filtering and a pair of low-pass filtering means
connected in series to each high-pass filtering means and comprising a digital filter of variable
filter coefficient for low-pass filtering, Addition means for adding the signals of the channels,
absolute value conversion means for absoluteizing the signals added by the addition means, and
averaging means for averaging the signals absoluteized by the absolute value conversion means
Storage means for predetermining and storing coefficient generation data for generating filter
coefficients such that the frequency characteristic in the predetermined band is flat, and the
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storage A band emphasizing circuit comprising: selecting means for selecting the smaller one of
the coefficient generation data stored in the stage and the signal averaged by the averaging
means; A bandwidth enhancement circuit is provided.
[0016]
A circuit for emphasizing or attenuating a predetermined band of a digital signal of two channels
by using a digital filter having a filtering characteristic determined by a filter coefficient, wherein
each of the digital signals of two channels is input and a predetermined high band is input. A pair
of high-pass filtering means for filtering, a pair of low-pass filtering means connected in parallel
to each high-pass filtering means and comprising a digital filter of variable filter coefficients for
low-pass filtering, Addition means for adding the signals of the channels, absolute value
conversion means for absoluteizing the signals added by the addition means, and averaging
means for averaging the signals absoluteized by the absolute value conversion means Storage
means for predetermining and storing coefficient generation data for generating filter
coefficients such that the frequency characteristic in the predetermined band is flat, and the
storage Bandwidth enhancement circuit characterized by comprising a selection means for
selecting the larger one of the averaged signal by a coefficient generation data stored in stages
and the averaging means, the is also provided.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the drawings.
FIG. 1 is a block diagram of a band emphasizing circuit according to a first embodiment of the
present invention.
[0018]
This band emphasizing circuit has an L channel filter 100 and an R channel filter 110 for
filtering digital two-channel stereo signals input via digital input terminals Lin and Rin.
The L channel filter 100 and the R channel filter 110 have the same configuration, and the
signals Lout and Rout are respectively output.
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[0019]
The L channel filter 100 connects the high frequency emphasizing circuit 20 whose transfer
function is fixed and the low frequency emphasizing circuit 30 whose transfer function is
variable by changing the filter coefficient in series, and further outputs the output of the low
frequency emphasizing circuit 30 It comprises an amplifier 40 for amplification, an amplifier 41
for directly amplifying a digital signal supplied to a band emphasis circuit, and an adder 43 for
summing the output signals of the amplifier 40 and the amplifier 41 and outputting the result as
Lout.
[0020]
The amplifiers 40 and 41 are respectively configured to change the gain from 0 to 1 depending
on the setting, and the output signals of the amplifiers 40 and 41 are added by the adder 43 so
that the gains of the amplifiers 40 and 41 By being changed, it is possible to change the degree
of overall emphasis in the L channel filter 100.
[0021]
Further, the high frequency emphasizing circuit 20 delays the signal, a multiplier 25 which
multiplies the original signal delayed by the delay element 23 by a predetermined coefficient,
and a multiplication result of the delayed signal and the multiplier 25 , The multiplier 24 for
multiplying the above-mentioned original signal by a predetermined coefficient, and the product
of the multiplier 24 that is obtained by inverting the sign of the digital signal input through the
digital input terminal Lin. And an adder 22 for adding, and a digital filter configured to
emphasize a predetermined high frequency band with a fixed transfer function regardless of the
level of the input signal, and the transfer function hhpf (z) Is expressed by the following equation
(1).
[0022]
hhpf (z) = − (1 / z) · {1−0.5 × (1 / z)} (1) Further, the low-frequency emphasis circuit 30 delays
the signal, and the output of an inverter 73 described later. And an adder 31 for adding the
multiplication result of the multiplier 34 and the output signal from the high frequency
emphasizing circuit 20, and an adder 74 to be described later. It has a multiplier 35 which
multiplies the addition result and the signal delayed by the delay element 32, and an adder 33
which adds the multiplication result of the multiplier 35 and the output signal from the high
frequency emphasizing circuit 20, The cyclic digital filter is configured to emphasize the low
frequency band according to the input level while changing the transfer function according to the
multiplication result of the multiplier 34 and the multiplier 35.
