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DESCRIPTION JP2000175286

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DESCRIPTION JP2000175286
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio apparatus having an analog input / output terminal and a digital input / output terminal
and an output mute function.
[0002]
2. Description of the Related Art Many digital audio devices such as effectors have an analog
input / output terminal and a digital input / output terminal. In this type of audio apparatus, as
shown in FIG. 4, an A / D converter 2 mainly composed of the digital signal processing circuit 1
and converting an analog input signal from the analog input terminal 11 into a digital signal is
provided at the previous stage. Further, D / A converters 3 for converting the digital output from
the digital signal processing circuit 1 into an analog output and outputting the analog output to
the analog output terminal 12 are provided at the subsequent stage thereof. The digital signal
input from the digital input terminal 13 is also processed by the digital signal processing circuit
1. The digital output signal processed by the digital signal processing circuit 1 is output via the
digital output terminal 14 as it is in digital form.
[0003]
In this type of audio apparatus, the analog input / output terminals 11 and 12 are normally
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connected to the internal circuit when the power is turned on, and the analog input / output
terminals 11 and 12 are connected in the through state when the power is turned off. ing. This is
to minimize the influence on peripheral devices by turning off the power and disconnecting the
internal circuit from the analog input / output terminals 11 and 12 when a trouble occurs inside
the device. Therefore, as shown in the figure, the switches 4 and 5 are respectively inserted on
the analog input and output sides of the device, and when the power is off, the analog input and
output terminals 11 and 12 are connected to the signal through circuit 6 by this switch. In the
through state, the analog input / output terminals 11 and 12 are connected to the internal circuit
when the power is on.
[0004]
Also, in this type of audio apparatus, although recovery processing is performed when the digital
signal input is out of lock, the mute circuit 7 for muting the output so as not to output noise
during that time is used as the output stage of the internal circuit. Provided. The mute circuit 7 is
configured by a relay or configured by being built in a semiconductor.
[0005]
However, in the above-described conventional audio apparatus, when the muting circuit is
configured by a relay, the relay for the muting circuit is provided separately from the relay
switch used for the signal through circuit 6. There is a problem that the cost is high because it is
necessary. Further, in the case where the muting circuit is built in a semiconductor, there is a
problem that the circuit becomes complicated and the characteristic is deteriorated.
[0006]
The present invention has been made in view of such a point, and it is an object of the present
invention to provide an audio apparatus with a signal through function and an output muting
function which can achieve cost reduction without causing circuit complication and characteristic
deterioration. I assume.
[0007]
An audio apparatus according to the present invention performs predetermined signal processing
on input signals inputted from an analog input / output terminal, a digital input / output
terminal, an analog input terminal and / or a digital input terminal. Signal processing means for
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outputting to an analog output terminal and / or a digital output terminal, and a signal through
circuit for leading an input signal inputted to an analog input terminal to an analog output
terminal without supplying it to the signal processing means; A first relay switch which
alternatively connects the analog input terminal to each input of the signal processing means and
the signal through circuit, and an analog output terminal is alternatively connected to each
output of the signal processing means and the signal through circuit Connecting both the first
relay switch and the second relay switch to the side of the signal processing means. In the fixed
state, both the first and second relay switches are connected to the side of the signal through
circuit to make the signal through state, and when the mute command signal is input, only the
second relay switch is the signal processing means. A control means is provided for controlling
the first and second relay switches so as to be separated from the side and put into an output
mute state.
[0008]
According to the present invention, the first relay switch provided on the input side and the
second relay switch provided on the output side are controlled independently by the control
means, and the first and second relay switches are normally controlled. Connected to the signal
processing means, the first and second relay switches are connected to the signal through circuit
in a specific state such as power off to make the signal through state, and when the mute
command signal is input, only the second relay switch The output of the signal processing means
is separated and put into an output muted state.
For this reason, the second relay switch can be shared to create two states of the signal through
state and the output mute state, and the cost can be reduced by the amount that the separate
relay switch does not have to be provided for the mute. it can.
In addition, since it is not necessary to incorporate a mute circuit in the internal circuit, the
circuit is simplified and the characteristics are not deteriorated.
[0009]
As the control means, for example, a delay circuit for delaying the timing of the output change
with the power on of the device by a predetermined time is added, and the signal processing
means are both the first and second relay switches by the output through this delay circuit.
Generating a control signal for connecting to the side of the signal processing circuit, and
generating a control signal for disconnecting only the second relay switch from the signal
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processing means by the output through the delay circuit and the mute signal. The first and
second relay switches can be connected to the side of the signal processing means after the
internal circuit is stabilized, and noise and the like are prevented when the power is turned on.
The second relay switch can be disconnected immediately in response to the mute signal, and
noise generation at power off can be effectively prevented. It is possible.
[0010]
As the signal processing means, the polarity form of the mute signal to be generated and output
is made low active, and the power is turned off by making the mute signal low active at least for
a predetermined time immediately after the output change timing accompanying the power off.
The second relay switch is driven so as to be separated from the signal processing means by the
remaining power for a short time immediately after, and noise generation at the time of poweroff can be more reliably prevented.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present
invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an essential configuration of a digital audio apparatus
according to an embodiment of the present invention.
