JP2009253404A - Communication device - Google Patents

Abstract

To provide a communication device capable of improving call quality by suppressing echo during a call according to a side sound signal generated.
When the difference between the volume of the side sound signal R and the specified value is equal to or less than “6 dB”, the magnitude of the audio signal transmitted from the microphone 24a is reduced by the difference and generated. The magnitude of the side sound signal R is reduced. Therefore, the side sound signal R input to the speaker 24b of the handset 24 becomes small, so that the echo (echo) generated during the call can be suppressed and the call quality can be improved. In addition, when the difference between the volume of the side sound signal R and the specified value exceeds “6 dB”, the size of the audio signal transmitted from the microphone 24 a is limited to a certain amount (“6 dB”). Since it is not reduced, it can be suppressed that the size of the audio signal transmitted from the microphone 24a becomes too small and the other communication device cannot hear the sound.
[Selection] Figure 4

Description

  The present invention relates to a communication device.

2. Description of the Related Art Conventionally, there is known a communication device capable of making a call by transmitting / receiving an audio signal to / from a counterpart communication device via a telephone line. In this type of communication device, when an audio signal is transmitted from one communication device to the other communication device, if the path connecting each communication device and the telephone line is not matched with a predetermined impedance, the microphone of the handset A part of the audio signal is input to the speaker of the receiver without being input to the telephone line. When the sound signal is emitted from the speaker of the handset, echo (echo) occurs in the sound during the call. The following Patent Document 1 generates a small white noise (noise) signal, synthesizes a white noise (noise) signal with an audio signal received via a line, and emits sound from a speaker. A technique for reducing the response to a certain extent is described.
JP 2006-19983 A (0036 paragraph etc.)

  However, in the technique described in Patent Document 1 described above, a sound corresponding to white noise (noise) is always emitted from the speaker of the receiver, so that there is a problem that the voice quality during a call is deteriorated.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a communication device capable of improving the call quality by suppressing the echo during a call according to the side sound signal generated. And

  In order to achieve this object, the communication device according to claim 1 includes: a first output unit that converts a sound into a sound signal and outputs the sound; and a sound emitting unit that converts an input sound signal into a sound and emits the sound. The first output means and the sound emitting means are connected to a line, and a sound signal is transmitted / received to / from an external communication device via the line, and the line and the first output means Via the two-wire four-wire conversion means for matching the impedance between the paths to which the line is connected and the impedance between the paths to which the line and the sound emitting means are connected, and the two-wire four-wire conversion means, A second output means for outputting a survey signal whose magnitude of the sound signal is a first set value to the line; and when the survey signal is output by the second output means, the communication device and the line Sidetone caused by impedance mismatch between paths Detection means for detecting the magnitude of the signal, and signal control means for reducing the magnitude of the sound signal output from the first output means based on the magnitude of the side sound signal detected by the detection means; It has.

  The communication device according to claim 2 is the communication device according to claim 1, wherein the signal control means is configured such that a value indicating the magnitude of the side sound signal detected by the detection means is equal to or less than a second set value. First detection means for determining the side sound signal, and when the first determination means determines that a value indicating the magnitude of the side sound signal exceeds the second set value, the detection means detects the detection signal. A calculating means for calculating a difference between the value indicating the magnitude of the side sound signal and the second set value, and output from the first output means when the difference calculated by the calculating means is equal to or less than a predetermined value. The sound signal is reduced to a magnitude corresponding to the difference calculated by the calculating means.

  The communication device according to claim 3 is the communication device according to claim 2, wherein the signal control means outputs the first output means when the difference calculated by the calculation means exceeds the predetermined value. The sound signal to be played is reduced to a magnitude corresponding to the predetermined value.

  The communication device according to claim 4 is the communication device according to any one of claims 1 to 3, wherein a value indicating a magnitude of a sound signal output from the first output means is equal to or less than a third set value. The second determination means for determining the value of the sound signal output from the first output means by the second determination means is determined to exceed the third set value, Signal attenuating means for reducing the magnitude of the sound signal input to the sound emitting means.

  The communication device according to claim 5 is the communication device according to any one of claims 1 to 4, wherein the two-wire / four-wire conversion means is provided between the line, the first output means, and the sound emitting means. A plurality of impedance circuits connected to each other and having impedance characteristics; connection means for connecting one or more impedance circuits between the line and the first output means and the sound emission means; and the second output means A connection control means for connecting, by the connection means, an impedance circuit having the smallest value indicating the magnitude of the side sound signal detected by the detection means when the survey signal is output by .

  The communication apparatus according to claim 6 is the communication apparatus according to any one of claims 1 to 5, wherein the second output means has a sound signal having the first predetermined value as the investigation signal. A plurality of sound signals having different frequencies are output to the line, the detecting means detects the side sound signal for the plurality of different frequencies, and the signal control means is detected by the detecting means. Based on the magnitudes of a plurality of side sound signals having different frequencies, the magnitude of the sound signal output from the first output means is reduced.

  According to the communication apparatus of the first aspect, the investigation signal whose sound signal has the first set value is sent to the second output means via the two-wire / four-wire conversion means for matching the impedance between the paths. Is output by. When the inspection signal is output, the detection means detects the magnitude of the side sound signal caused by the impedance mismatch between the communication device and the line, and based on the detected side sound signal magnitude. Thus, the magnitude of the sound signal output from the first output means is reduced by the signal control means. If the magnitude of the sound signal output from the first output means to the line is reduced, the magnitude of the side sound signal generated is also reduced, so the side sound signal input to the sound emitting means is reduced. Can do. Therefore, since the size of the side sound signal input to the sound emitting means can be reduced based on the size of the side sound signal detected by the detecting means, the echo during the call caused by the side sound signal is suppressed. Thus, there is an effect that the call quality can be improved.

  According to the communication device of the second aspect, in addition to the effect produced by the communication device of the first aspect, a value indicating the magnitude of the side sound signal detected by the detection unit of the signal control unit is equal to or less than the second set value. When the first determination means determines whether there is a side sound signal and the value indicating the side sound signal exceeds the second set value, it indicates the side sound signal detected by the detection means. The difference between the value and the second set value is calculated by the calculation means. When the difference is less than or equal to the predetermined value, the sound signal output from the first output means is reduced to a magnitude corresponding to the difference calculated by the calculation means. Therefore, the sound signal output from the first output means can be reduced to a magnitude corresponding to the difference between the magnitude of the side sound signal and the second set value, and the sound signal output from the first output means is reduced. There is an effect that it is possible to prevent the lowering than necessary.

