JPH055420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a voice switch device used for switching the communication direction of a public address telephone, that is, the transmitting/receiving state.

(Prior Art) Generally, a pair of audio switches inserted into the transmitting and receiving signal paths of a loudspeaker telephone sets the transmission so that a high-level audio signal is transmitted based on the result of comparing the audio signal levels of both the transmitting and receiving signals.・It is designed to switch the receiving signal path. However, because it is difficult to distinguish background ambient noise contained in an audio signal from transmitted voice, malfunctions are likely to occur under high noise conditions.In other words, when the ambient noise level on one side is high and the other side is low, The audio switch always operates to send the audio input to the telephone with the higher noise level to the telephone with the lower noise level. In order to reverse this situation, it is necessary to input a voice at a level louder than the higher noise level to the lower noise level phone.

The transmitted voice level during a conversation using a public address telephone is usually several dB or more higher than the background ambient noise level. Therefore, even if you switch between sending and receiving by comparing the absolute levels of the outgoing audio signals, the outgoing call from the high-noise environment will be dominant, and the interruption will not occur from the telephone placed in the low-noise environment. It becomes difficult.

In order to make loudspeaker calls under such high-noise conditions, conventionally a circuit for forcibly reversing the audio switch has been provided, and this circuit has been used for, for example, press-to-press
There was a device that allowed you to send a call while moving the talk button, but although it was called a loudspeaker, it required cumbersome manual push-button operations, making it inconvenient to use. Furthermore, in order to compare the absolute levels of audio signals, it is necessary to distinguish between the audio signal and the noise signal contained therein. As this identification method, methods have been proposed in which the signal levels of voice and noise are detected using filters of several frequencies, and methods in which the input signal levels are averaged over a long period of time.

In addition, there was a system that applied different time constants to the input signal level, extracted the audio signal and ambient noise separately, and operated the audio switch while comparing the levels of each (for example, (Refer to Publication No. 152262/1983).

(Problem to be solved by the invention) However, in the identification method using a filter, the size of the circuit increases depending on the frequency point to be detected.
It has become complicated and difficult to configure at low cost. A device that averages the input signal level over a long period of time has drawbacks such as slow response speed and inability to handle accurate real-time processing, and erroneous detection of stationary signals such as beeps. Furthermore, both methods are insufficient in practical terms to detect ambient noise levels and audio signal absolute levels with high accuracy without impairing naturalness.

Further, if a different time constant is applied to the input signal, the noise level cannot be accurately detected by itself.

(Means for Solving the Problems) This invention has been made to solve the above-mentioned problems of the conventional art. The purpose of the present invention is to provide a voice switch device that allows natural loudspeaker calls without being aware of the differences, and will be described in detail below based on the embodiments shown in the drawings.

Figure 1 is a circuit block diagram of a loudspeaker telephone.
The audio switch device 10 includes an audio switch section 12 inserted into a transmission signal path 11, a rectification and smoothing circuit 15 that rectifies and smoothes the transmission signal on the input side to generate an envelope signal, and a rectification and smoothing circuit 15 that generates an envelope signal by rectifying and smoothing the transmission signal on the input side. an S/N ratio detection device 16 that detects the ratio of the audio signal included in the transmission signal to ambient noise, that is, the S/N ratio; and an audio switch unit 14 inserted in the reception signal path 13;
A rectifying and smoothing circuit 17 for obtaining an envelope signal from the received signal on the input side, and an S/N ratio detection device for detecting the S/N ratio between the audio signal included in the received signal and ambient noise from the envelope signal. 18, a comparing section 19 that compares the S/N of the transmitting signal and the S/N of the specific receiving signal, and a comparing section 19 that is inserted into the signal path 11 or 13 having a larger S/N ratio based on the comparison result. It includes a switching control section 20 that switches and controls the audio switch section 12 or 14 to a closed state, and also switches and controls the audio switch section 14 or 12 inserted into the signal path 13 or 11 with the smaller S/N ratio. There is.

A microphone 21 and transmitting amplifiers 22 and 23 are connected to the transmitting signal path 11, and a receiving signal path 13 is connected to the transmitting signal path 11.
A speaker 24 and receiver amplifiers 25 and 26 are connected to the . The transmitting amplifier 23 at the rear stage and the receiving amplifier 25 at the front stage are connected to a connection terminal 28 to a telephone line via a side sound protection circuit 27.

