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DESCRIPTION JP2014179729

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DESCRIPTION JP2014179729
Abstract: The present invention provides a highly responsive howling reduction system
applicable to an acoustic system including a microphone, an amplifier and a speaker. SOLUTION:
The 90 ° delay accuracy of an analog phase adjustment circuit is increased by using a D-FF 7
for phase adjustment of an analog phase synchronization circuit for obtaining a signal of the
same frequency as howling. An active noise control (ANC) circuit 5 using an analog electronic
circuit outputs an analog signal of the same amplitude as the howling and in antiphase. The
adder 6 adds the howling signal and the output signal of the ANC circuit 5 to reduce the howling
signal. [Selected figure] Figure 1
Howling reduction system and analog electronic circuit used therefor
[0001]
The present invention relates to a howling reduction system for reducing howling generated in
an acoustic system and an analog electronic circuit used therefor.
[0002]
In an acoustic system that amplifies a signal obtained by a microphone with an amplifier and
outputs it from a speaker, howling may occur if the output from the speaker is sufficiently large,
and one of the factors that limit the output from the microphone to the speaker It has become
one.
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This howling can be reduced only by the analog electronic circuit, and howling can be effectively
reduced by superimposing a reduced signal of the same amplitude and in antiphase with the
howling frequency.
[0003]
According to Patent Document 1, by using an active noise control circuit (ANC circuit) using an
analog electronic circuit, an analog signal in reverse phase to the howling frequency is output
from the PLL circuit to cancel the howling frequency. ing.
[0004]
Patent Document 1: Japanese Patent Application Publication No. 2008-07082
[0005]
In a conventional howling reduction analog electronic circuit, an output signal of a phase
synchronization circuit (PLL circuit) advances by 90 ° with respect to an input signal, and
therefore, an integrator is used as a circuit for delaying the phase by 90 °.
However, since an offset usually appears on the output signal of the integrator, the duty ratio
does not necessarily become 50%, so that a phase delay of 90 ° can not be obtained. As a result,
for the howling signal and the output signal of the ANC circuit There is a problem that a phase
difference occurs and howling can not be sufficiently reduced.
[0006]
An object of the present invention is to realize an effective howling reduction system by
providing a circuit configuration that eliminates the phase difference between the howling signal
and the output signal of the ANC circuit.
[0007]
In order to solve the above problems, the present invention is an analog electronic circuit used in
a howling reduction system, which comprises an analog multiplier, a low pass filter, and a voltage
control oscillator, receives a howling signal, and detects a howling frequency. An analog PLL
circuit that outputs a signal of the same frequency, and an analog phase adjustment circuit that
receives an output signal of the analog PLL circuit and outputs a signal obtained by combining
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the phase of the howling signal and the output signal of the analog PLL circuit. And an analog
active noise control circuit which receives an output signal of the analog phase adjustment circuit
and outputs an analog signal of the same amplitude and opposite phase to the signal of the
howling frequency, the howling signal and the analog active noise control Superimpose the
output signal of the circuit Comprising an analog adder for attenuating the feedback signal, the
said analog phase adjusting circuit, a first feature in that it is constituted by the flip-flop.
[0008]
The second feature of the present invention is that the flip-flop is a D flip-flop, and an output
signal of the analog multiplier is used as a clock of the D-FF.
[0009]
The present invention further comprises a microphone for collecting sound, an amplifier for
amplifying the output of the microphone, the analog electronic circuit, and a speaker for
converting the output signal of the analog electronic circuit into sound. It features a howling
reduction system.
[0010]
According to the present invention, it is possible to obtain a signal of a frequency synchronized in
antiphase with the howling frequency, and howling can be effectively reduced by superposing
the signal on the howling frequency.
[0011]
It is a block diagram showing composition of a howling reduction analog electronic circuit
concerning a 1st embodiment of the present invention.
It is a block diagram which shows the structure of the conventional analog electronic circuit for
howling reduction.
Simulation of an output signal of a voltage controlled oscillator (VCO) and an output signal of a D
flip flop (D-FF) constituting an analog phase synchronization circuit (PLL circuit) of an analog
electronic circuit for howling reduction according to the first embodiment of the present
invention It is a result.
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It is a simulation result of the output signal of the voltage controlled oscillator (VCO) which
comprises the analog phase-locked loop circuit (PLL circuit) of the conventional analog electronic
circuit for howling reduction, and the output signal of an integrator.
[0012]
First Embodiment Taking a sound system system including a microphone, an amplifier, and a
speaker as an example, the howling reduction system according to the present embodiment will
be described with reference to the conventional analog electronic circuit for howling reduction
according to FIGS. It demonstrates in detail, comparing.
[0013]
First, the howling reduction analog electronic circuit according to the present embodiment will
be described in detail with reference to FIG.
[0014]
In FIG. 1, an input is an external input sound, which is a signal which is converted into an
electrical signal by a microphone not shown and amplified by an amplifier not shown.
The output is an amplified electrical signal, which is converted into sound by a speaker not
shown in the figure, and the converted sound is output as an output sound from the speaker.
[0015]
The howling reduction analog electronic circuit according to the present embodiment is a circuit
for reducing the gain of the howling frequency.
When howling occurs, the howling signal including the howling frequency is input to the PLL
circuit configured of the multiplier 1, the low pass filter (LPF) 2 and the voltage controlled
oscillator (VCO) 3.
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The PLL circuit is a circuit for detecting the howling frequency and outputting the same
frequency, and the phase of the output signal is advanced by 90 ° with respect to the howling
signal.