  According to the communication device according to claim 3, in addition to the effect produced by the communication device according to claim 2, the signal control means is configured such that the difference calculated by the calculation means exceeds the predetermined value. The sound signal output from the first output means is reduced to a magnitude corresponding to a predetermined value. Therefore, even if the difference calculated by the calculating means exceeds a predetermined value, the sound signal output from the first output means is reduced only to a value corresponding to the predetermined value, and is transmitted to an external communication device. There is an effect that it is possible to suppress that the sound signal is too low and it becomes difficult to receive the sound signal in the external communication device.

  According to the communication device of the fourth aspect, in addition to the effect produced by the communication device according to any one of the first to third aspects, the value indicating the magnitude of the sound signal output from the first output means is set to the third setting. When it is determined by the second determination means whether the value is equal to or less than the value, and it is determined that the value indicating the magnitude of the sound signal output from the first output means exceeds the third set value, The magnitude of the input sound signal is reduced by the signal attenuation means. Since the side sound signal is mainly a part of the sound signal output from the first output means, it occurs when the sound signal is output from the first output means. When the magnitude of the sound signal from the first output means exceeds the third set value, the magnitude of the sound signal input to the sound emitting means can be reduced, so that the echo during the call is further suppressed. As a result, the call quality can be further improved.

  According to the communication device of the fifth aspect, in addition to the effect produced by the communication device according to any one of the first to fourth aspects, when the investigation signal is output by the second output means, the connection control means An impedance circuit having the smallest value indicating the magnitude of the side sound signal detected by the detecting means is connected between the first output means and the sound emitting means by the connecting means. Can be reduced. Therefore, the side sound signal generated can be reduced most, so that the size of the side sound signal input to the sound emitting means can be reduced, and the call quality can be improved by suppressing the echo. There is.

  According to the communication device of the sixth aspect, in addition to the effect produced by the communication device according to any one of the first to fifth aspects, the sound signal has a first predetermined value and a plurality of sound signals having different frequencies. Is output to the line by the second output means, and the magnitude of the side sound signal generated is detected by the detection means for a plurality of different frequencies. The magnitude of the sound signal output from the first output means is reduced by the signal control means based on the magnitudes of a plurality of side sound signals having different frequencies detected by the detection means. Therefore, there is an effect that the magnitude of the side sound signal generated can be reduced according to the frequency characteristics of the line. For example, since the frequency characteristics of the line change depending on the line length of the line, the characteristics of the material, etc., there is an effect that the echo during the call can be suppressed according to such a change.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electrical configuration of a multifunction peripheral device (hereinafter referred to as “MFP (Multi Function Peripheral)”) 1 having a communication device according to an embodiment of the present invention. The MFP 1 is configured to be able to talk to an external communication device (not shown) connected via the telephone line network 100.

  When the MFP 1 according to the present embodiment makes a call with an external communication device (not shown) via the telephone line network 100, the impedance of the MFP 1 and the telephone line L to which the MFP 1 is connected is reduced. It suppresses the reverberation (echo) of voice caused by mismatch.

  Next, the electrical configuration of the MFP 1 will be described. The MFP 1 mainly includes a CPU 11, a ROM 12, a RAM 13, a flash memory 14, an operation button 15, an LCD 16, a scanner 21, a printer 22, a modem 23, a handset 24, a two-wire / four-wire conversion circuit 25, and an NCU 26.

  The CPU 11, ROM 12, RAM 13, and flash memory 14 are connected to each other via a bus line 28. The modem 23 and the handset 24 are connected to a 2-wire-4 wire conversion circuit 25, and the 2-wire-4 wire conversion circuit 25 is connected to the NCU 26. Further, the operation button 15, the LCD 16, the scanner 21, the printer 22, the modem 23, the handset 24, the 2-wire / four-wire conversion circuit 25, the NCU 26, and the bus line 28 are connected to each other via the input / output port 29. .

  The CPU 11 is connected to the control of each function of the MFP 1 and the input / output port 29 according to fixed values and programs stored in the ROM 12, RAM 13, and flash memory 14, or various signals transmitted / received via the NCU 26. It is the arithmetic unit which controls each part.

  The ROM 12 is a rewritable nonvolatile memory that stores a control program executed by the MFP 1. Each program for executing the sound quality adjustment process shown in the flowchart of FIG. 4 and the impedance matching process shown in the flowchart of FIG. 5 is stored in the ROM 12.

  The ROM 12 is provided with a switch setting table memory 12a. The switch setting table memory 12a is a memory in which a switch setting table used in an impedance matching process (see FIG. 5) described later is stored.

  Here, the switch setting table will be described with reference to FIG. FIG. 2 is a schematic diagram schematically showing the contents of the switch setting table. The switch setting table is a table for individually setting (switching) the states of five switches SW1 to SW5 provided in a 2-wire to 4-wire conversion circuit 25 (see FIG. 3) described later. Although details will be described later, by changing each of the switches SW1 to SW5, the output impedance of the MFP 1 is changed to 32 kinds of values to match the impedance of the MFP 1 and the telephone line L to which the MFP 1 is connected. Can do.

  The switch setting table includes a switch setting number n and setting flags of the switches SW1 to SW5 corresponding to the switch setting number n, and each switch setting number corresponds to the one switch setting number. A setting flag for the switch SW1, a setting flag for the switch SW2, a setting flag for the switch SW3, a setting flag for the switch SW4, and a setting flag for the switch SW5 are associated with each other. The switch setting table includes all (32 types) switch settings that can be set using the switches SW1 to SW5.

  The setting flag is a flag indicating whether the state of the switches SW1 to SW5 is set to ON (short circuit state) or OFF (open state), and this setting flag is OFF (for example, “0”). If there is, the state of the switches SW1 to SW5 corresponding to the setting flag is set to OFF, and both ends of the switches SW1 to SW5 are opened. On the other hand, if the setting flag is on (eg, “1”), the states of the switches SW1 to SW5 corresponding to the setting flag are set to on, and both ends of the switches SW1 to SW5 are short-circuited.

  For example, as shown in FIG. 2, the switch setting number “1” includes a setting flag “0” for the switch SW1, a setting flag “0” for the switch SW2, a setting flag “0” for the switch SW3, and a switch SW4. Is associated with the setting flag “0” of the switch SW5. For example, the switch setting number “2” includes a setting flag “1” of the switch SW1, a setting flag “0” of the switch SW2, a setting flag “0” of the switch SW3, and a setting flag “0” of the switch SW4. ”And the setting flag“ 0 ”of the switch SW5. Similarly, the setting flags of the switches SW1 to SW5 corresponding to the switch setting numbers are associated with the other switch setting numbers “3 to 32”, and thus the description thereof is omitted.

