JP5189515B2 - Intercom system - Google Patents

Description

  The present invention relates to an intercom system, and more particularly to an intercom system that switches a call direction by a voice switch.

A conventional interphone system is widely used in a configuration in which an alternate call is controlled by a voice switch. The voice switch is configured to compare the voice level of the transmission sent from the room master unit and the reception level sent from the entrance cordless handset, and to transmit the voice with higher priority, and vice versa depending on the direction of the call. A loss is inserted into the direction audio signal to prevent the occurrence of echo and howling (for example, see Patent Document 1).
On the other hand, there is a technique for minimizing the occurrence of echoes by providing an echo canceller that digitally processes and eliminates the occurrence of echoes in addition to the voice switch (see, for example, Patent Document 2).

JP 2005-303729 A JP-A-7-162537

The above-described switching configuration using only the voice switch is necessary to insert a large loss of about 40 dB in the entire transmission / reception to prevent echo and howling, especially when hands-free calling is possible and the case has a large amount of acoustic feedback. However, when the amount of insertion loss is increased in this way, the switching characteristics of transmission / reception become dull, and there is a problem that the head of the talk is cut off. In this regard, the configuration in which the echo canceller is provided in addition to the voice switch can reduce the burden on the voice switch, and thus it is possible to suppress the occurrence of the head break.
However, since the echo canceller uses a digital signal processing circuit such as a DSP, the cost is high and it is not practical to use it for an interphone system.

  Therefore, the present invention has been made to solve this problem. Even when the amount of acoustic feedback is large, the voice switch can be used in a better direction without using an echo canceller comprising a digital signal processing circuit such as a DSP. It is an object of the present invention to provide an intercom system capable of switching between.

In order to solve the above-mentioned problems, the invention of claim 1 has an entrance cordless handset having a function of calling a resident and making a call, and a room base phone having a function of responding to a call from the entrance cordless handset. In an intercom system equipped with a voice switch that selectively passes either the transmitted voice transmitted from the room master to the entrance handset or vice versa, the voice and the communication unit of the room master Between the switch, a PDM converter that generates a bit stream by pulse density modulating the received voice signal output from the voice switch, and a shift register that holds an arbitrary number of samples of the bit stream output from the PDM converter The transfer function of the echo path generated by the received voice to derive the pseudo-acoustic feedback signal by acting on the bit stream of the shift register is composed of analog elements An analog transfer function calculation unit and an analog echo suppression unit that subtracts the pseudo-acoustic feedback signal from the transmitted voice signal, and the output of the analog echo suppression unit subtracted by the pseudo-acoustic feedback signal is used as the transmitted voice signal. It is input to a switch.
According to this configuration, the analog transfer function calculation unit derives a pseudo acoustic feedback signal that matches the feedback characteristics of the room master unit case, thereby forming a pseudo echo canceller circuit. By providing the input unit, the amount of wraparound of the received voice can be reduced. As a result, it is possible to reduce the amount of insertion loss inserted into the received voice signal when transmitting the transmitted voice signal in the voice switch, and to improve the switching speed of the voice switch and prevent the voice from being cut off due to switching. Is possible. In addition, the pseudo echo canceller circuit is formed with an analog circuit, so that it can be configured at low cost.

The invention of claim 2 has an entrance cordless handset having a function of calling and calling a resident, and an in-room master unit having a function of responding to a call from the entrance cordless handset. In an interphone system equipped with a voice switch that selectively passes either the transmitted voice transmitted to the machine or the received voice of the opposite, the voice switch is connected between the telephone unit and the voice switch. A PDM converter that generates a bit stream by modulating the pulse density of the transmitted voice signal to be output, a shift register that holds an arbitrary number of samples of the bit stream output from the PDM converter, and a bit stream of the shift register An analog transfer function calculation unit composed of analog elements for the transfer function of the echo path generated by the transmitted voice to derive the pseudo-acoustic feedback signal. An analog echo suppression unit that subtracts the pseudo acoustic feedback signal from the received voice signal, and the output of the analog echo suppression unit subtracted by the pseudo acoustic feedback signal is input to the voice switch as the received voice signal. To do.
According to this configuration, a pseudo-acoustic feedback signal derived according to the feedback characteristics of the entrance unit case can be derived by the analog transfer function calculation unit, so that a pseudo echo canceller circuit can be formed. By providing in the section, the amount of wraparound of the transmitted voice can be reduced. As a result, it is possible to reduce the amount of insertion loss that is inserted into the transmitted voice signal when the received voice signal is transmitted in the voice switch, and to improve the voice switch switching speed and prevent the voice from being cut off by switching. Is possible. In addition, the pseudo echo canceller circuit is formed with an analog circuit, so that it can be configured at low cost.