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[0023]
Furthermore, an adder 42 for adding digital signals of two channels input through the digital
input terminals Lin and Rin, an absolute value conversion circuit 51 for converting the added
signal by the adder 42 into an absolute value, and the absolute value conversion Shifter 52 for
shifting the signal absolute-valued by circuit 51 to the LSB side by 6 bits, averaging circuit 60 for
averaging the signals shifted by this shifter 52, and coefficient generation for generating filter
coefficients Memory 53, 54 for storing data for the image data, a switch 70 for selecting the
smaller one of the averaging signal (a) by the averaging circuit 60 and the coefficient generation
data (b) stored in the memory 53, and this switch 70, shifter 71 for shifting the digital signal (g)
selected by 70 to the LSB side by 2 bits, and digital signal (g) for 3 bits only It includes a shifter
73 for shifting the SB-side, an inverter 73 for inverting the shift result of the shifter 71, an adder
74 for adding the shift result and the coefficient generation data stored in the memory 54 by the
shifter 72.
[0024]
For example, if the digital signal is a two's complement representation, the absolute value
conversion circuit 51 passes data with a code bit of 0 as it is, and data with a code bit of 1 inverts
“1” and “0”. It may be configured to perform processing of adding “1”, and the signal
converted into an absolute value in order to obtain a value such that the signal level is not
saturated in the averaging circuit 60 of the next stage is The data is shifted to the LSB side by 6
times, that is, 6 bits and input to the averaging circuit 60.
A multiplier may be provided to multiply the signal by 0.5 before the addition by the addition
circuit 42 and the shift amount in the shifter 52 may be 2 to 5 times.
[0025]
The averaging circuit 60 adds a delay element 63 for delaying the signal, a shifter 64 for shifting
the delay signal of the delay element 63 to the LSB side by 13 bits, and adds the delay signal of
the delay element 63 and the shift result of the shifter 64. An adder 62, an adder 61 for adding
the addition result by the adder 62 and the shift result by the shifter 52, and a delayed signal by
the delay element 63 shifted by 13 bits to the LSB side is a signal (a) It has a shifter 65 for
output, and functions as a kind of integration circuit, and its transfer function H (z) is expressed
by the following equation (2).
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[0026]
H (z) = 2-13 · z-1 / (1-(1-2-13) z-1) (2) Furthermore, in the memory 53, for example, the level of
the digital input signal is 0 (dB) A value at which the frequency characteristic of L-channel filter
100 (also R-channel filter 110) becomes flat (MAX: 0.318), and a value at which the frequency
characteristic becomes flat when larger than -5 (dB) (MID : Three kinds of coefficient generation
data with a value (MIN: 0.101) that makes the frequency characteristic flat when it is larger than
0.179) and -10 dB are stored, and coefficient generation data to be selected by operation Is
configured to be switchable.
[0027]
Similarly, in the memory 54, the frequency characteristic of the L channel filter 100 (also for the
R channel filter 110) becomes flat when the digital input signal level is 0 (dB) (MAX: 0.0398),
Three kinds of data for generating coefficients, the value that the frequency characteristic
becomes flat at -5 (dB) (MID: 0.0224), and the value that the frequency characteristic becomes
flat at -10 dB (MIN: 0.0126) Is stored, and when MAX, MID and MIN of the memory 53 are
selected, the memory 53 and the memory 54 operate in conjunction with each other so that
MAX, MID and MIN are also selected in the memory 54 respectively.
As the values become MIN, MID, and MAX, the value of the coefficient generation data increases
and the degree of low range emphasis increases.
[0028]
Also, the switch 70 compares the magnitude relationship between the signal (a) averaged by the
averaging circuit 60 and the coefficient generation data (b) stored in the memory 53 and
corresponding to the level of the input signal. The smaller signal (g) is supplied to the shifters 71
and 72.
[0029]
Thus, the transfer function hdbb (z) of the low band emphasizing circuit 30 is expressed by the
following equation (3).
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hdbb (z) = [1- (1 / z) * {(1-c) -0.125 * g}] / {1- (1 / z) * (1-0.25 * g)} (3) where c is coefficient
generation data called from the memory 54, and g is a signal supplied to the shifters 71 and 72.
[0030]
Next, the operation of this band emphasizing circuit will be described.
Now, it is assumed that a digital two-channel stereo signal is input through the digital input
terminals Lin and Rin.
The left and right digital signals are added by the adder 42, the added signal is converted into an
absolute value by the absolute value conversion circuit 51, and the converted signal is shifted to
the LSB side by 6 bits by the shifter 52.
[0031]
Next, the shifted signal is averaged by the averaging circuit 60 to be the signal a and supplied to
the switch 70, while the coefficient generation data corresponding to the input signal level is
read out from the memory 53. The signal b is supplied to the switch 70.