  In an impedance matching process (see FIG. 5) to be described later, when an instruction to switch each of the switches SW1 to SW5 to a setting corresponding to the switch setting number “1” is executed, the CPU 11 refers to the contents of the switch setting table. The setting flags of the switches SW1 to SW5 corresponding to the switch setting number “1” are read. Then, the CPU 11 inputs an instruction corresponding to the read setting flag to each of the switches SW1 to SW5, and the state of each switch is switched to a state corresponding to the read setting flag.

  Returning to FIG. 1, the description will be continued. The RAM 13 is a rewritable volatile memory, and is a memory for temporarily storing various data when each operation of the MFP 1 is executed. The RAM 13 is provided with a switch setting number memory 13a, a detected sound volume memory 13b, and a matching end flag memory 13c. Each of the memories 13a to 13c is a memory in which values are set by an impedance matching process (see FIG. 5) described later.

  Here, the telephone line network 100 and processing performed by the impedance matching processing (see FIG. 5) will be briefly described.

  When MFP 1 calls a communication device (not shown) on the other side and is connected to the communication device on the other side via telephone network 100, first, MFP 1 is installed via telephone line L. Connected to a telephone exchange (hereinafter referred to as “the telephone exchange on the MFP 1 side”) that performs line switching processing in a certain area. Next, the telephone switch on the MFP 1 side is a telephone switch (hereinafter referred to as “the other party's telephone switch”) that performs line switching processing in the area where the other party's communication device is installed via a dedicated line called a trunk communication line. Connected). Then, the other party's telephone exchange and the other party's communication device are connected via the telephone line L, and the calling side MFP 1 and the other party's communication device are connected so as to be able to talk. .

  Here, when voice is input to the microphone (hereinafter referred to as “microphone”) 24 a of the handset 24 in the MFP 1, the voice is converted into a voice signal and input to the telephone line L. Ordinarily, when the input voice signal passes through the telephone line L and reaches the telephone exchange on the MFP 1 side, it is transmitted to the telephone exchange on the other party side via the backbone communication line, and the telephone exchange on the other party side. To the other communication device. When the voice signal is received by the communication apparatus on the other side, the voice signal is converted into voice and emitted.

  However, if the impedances of the MFP 1 and the telephone line L connected to the MFP 1 are mismatched, a voice signal to be input to the telephone line L via the two-wire / four-wire conversion circuit 25 is partially A phenomenon occurs in which the 2-wire to 4-wire conversion circuit 25 wraps around to the speaker 24b of the handset 24. Hereinafter, the sound signal that circulates from the 2-wire to 4-wire conversion circuit 25 to the speaker 24b of the handset 24 is referred to as a side sound signal R. When the side tone signal R is generated, the sound emitted from the speaker 24b of the handset 24 is reverberated (echo), so that the user feels uncomfortable or uncomfortable with the call. That is, when the side sound signal R is generated, the call quality is deteriorated.

  In general, the telephone line L includes a wide variety of lines such as an analog line, an ISDN (Integrated Services Digital Network) line, an ADSL (Asymmetric Digital Subscriber Line) line, and an optical fiber line. ing. Therefore, the impedance of the telephone line L to which the MFP 1 is connected varies greatly depending on the type of the telephone line L used by the user and the line length of the telephone line L from the MFP 1 to the telephone exchange on the MFP 1 side. That is, impedance matching is difficult because the impedance of the telephone line L to which the MFP 1 is connected varies greatly depending on the user's usage environment.

  Therefore, impedance matching processing (see FIG. 5) is performed to switch the states of the five switches SW1 to SW5 provided in the 2-wire to 4-wire conversion circuit 25, so that MFP1 and the telephone to which MFP1 is connected are connected. The impedance with the line L is matched. Further, in order to detect whether the impedance is matched, the tone signal generation circuit 23a of the modem 23 generates a tone signal S (for example, an electric signal indicating a sound having a frequency of “1 kHz” and a volume of “−10 dBm”). And continue to input to the telephone line L. Then, the switch setting numbers “1” to “32” are sequentially switched from the two-wire / four-wire conversion circuit 25 to the handset 25 while switching the state of each switch SW1 to SW5 to the setting corresponding to the switch setting number. The magnitude of the side sound signal R is detected by the tone signal detection circuit 23b.

  Here, returning to FIG. 1, the description will be continued. The switch setting number memory 13a of the RAM 13 stores the side sound detected by the tone signal detection circuit 23b among the switch setting numbers used for the impedance matching setting after the execution of the impedance matching process (see FIG. 5). This is a memory in which the switch setting number with the smallest signal R is stored. When initialized, the switch setting number “1” is stored.

  The detected sound volume memory 13b stores the smallest value of the side sound signal R detected by the tone signal detection circuit 23b after the impedance matching process (see FIG. 5) is started. It is. When initialized, the volume of the tone signal S output from the tone signal generation circuit 23a of the modem 23 (for example, “−10 dBm”) is stored.

  The matching end flag memory 13c indicates whether or not the impedance between the MFP 1 and the telephone line L to which the MFP 1 is connected can be matched when the impedance matching process (see FIG. 5) is executed. Is a memory in which is stored.

  Specifically, in the impedance matching process (see FIG. 5), when the magnitude of the side sound signal R detected by the tone signal detection circuit 23b is equal to or less than a specified value (for example, “−30 dBm”), When the alignment end flag is set to ON (for example, “1”) and attempts are made to set all (32) switch setting numbers, but the side sound signal R has exceeded the predetermined value, it is turned OFF. (For example, “0”). When initialized, it is set to off (for example, “0”).

  The flash memory 14 is a rewritable nonvolatile memory, and the data stored in the flash memory 14 is retained even after the MFP 1 is turned off. The flash memory 14 is provided with a transmission volume level memory 14a and a reception volume level memory 14b.

  The transmission volume level memory 14a is a memory in which the transmission volume level of the microphone 24a of the handset 24 is stored. The transmission volume level indicates the magnitude of the audio signal output from the microphone 24a when the audio is input to the microphone 24a, and is indicated by a value from “1” to “7”, for example. The smaller the value, the smaller the audio signal output from the microphone 24a, and the larger the value, the larger the audio signal output. In the initial state, “4” is set.

  The received sound volume level memory 14b is a memory in which the received sound volume level of the speaker 24b of the handset 24 is stored. The received sound volume level indicates the volume of sound emitted from the speaker 24b when an audio signal is input to the speaker 24b, and is represented by a value from “1” to “7”, for example. The smaller the value is, the smaller the sound emitted from the speaker 24b is. The larger the value is, the larger the sound is emitted. In the initial state, “4” is set.