According to a third aspect of the present invention, in the configuration of the first or second aspect, the sampling frequency of the analog transfer function calculation unit is lower than the sampling frequency of the PDM conversion unit, and the analog transfer function calculation unit outputs the PDM conversion unit . An operation is performed based on a bit signal obtained by thinning a bit stream.
According to this configuration, the analog transfer function calculation unit is configured by thinning out the bit stream output from the PDM conversion unit. Therefore, the circuit configuration of the analog transfer function calculation unit can be simplified, and the circuit can be configured at low cost.

According to a fourth aspect of the present invention, in the configuration according to the third aspect, the sampling frequency of the analog transfer function calculation unit is an integral fraction of the sampling frequency of the PDM conversion unit and is 20 kHz or more. To do.
According to this configuration, the analog transfer function calculation unit can be configured simply while maintaining the function of echo simulation generation.

According to the present invention, a pseudo-acoustic feedback signal can be formed by deriving a pseudo-acoustic feedback signal in accordance with the feedback characteristics of an echo path to be suppressed by the analog transfer function calculation unit, and a voice to be transmitted to the voice switch can be formed. By providing the signal input unit, the amount of sound wraparound can be reduced. As a result, the insertion loss amount of the voice switch can be reduced, and the switching speed of the voice switch can be improved to prevent the voice from being cut off due to the switching.
Since the analog transfer function calculation unit is configured by thinning out the bit stream of the PDM conversion unit, the circuit configuration of the analog transfer function calculation unit can be simplified, and the circuit can be configured at low cost.

It is a circuit block diagram which shows an example of the intercom system which concerns on this invention. It is the schematic of the 2nd echo compression processing circuit of FIG.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 is a circuit block diagram showing an example of an intercom system according to the present invention. 1 is an entrance cordless handset having a function of calling a resident and talking, and 2 is a function responding to a call from the entrance cordless handset 1. It is a living room base unit provided, and both are connected by a transmission line L1.

  The entrance terminal 1 includes a camera 11 for imaging a visitor, a video processing circuit 12 for transmitting a video signal to the living room base unit 2 via a transmission line L1, a microphone 13 and a speaker 14 constituting a call unit 15. , A microphone amplifier 13a for amplifying the sound collected by the microphone 13, a speaker amplifier 14a for reporting sound from the speaker 14, and an echo compression processing circuit (first echo compression processing circuit) for suppressing the acoustic feedback amount of the front door 1 16, a call button 17 for performing a call operation, a slave unit communication processing circuit 18 for communicating with the room master unit 2, and the like.

  The living room master unit 2 includes a video processing circuit 21 that performs demodulation processing of a transmitted video signal, a monitor 22 that displays video captured by the camera 11, an operation unit 23 that performs various operations such as response operation and video display operation, A voice switch 24 that selectively passes either the transmitted voice transmitted from the living room master unit 2 to the entrance cordless handset 1 or vice versa, and an echo compression process for suppressing the acoustic feedback amount of the living room master unit 2 A circuit (second echo compression processing circuit) 25, a microphone 26 and a speaker 27 constituting the communication unit 28, a microphone amplifier 26 a that amplifies the sound collected by the microphone 26, a speaker amplifier 27 a for reporting sound from the speaker 27, and a room A master unit CPU 29 for controlling the master unit 2 as a whole, a master unit communication processing circuit 30 for communicating with the entrance slave unit 1 and the like are provided, and a hands-free call is possible.

  FIG. 2 shows an outline of the second echo compression processing circuit 25. Since the first echo compression processing circuit 16 has the same configuration, the second echo compression processing circuit 25 will be described as a representative. As shown in FIG. 2, the second echo compression processing circuit 25 includes a PDM conversion unit 35 that generates a bit stream by performing pulse density modulation on the received voice signal [1] output from the voice switch 24, and a PDM conversion unit. 35, a shift register 36 that stores a predetermined length of the bit stream generated in 35, and an analog transfer function calculation unit 37 that is configured by an analog circuit and generates a pseudo acoustic feedback signal by acting on the bit stream stored in the shift register 36. And an analog echo suppression unit 38 that subtracts an acoustic feedback signal composed of an analog circuit and approximated by the analog transfer function calculation unit 37 from the transmitted voice signal [4] and outputs a voice switch input signal [3]. I have.