As shown in FIG. 2, the S/N ratio detection devices 16 and 18 sample the input signal appearing at the input terminal 29 at regular intervals, for example, every 10 milliseconds, and determine the input signal level at the current time t(n). The first hold unit 30 that holds the input signal level, and the second hold unit 31 that holds the input signal level at the previous time t(n-1), compare the current input signal level with the previous time and determine the input signal level. A comparison unit 32 detects a local minimum value when the level increases, for example, when the difference signal between the two changes from negative to positive, and a calculation unit 33 recalculates the noise signal level when a local minimum value is detected. , a storage unit 34 that stores the noise signal level calculated here, an audio signal level detection unit 35 that subtracts the noise signal level from the input signal level to extract only the audio signal, and a ratio between the audio signal level and the noise signal level. S/N ratio calculation unit 36 that calculates and outputs it to the output terminal 37
It has the following.

The comparison unit 32 also compares the current noise signal level stored in the storage unit 34 and the input signal level. When the noise signal level is calculated by the calculation unit 33, the applied time constant varies depending on the magnitude relationship between the local minimum value or the input signal level and the current noise signal level, and these different types of time constants are used. is set in the time constant control section 38. That is, the minimum value detected by the comparison section 32 is stored in the storage section 3.
When the current noise signal level stored in 4 is exceeded, a slow time constant of, for example, plus 1 dB/s is applied, and the calculation unit 3
3, the noise signal level is recalculated and stored in the storage unit 34.
The content of is being rewritten and updated.
Additionally, when the current noise signal level exceeds the detected minimum value or input signal level, e.g.
A fast time constant of -2 dB/sec is applied, and the noise signal level is recalculated by the calculation unit 33 so that it gradually decreases to its minimum value or input signal level,
Based on this calculation result, the noise signal level in the storage section 34 is sequentially rewritten and updated.

In the audio switch device 10 shown in FIG. 1, the transmission signal includes, in addition to the transmission audio signal input to the microphone 21 and the background ambient noise signal,
Three types of signals including loop signals from the speaker 24 are included. When the audio switch units 12 and 14 are in the transmitting state, the amount of wraparound signals is almost negligible;
When the receiver switches to the receiving state, noise signals and loop signals become the main signals. The amount of this feedback signal can be obtained by subtracting the noise signal level detected in the transmitting state before switching to the receiving state from the above signal input to the microphone 21. The configuration for this is shown in FIG. Not shown in the embodiment. In the same way, the amount of loop signals included in the received signal is also detected, and the configuration for detecting the S/N ratio from the transmitted and received signals from which such loop signals are canceled and removed is similar to the embodiment shown in FIG. It is shown. The audio switch units 12 and 14 also include the transmitting/receiving signal path 11,
Even if 13 are completely opened and closed alternately,
The amount of signal passing attenuation may be adjusted by changing the open/closed state.

(Function) It is configured as described above, and the S/
When the N ratio is greater than the S/N ratio of the received signal, the audio switch units 12 and 14 are controlled to be closed and opened, respectively, and are in the transmitting state. When the S/N ratio of the received signal exceeds the S/N ratio of the transmitted signal, the audio switch units 12 and 14 are controlled to switch between an open state and a closed state, respectively, and the transmitting state is switched to the receiving state. In this way, the S/N ratios of the transmitting and receiving signals are compared, and based on the magnitude relationship, switching control of the audio switch units 12 and 14 is performed, and the transmitting and receiving states are switched. Even if two or more telephones used for loudspeaker calls are placed in environments with different amounts of ambient noise, if the ambient noise signal level and the transmitting/receiving audio signal level are independent of each other, the audio switch unit 12, 14 switching control is not affected. Therefore, there is no possibility that a one-sided communication path will be formed from the side of the loud noise side or the caller who makes a louder voice, and even from the side of the low noise side or the receiver who makes a softer voice. The loudspeaker calls can be easily interrupted and alternated.

For example, when one loudspeaker telephone is connected to
We conducted a loudspeaker call experiment by installing one in a noisy room with a noise level of about 60 dB, and the other loudspeaker phone in a quiet room (soundproof room) with an ambient noise level of about 20 dB.
As a result, each caller can reduce the amount of ambient noise by a few dB.
It was confirmed that the transmitting and receiving states can be switched without any unnaturalness or trouble at normal conversation levels, where the voice is louder than the normal conversation level.

As shown in FIG. 3, the S/N ratio detection devices 16 and 18 store the input level when there is no signal at time t(1) in the storage unit 34 as the noise signal level shown by dotted lines and diagonal lines, and The value is maintained until t(16). At time t(16), the input signal level at this time is set in the first hold unit 30, and the input signal level at time t(15) just before this is set in the second hold unit 31, so that both signal levels are are compared by the comparator 32, and since the signal level has changed from negative to positive, it is detected that the input signal level at time t(15) is the minimum value. The minimum value detected in this way is larger than the noise signal level, so for example
A slow rise time constant of 1 dB/sec is applied to calculate the noise signal level in calculation unit 33 and set in storage unit 34.