  The operation buttons 15 are provided with numeric buttons for inputting telephone numbers, buttons for setting functions such as a scanner function and a print function, and input buttons for instructing various operations. Yes. The LCD 16 is a display device for displaying menus, operation states, and the like according to the operation of the operation buttons 15. When the user operates the operation button 15, information corresponding to the operation is displayed on the LCD 16.

  The scanner 21 reads an image from a document set at a predetermined reading position (not shown) and generates image data that can be displayed on the LCD 16 or printed by the printer 22. The image data read by the scanner 21 is stored in a predetermined storage area in the RAM 13.

  The printer 22 is composed of an ink jet printer that prints an image on a recording sheet set at a predetermined paper feed position (not shown). The printer 22 includes a print head that uses four colors of C (cyan), M (magenta), Y (yellow), and K (black), a paper feeding device, and a recovery device, and performs color printing. The print head is provided with a plurality of nozzles (ink ejection ports), and the recording paper is fed by the paper feeding device while the ink is ejected from the nozzles, and the image is printed on the recording paper.

  The modem 23 modulates the image data to be transmitted by the facsimile function into a voice signal that can be transmitted to the telephone network 100 and transmits it through the NCU 26, or receives the voice signal input from the telephone network 100 through the NCU 26. It is received and demodulated into image data so that it can be displayed on the LCD 16 or recorded on recording paper by the printer 21.

  The modem 23 is provided with a tone signal generation circuit 23a and a tone signal detection circuit 23b. The tone signal generation circuit 23a is a circuit for generating a tone signal S (for example, an electric signal indicating a sound having a frequency of “1 kHz” and a volume of “−10 dBm”). The tone signal S generated by the tone signal generating circuit 23a is input to the telephone line L via the 2-wire-4 wire converting circuit 25 and the NCU 26.

  The tone signal detection circuit 23b has a side sound signal R that wraps around the speaker 24b of the handset 24 from the two-wire / four-wire conversion circuit 25 due to impedance mismatch between the MFP 1 and the telephone line L to which the MFP 1 is connected. Is a circuit for detecting

  The handset 24 is a device for making a call with a communication device (not shown) on the other side connected via the telephone line network 100, and includes a microphone 24a, a speaker 24b, and an echo cancellation circuit 24c. And have. The microphone 24a and the speaker 24b are connected to the 2-wire-4 conversion circuit 25 via an echo cancellation circuit 24c.

  The microphone 24a converts the input sound into an audio signal (electric signal) and outputs it. When the MFP 1 is connected to a communication device (not shown) on the other side via the telephone line network 100 so that a call can be made, the user can make a call with the communication device on the other side using the handset 24. it can.

  The sound emitted from the user is first input to the microphone 24a and converted into a sound signal. The converted audio signal is amplified to a magnitude corresponding to the transmission volume level stored in the transmission volume level memory 14 a of the flash memory 14, and then telephoned via the two-wire / four-wire conversion circuit 25 and the NCU 26. The data is input to the line network 100 and transmitted to the communication apparatus on the other side.

  The speaker 24b converts the input audio signal into sound and emits the sound, and the audio signal transmitted from the communication device (not shown) on the other side reaches the MFP 1 via the telephone line network 100. Then, the signal is input to the speaker 24b via the NCU 26 and the two-wire / four-wire conversion circuit 25 via the echo cancellation circuit 24c. Then, the audio signal input to the speaker 24b is amplified to a magnitude corresponding to the received sound volume level stored in the received sound volume level memory 14b of the flash memory 14, and then converted into sound and emitted.

  The echo cancellation circuit 24c is a circuit for reducing echo when echo (echo) occurs during a call. Specifically, based on the audio signal output from the microphone 24a, a signal (hereinafter referred to as “echo suppression signal”) in which the phase is inverted with respect to the audio signal output from the microphone 24a is generated. Since a part of the sound signal output from the microphone 24a is the side sound signal R, the echo suppression signal is a sound signal having a phase opposite to that of the side sound signal R.

  Then, the generated echo suppression signal and the audio signal received via the telephone line 100 are mixed in accordance with the delay time at which echo occurs. Since the side signal R is superimposed on the voice signal received via the telephone line 100, the generated echo suppression signal and the voice signal received via the telephone line 100 are mixed to receive the voice signal. The size of the side sound signal R overlapping the sound signal thus made can be reduced. Then, the mixed audio signal is input to the speaker 24b instead of the audio signal received via the telephone line 100. That is, since the speaker 24b emits a sound having a small side sound signal R, the echo is reduced.

  Further, the echo cancellation circuit 24c can vary the signal attenuation amount of the sound signal received via the line in several steps (for example, “large, medium, small”, etc.) in accordance with an instruction from the CPU 11. it can.

  The two-wire / four-wire conversion circuit 25 is a circuit for matching the impedance between the MFP 1 and the telephone line L to which the MFP 1 is connected. The NCU 26 is connected to the telephone line network 100 and controls the transmission of a dial signal to the telephone line network 100 and the response of a calling signal from the telephone line network 100.

  Here, the two-wire / four-wire conversion circuit 25 will be described with reference to FIG. FIG. 3 is a circuit diagram showing an example of the circuit configuration of the 2-wire / four-wire conversion circuit 25. Originally, the two-wire / four-wire conversion circuit 25 and the telephone line L are connected via the NCU 26, but the description of the NCU 26 is omitted here for the sake of simplicity. That is, the description will be made on the assumption that the 2-wire-4 wire conversion circuit 25 and the telephone exchange are connected only by the telephone line L.

  The two-wire / four-wire conversion circuit 25 is a circuit for matching the impedance between the MFP 1 and the telephone line L to which the MFP 1 is connected. The transformer circuit 41, the reception amplifier circuit 42, the transmission amplifier circuit 43, A switching circuit 44 and an impedance matching circuit 45 are included.

  The transformer circuit 41 is a circuit for electrically insulating the telephone line L and the MFP 1 and includes a line transformer LT and a coupling capacitor C1 for cutting a direct current component of the signal.

  One end of the primary side of the line transformer LT is connected to one of the two telephone lines L, and the other end of the line transformer LT is connected to the other end of the telephone line L. . One end of the coupling capacitor C1 is connected to one end on the secondary side of the line transformer LT, and the other end on the secondary side of the line transformer LT is connected to the ground GND. The other end of the coupling capacitor C1 is connected to one end of a switch SW1 of an impedance matching circuit 45 (described later), one end of a resistor R7, and one end of a resistor R1 of a reception amplifier circuit 45 (described later).

