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JPH05191885

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DESCRIPTION JPH05191885
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic signal equalizer circuit for enabling the reproduction of rich sound for auditory sense
when reproducing a band-limited audio signal.
[0002]
2. Description of the Related Art For transmission recording of an acoustic signal, there is a
suitable band. For example, 0 to 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. 2B, 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. As a matter of course, the component higher than fC is not reproduced, and a
sound different from the original sound is reproduced.
[0004]
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1
When the sound collection technology is excellent as in recent years and the performance of the
playback device 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 or more 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.
[0005]
In the prior art, the object was to reproduce an acoustic signal under the band limitation of the
transmission system described above. However, assuming that the original sound source has a
frequency distribution of fA as shown in FIG. 2A, since the transmission band of the transmission
system or recording system is limited as described above, the acoustic signal has a cutoff
frequency of fC. Low-pass filter, and the signal of fA> fC is deleted. 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.
[0006]
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.
[0007]
The object of the present invention is to provide a mode function capable of adding a high
frequency component in the audible range that has been deleted by the transmission system
when reproducing a band-limited audio signal, and by operating this mode function as needed,
rich reproduced audio In order to make it possible to obtain an acoustic signal equalizer circuit.
[0008]
In order to achieve the above object, an acoustic signal equalizer circuit according to a first
aspect of the present invention comprises an acoustic signal, a low frequency component signal
below a predetermined cutoff frequency, and a cutoff frequency above the cutoff frequency.
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2
Frequency component separation means for separating into a plurality of high frequency
component signals divided into a plurality of different frequency bands, an amplitude detection
means for obtaining the detection signal by amplitude detecting the respective high frequency
component signals, and the respective high frequency component signals Harmonic component
extraction means for extracting harmonic component signals each having a predetermined
multiple from the above, amplitude modulation means for obtaining the respective amplitude
modulation signals gain-controlled by amplitude-modulating the respective harmonic component
signals with the detection signal, and And signal combining means for combining each of the
amplitude modulation signals and the low frequency component signal of the acoustic signal to
obtain a combined signal.
[0009]
In the acoustic signal equalizer circuit according to the second aspect of the present invention,
the acoustic signal is divided into a low frequency component signal having a predetermined
cutoff frequency or less and a plurality of high frequency components divided into a plurality of
different frequency bands above the cutoff frequency. Frequency component separation means
for separating into signals, Amplitude detection means for amplitude detection of each high
frequency component signal to obtain a detection signal, zero cross point for detecting the zero
cross point of each high frequency component signal and outputting each zero cross signal A
detection means, Amplitude modulation means for obtaining amplitude modulated signals gain
controlled by amplitude modulating the respective zero cross signals with the detected signal,
and respective difference component signals between the respective amplitude modulated signals
and the respective high frequency component signals It has a difference component signal output
unit to be extracted, and a signal combination unit to combine the above-mentioned each
difference component signal and the low frequency component signal of the acoustic signal to
obtain a composite signal. Acoustic signal equalizer circuit according to claim.
[0010]
Further, according to the acoustic signal equalizer circuit of the third aspect of the present
invention, the acoustic signal is divided into a low frequency component signal below a
predetermined cutoff frequency and a plurality of high frequency component signals divided into
a plurality of different frequency bands above the cutoff frequency. , Frequency component
separating means for separating, amplitude detecting means for obtaining the detection signal by
amplitude detecting the respective high frequency component signals, and zero crossing
detection for detecting the zero crossing points of the respective frequency component signals
and outputting the respective zero crossing signals Means, amplitude modulation means for
amplitude-modulating the respective zero-crossing signals with the detection signal to obtain
respective amplitude-modulated signals, and extracting respective sum component signals of the
respective amplitude-modulated signals and the respective frequency component signals And
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signal combining means for obtaining the combined signal by combining the respective sum
component signals and the low frequency component signal of the acoustic signal. To.
[0011]
An acoustic signal equalizer circuit according to a fourth aspect of the present invention is the
circuit according to the first, second or third aspect of the present invention, wherein the
selective output means selects and outputs either the composite signal or the acoustic signal. It is
characterized by having.
[0012]
In the circuit of the first invention, the acoustic signal is separated into the low frequency
component signal and the high frequency component signal divided into a plurality of different
frequency bands.
Each high frequency component signal is amplitude-detected to obtain a detection signal and to
extract each harmonic component signal of a predetermined multiple.
Gain-controlled amplitude modulation signals obtained by amplitude modulation of the
respective harmonic component signals by the detection signal are combined with the low
frequency component signals.
