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JPH05260588

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DESCRIPTION JPH05260588
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high
frequency component generation of an audio signal suitable as a square circuit or the like of an
acoustic signal equalizer circuit for enabling reproduction of audibly rich sound when
reproducing band-limited audio signals. It relates to a circuit.
[0002]
2. Description of the Related Art For transmission recording of an acoustic signal, there is a
suitable band. For example, 15 kHz for FM broadcasting and 0 to 20 kHz for CD are preferable
transmission bands. Assuming that the upper limit frequency of this transmission band is fC, this
can be viewed as a kind of low pass filter (LPF) with fC as a cutoff frequency, and the frequency
of the sound source is less than fC as shown in FIG. There is no problem because the signal is
recorded or transmitted as it is even through the low pass filter (LPF).
[0003]
However, as shown in FIG. 7B, when there is a component of fc or more in the sound source, the
component of fc or more is removed by the low pass filter (LPF) and transmitted or recorded as
shown in FIG. 2C. As a matter of course, a component higher than fc is not reproduced, and a
sound different from the original sound is reproduced. If the sound collection technology is
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excellent as in recent years and the performance of the playback equipment is improved, it may
be felt that the sound quality is degraded if the component of 15 kHz or more in FM and the
component of 20 kHz in CD are removed. Generally, an audible sound is said to be 20 Hz to 20
kHz, but the sensitivity does not necessarily become zero at 20 kHz.
[0004]
In the past, the reproduction target of the acoustic signal under the band limitation of the
transmission system described above was aimed. However, assuming that the original sound
source has a frequency distribution of fA as shown in FIG. 7A, since the transmission band of the
transmission system and recording system is limited as described above, the acoustic signal has a
cutoff frequency of fc. Low-pass filter, and the signals fA to fC are eliminated. As a result, even if
the reproduction system faithfully reproduces, the component of fA> fC can not be reproduced,
which is a problem from the viewpoint of faithful reproduction.
[0005]
That is, since the fA> fC band to be deleted contains a frequency component that generates rich
high-frequency tones, this component is cut by a transmission system equivalent to the LPF as in
the prior art. Then, there is a problem that the faithful reproduction of the original sound is
impossible and the sound quality is deteriorated. Therefore, when playing back a band-limited
audio signal, a mode function is added that can add high frequency components in the audible
range that were deleted by the transmission system, and this mode function is used as needed to
obtain rich playback sound. An acoustic signal equalizer circuit has been proposed to make it
possible.
[0006]
However, the conventional squaring circuit used to obtain harmonic components of the audio
signal in the equalizer circuit according to the present invention has a squared output e0 = E2 =
cos2ω1t = 1/2 + 1/2 (cos2ω1t) from the input audio signal E = cos ω1t. , And it is configured to
extract the harmonic component cos2ω1t by the filter from this e0.
[0007]
If the input speech signal consists of the above-mentioned single frequency component, it may be
a conventional square circuit, but if it consists of the complex wave as described below, the
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following problems occur. .
[0009]
That is, when the input speech signal is the complex wave E as shown in equation (1), the output
e of the conventional square circuit is not only the desired harmonic components cos 2 ω 1 and
cos 2 ω 2 as shown in equation (2) The intermodulation component cos (ω1 + ω2) is included.
The frequency component of the complex wave E, which is an input voice signal, is as shown in
FIG. 4A, and the output e has the frequency distribution of FIG. 4B, and the (ω1 + ω2)
component is redundant.
[0010]
The intermodulation component of the (ω1 + ω2) component degrades the sound quality.
For this purpose, a narrow band band pass filter group is added to the input voice signal of the
complex wave of equation (1), and each filter output is added to a square circuit, and the squared
output is added to intermodulation component There is a way to reduce the occurrence of
[0011]
However, this method requires a squaring circuit to the output of each filter, and each squaring
output has to be added, which has a disadvantage that the circuit configuration becomes
complicated.
[0012]
An object of the present invention is to propose a high frequency component generating circuit
for reducing intermodulation components and reducing auditory strangeness with a simple
circuit configuration when generating harmonic component signals of audio component signals. .