  The reception amplifier circuit 42 has a function of a low-pass filter that amplifies an audio signal transmitted from the telephone line L to a predetermined level and allows a signal of a predetermined frequency band or less to pass.

  The reception amplifier circuit 42 includes an operational amplifier OP1, resistors R1, R2, and R3, and a capacitor C2. One end of the resistor R1 is connected to the other end of the coupling capacitor C1 of the transformer circuit 41 (described above), one end of the switch SW1 of the impedance matching circuit 45 (described later), and one end of the resistor R7.

  The other end of the resistor R1, one end of the resistor R3, and one end of the capacitor C2 are connected to the negative input terminal of the operational amplifier OP1, and the other end of the capacitor C2 is connected to the other end of the resistor R3. An output terminal of OP1 is connected to one end of a switch SW7 of a switching circuit 44 (described later).

  Further, one end of a resistor R2 is connected to the positive input terminal of the operational amplifier OP1, and one end of a resistor R9 of an impedance matching circuit 45 (described later), one end of a resistor R10, and an impedance block Z2 are connected to the other end of the resistor R2. , One end of the impedance block Z3, one end of the switch SW4, and one end of the switch SW5 are connected to each other.

  The transmission amplifier circuit 43 amplifies the audio signal output from the tone signal generation circuit 23a of the modem 23 or the microphone 24a of the handset 24 to a predetermined level and passes a signal of a predetermined frequency band or lower. It has the function of.

  The transmission amplifier circuit 43 includes an operational amplifier OP2, a coupling capacitor C5 for cutting a DC component of the signal, resistors R4, R5, and R6, and capacitors C3 and C4. One end of the resistor R5, one end of the resistor R4, and one end of the capacitor C4 are connected to the negative input terminal of the operational amplifier OP2, and the other end of the resistor R5 is connected to the switch SW6 of the switching circuit 44 (described later). One end is connected.

  The other end of the resistor R4 is connected to the other end of the capacitor C4, one end of the coupling capacitor C5, and the output terminal of the operational amplifier OP2. The other end of the coupling capacitor C5 is impedance matched (described later). One end of the impedance block Z1 of the circuit 45, the other end of the resistor R7, and one end of the resistor R8 are connected to each other.

  One end of the capacitor C3 and one end of the resistor R6 are connected to the positive input terminal of the operational amplifier OP2, respectively, the other end of the capacitor C3 is connected to the ground GND, and the voltage “+ 5VDC” is connected to the other end of the resistor R6. Is applied.

  The switching circuit 44 is a circuit for switching whether the modem 23 is connected to the telephone line L or whether the handset 24 is connected to the telephone line L, and includes a switch SW6 and a switch SW7. These switches SW6 and SW7 are provided with one connection terminal on one end side and two connection terminals (connection terminal A and connection terminal B) on the other end side. The connection terminal is connected to one of the other connection terminals (connection terminal A, connection terminal B). For example, while a high signal is input from the CPU 11, one end of each of the switches SW6 and SW7 is connected to the connection terminal A on the other end side, and when a low signal is input, each of the switches SW6 and SW7 is connected. One end and the connection terminal B on the other end side are connected.

  More specifically, in this embodiment, the modem 23 is connected to the connection terminal A, and the handset 24 is connected to the connection terminal B. That is, the other end of the resistor R5 of the transmission amplifier circuit 43 (described above) is connected to the connection terminal on one end side of the switch SW6, and the tone signal generation of the modem 23 is connected to the connection terminal A on the other end side of the switch SW6. The output terminal of the circuit 23a is connected, and the output terminal of the microphone 24a of the handset 24 is connected to the connection terminal B on the other end side of the switch SW6.

  Further, the output terminal of the operational amplifier OP1 of the reception amplifier circuit 42 (described above), the other end of the resistor R3, and the other end of the capacitor C2 are connected to the connection terminal on one end side of the switch SW7. The input terminal of the tone signal detection circuit 23b of the modem 23 is connected to the connection terminal A on the other end side of the switch SW7, and the () echo cancellation circuit of the handset 24 is connected to the connection terminal B on the other end side of the switch SW7. A speaker 24b is connected (via 24c).

  The impedance matching circuit 45 is a circuit for matching the impedance between the MFP 1 and the telephone line L to which the MFP 1 is connected. The impedance matching circuit 45 includes impedance blocks Z1, Z2, Z3, Z4, Z5 and switches SW1, SW2, SW3, SW4. , SW5 and resistors R7, R8, R9, R10.

  The impedance blocks Z1 to Z5 are circuit blocks configured by connecting a plurality of circuit elements among resistors, coils, and capacitors, which are circuit elements, in parallel, series, or a combination of parallel and series. When both ends of Z1 to Z5 are measured, each has a predetermined impedance characteristic. The impedances of the impedance blocks Z1 to Z5 may be different from each other, all may be the same, or some of them may be the same.

  The switches SW1 to SW5 connect circuit elements connected to both ends in accordance with an instruction from the CPU 11 (hereinafter referred to as a switch being turned on) or disconnect the circuit elements from each other (hereinafter referred to as switch being turned off). It is said that). For example, the switches SW1 to SW5 are turned on while the high signal is input from the CPU 11, both ends of the switches SW1 to SW5 are connected (short-circuited), and the switches SW1 to SW1 are input while the low signal is input. SW5 is turned off and both ends of the switches SW1 to SW5 are opened.

  One end of the switch SW1 is connected to the other end of the coupling capacitor C1 of the transformer circuit 41 (described above), one end of the resistor R7, and one end of the resistor R1 of the reception amplifier circuit 42 (described above). .

  The other end of the impedance block Z1 is connected to the other end of the switch SW1, and one end of the impedance block Z1 is connected to the other end of the resistor R7, one end of the resistor R8, and the reception amplifier circuit 42 (described above). The other end of the capacitor C5 is connected.

  One end of the switch SW2, one end of the switch SW3, and the other end of the resistor R9 are connected to the other end of the resistor R8, and the other end of the impedance block Z2 is connected to the other end of the switch SW2. The other end of the impedance block Z3 is connected to the other end.

  One end of the impedance block Z2 includes one end of the impedance block Z3, one end of the resistor R9, one end of the resistor R10, one end of the switch SW4, one end of the switch SW5, and the resistor R2 of the reception amplifier circuit 42 (described above). The other end of each is connected.