In FIG. 1, the digital signal processing circuit 1 is configured by an effector, an equalizer, or the
like, such as a DSP (Digital Signal Processor) that executes desired signal processing in the form
of digital data. An A / D converter 2 for converting an analog signal to digital data is provided in
the previous stage, and a D / A converter 8 for converting digital data from the digital signal
processing circuit 1 to an analog signal is provided in the subsequent stage. . The analog input
terminal 11 is alternatively connected to the input end of the A / D converter 2 or the input end
of the signal through circuit 6 by the first relay switch 21. The analog output terminal 12 is
alternatively connected to the output end of the D / A converter 8 or the output end of the signal
through circuit 6 by the second relay switch 22. The relay switches 21 and 22 are controlled by
a control circuit 23 described later. The digital input signal from the digital input terminal 13 is
directly input to the digital signal processing circuit 1 and processed. The digital output signal
from the digital signal processing circuit 1 can also be output directly from the digital output
terminal 14. The resistors 24 and 25 are pull-down resistors at the time of high impedance of the
analog input / output terminal.
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[0012]
A portion for controlling the relay switches 21 and 22 of the control circuit 23 is configured
roughly as shown in FIG. One terminal of each of the relay switches 21 and 22 is connected to a
power supply terminal (+ V). A resistor 31 and a capacitor 32 are connected in series between
the power supply terminal and the ground terminal, and this constitutes a delay circuit 33. The
output of the delay circuit 33 is connected to the other terminal of the first relay switch 21 via
the inverter 34. The output of the delay circuit 33 is also supplied to one input of the AND gate
35. The mute signal is input to the other input of the AND gate 35. The output of the AND gate
35 is connected to the other terminal of the second relay switch 22 via the inverter 36.
[0013]
The control of the relay switches 21 and 22 of the control circuit 23 is as shown in Table 1
below. Here, that the relay switches 21 and 22 are in the off state means that the analog input
terminals 11 and 12 are connected to the signal through circuit 6.
[0015]
FIG. 3 is a diagram for explaining the operation of this apparatus. When the power is off, as
shown in FIG. 3A, the relay switches 21 and 22 are in the off state, and the analog signal input
from the analog input terminal 11 is directly output to the analog output terminal 12. It is a
state.
[0016]
When the power is turned on, the rise of the output is delayed by the delay circuit 33 of FIG. 2
than the power is turned on. Therefore, the input of the inverter 34 becomes high level after the
internal circuit is stabilized. The mute signal is low active, and the input of the inverter 36 also
goes high. As a result, the outputs of the inverters 34 and 36 become low level, and the relay
switches 21 and 22 are turned on. In this state, as shown in FIG. 3B, the signal input from the
analog input terminal 11 is input to the digital signal processing circuit 1 through the A / D
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converter 2, and predetermined processing is executed. It will be in the normal state. The digital
signal processing circuit 1 executes a selected one of four processes of analog-analog, analogdigital, digital-analog and digital-digital.
[0017]
When the mute signal input to the control circuit 23 becomes active (low level) due to a system
lockout (clock out of synchronization between the system basic clock and the processing data
signal) in the digital signal processing circuit 1, etc. Since the output goes low and the output of
the inverter 36 goes high, only the second relay switch 22 is turned off. As a result, as shown in
FIG. 3C, the input of the analog input signal to the digital signal processing circuit 1 is not
interrupted, and only the analog output from the circuit 1 is attenuated. Therefore, since the
input signal is still supplied to the digital signal processing circuit 1 even when the digital lock
out or the like occurs, the clock synchronization recovery operation continues without any
problem even during the mute period of the analog output, and as a result, the input It is easier
to recover earlier than in the case of breaking off, and the mute signal returns to the high level as
long as the unlocking is eliminated, whereby the relay switch returns to the normal state.
[0018]
Note that this device detects the timing at which the power supply voltage starts to drop, which
can occur due to all power off including user operation and unexpected accident etc., and at least
immediately after the timing of this output change and the remaining power on the power supply
side. The mute signal is made low active for as long as there is a. Specifically, the power supply
voltage is monitored, and it is determined that the power is turned off, for example, when the
power supply voltage is lowered by about 10%, and the mute signal is changed to low active.
Thus, immediately after the power off timing, the second relay switch is driven by the remaining
power of the power (the accumulated amount of the power supply capacitor etc.) and
intentionally disconnects the analog output from the digital signal processing circuit 1 though in
a short time. Driving is performed, whereby pop noise and the like when the power is off can be
reduced more reliably. Also, in the case where the power supply is automatically turned off when
an abnormality in the internal circuit is detected, the adverse effect can be similarly minimized.
[0019]
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As described above, according to the present invention, the second relay switch can be shared to
create two states of signal through state and output mute state, and relays separately for mute
are used. The cost can be reduced by the amount that the switch need not be provided. In
addition, since there is no need to incorporate a mute circuit in the internal circuit, the circuit is
simplified and the characteristic is not deteriorated.
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