[0016]
The D-FF 7 is a circuit for delaying the phase by 90 °, and the D-FF 7 aligns the phase of the
howling signal and the output signal of the PLL circuit.
In order to match the phase of the howling signal and the output signal of the PLL circuit, the
output signal of the multiplier 1 is input to the D-FF 7 as a clock.
Therefore, the D-FF 7 constitutes an analog phase adjustment circuit for matching the phase of
the howling signal and the output signal of the PLL circuit.
[0017]
The ANC circuit 5 is a circuit for adjusting the amplitude of the signal to cancel the howling
signal. The adder 6 is a circuit for adding the howling signal and the output signal of the ANC
circuit 5 to reduce the howling signal.
[0018]
Next, the operation of the howling reduction analog electronic circuit according to the present
embodiment will be described.
[0019]
The howling signal is input to the PLL circuit as an input, and then the PLL circuit outputs the
same frequency as the howling signal.
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The output signal of the PLL circuit is 90 ° out of phase with the input signal. The output signal
of the PLL circuit is input to the D-FF 7 as a circuit for delaying the phase by 90 ° so that the
phase shift is canceled and an output signal without phase shift is obtained. The output signal of
multiplier 1, which is about twice the frequency of the output frequency of the PLL circuit, is
input to D-FF 7 as a clock by comparator 8 as a clock, synchronized with the clock, 90 ° A signal
whose phase is delayed is output. Thereby, the phase shift of the PLL circuit is canceled out, and
an output signal without phase shift is obtained.
[0020]
The ANC circuit 5 outputs the amplitude of the opposite phase based on the frequency
information output from the D-FF 7. The ANC circuit 5 operates such that the difference between
the output signal of the ANC circuit 5 and the signal obtained by howling becomes zero.
[0021]
In the adder 6, the howling input signal and the output signal of the ANC circuit 5 are
superimposed, the howling signal is reduced, and the reduced signal is output as an output
signal. This output signal is input to the ANC circuit 5 as a feedback signal. Based on the input
feedback signal, the amplitude of the ANC circuit 5 is adjusted so as to be in the same phase and
in the opposite phase to the howling signal.
[0022]
Next, a conventional howling reduction analog electronic circuit will be described according to
FIG. 2 in order to compare with the howling reduction analog electronic circuit according to the
present embodiment.
[0023]
In FIG. 2, the functions and operations of the input, the output, the PLL circuit, the ANC circuit 5
and the adder 6 are the same as those described in the howling reduction analog electronic
circuit according to the present embodiment.
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In the conventional howling reduction analog electronic circuit, the integrator 4 is used as a 90
° phase delay circuit instead of the D-FF 7 of the howling reduction analog electronic circuit
according to the present embodiment. An analog phase adjustment circuit is configured to adjust
the phase of the signal and the output signal of the PLL circuit.
[0024]
FIG. 3 shows simulation results regarding the output signal of the VCO 3 of the analog electronic
circuit for howling reduction according to the present embodiment and the main power of the DFF 7. The simulation results show that the duty ratio of the output signal of D-FF 7 is about 50%
and its phase is delayed by about 90 ° with respect to the output signal of the VCO. Therefore,
the phase shift due to the PLL circuit whose phase is advanced by 90 ° is sufficiently canceled
out, and the output signal with less phase shift is obtained by the analog electronic circuit for
howling reduction according to the present embodiment, and as a result, howling is sufficiently
reduced. Can be expected to
[0025]
FIG. 4 shows simulation results of the output signal of the VCO 3 and the output signal of the
integrator 4 of the conventional howling reduction analog electronic circuit. The simulation
results show that the duty ratio of the output signal of the integrator 4 is not 50%, and that the
phase is not delayed by 90 ° with respect to the output signal of the VCO 3. Therefore, in the
conventional howling reduction analog electronic circuit using the integrator as a 90.degree.
Phase delay circuit, the phase shift due to the PLL circuit advanced in phase by 90.degree. Is not
sufficiently canceled out. As a result, it is expected that howling is not sufficiently reduced.
[0026]
As described above, in the present embodiment, in place of the integrator conventionally used as
the 90 ° delay circuit in the ANC circuit 5, use of the D-FF 7 which holds the inverted value at
the falling of the clock is used. It is the first feature. The second feature is to synchronize with the
howling signal by using the output signal of the multiplier 1 constituting the PLL circuit as the
clock of the D-FF 7.
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[0027]
Since the output signal of the PLL circuit is a pulse wave, the output signal can be regarded as a
binary value of High and Low, and by using a frequency signal twice that of the output signal of
the PLL circuit as a clock of D-FF 7, D A 90 ° phase delay can be obtained with a duty ratio of
50% as an output signal of the -FF. Second Embodiment In the first embodiment described above,
the D-FF is used. Alternatively, another flip-flop, for example, a JK flip-flop or an RS flip-flop may
be used. . Further, each circuit constituting the analog electronic circuit of the present invention
may have a configuration other than that of the above-described embodiment as long as the
function can be realized.
[0028]
The present invention can be used to reduce or prevent howling that may occur in an acoustic
system in which positive feedback is configured by a route of a microphone, an amplifier, a
speaker, a sound, and a microphone.
[0029]
1 Multiplier 2 LPF (low pass filter) 3 VCO (voltage controlled oscillator) 4 integrator 5 ANC
circuit (active noise control circuit) 6 adder 7 D-FF (D flip flop) 8 comparator
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