[0032]
At this time, the switch 70 performs switching operation so as to supply the smaller one of the
signal a and the signal b as the signal g to the shifters 71 and 72.
As a result, if the relationship between the magnitudes of the signal a and the signal b is “a ≧
b”, the signal g = b, and if “a <b”, the signal g = a.
[0033]
Next, the signal g is shifted 2-2 times (0.25 times) by the shifter 71, that is, shifted to the LSB
side by 2 bits, and then inverted by the inverter 73 to form the low pass emphasizing circuit 30.
It is used as a filter coefficient of the digital filter, and defines the pole of the filter characteristic.
08-05-2019
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[0034]
Further, the signal g is shifted 2-3 times (0.125 times) by the shifter 72, that is, shifted to the LSB
side by 3 bits, and the adder 74 further shifts the coefficient generation data stored in the
memory 54. The value shifted by 72 is subtracted, and this subtracted value is similarly used as
the filter coefficient of the cyclic digital filter that constitutes the low-pass emphasis circuit 30,
and defines the zero point of the filter characteristic. .
Therefore, the pole and the zero point of the low range emphasis circuit 30 are appropriately
controlled by the signal level, and the transfer function of the low range emphasis circuit 30 is
changed.
[0035]
On the other hand, the digital two-channel stereo signal through the digital input terminals Lin
and Rin is low by the low band emphasis circuit 30 in which the high frequency band
emphasizing circuit 20 emphasizes a predetermined high frequency band and the transfer
function is sequentially changed. The frequency band is emphasized.
Further, the emphasizing signal is amplified by the amplifier 40, and the amplified signal and the
digital stereo signal amplified by the amplifier 41 are added by the adder 43 and output as Lout
and Rout.
[0036]
In this embodiment, the zero point and the pole of the transfer function of the low band
emphasizing circuit 30 can be simultaneously changed according to the input signal level, and
the frequency characteristic can be changed relatively easily.
Incidentally, if the pole is always made larger than the zero point on the real axis of the Z plane,
the low band comes to be lifted, and for example, the frequency characteristic of raising the low
band as the level of the input signal is smaller is obtained be able to.
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[0037]
As described above, in this embodiment, it is possible to use, as filter coefficients, digital input
signals that have been subjected to various kinds of processing such as absolute value
conversion, averaging, shifting, multiplication of predetermined coefficients, etc. It is possible to
change the frequency characteristic of the filter according to the input signal level by converting
the frequency into a signal and using a value dependent on the digital input signal as the filter
coefficient. Since the filter coefficient is generated by applying the above processing, even if the
levels of the left and right signals are different, it is possible to change the frequency
characteristic of the filter according to the averaged signal level.
Further, the absolute value circuit 51 performs absolute value conversion of the digital signal,
and the averaging circuit 60 performs averaging of the absolute value signal, and further
converts the averaged signal into filter coefficients. Therefore, stable filtering can be performed
even on a signal with a large level change such as an audio signal.
[0038]
Also, since the filter coefficient is generated using the coefficient generation data that makes the
frequency characteristic stored in the memories 53 and 54 flat, the frequency characteristic
when generating the filter coefficient according to the input signal level It is possible to easily
generate a filter coefficient such that is flat.
[0039]
FIG. 2 is an explanatory diagram of a frequency characteristic of the band emphasizing circuit
according to the first embodiment of the present invention.
2, the horizontal axis represents frequency (unit (kHz)), the left vertical axis represents the gain
(unit (dB)) of the entire band emphasizing circuit, and the value on the right side of FIG. 2
represents the input signal level.
[0040]
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Note that for each input signal level of 0, -10, -20, -30, -40 (dB), the solid line indicates MAX, the
dotted line indicates MID, and the dotted line with a larger dot interval than this dotted line
indicates the case where MIN is selected. There is.
[0041]
As shown in FIG. 2, when the input signal level is 0 (dB), the low band is not lifted and only the
high band is emphasized by about 4 (dB), and the input signal level is -10 (dB) Depending on the
coefficient generation data read out from the memories 53 and 54, the manner in which the low
band is lifted changes.
Since the signal a is selected when MAX is selected, the value corresponding to the input signal
level -10 (dB) is the value defining the pole, while MAX is also selected in the memory 54 The
low band is raised by about 7 (dB).
