JPH047625B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an intercom call control system,
In particular, the present invention relates to this type of method for improving call quality in a system in which both loudspeaker and handset call states coexist.

[Technical background of the invention and its problems]

Conventionally, in an intercom communication device, terminals 1 and 1' are connected via an exchange 2, as shown in FIG. The terminals 1 and 1' have loudspeakers 3,
3', amplification microphones 4, 4', handset receivers 5, 5', and handset microphones 6, 6', and the exchange 2 is generally equipped with an audio switch circuit 7 and a hook-up detection circuit 8. It is true.

In this case, when the handset is turned up, a switch (not shown) switches the loudspeaker 3 or 3' to the handset receiver 5 or 5', and switches the loudspeaker microphone 4 or 4' to the handset microphone 6 or 6'. With,
This is done by adjusting the respective amplifier gains. These controls are performed within the terminals 1 and 1', and no particular control is performed in the exchange 2 (for example, the voice switch circuit 7).

However, with this control, there is a problem in that the speech loss and detection loss in the voice switch circuit 7 remain in the loudspeaker state, so that the deterioration in speech quality caused by the voice switch circuit cannot be significantly improved.

On the other hand, if you want to make simultaneous calls, terminal 1,
1' is detected by the hook-up detection circuit 8 of the exchange 2, and a simultaneous call state is established.

However, in this case, there is a problem that the speech level is limited due to the howling margin, and there is also a problem that the sidetone on the handset side is large due to acoustic feedback on the amplification side, making it difficult to communicate.

[Purpose of the invention]

The present invention has been devised in view of the above-mentioned conventional difficulties, and provides a public address intercom that improves call quality by controlling call loss during calls and detection loss due to volume feedback using a hook-up detection circuit and an auto gain control circuit of the handset. The aim is to provide a call control system.

[Summary of the invention]

In order to achieve such an object, the intercom call control system of the present invention connects multiple terminals capable of both loudspeaker calls and handset calls through multiple call paths, and controls calls between the terminals. In the intercom call control system, a hook-up detection circuit for detecting a hook-up of the handset in each terminal, a call loss circuit inserted in each call path to prevent howling, and the audio output in each call path are compared. and a voice output comparison circuit that determines the direction of the call, and a voice output comparison circuit that detects the amount of voice feedback when receiving a call and is connected to each of the communication paths in order to prevent the effect of the amount of voice feedback on the voice output comparison circuit. and a control means for controlling the call loss circuit and the detection loss circuit using a detection signal from the pickup detection circuit and an output signal from the audio output comparison circuit.

[Embodiments of the invention]

Preferred embodiments of the present invention will be described below with reference to the drawings.

A block circuit diagram of the intercom call control system of the present invention is shown in FIG. In FIG. 1, a terminal on the A side and a terminal on the B side are connected by communication paths l ₁ and l ₂ , and the communication paths l ₁ and l ₂ generally include FETs, transistors, electronic attenuator ICs, etc. Call loss circuits 10 and 11 are inserted, which are composed of elements whose gain changes depending on the DC potential. The call loss circuits 10 and 11 are connected to send signals from a call loss controller 12, which is a control means that is generally composed of an amplifier such as an operational amplifier that can control the DC level. The call loss controller 12 is connected to hook-up detection circuits 13 and 14, and automatic gain control (hereinafter referred to as "AGC"), which is generally composed of a rectifier circuit, a smoothing circuit, a comparator circuit, etc., and is connected to the call paths _l1 and _l2 , respectively.
) circuits 15, 16 and generally rectifier circuits,
It is connected to send a signal from an audio output comparison circuit 17 composed of a smoothing circuit and a comparator circuit. In addition, each of the communication paths l ₁ and l ₂ is generally
FET, transistor or electronic attenuator IC
Detection loss circuits 18 and 19, which are composed of elements whose gain changes depending on the DC potential, are connected, and these are connected to send signals to the audio output comparison circuit 17. Here, as will be described later, the detection loss is the loss that is connected to each communication path in order to detect the amount of voice feedback at the time of reception and prevent the influence of the amount of voice return to the audio output comparison circuit 17. means. Furthermore, the hook-up detection circuit 13 and the AGC circuit 1
6 and the audio output comparison circuit 17 are connected to a detection loss controller 2, which is a control means generally composed of an amplifier capable of controlling the DC level, such as an operational amplifier.
0 and is connected to the detection loss circuit 18 by this detection loss controller 20. Similarly, the pickup detection circuit 14, the AGC circuit 15, and the audio output comparison circuit 17 are connected to the detection loss controller 21.
is connected to the detection loss circuit 19.