[0013]
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In order to achieve the above object, the high frequency component generation circuit of an
audio signal according to the present invention comprises: from an audio component signal, a
plurality of odd harmonic component signals composed of a plurality of odd harmonic
components; A first harmonic component signal consisting of a sum component of the even
harmonic component with the synthesized even harmonic component signal and a second
harmonic consisting of a difference component between the odd harmonic component signal and
the even harmonic component signal Harmonic component generation means for generating a
wave component signal, multiplication means for multiplying the first and second harmonic
component signals and outputting a multiplication signal, and combining and combining the
multiplication signal and the voice component signal And signal combining means for obtaining a
signal.
[0014]
Further, the harmonic component generation means of the above-mentioned configuration
comprises, from the speech component signal, an odd harmonic component signal composed of a
plurality of odd harmonic components and a combined even harmonic component signal a
plurality of even harmonic components. First harmonic component extraction means for
extracting a first harmonic component signal consisting of a sum component of the first and
second harmonic component signals, and a difference between the odd harmonic component
signal and the even harmonic component signal from the first harmonic component signal And
second harmonic component generation means for generating a second harmonic component
signal composed of components.
Also, the second harmonic component generation means may include delay circuits with different
delay times to which the first harmonic component signal is added, an output of each delay
circuit, and the first harmonic component signal. And a subtraction circuit that subtracts the first
harmonic component signal from the output of the addition circuit.
[0015]
In the circuit of the present invention, the first harmonic component signal and the second
harmonic component signal are generated from the speech component signal, and the first
harmonic component signal is generated from a plurality of odd harmonic components. It
comprises a sum component of the synthesized odd harmonic component signal and the
synthesized even harmonic component signal of the plurality of even harmonic components.
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The second harmonic component signal is composed of the difference component between the
odd harmonic component signal and the even harmonic component signal.
[0016]
The first and second harmonic component signals are multiplied, and the multiplication output
and the voice component signal are combined to obtain a combined signal including the
harmonic component whose intermodulation component is reduced.
In this case, first, the first harmonic component signal may be extracted from the voice
component signal, and the second harmonic component signal may be generated from the first
harmonic component. Also, the second harmonic component signal may be generated as follows.
That is, the first harmonic component signal is added to a plurality of delay circuits to generate
component signals of different delay times, each component signal and the first harmonic
component signal are added, and the sum output is output from the first output. The harmonic
component signal is subtracted to obtain a second harmonic component signal.
[0017]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle method of the
harmonic component generation circuit of the present invention will be described below with
reference to the drawings. It is effective to add a harmonic component to the voice signal to
improve the sound quality as described above with respect to the frequency component of fL = 2
kHz or more of the voice signal, and is now a high frequency component of fL or more of the
voice signal e. Assuming that e1 is a complex wave of equation (1), this is temporarily separated
by a filter group at an interval of band fB (.omega.B = 2.pi.fB), and as shown in FIG. Assuming that
the synthesized odd harmonics component signal of all odd harmonics EA1 to EAn of every unit
is EA and the even harmonic component signal synthesized of all evens harmonics EB1 to EBn of
even number is EB, e1 Is
[0018]
On the other hand, assuming that the difference between EA and EB is e2, if e1 is multiplied by
e2, then, for example, if EA is cos ω 1 t in equation (1) and EB is k cos ω 2 t, the multiplication
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output is Since e1e2 is, the high frequency component [e1e2] H of the multiplication output is
[0019]
However, if the frequency of the complex wave of equation (1) is within fB,
[0020]
The difference between the equations (7) and (8) is the presence or absence of the (ω1 + ω2)
component, and the (ω1 + ω2) component in the equation (8) is an intermodulation component,
which, as described above, is audible. It is better not to.
This correlation modulation component is generated by the difference between ω1 and ω2 (f1f2 in FIG. 3) as shown in FIG. 3, and equation (8) or (9) holds.