[0013]
In the circuit according to the second aspect of the present invention, the zero crossing point of
each high frequency component signal is detected, and the obtained zero crossing signal is
amplitude-modulated by the detection signal.
And each difference component signal of each amplitude modulation signal and each high
frequency component signal and the said low frequency component signal are synthesize |
combined.
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[0014]
Furthermore, in the circuit of the third aspect of the present invention, the sum component signal
of each amplitude modulation signal obtained by amplitude modulating the zero cross signal and
each high frequency component signal is synthesized with the low frequency component signal.
[0015]
According to the circuit of the fourth aspect of the invention, the synthesized signal and the
acoustic signal can be arbitrarily selected and output in each of the circuits.
[0016]
Embodiments of the present invention shown in the drawings will be described below.
FIG. 1 shows an embodiment of an acoustic signal equalizer circuit according to the first
invention.
In the figure, 1 is a band-limited acoustic signal, 2 is a splitter, and corresponds to the frequency
component separation means.
The branching filter 2 is composed of, for example, one low pass filter having a cutoff frequency
fL and four narrow band pass filters having a center frequency of fH1, fH2, fH3 and fH4 having a
center frequency of fL or more, and 3 is Output terminals of the low frequency component signal
EL, and 4 to 7 are output terminals of the high frequency component signals EH1 to EH4.
8-1 to 8-4 are square circuits, and 9-1 to 9-4 are band pass filters having a center frequency of
2fH1 to 2fH4, and constitute the harmonic component extraction means.
[0017]
10-1 to 10-4 are gain control circuits (or amplitude modulation circuits), which constitute the
amplitude modulation means.
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Reference numerals 11-1 to 11-4 denote envelope detectors, which constitute the amplitude
detection means. An addition circuit 12 corresponds to the signal combining means. 13 is an
output signal, and 14-1 to 14-4 are attenuators. A switch 15 constitutes the selection output
means.
[0018]
The acoustic signal 1 is separated by the demultiplexer 2 into a low frequency component signal
EL having a cutoff frequency fL or less and high frequency component signals EH1 to EH4 of
different frequency bands of channels.
[0019]
The respective high frequency component signals EH1 to EH4 are applied to squaring circuits 81 to 8-4 and envelope detectors 11-1 to 11-4, and the outputs of the squaring circuits are
bandpass filters 9-1 to 9-4. The harmonic component signals of 2fH1 to 2fH4 centers are
extracted respectively through.
[0020]
Here, for example, assuming that the high frequency component signal EH1 centered on fH1 is
EH1 = e1 cos ω H1t (1), the squared output EH12 is EH12 = (e12 / 2) + (e12 / 2) cos 2 ωH1t
(2)
[0021]
The component of the second term of the equation (2) is extracted through the band pass filter.
FIG. 3 (a) shows the output characteristics of the branching filter 2, and FIG. 3 (b) shows the
output characteristics of the band pass filters 9-1 to 9-4, respectively. The component of 2fH1 is
the component of a1, 2fH2. When components of a2 and 2fH3 are added to components of fL or
less with a3 and 2fH4 components as a4 as shown in FIG. 3C, the components lost by the cutoff
filter of fL can be restored.
[0022]
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The envelope detectors 11-1 to 11-4 detect the amplitudes of the high frequency component
signals EH1 to EH4 and send the detected signals to the gain control circuits 10-1 to 10-4,
respectively.
Each gain control circuit amplitude-modulates each of the harmonic component signals
according to each of the detection signals, and outputs an amplitude-modulated signal whose
gain is controlled to be proportional to the amplitudes a1 to a4 of EH1 to EH4. A low frequency
component signal EL is synthesized by the adder circuit 12 through 14-4.
[0023]
Originally, harmonic distortion should be small, but as shown in the auditory sensitivity diagram
of FIG. 4, the auditory sense is sensitive to the phase of the sound below the frequency f0 (1.5 to
2.5 kHz) However, it is known that for the signal of f0 or more shown by the solid line in FIG. 4,
only the amplitude is insensitive to the phase.
[0024]
Therefore, if fC> f0 in FIG. 3, the component above fC does not feel as distortion, and the
amplitude is close to the original signal source, ie, the signal before blocking at fC, as shown in
FIG. It is.
[0025]
Of course, in the embodiment of FIG. 1, the coefficients of the attenuators 14-1 to 14-4 can be
made zero and the harmonic components can be made zero.
Furthermore, it is also possible to add a third harmonic component obtained by multiplying each
of the high frequency component signals EH1 to EH4 and the output component of each square
circuit.
Further, a switch 15 may be provided so that the output signal 13 (synthesized signal) from the
addition circuit 11 and the acoustic signal can be selected.