Now, a case where a call is transmitted from side A to side B will be explained. First, when talking from the A side to the B side using amplification, the audio output on the communication path _l1 is passed through the detection loss circuit 18, and the audio output on the communication path _l2 is passed through the detection loss circuit 19, and the audio output is compared. circuit 1
7 is input. In this case, since the audio output on the communication path l ₁ is large, the audio output comparison circuit 17 reduces the loss (0 dB) of the communication loss circuit 10 of the communication path l ₁ and increases the loss of the communication loss circuit 11 of the communication path l ₂ . (-40dB) Call Loss Controller 1
Control 2. In this case, the sound from the loudspeaker is input to the loudspeaker microphone on the B side,
In order to prevent the audio output comparison circuit 17 from malfunctioning due to the amount of return, the loss of the detection loss circuit 18 of the communication path _l1 is reduced (0 dB), and the loss of the detection loss circuit 19 of the communication path _l2 is increased (- 20 dB).

Next, a case will be explained in which the B side picks up the handset. The up of the handset of the terminal on the B side is detected by the hookup detection circuit 14, and this detection signal causes the call loss controller 12 to reduce the loss of the call loss circuit 11 of the call path _l2 to be less than that during the loudspeaker call (- 40dB to -20dB)
(Figure 2). This is because the howling margin of the communication path increases as the handset picks up, so the system detects the pickup and controls the call loss controller 12 to reduce the call loss on the communication path _l2 . Further, in this case, the detection signal from the pickup detection circuit 14 causes the loss in the detection loss circuit 19 to be lower than that in the case of loudspeaking (from -20 dB to 0 dB) (FIG. 3). This is because as the handset increases, the amount of sound returned to the B side is reduced compared to when amplifying the sound.

Conversely, when the A side picks up the handset, the detection signal from the pickup detection circuit 13 causes the call loss controller 12 to reduce the loss in the call loss circuit 11 of the call path _l2 compared to the case of a loudspeaker call, but the detection signal The loss of the loss circuit 19 is set to be the same as that during loudspeaking.

Furthermore, when the handset is picked up on both sides A and B, the howling margin of the communication path increases even more than when one side is amplified, so the detection signals from the pickup detection circuits 13 and 14 cause the call loss controller 12 to adjust the communication path. The loss of the _second speech loss circuit 11 is further reduced (from -20 dB to 0 dB) than when one is used for amplification.

In addition, when the audio level is higher than necessary, that is, as shown in FIG. 4, the AGC circuits 15 and 16
To prevent the output of the call loss circuit ₁₀ from becoming too large when the voice level starts operating from a predetermined level (threshold point C), the detection loss circuit 19 and The call loss controller 12 and the detection loss controller 21 are controlled to reduce the loss of the call loss circuit 11. That is, the loss of the detection loss circuit 19 is reduced, and the loss of the call loss circuit 11 is also reduced.

The above shows the effect on transmission from the A side to the B side, but in the case of transmission from the B side to the A side, each circuit has the opposite effect to the above. It is something.

As a simple method for preventing side sounds caused by acoustic feedback, as shown in FIG.
This can also be improved by providing an AGC circuit 23 on the second line. This is effective because the amount of feedback from the speaker 24 is greater than that from the audio input.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the present invention, the call loss during a call and the detection loss due to volume feedback are controlled by the detection signal of the pickup circuit, so that the call state can be adjusted to the handset and the loudspeaker. Good call quality can be achieved regardless of the speaker. In other words, there are no restrictions on the call level, and the sidetone level can be determined appropriately. Also, you can talk without having to switch the audio switch, and if you make a call above the threshold of the AGC circuit, the voice quality will improve. , the switching of the audio switch also becomes better.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing the intercom call control method of the present invention, FIGS. 2 and 3 are graphs showing control of the call loss controller and the detection loss controller by the hook-up detection circuit,
Figure 4 is a graph showing the control of the call loss and detection loss controller by the AGC circuit, Figure 5 is an explanatory diagram showing a simple method of suppressing sidetone by acoustic feedback, and Figure 6 is a graph showing the control of the call loss and detection loss controller by the AGC circuit. FIG. 2 is a system diagram showing a phone call. l ₁ , l ₂ ... call path, 10, 11 ... call loss circuit, 12 ... call loss controller (control means),
13, 14...Hookup detection circuit, 15, 1
6...Auto gain control circuit (AGC circuit), 17...Audio output comparison circuit, 18, 19...
...Detection loss circuit, 20, 21...Detection loss controller (control means).

Claims (1)

[Scope of Claims] 1. An intercom call control method in which a plurality of terminals capable of both loudspeaker calls and handset calls are connected via a plurality of call paths, and calls between the respective terminals are controlled, comprising: a lift-up detection circuit for detecting a lift-up of the handset; a call loss circuit inserted in each of the communication paths to prevent howling; and an audio output comparison for determining the direction of communication by comparing the audio outputs in each of the communication paths. a detection loss circuit connected to each of the communication paths for detecting the amount of voice feedback when receiving a call and preventing the influence of the amount of voice feedback on the voice output comparison circuit; An intercom call control system comprising: control means for controlling a detection loss circuit using a detection signal from the pickup detection circuit and an output signal from the audio output comparison circuit. 2. The intercom call control system according to claim 1, characterized in that an auto gain control circuit for sending a signal to the control means is connected to each of the communication paths in order to control the audio level in each of the communication paths. .