That is, as apparent from FIG. 3, 0 <(f1−f2) ≦ fB intermodulation component (f1 + f2) present fB
<(f1−f2) ≦ 2fB intermodulation component (f1 + f2) absent 2fB <(f1−f2) ≦ 3fB
intermodulation component (f1 + f2) present::
[0021]
As a result, an intermodulation component may or may not be generated every fB. FIG. 1 shows
an embodiment of a harmonic component generation circuit of an audio signal according to the
present invention based on the principle described above, wherein 1 is a high pass filter (HPF)
and corresponds to the first harmonic component extraction means. A square wave distributed
filter device 2 corresponds to the second harmonic component generating means. Reference
numeral 3 denotes a multiplication circuit, which corresponds to the multiplication means. 4 is a
high pass filter (HPF), 5 is a level control circuit, 6 is an addition circuit, and these constitute the
signal combining means.
[0022]
In the above embodiment, the audio component signal e is added to the high pass filter 1 to
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extract the first harmonic component signal e1 (= EA + EB) of f2 or more. This signal e1 is added
to the square wave filter device 2, and this device includes the filter group having a substantially
square frequency distribution shown in FIG. 2, and the signal e1 to the second harmonic
component signal e2 ( = EA-EB) is generated.
[0023]
The first and second harmonic component signals e1 and e2 are input to the multiplication
circuit 3, the multiplication signal e1e2 of the equation (5) is output, and the high-pass filter 4
outputs it as shown in the equation (7) (or the equation 8). The high frequency components [e1,
e2] H are extracted and the additional level α is adjusted by the level control circuit 5, and the
addition circuit 6 adds them to the voice component signal e to obtain the synthesized signal eO.
Assuming that the voice component signal e is e = cos ω 1 t + k cos ω 2 t, the synthesized signal
e 0 is
[0025]
Thus, e0 in equation (9) is the desired output, and an intermodulation component exists in e0 in
equation (10). However, the intermodulation component is not necessarily included as in the
prior art, and in the scheme of the present invention, the intermodulation product is statistically
halved. FIG. 5 shows an example of the configuration of the square wave distributed filter device
2, and 9 to 12 are delay circuits with delay times of τ, τ / 3, τ / 5, and τ / (2n + 1),
respectively, and coefficients of 13 to 16 are each shown. The amplitude controllers k1, k3, k5
and k2n + 1, 17 is a summing circuit, 18 is a subtractor (differential amplifier), and 19 is a gain
control circuit.
[0026]
In the device of FIG. 5, the input signal passes through the delay circuits 9 to 12 and the
amplitude controllers 13 to 16 so that the respective outputs are k1ε-jωτ, k3ε-jω (τ / 3),
k5ε-jω (τ / 5). , K2n + 1ε-jω (τ / (2n + 1)). Here, when there are no delay circuits 10 to 12
and k3, k5... K2n + 1 is 0, the output of the addition circuit 17 is compared with the input signal,
[0027]
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The frequency characteristic ¦ k1 (ω) ¦ However, k1 <1. FIG. 6 (a) shows a characteristic diagram
of ¦ k1 (ω) ¦. When the delay circuits 10 to 12 etc. are added, the front end output is
[0028]
【0028】となる。 Here, if k3, k5,... K2n + 1 <1, then the frequency characteristic ¦ k2 (ω) ¦
in this case is obtained. In this case, k3 = -k1 / 3, k5 = -k1 / 5
[0029]
When it is set to (13), the equation (13) has a characteristic in which a square wave distribution
is added as shown in FIG. 6 (b).
[0030]
The output of the addition circuit 17 is input to a subtractor 18, and after subtracting the input
signal, the amplitude is adjusted by the gain control circuit 19 to obtain an output e2 of a square
wave distribution shown in FIG. 6 (c).
As apparent from FIG. 6, the polarity of each signal changes every ω = π / 2, and if it is set as τ
= 1 msec, the polarity is inverted every f = 500 Hz.
[0031]
As described above, according to the harmonic component generation circuit of the present
invention, high frequency components with few intermodulation components can be generated,
and it is used for the front equalizer circuit etc. Sound can be obtained.
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