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[0026]
FIG. 5 shows an embodiment of an acoustic signal equalizer circuit according to the second
invention, wherein the same reference numerals as in FIG. 1 denote the same or similar circuits,
and 16-1 to 16-4 are zero cross generators, Configure.
The differential amplifiers 17-1 to 17-4 constitute the difference component signal output
means.
[0027]
First, the high frequency component signal EH1 (FIG. 6 (a)) from the splitter 2 is applied to the
zero cross generator 16-1, and it is a clear square wave zero cross signal (FIG. 6) with rising and
falling at the 0 level. Converted to (b).
[0028]
The amplitude detector (envelope detector) 11-1 detects the amplitude shown by the broken line
in FIG. 6 (a), and the amplitude modulator 10-1 amplitude-modulates the above-mentioned zero
cross signal by the detection signal and performs gain control. An amplitude modulation signal of
the waveform shown in FIG. 6 (c) is obtained.
The amplitude modulation signal and the high frequency component signal EH1 are applied to a
differential amplifier 17-1 to obtain a difference component signal of both signals shown in FIG.
6 (d). Since the amplitude modulation signal (FIG. 6 (c)) has the same amplitude as the high
frequency component signal EH1 (FIG. 6 (a)), in the difference component signal, the
fundamental wave component is canceled and the harmonic component is mainly It has become.
The difference component signal is adjusted in the harmonic component by passing through the
attenuator 14-1 and input to the addition circuit 11.
[0029]
Similar processing is performed on the other high frequency component signals EH2 to EH4
from the splitter 2, and the addition circuit 11 combines the difference component signals and
the low frequency component signal EL to generate a composite signal (FIG. e)) 13 is output to
the switch 15.
08-05-2019
8
[0030]
FIG. 7 shows an embodiment of an acoustic signal equalizer circuit according to the third
invention, wherein the same reference numerals as in FIG. 5 denote the same or similar circuits,
and 18-1 to 18-4 denote adders, and said sum component signal output means Configure
19-1a, 19-1b, 19-2a, 19-2b, 19-3a, 19-3b, 19-4a, 19-4b respectively have their associated
coefficients k1, (1-k1), k2, (1- k2), k3, (1-k3), k4 and (1-k4) are one pair of attenuators
respectively.
[0031]
The high frequency component signal EH1 is applied to the zero cross generator 16-1, and
generates the zero cross signal shown in FIG. 8B, for example, assuming that EH1 has the
waveform of FIG. The zero cross signal is amplitude-modulated by the amplitude detection signal
in the amplitude modulator (or gain control circuit) 10-1 and outputs an amplitude-modulated
signal whose gain is controlled to be equal to EH1. The amplitude modulation signal and the high
frequency component signal EH1 are multiplied by k1 times and (1-k1) times by passing through
the attenuators 19-1a and 19-1b, respectively, and are added by the adder 18-1 to be shown in
FIG. It is sent to the addition circuit 11 as a sum component signal of the waveform.
[0032]
Similar processing is performed for the high frequency component signals EH2, EH3 and EH4,
but the coefficients of the attenuators are set to k1 <k2 <k3 <4. The adder circuit 11 combines
each sum component signal and the low frequency component signal EL, and outputs the
combined signal 13 to the switch 15.
[0033]
As described above, according to the acoustic signal equalizer circuit of the present invention, it
is possible to reproduce audio quality rich in auditory sense by adding out-of-band highfrequency component signals at the time of reproduction of band-limited acoustic signals. Can.
08-05-2019
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[0034]
Brief description of the drawings
[0035]
1 is a block diagram showing an embodiment of the first invention of the present application.
[0036]
2 is a characteristic diagram showing the relationship between the frequency fA of the sound
signal and the transmission band.
[0037]
3 is a frequency characteristic diagram for explaining the operation of the embodiment of FIG.
[0038]
4 is an explanatory view of the frequency characteristics of hearing.
[0039]
5 is a block diagram showing an embodiment of the second invention of the present application.
[0040]
6 is a waveform diagram for explaining the operation of the embodiment of FIG.
[0041]
7 is a block diagram showing an embodiment of the third invention of the present application.
[0042]
8 is a waveform diagram for explaining the operation of the embodiment of FIG.
[0043]
Explanation of sign
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[0044]
DESCRIPTION OF SYMBOLS 1 acoustic signal 2 splitter 8-1 to 8-4 square circuit 10-1 to 10-4
gain control (amplitude modulation) circuit 11-1 to 11-4 envelope (amplitude) detection circuit
12 addition circuit 15 switch 16 -1 to 16-4 differential amplifier 18-1 to 18-4 adder
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