Then, the noise signal level is taken into the calculation unit 33 and continues to rise so as to approach the minimum value at time t (15), but when the second minimum value at time t (18) is detected, this time The applied time constant remains the same and the noise signal level continues to rise so as to asymptotically approach this second minimum value. However, at time t
When the noise signal level exceeds the input signal level in (25), this is detected by the comparator 32, and a fast falling time constant of, for example, -2 dB/sec is applied.
The noise signal level is calculated by the calculation section 33 and set in the storage section 34. The noise signal level continues to fall asymptotically to the input signal level, but when the third minimum value at time t (27) is detected, this minimum value is taken into the calculation unit as the noise signal level. , is set as is in the storage unit 34, and this value is maintained. Next, time t(38)
When the fourth minimum value of is detected, the noise signal level starts to rise again, but when it exceeds the input signal level at time t (42), it starts to fall again. Even if the minimum value at time t (44) is detected during this downward movement, the downward state continues because the noise signal level exceeds this minimum value. At time t (46), the signal has returned to the initial no-signal level.

The noise signal level obtained in this way is
The detection section 35 subtracts the input signal level to obtain the audio signal level, and the S/N ratio calculation section 36 obtains the ratio between the audio signal level and the noise signal level, that is, the S/N ratio.

In this way, in the calculation unit 33 that calculates the noise signal level, by applying a large time constant in the upward direction and a small time constant in the downward direction, the ambient noise can be rapidly reduced and At the same time, accurate S/N ratio can be obtained even if the transmitted voice is degraded. Since the noise signal level cannot exceed the detected input signal level or this minimum value,
The falling time constant is set small. Also, the minimum values at times t(1)(27)(44) are detected as noise signal levels, but the minimum values at times t(15)(18)
If the minimum value of (38) is directly detected as a noise signal level, it is not known at each point in time whether it is a noise signal level or not, resulting in an erroneous detection. To avoid this, the rise time constant when calculating the noise signal level is set large.
The noise signal level gradually increases, but is quickly corrected in response to the next deeper minimum in the input signal level. By utilizing the minimum value of the force level in this way, more accurate detection of the ambient noise level becomes possible. Note that when a steady signal such as a beep is input, a constant continuous lowest level is detected as a noise signal level, the same as the minimum value when there is no signal in FIG.

(Effects of the Invention) As described above, according to the present invention, the ambient noise level is accurately detected, the S/N ratio between the audio signal included in the transmitting/receiving signal and the ambient noise is compared, and the transmitting/receiving state is determined. By switching between loudspeaker telephones with different background ambient noises, it is possible to easily interrupt from the low-noise side, and it is possible to have a natural loudspeaker call without being aware of the difference in ambient noise. You can get excellent results.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of a loudspeaker telephone embodying the present invention, FIG. 2 is a circuit block diagram of an S/N ratio detecting device, and FIG. 3 is a waveform diagram for explaining its operation. 10... Audio switch device, 11... Sending signal path, 12, 13... Audio switching section, 14... Receiving signal path, 16... S/N ratio detection device, 19...
Comparison section, 20... Switching control section, 30, 31...
Sampling/hold section, 32... Comparison section, 3
3...Noise level calculation unit, 34...Noise level storage unit, 35...Audio signal level detection unit, 36...
S/N ratio calculation section, 38... time constant control section.

Claims (1)

[Claims] 1 A pair of audio switch sections inserted into the transmitting signal path and the receiving signal path of the loudspeaker telephone, an S/N ratio detection device for detecting the S/N ratio of the transmitting signal, and an S/N ratio of the receiving signal. an S/N ratio detecting device for detecting the received signal and a comparing section for comparing the S/N ratios of the received signal and the transmitted signal; and a switching control section that switches the audio switch section inserted into the signal path with the smaller S/N ratio to the closed state, and switches the audio switch section inserted into the signal path with the smaller S/N ratio to the open state. In the audio switch device, the transmitting/receiving state is switched based on the magnitude relationship of the transmitting signal, the S/N ratio detecting device detecting the S/N ratio of the transmitting signal, and the S/N ratio of the receiving signal.
The S/N ratio detection device for detecting the ratio is configured to asymptotically approach the value stored as the current ambient noise level to the minimum value of the transmitting/receiving signal level in updating the ambient noise level value. , when the minimum value is larger than the value stored as the current ambient noise level, slowly using a large time constant, and when the minimum value is smaller than the value stored as the current ambient noise level, A voice switch device characterized in that it uses a small time constant to quickly asymptote.