When the input signal level is -10 (dB), if MIN is selected in the memory 54, the low band is
raised by about 3 (dB), resulting in a constant low band filtering characteristic.
[0042]
When the input level is -10 (dB) or less, the signal a is selected in any case to emphasize the low
range, and in any case, the low range emphasis is performed when MAX is selected. .
[0043]
Also, FIG. 3 is a diagram showing the frequency characteristics particularly when MID is selected
in the memories 53 and 54, and as in FIG. 2, the horizontal axis represents frequency (unit (kHz))
and the left vertical axis represents a band emphasizing circuit. The overall gain (unit (dB)), the
value on the right side of the figure indicates the input signal level.
As shown in FIG. 3, as the input signal level is smaller, the lower range is emphasized.
[0044]
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FIG. 4 is a block diagram of a band emphasizing circuit according to a second embodiment of the
present invention.
This embodiment is characterized in that a low frequency emphasizing circuit is connected in
parallel to a high frequency emphasizing circuit fixed to a transfer function to change only the
pole of the low frequency emphasizing circuit.
[0045]
This band emphasizing circuit includes an L channel filter 120 and an R channel filter 130 for
filtering each of the digital two-channel stereo signals input through the digital input terminals
Lin and Rin.
The L channel filter 120 and the R channel filter 130 have the same configuration, and the
signals Lout and Rout are respectively output.
[0046]
The L channel filter 120 includes a high pass emphasizing circuit 80 having a fixed transfer
function, a low pass emphasizing circuit 90 having a variable transfer function by changing the
filter coefficient, and a multiplier 95 (coefficient C7 is, for example, 0.085). Connected in parallel.
[0047]
High-frequency emphasizing circuit 20 has a multiplier 81 for multiplying the digital signal by
coefficient C2 (for example, −1), a delay element 83 for delaying the signal, and a coefficient
C10 (for example, 0. 10) for the signal delayed by delay element 83. 5) A multiplier 84 for
multiplying, an adder 82 for adding the multiplication result by the multiplier 81 and the
multiplication result by the multiplier 84, and the signal delayed by the delay element 83 and the
multiplication result by the multiplier 95 An adder 86, an amplifier 85 capable of amplifying the
addition result from the adder 86 with a gain set to 0 to 1, and addition of a digital signal input
through the digital input terminal Lin and an amplification signal by the amplifier 85 are
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performed. It is a digital filter that has an adder 87 and is configured to emphasize a
predetermined high frequency band with a fixed transfer function regardless of the level of the
input signal.
By changing and setting the gain of the amplifier 85, it is possible to change the degree of overall
emphasis in the L channel filter 120.
[0048]
The low-frequency emphasis circuit 90 further includes a delay element 93 for delaying the
signal, a multiplier 94 for multiplying the output of the switch 170 described later and the signal
delayed by the delay element 93, and the multiplication result of the multiplier 94. An adder 91
for adding the digital signal input through the digital input terminal Lin, and an adder 92 for
adding the addition result of the adder 91 and the signal delayed by the delay element 93,
multiplication The cyclic digital filter is configured to emphasize the low frequency band
according to the input level while changing its transfer function according to the multiplication
result of the unit 94.
[0049]
Furthermore, multipliers 141 and 142 which multiply the coefficient 0.5 by each of the digital
signals of two channels input through the digital input terminals Lin and Rin, and an adder 140
which adds the multiplication results of these multipliers 141 and 142. An absolute value
conversion circuit 150 for converting the addition signal from the adder 140 into an absolute
value, a multiplier 151 (coefficient c3) for multiplying the signal absolute value converted by the
absolute value conversion circuit 51 by a predetermined coefficient, 152 (coefficient c5), an
averaging circuit 160 for averaging the multiplication results of the multipliers 151 and 152, a
memory 180 for storing coefficient generation data for generating filter coefficients, and an
averaging circuit 160. It has a switch 170 for selecting the larger one of the averaging signal (a)
and the coefficient generation data (b) stored in the memory 180. Selected signal by the switch
170 (g) is configured to be supplied to the multiplier 94.
[0050]
The multipliers 151 and 152 provided between the absolute value circuit 150 and the averaging
circuit 160 are for eliminating saturation of the signal so as to be averaged by the averaging
circuit 160. It functions as a shifter if it is set to the power of.
[0051]
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The averaging circuit 160 adds a delay element 162 for delaying the signal, a multiplier 163 for
multiplying the delay signal of the delay element 162 by the coefficient C4, and an addition for
adding the multiplication result of the multiplier 163 and the multiplication result of the
multiplier 152. , And functions as a kind of integration circuit.