  One end of the impedance block Z4 is connected to the other end of the switch SW4, and one end of the impedance block Z5 is connected to the other end of the switch SW5. The other end of the impedance block Z4 and the other end of the resistor R10 are connected to the other end of the impedance block Z4, and a reference voltage REF is applied.

  According to the two-wire / four-wire conversion circuit 25 described above, either the modem 23 or the handset 24 can be selectively connected to the telephone line L by switching the switches SW6 and SW7.

  For example, when the switch SW1 is turned on, the impedance block Z1 is connected in parallel to the resistor R7, so that the impedance of the path between the reception amplifier circuit 42 and the transmission amplifier circuit 43 and the transformer 41 changes. When the switch SW2 is turned on, the impedance block Z2 is connected in parallel to the resistor R9, so that the impedance of the path between the reception amplifier circuit 42 and the transmission amplifier circuit 43 and the transformer 41 changes. Similarly for the other switches SW3 to SW5, when the switch is turned on, the impedance of the path between the reception amplifier circuit 42 and the transmission amplifier circuit 43 and the transformer 41 changes.

  That is, by turning on and off the switches SW1 to SW5, the impedance of the path between the reception amplifier circuit 42 and the transmission amplifier circuit 43 and the transformer 41 can be changed. The impedance of the telephone line L to which the MFP 1 is connected varies greatly depending on the line length of the telephone line L from the MFP 1 to the telephone switch on the MFP 1 side. Even in such a case, the impedances of the MFP 1 and the telephone line L to which the MFP 1 is connected can be matched.

  Next, the sound quality adjustment process executed by the CPU 11 of the MFP 1 will be described with reference to FIG. FIG. 4 is a flowchart showing the sound quality adjustment processing of the MFP 1. This sound quality adjustment process is a process for reducing echo (echo) generated during a call, and is a process executed when the main power supply of the MFP 1 is turned on. In this sound quality adjustment process, first, the telephone line L with the MFP 1 side telephone exchange is closed (S1), and the impedance matching process is executed (S2).

  Here, the impedance matching process (S2) executed by the CPU 11 of the MFP 1 will be described with reference to FIG. FIG. 5 is a flowchart showing the impedance matching process (S2) of the MFP1. The impedance matching process (S2) is a process for matching the impedance between the MFP 1 and the telephone line L to which the MFP 1 is connected.

  In this impedance matching process (S2), first, the switch setting number memory 13a, the detected sound volume memory 13b, and the matching end flag memory 13c of the RAM 13 are initialized (S11). When each is initialized, the switch setting number memory 13a stores the switch setting number “1”, and the detection volume memory 13b stores the volume of the tone signal S (for example, “−10 dBm”). The matching end flag in the matching end flag memory 13c is set to off.

  Next, the tone signal generation circuit 23a of the modem 23 generates a tone signal S (for example, an electrical signal indicating a sound having a frequency of “1 kHz” and a volume of “−10 dBm”) and inputs the generated tone signal S to the telephone line L (S12). ). Here, the switches SW6 and SW7 of the 2-wire-4wire conversion circuit 25 are switched and the modem 23 is connected to the telephone line L.

  Then, the value of the variable n is initialized to “0” (S13), and “1” is added to the variable n (S14). Next, referring to the switch setting table in the switch setting table memory 12a of the ROM 12, the setting (setting flag) of each switch SW1 to SW5 corresponding to the value of the variable n is acquired (S15). And based on the acquired setting (setting flag) of each switch SW1-SW5, the setting of each switch SW1-SW5 is changed (S16).

  Next, the tone signal detection circuit 23b of the modem 23 detects the side sound signal R (that is, a part of the tone signal S that wraps around the reception amplifier circuit 42), and acquires the volume of the side sound signal R (S17). ). It is determined whether the volume of the acquired sidetone signal R is equal to or less than a specified value (for example, “−30 dBm”) (S18), and when the volume of the acquired sidetone signal R is equal to or less than the specified value (S18). : Yes), the matching end flag stored in the matching end flag memory 13c of the RAM 13 is set to ON (S26), and this impedance matching process is ended.

  In the process of S18, when the volume of the acquired sidetone signal R exceeds a specified value (for example, “−30 dBm”) (S18: No), the volume of the acquired sidetone signal R is detected by the RAM 13. It is determined whether the volume is lower than the volume stored in the volume memory 13b (S19).

  In the process of S19, if the volume of the acquired sidetone signal R is smaller than the volume stored in the detected volume memory 13b (S19: Yes), the acquired volume of the sidetone signal R is stored in the detected volume memory 13b. Store the value of the variable n in the switch setting number memory 13a of the RAM 13 (S20). In the process of S19, when the volume of the acquired sidetone signal R is equal to or higher than the volume stored in the detected volume memory 13b (S19: No), the process of S20 is skipped and the process proceeds to S21. .

  Next, it is determined whether or not the value of the variable n is “32” (S21). If the value of the variable n has not reached “32” (S21: No), the process returns to S14, and the above-described S14 Each process of ~ S21 is repeated. On the other hand, when the value of the variable n is “32” (S21: Yes), the states of the switches SW1 to SW5 are set to all possible states (32 states). This means that the volume of R could not be reduced below a specified value (for example, “−30 dBm”).

  In that case, the generation of the tone signal S that is continuously generated by the tone signal generation circuit 23a of the modem 23 is first stopped (S22). Next, referring to the switch setting table of the switch setting table memory 12a of the ROM 12, the setting (setting flag) of each switch SW1 to SW5 corresponding to the switch setting number stored in the switch setting number memory 13a of the RAM 13 is acquired. (S23).

  Then, based on the acquired setting (setting flag) of each switch SW1 to SW5, the setting of each switch SW1 to SW5 is changed (S24), and the matching end flag stored in the matching end flag memory 13c of the RAM 13 is turned off. (S25), and this impedance matching process is terminated.

  By the impedance matching process of the flowchart of FIG. 5 described above, it is possible to appropriately match the impedance between the MFP 1 and the telephone line L to which the MFP 1 is connected. Specifically, the impedance of the MFP 1 and the telephone line L to which the MFP 1 is connected can be matched so that the volume of the side sound signal R is a specified value (for example, “−30 dBm”) or less. For example, if the specified value is set to a volume (eg, “−30 dBm”) of the side sound signal R having such a magnitude that the user does not feel uncomfortable or uncomfortable even when echo (echo) occurs during a call, Since the user can comfortably make a call without feeling uncomfortable or uncomfortable during the call, the call quality can be maintained at a certain level or higher. Even if the states of the switches SW1 to SW5 are not set to all the states that can be set (32 states), the impedance matching process is terminated when the value falls below a specified value. The execution time of the adjustment process can be shortened.