The analog transfer function calculation unit 37 receives a signal obtained by thinning out the bit string of the shift register 36 at a predetermined interval. Each input unit is provided with a variable resistor Rv. By adjusting the variable resistor Rv, a transfer function of an echo path to be suppressed is constructed in a pseudo manner, and a pseudo acoustic feedback signal is generated.
Specifically, assuming that the sampling frequency of the PDM converter 35 is Fs1 and the sampling frequency of the analog transfer function calculator 37 is Fs2, Fs1 / Fs2 is thinned out from the 1-bit data stream, and the analog transfer function calculator 37 An acoustic feedback signal is derived. For example, when Fs1 = 1 MHz and Fs2 = 40 kHz, 25-bit thinning is performed and input to the analog transfer function calculation unit 37. If the number of samples held in the shift register 36 is 256 bits, the sample is input after being thinned to 10 bits. The number of sample bits held by the shift register 36 is arbitrary, and may be set in consideration of the sampling frequency Fs1 of the PDM converter 35 and the sampling frequency Fs2 of the analog transfer function calculator 37.

The intercom system configured as described above operates as follows. However, since the basic operation of responding while viewing the captured image of the camera 11 in the living room master unit 2 when a call is made from the entrance cordless handset unit 2 is the same as the conventional one, the description thereof is omitted. Here, the second echo compression processing circuit is omitted. A specific description will be given focusing on the operation of No. 25.
An analog voice signal (received voice signal) input from the microphone 13 of the entrance cordless handset 1 is transmitted to the room base phone 2 via the first echo compression processing circuit 16, the cordless handset communication processing circuit 18, and the transmission line L1. . The received voice signal transmitted to the base unit communication processing circuit 30 of the living room base unit 2 is sent to the second echo compression processing circuit 25 via the voice switch 24. In the second echo compression processing circuit 25, the analog received voice signal transmitted from the voice switch 24 is output to the speaker amplifier 27a without being processed (voice switch output signal [2]). Modulated to generate a pseudo echo signal (pseudo acoustic feedback signal).

  As described above, the analog transfer function calculation unit 37 performs signal thinning out from the bit stream output from the PDM conversion unit 35 and derives a pseudo acoustic feedback signal. The derived pseudo acoustic feedback signal is sent to the analog echo suppression unit 38 together with the analog acoustic input signal (speech voice signal [4]) input from the microphone 26 of the room master unit 2. The analog echo suppression unit 38 performs a process of subtracting the pseudo acoustic feedback signal from the transmitted voice signal, and transmits the subtracted transmitted voice signal (voice switch input signal [3]) to the subsequent voice switch 24.

  The sampling frequency Fs2 of the analog transfer function calculation unit 37 is preferably set to 1 / integer of the sampling frequency Fs1 of the PDM conversion unit 35 for easy sampling. Moreover, since generation | occurrence | production of a pseudo echo signal will become difficult if too low, it is preferable that it is higher than an audible frequency, specifically 20 kHz or more. Further, the variable resistance Rv provided in each signal input unit of the analog transfer function calculation unit 37 has a value depending on characteristics of the pseudo acoustic feedback signal generation target, for example, the case shape of the room base unit 2 and the arrangement of the microphone 26 and the speaker 27. Is determined.

In this way, a pseudo-acoustic feedback signal is derived by the analog transfer function calculation unit 37 in accordance with the feedback characteristics of the parent room case, so that a pseudo echo canceller circuit can be formed. By providing the input unit, the amount of wraparound of the received voice can be reduced. As a result, the amount of insertion loss inserted into the received voice signal when the transmitted voice signal is transmitted by the voice switch 24 can be reduced, and the switching speed of the voice switch 24 is improved to cut off the head of the voice due to switching. It becomes possible to prevent.
In addition, since the analog transfer function calculation unit 37 serving as a pseudo echo canceller circuit is formed by an analog circuit and the bit stream output from the PDM conversion unit 35 is thinned out, the circuit configuration of the analog transfer function calculation unit 37 is configured. It can be simplified and the circuit can be configured at low cost.
Further, by setting the sampling frequency of the transfer function of the echo path to be suppressed to 1 / integer of the sampling frequency of the PDM conversion unit 35 and 20 kHz or more, analog transfer function calculation is maintained while maintaining the function of echo generation. The part 37 can be configured simply.