[0052]
Furthermore, in the memory 180, for example, when the level of the digital input signal is
smaller than -29.9 (dB), the frequency characteristic of the L channel filter 120 (same for the R
channel filter 130) is constant (each input level A value (MAX: 0.0016) which results in
overlapping if the characteristics are translated, a value (MID: 0.020), which makes the frequency
characteristic constant when smaller than -8 (dB), -4 (dB) Three types of coefficient generation
data having a value (MIN: 0.032) at which the frequency characteristics become constant when
small are stored, and are configured to be able to switch the coefficient generation data to be
selected by an operation.
[0053]
Further, the switch 170 compares the magnitude relationship between the signal (a) averaged by
the averaging circuit 160 and the coefficient generation data (b) stored in the memory 180 and
corresponding to the level of the input signal. , And supplies the larger signal (g) to the multiplier
94.
[0054]
Thus, the transfer function of the low band emphasis circuit 90 is expressed by the following
equation (4).
Z-1 / (1- (1-g) Z-1) (4) where g is a signal supplied to the multiplier 94.
[0055]
Next, the operation of this band emphasizing circuit will be described.
Now, it is assumed that a digital two-channel stereo signal is input through the digital input
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terminals Lin and Rin.
The left and right digital signals are multiplied by 0.5 by multipliers 141 and 142 respectively,
the left and right signals multiplied by 0 and 5 are added by adder 140, and the added signal is
converted to an absolute value by absolute value conversion circuit 150, The absolute valued
signals are multiplied by C3 and C5 by multipliers 151 and 152, respectively.
[0056]
Next, the signals multiplied by these multipliers 151 and 152 are averaged by the averaging
circuit 160 to be the signal a and supplied to the switch 170, while the coefficient generation
data corresponding to the input signal level is a signal It is read from the memory 180 as b and
supplied to the switch 170.
At this time, the switch 170 performs switching operation so as to supply the larger one of the
signal a and the signal b as the signal g to the multiplier 94.
Thus, if the relationship between the magnitudes of the signal a and the signal b is "a「 b ", the
signal g = a, and if a <b, the signal g = b.
[0057]
Next, the signal g is supplied to the multiplier 94 to be used as the filter coefficient of the cyclic
digital filter that constitutes the low-pass emphasis circuit 90 to define the pole of the filter
characteristic.
Therefore, the pole of the low range emphasis circuit 90 is appropriately controlled by the signal
level, and the transfer function of the low range emphasis circuit 90 is changed.
[0058]
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On the other hand, the digital two-channel stereo signal through the digital input terminals Lin
and Rin is low by the low-frequency emphasis circuit 90 in which the high-frequency emphasis
circuit 80 emphasizes a predetermined high frequency band and the transfer function is
sequentially changed. The frequency band is emphasized and output as Lout and Rout. The
output of the low range emphasis circuit 90 is multiplied by the coefficient c7 by the multiplier
95 and supplied to the adder 86 of the high range emphasis circuit 80.
[0059]
In this embodiment, it is possible to change the pole of the transfer function of the low range
emphasis circuit 90 according to the input signal level. Therefore, also in this embodiment,
digital input signals are subjected to various processing such as absolute value conversion,
averaging, multiplication of predetermined coefficients, etc. and converted so as to be used as
filter coefficients. By using a value dependent on the digital input signal as the filter coefficient, it
is possible to change the frequency characteristic of the filter according to the input signal level.
In addition, since absolute value conversion, averaging, and the like are performed, stable
filtering can be performed even if the amplitude change is severe.
[0060]
Although the band emphasizing circuit described above is suitable for the field of audio etc.
especially if it is for low band emphasis, the emphasis band is not particularly limited to the low
band, but for the middle band or high band Also good.
[0061]
As described above, according to the invention as set forth in claim 1, the coefficient generation
means adopts as a filter coefficient a signal obtained by processing a digital signal input to one or
more digital filters. It becomes possible to change the frequency characteristics of the filter in
accordance with the level of the input signal.
[0062]
According to the second aspect of the present invention, in addition to the effect of the first
aspect, the coefficient generation means calculates the filter coefficient using a signal obtained
by adding digital signals input to each of the plurality of digital filters. This makes it possible to
change the frequency characteristics of the filter in accordance with the averaged signal level
even in the case of stereo signals, for example, even if the levels of the left and right signals are
different.