  In addition, even when the states of the switches SW1 to SW5 are set to all possible states (32 states), the volume of the side sound signal R does not fall below a specified value (for example, “−30 dBm”). In this case, the states of the switches SW1 to SW5 can be set so that the volume of the side sound signal R is minimized. That is, the impedance between the MFP 1 and the telephone line L to which the MFP 1 is connected can be appropriately matched within a possible range. Therefore, even when the volume of the side sound signal R does not become the specified value or less, the generation of the side sound signal R can be reduced most, so that the side sound signal R input to the speaker 24b of the handset 24 is reduced most. Thus, the echo (echo) can be most suppressed. Therefore, it is possible to improve the call quality by suppressing the echo generated during the call.

  Now, the description returns to the flowchart of FIG. When the processing of S2 is completed, next, the telephone line L closed with the telephone exchange is released (S3). Then, it is determined whether the alignment end flag stored in the alignment end flag memory 13c of the RAM 13 is on (S4). If the alignment end flag is on (S4: Yes), the MFP 1 and the MFP 1 are connected. Impedance matching with the telephone line L to be performed, and the volume of the side tone signal R is equal to or less than a specified value (eg, “−30 dBm”). The adjustment process ends.

  In the process of S4, when the matching end flag is off (S4: No), the volume of the side sound signal R exceeds a specified value (for example, “−30 dBm”) and echoes (echo) during a call. Therefore, processing to suppress the echo is performed.

  First, it is determined whether or not the difference between the sound volume stored in the detected sound volume memory 13b of the RAM 13 and a specified value (for example, “−30 dBm”) is “6 dB” or less (S5), and the detected sound volume memory 13b. When the difference between the stored sound volume and the specified value is “6 dB” or less (S5: Yes), the transmitted sound volume level of the transmitted sound volume level memory 14a of the flash memory 14 is set to the difference from the specified value. A smaller value is set (S6), and this sound quality adjustment process is terminated.

  For example, when the volume of the detected volume memory 13b is “−28 dBm” and a specified value (“−30 dBm”), the magnitude of the audio signal output from the microphone 24a is reduced by the difference from the specified value. I will let you. For example, when the transmission volume level of the transmission volume level memory 14a of the flash memory 14 is decreased by “1”, the difference from the specified value is reduced when the size of the audio signal output from the microphone 24a decreases by “1 dB”. Is “2 dB”, the transmission level of the transmission volume level memory 14a is lowered by “2”.

  In the process of S5, when the difference between the volume stored in the detected volume memory 13b of the RAM 13 and the specified value exceeds “6 dB” (S5: No), the transmission volume level memory 14a of the flash memory 14 Is set smaller by “6 dB” (S7). Here, instead of lowering the transmission volume level by the difference from the specified value, reducing the transmission volume level by “6 dB” is because the size of the audio signal transmitted from the microphone 24a becomes too small, and the other party's communication This is to prevent the device from hearing sound. Next, the signal attenuation amount of the echo cancellation circuit 24c of the handset 24 is set to "large" (S8), that is, the echo cancellation effect is set to the maximum, and this sound quality adjustment process is terminated.

  According to the sound quality adjustment process of the flowchart of FIG. 4 described above, the size of the sound signal transmitted from the microphone 24a is reduced according to the volume of the side sound signal R, and the size of the generated side sound signal R is reduced. Can do. Therefore, since the side sound signal R input to the speaker 24b of the handset 24 is small, it is possible to suppress echo (echo) that occurs during a call.

  When the difference between the volume of the side sound signal R and the specified value (“−30 dBm”) is “6 dB” or less, the size of the audio signal transmitted from the microphone 24a is decreased by the difference. Thus, it is possible to suppress echo (echo) that occurs during a call. Therefore, it is possible to suppress the size of the audio signal transmitted from the microphone 24a from becoming excessively small.

  When the difference between the volume of the side sound signal R and the specified value (“−30 dBm”) exceeds “6 dB”, the size of the audio signal transmitted from the microphone 24 a is set to “6 dB”. The echo cancellation effect by the echo cancellation circuit 24c can be maximized. Therefore, the echo (echo) generated during a call can be suppressed. Further, even when the difference between the volume of the side sound signal R and the specified value is large (exceeds “6 dB”), the magnitude of the audio signal transmitted from the microphone 24 a is limited to a certain amount (“6 dB”). Therefore, it is possible to prevent the sound signal transmitted from the microphone 24a from becoming too small and the other communication device from hearing the sound.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications and changes can be easily made without departing from the spirit of the present invention. Can be inferred. For example, the numerical values given in the above embodiments are merely examples, and other numerical values can naturally be adopted.

  For example, in the MFP 1 of the present embodiment, the magnitude of the side sound signal R generated in the two-wire / four-wire conversion circuit 25 is detected due to impedance mismatch between the MFP 1 and the telephone line L to which the MFP 1 is connected. However, after the tone signal S is input to the telephone line L, the magnitude of the tone signal S (hereinafter referred to as “reflected tone signal”) that returns from the telephone switch on the MFP 1 side through the telephone line L is detected. Also good. If the impedances of the telephone line L to which the MFP 1 is connected and the telephone exchange on the MFP 1 side are mismatched, a reflected tone signal is generated, returns to the MFP 1 through the telephone line L, and is emitted from the speaker 24b. Reverberation (echo) occurs. In such a case, if the impedance of the path between the MFP 1 and the telephone switch on the MFP 1 side is matched so that the magnitude of the reflected tone signal is minimized, the magnitude of the reflected tone signal returned to the MFP 1 Therefore, it is possible to suppress the echo (echo) and improve the call quality. Further, the impedance of each path may be matched based on the magnitudes of the reflected tone signal and the side sound signal R.

  In the present embodiment, as an example of the tone signal S, an electric signal indicating a sound having a frequency of “1 kHz” and a volume of “−10 dBm” is used, but the frequency within the audible band (“20 Hz to 20 kHz)” is used. In this embodiment, “1 kHz”, which is considered to be the easiest for humans to listen to, is used.

  In this embodiment, only one type of tone signal S is used. However, tone signals S having a plurality of frequencies (for example, “500 Hz”, “2 kHz”, etc.) are separately input to the telephone line L. Also good. Further, tone signals S having a plurality of frequencies may be simultaneously input to the telephone line L (with each frequency superimposed). If the side tone signal R or the reflected tone signal is detected for each frequency input to the telephone line L, the impedance of each path can be matched according to the frequency characteristics of the telephone line L. R and reflected tone signals can be reduced. Therefore, the side sound signal R and the reflected tone signal input to the speaker 24b can be reduced, so that the echo (echo) generated during a call can be suppressed and the call quality can be improved.