As described above, the configuration in which the echo component is deleted from the transmitted voice signal to reduce the load on the voice switch 24 and the operation is smoothed has been described. However, the operation of the first echo compression processing circuit 16 provided in the entrance cordless handset 1 has been described. The same applies to the case where the operation of the voice switch 24 is made smooth with respect to the received voice, and this will be briefly described using the reference numerals of the respective components in FIG.
The PDM conversion unit 35 of the first echo compression processing circuit 16 generates a 1-bit data stream from the transmission voice signal transmitted from the room master unit 2. The analog transfer function calculation unit 37, which has determined the variable resistance Rv based on the shape of the entrance unit 1 based on this signal, derives the pseudo acoustic feedback signal, and the analog echo suppression unit 38 subtracts the pseudo acoustic feedback signal. A received voice signal is generated and sent to the voice switch 24 of the living room master unit 2.

  In this way, by deriving a pseudo acoustic feedback signal that matches the feedback characteristics of the entrance unit case by the analog transfer function calculation unit, a pseudo echo canceller circuit can be formed, and this circuit can be used as the voice input unit of the voice switch. By providing, it is possible to reduce the amount of circulated voice. As a result, it is possible to reduce the amount of insertion loss that is inserted into the transmitted voice signal when the received voice signal is transmitted in the voice switch, and to improve the voice switch switching speed and prevent the voice from being cut off by switching. Is possible. In addition, the pseudo echo canceller circuit is formed with an analog circuit, so that it can be configured at low cost.

In the above embodiment, the first echo compression processing circuit 16 is provided in the entrance cordless handset 1. However, the first echo compression processing circuit 16 may be provided in the room base phone 2, and the received voice path to the received voice input unit of the voice switch 24 may be provided. It may be provided on the way. In addition, although the echo compression processing circuits 16 and 25 are provided in both the transmission direction and the reception direction, it is effective to provide only one that is likely to generate an echo.

  1 .. Entrance cordless handset 2.. Living room master 16.. First echo compression processing circuit 24.. Voice switch 25. Second echo compression processing circuit 35. PDM conversion unit 36. Shift register 37... Analog transfer function calculation unit 38.. Analog echo suppression unit Rv.

Claims (4)

There is an entrance cordless handset having a function of calling a resident and making a call, and an in-home master device having a function of responding to a call from the entrance cordless handset, and is transmitted from the in-room master to the entrance cordless handset. In an intercom system equipped with a voice switch that selectively passes either the transmitted voice or the reverse received voice,
A PDM converter that generates a bit stream by performing pulse density modulation on the received voice signal output from the voice switch between the voice unit of the living room master unit and the voice switch;
A shift register that holds an arbitrary number of samples in the bitstream output by the PDM converter;
An analog transfer function operation unit configured by an analog element, which acts on the bit stream of the shift register to generate a transfer function of an echo path generated by the received voice in order to derive a pseudo acoustic feedback signal;
An analog echo suppression unit that subtracts the pseudo-acoustic feedback signal from the transmitted voice signal;
The interphone system, wherein an output of the analog echo suppression unit subtracted by the pseudo acoustic feedback signal is input to the voice switch as a transmission voice signal. There is an entrance cordless handset having a function of calling a resident and making a call, and an in-home master device having a function of responding to a call from the entrance cordless handset, and is transmitted from the in-room master to the entrance cordless handset. In an intercom system equipped with a voice switch that selectively passes either the transmitted voice or the reverse received voice,
A PDM converter that generates a bit stream by performing pulse density modulation on a transmitted voice signal output from the voice switch between the voice unit of the entrance unit and the voice switch;
A shift register that holds an arbitrary number of samples in the bitstream output by the PDM converter;
An analog transfer function operation unit configured by an analog element, which acts on the bit stream of the shift register to generate a transfer function of an echo path generated by the transmitted voice in order to derive a pseudo acoustic feedback signal;
An analog echo suppression unit that subtracts the pseudo-acoustic feedback signal from the received voice signal;
The intercom system, wherein an output of the analog echo suppression unit subtracted by the pseudo-acoustic feedback signal is input to the voice switch as a received voice signal. The sampling frequency of the analog transfer function calculation unit is lower than the sampling frequency of the PDM conversion unit, and the analog transfer function calculation unit performs calculation based on a bit signal obtained by thinning out the bit stream output from the PDM conversion unit. The intercom system according to claim 1 or 2, wherein 4. The intercom system according to claim 3, wherein a sampling frequency of the analog transfer function calculation unit is 1 / integer of a sampling frequency of the PDM conversion unit and 20 kHz or more.

Images