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[0063]
Furthermore, according to the third aspect of the present invention, in addition to the effect of
any of the first and second aspects, the absolute value conversion means absoluteizes one or
more digital signals input to the digital filter, and averages The averaging means averages this
absolute value signal, and the converting means further converts this averaged signal into filter
coefficients, so that it is stable even for signals such as audio signals with severe level changes.
Filtering can be performed.
[0064]
Furthermore, according to the fourth aspect of the invention, in addition to the effect of the third
aspect, the selection means generates the filter coefficient stored in the storage means such that
the frequency characteristic becomes as predetermined. Since one of the coefficient generation
data is selected with reference to the magnitude relationship between the coefficient generation
data corresponding to the filter coefficient generated by processing the coefficient generation
data and the digital input signal, the level of the input signal is selected. Accordingly, it becomes
possible to change the frequency characteristics and also to change the degree of the band
emphasis.
[0065]
According to the invention of claim 5, each pair of high-pass filtering means inputs each of the
digital signals of the two channels to perform predetermined high-pass filtering, and
subsequently, a pair of variable filter coefficients is obtained. Low-pass filtering means, low-pass
filtering means, addition, absolute value conversion, averaging of both signals, and further, the
selection means is the filter coefficient generation data stored in the storage means and digital
Changing only the low frequency characteristic according to the amplitude of the input signal by
selecting the smaller one of the filter coefficient generation data corresponding to the filter
coefficient generated by processing the input signal It is also possible to change the degree of
band emphasis.
Furthermore, stable filtering can be performed even if the amplitude change is severe.
[0066]
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Furthermore, according to the invention as set forth in claim 6, each of the digital signals of two
channels is inputted by a pair of high-pass filtering means to perform predetermined high-pass
filtering, and a pair of variable filter coefficients is provided. Low pass filtering is performed by
low pass filtering means, addition, absolute value conversion, averaging of both signals are
further performed, and furthermore, the selection means is the filter coefficient generation data
and digital input stored in the storage means It is possible to change only the low frequency
characteristic according to the amplitude of the input signal by selecting the larger one of the
filter coefficient generation data corresponding to the filter coefficient generated by processing
the signal. As well as being possible, it is also possible to change the degree of band emphasis.
Furthermore, stable filtering can be performed even if the amplitude change is severe.
[0067]
Brief description of the drawings
[0068]
FIG. 1 is a block diagram of a band emphasizing circuit according to a first embodiment of the
present invention.
[0069]
FIG. 2 is an explanatory diagram of a frequency characteristic of the band emphasizing circuit
according to the first embodiment of the present invention.
[0070]
FIG. 3 is an explanatory diagram of a frequency characteristic of the band emphasizing circuit
according to the first embodiment of the present invention.
[0071]
FIG. 4 is a block diagram of a band emphasizing circuit according to a second embodiment of the
present invention.
[0072]
Explanation of sign
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19
[0073]
20: high frequency emphasizing circuit, 21: adder, 22: adder, 23: delay element, 24: multiplier,
25: multiplier, 30: low band emphasizing circuit, 31: adder, 32: delay element, 33 ... Adder, 34 ...
Multiplier, 35 ... Multiplier, 40 ... Amplifier, 41 ... Amplifier, 42 ... Adder, 51 ... Absolute value
circuit, 52 ... Shifter, 53 ... Memory, 54 ... Memory, 60 ... Averaging Circuits 61 Adders 62 Adders
63 Delays Elements 64 Shifters 65 Shifters 70 Switches 71 Shifters 72 Shifters 73 Inverters 74
Adders 80 High Frequency Highlighting circuit 81 Multiplier 82 Adder 83 Delay element 84
Multiplier 85 Amplifier 86 Adder 87 Adder 90 Low-pass emphasis circuit 91 Adder 92 ... Adder,
93 ... Delay element, 94 ... Multiplier, 95 ... Multiplier, 00 ... L channel filter, 110 ... R channel
filter, 120 ... L channel filter, 130 ... R channel filter, 140 ... adder, 141 ... multiplier, 142 ...
multiplier, 150 ... absolute value circuit, DESCRIPTION OF SYMBOLS 151 ... Multiplier, 152 ...
Multiplier, 160 ... Averaging circuit, 161 ... Adder, 162 ... Delay element, 163 ... Multiplier, 170 ...
Switch, 180 ... Memory
08-05-2019
20
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