  Further, in the impedance matching process (see FIG. 5) of the present embodiment, the process ends when the volume of the side sound signal R becomes equal to or less than a specified value, but all the states in which the states of the switches SW1 to SW5 can be set ( It is also possible to use a setting in which the volume of the side sound signal R is the smallest among the settings. By doing so, the impedance of the MFP 1 and the telephone line L to which the MFP 1 is connected can be optimally matched, so that the side sound signal R generated can be minimized. Therefore, the side sound signal R input to the speaker 24b of the handset 24 is the smallest, so that the echo (echo) that occurs during a call can be suppressed most.

  In the present embodiment, the state of each of the switches SW1 to SW5 in the two-wire / four-wire conversion circuit 25 is switched to vary the impedance of the path between the reception amplifier circuit 42, the transmission amplifier circuit 43, and the transformer 41. However, even when the impedance of the path between the reception amplifier circuit 42 and the transmission amplifier circuit 43 and the transformer 41 is a fixed value, if this embodiment is applied, echo (echo) generated during a call is suppressed. can do. That is, if the size of the audio signal transmitted from the microphone 24a is reduced according to the volume of the side sound signal R, the size of the generated side sound signal R can be reduced, so that the speaker of the handset 24 The side sound signal R input to 24b becomes small, and the reverberation (echo) generated during a call can be suppressed.

  In the present embodiment, the echo cancellation circuit 24c is provided. However, even when the echo cancellation circuit 24c is not provided, if this embodiment is applied, echo (echo) generated during a call can be suppressed. it can. That is, if the size of the audio signal transmitted from the microphone 24a is reduced according to the volume of the side sound signal R, the size of the generated side sound signal R can be reduced, so that the speaker of the handset 24 The side sound signal R input to 24b becomes small, and the reverberation (echo) generated during a call can be suppressed.

  In addition, the MFP 1 of the present embodiment is configured to detect the magnitude of the side sound signal R generated in the two-wire / four-wire conversion circuit 25, but in addition, the magnitude of the audio signal output from the microphone 24a is determined. If the size of the audio signal detected and output from the microphone 24a exceeds the reference value, the size of the audio signal input to the speaker 24b may be reduced. When the sound emitted from the user is input to the microphone 24a, a side sound signal R is generated, and the side sound signal is input to the speaker 24b to generate echo (echo). Therefore, if the sound signal input to the speaker 24b is reduced while the sound emitted from the user is input to the microphone 24a, the side sound signal R input to the speaker 24b can be reduced. Therefore, echo (echo) can be further suppressed.

1 is a block diagram showing an electrical configuration of an MFP having a communication apparatus according to an embodiment of the present invention. It is the schematic diagram which showed the content of the switch setting table typically. It is a circuit diagram which shows an example of a circuit structure of a 2 wire | wire 4 wire conversion circuit. 5 is a flowchart illustrating sound quality adjustment processing of the MFP. 6 is a flowchart illustrating an impedance matching process of the MFP.

Explanation of symbols

1 MFP (an example of a communication device)
23a Tone signal generation circuit (example of second output means)
23b Tone signal detection circuit (an example of detection means)
24c Echo cancellation circuit (an example of signal attenuation means)
24a Microphone (an example of first output means)
24b Speaker (an example of sound emission means)
25 2-wire-4 wire conversion circuit (an example of 2-wire 4-wire conversion means)
L Telephone line (an example of a line)
R Example of side sound signal S Tone signal (example of survey signal)
SW1 to SW5 switch (an example of connection means)
Z1-Z5 impedance block (an example of an impedance circuit)
S4 to S7 An example of signal control means S4, S18 An example of first determination means S5 An example of calculation means S8 An example of input control means S23, S24 An example of connection control means

Claims (6)

A first output means for converting sound into a sound signal and outputting; and a sound output means for converting the input sound signal into sound and releasing the sound, wherein the first output means and the sound output means are connected to the line. In a communication device that transmits and receives sound signals to and from an external communication device via the line,
2-wire 4-wire conversion means for matching impedance between paths connected to the line and the first output means, and impedance between paths connected to the line and the sound emitting means;
A second output means for outputting a survey signal whose magnitude of the sound signal is a first set value to the line via the 2-wire 4-wire conversion means;
Detecting means for detecting a magnitude of a side sound signal caused by impedance mismatch between paths of the communication device and the line when the investigation signal is output by the second output means;
And a signal control means for reducing the magnitude of the sound signal output from the first output means based on the magnitude of the side sound signal detected by the detecting means. . The signal control means includes
First determination means for determining whether a value indicating the magnitude of the side sound signal detected by the detection means is equal to or less than a second set value;
A value indicating the magnitude of the side sound signal detected by the detection means when the value indicating the magnitude of the side sound signal is determined by the first determination means to exceed the second set value. And calculating means for calculating a difference between the second setting value and the second setting value;
When the difference calculated by the calculating means is less than or equal to a predetermined value, the sound signal output from the first output means is reduced to a magnitude corresponding to the difference calculated by the calculating means. The communication device according to claim 1. The signal control means includes
The sound signal output from the first output means is reduced to a magnitude corresponding to the predetermined value when the difference calculated by the calculating means exceeds the predetermined value. 2. The communication device according to 2. Second determination means for determining whether a value indicating the magnitude of the sound signal output from the first output means is equal to or less than a third set value;
The sound signal input to the sound output means when the second determination means determines that the value indicating the magnitude of the sound signal output from the first output means exceeds the third set value 4. The communication device according to claim 1, further comprising: a signal attenuating unit that reduces the size of the communication device. 5. The two-wire / four-wire conversion means includes:
A plurality of impedance circuits connected between the line and the first output means and the sound emitting means, each having impedance characteristics;
Connecting means for connecting one or more impedance circuits between the line and the first output means and the sound emitting means;
Connection control means for connecting, by the connection means, an impedance circuit having the smallest value indicating the magnitude of the side sound signal detected by the detection means when the survey signal is output by the second output means. 5. The communication device according to claim 1, comprising: The second output means outputs, as the survey signal, a plurality of sound signals having a sound signal having a first predetermined value and different frequencies to the line.
The detecting means detects the side sound signal for the plurality of different frequencies;
The signal control means reduces the magnitude of the sound signal output from the first output means based on the magnitudes of a plurality of side sound signals having different frequencies detected by the detection means. The communication device according to any one of claims 1 to 5.

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