JPS6212249A - Voice switch equipment - Google Patents

Abstract

PURPOSE:To attain natural loudspeaking talking even between loudspeaker telephone sets where there is a difference in background noise by comparing the S/N between a voice signal included in transmission and reception signals and the surrounding noise to change over the transmission/reception state. CONSTITUTION:The S/N of the transmission/reception signals is compared and switching control is applied to voice switch sections 12, 14 based on the quantity to change over the transmission/reception state. Even when >2 sets of telephone sets in loudspeaker talking service are at different surrounding noise environments, the surrounding noise signal level and the transmission/ reception voice signal level do not singly give effect on the changeover control of the voice switch sections 12, 14. Thus, no unidirectional channel is formed by a high surrounding noise side or a sender having a larger voice and loudspeaking talking is attained alternately with ease of interruption from a receiver side with low noise or small voice.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a voice switching 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 public address telephone set is used to select a high-level audio signal to be transmitted based on the result of comparing the audio signal levels of both the transmitting and receiving signals. - The receiving signal path is switched. 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 voice switch always operates to send the voice input to the telephone with higher noise to the telephone with lower noise. 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.

In order to make loudspeaker calls under such high-noise conditions, conventional methods have included a circuit that forcibly inverts the audio switch, and this circuit can be activated, for example, by pressing a press-to-talk button, while transmitting a call. However, although it was called a loudspeaker call, it required cumbersome manual push-button operations.
The problem was that it was not easy 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.

(Problems to be Solved by the Invention) However, in the former identification method using a filter, the circuit becomes large and the El is complicated depending on the frequency point to be detected, making it difficult to configure it at low cost. In addition, the latter 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.

The transmitted voice level during a conversation using a public address telephone is usually several d13 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. There was a problem that it became difficult.

(Means for Solving the Problems) This invention was made to solve the above-mentioned conventional problems, and even if there is a difference in ambient noise between the sending side and the receiving side, it is possible to DESCRIPTION OF THE PREFERRED EMBODIMENTS The purpose of the present invention is to provide a voice switching device that allows natural loudspeaker calls without having to use loudspeakers, and will be described in detail below based on embodiments not shown in the drawings.

FIG. 1 is a circuit block diagram of a loudspeaker telephone, in which a voice switch device 10 includes a voice switch section 12 inserted into a transmit signal path 11, and rectifies and smoothes the transmit signal on the input side to produce an envelope signal. A rectifying and smoothing circuit 15 that generates the signal, an S/N ratio detecting device 16 that detects the ratio between the audio signal included in the transmitting signal and ambient noise, that is, the SIN ratio, from this envelope signal, and the receiving signal path 13. a voice switch section '14;
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 this envelope signal. 18, the S/N ratio of the transmitting signal and the S/N ratio of the receiving signal.
Based on the comparison result, the comparison section 19 that compares the S/N ratio with the S/N ratio is switched to the closed state of the audio switch section 12 or 14 inserted in the signal path 11 or 13 with the larger S/N ratio. A switching control section 20 is provided for switching and controlling the audio switch section 14 or 12 inserted into the signal path 13 or 11 with the smaller N ratio.

A microphone 21 and transmitting amplifiers 22 and 23 are connected to the transmitting signal path 11, and a speaker 24 and receiving amplifiers 25 and 26 are connected to the receiving signal path 13. 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.

The S/N ratio detection 6w116 converts the input signal appearing at the input terminal 29 at a fixed period, for example 10
A first hold unit 30 that samples the input signal level at the current time t(n) in milliseconds and holds the input signal level at the current time t(n).
Then, the second hold unit 31 that holds the input signal level at the previous time t(n-1) compares the current and previous input signal levels, and when the level increases, for example, A comparison unit 32 detects the minimum value by detecting when the difference signal between the two changes from negative to positive.
, a calculation section 33 that recalculates the noise signal level when a local minimum value is detected, a storage section 34 that stores the noise signal level calculated here, and a storage section 34 that subtracts the noise signal level from the input signal level to generate only the audio signal. It is provided with an audio signal level detection section 35 for extracting the audio signal level, and an S/N ratio calculation section 36 that calculates the ratio between the audio signal level and the noise signal level and outputs it to the output terminal 37.

The comparison unit 32 also compares the current noise signal level stored in the storage unit 34 and the input signal level. and,
When the noise signal level is calculated by 4 in the calculation unit 33, the time constant to be applied differs 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. It is set in the time constant control section 38. That is, when the minimum value detected by the comparison unit 32 exceeds the current noise signal level stored in the storage unit 34, a slow time constant of, for example, plus 1d8/second is applied, and the noise signal level is gradually increased to the minimum value. Thus, the noise signal level is recalculated by the calculating section 33, and the contents of the storage section 34 are rewritten and updated.

In addition, when the current noise signal level exceeds the detected minimum value or the input signal level, for example, -2 dB
A time constant of /' seconds is applied, and the noise signal level is recalculated in the calculation unit 33 so that it gradually decreases to its minimum value or the input signal level, and the noise signal level in the storage unit 34 is sequentially updated based on the calculation result. It is being rewritten and updated.

By the way, in the voice switch device 1o shown in FIG.
The transmission signal includes three types of signals: a transmission audio signal input to the microphone 21, a background ambient noise signal, and a loop signal from the speaker 24. When the audio switch units 12 and 14 are in the transmitting state, the amount of wraparound signals is almost negligible;
- When 14 switches to the receiving state, noise signals and wraparound signals become the main signals. This wraparound 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. 1. Not shown in the embodiment. Similarly, the configuration for detecting the S/N ratio from the transmitted/received signal in which most of the loop signals included in the received signal have been detected and such loop signals have been canceled out is shown in the embodiment of FIG. has been done. In addition, even if the audio switch sections 12 and 14 completely open and close the transmitting and receiving signal paths 11 and 13 alternately, they adjust the attenuation amount of the signal passing through the open and closed states. Also good.

(Function) With the above structure, when the S/N ratio of the transmitting signal is greater than the S/N ratio of the receiving signal, the audio switch section 1
2 and 14 are controlled to be in a closed state and an open state, respectively, and are in a transmitting state. The S/N ratio of the received signal is the S of the transmitted signal.
/N ratio, 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/ of the sending/receiving signal is
The N ratios are compared, and based on the magnitude relationship, switching control of the audio switch units 12 and 14 is performed, and the transmitting/receiving state is 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, one loudspeaker telephone is installed in a noisy room with an ambient noise level of about 60 dB, and the other loudspeaker telephone is installed in a quiet room (M-proof) with an ambient noise level of about 20 dB.
A public address call experiment was conducted.

As a result, it was confirmed that the transmitting and receiving states could be switched without any unnaturalness or trouble at a normal conversation level, in which each caller emitted a voice several d3 louder than the amount of ambient noise.

The S/N ratio detection device 18, as shown in FIG.
The input level when there is no signal in (1) is stored in the storage unit 34 as the noise signal level shown by dotted lines and diagonal lines, and this value is maintained until time t(ie). Time t(ie
), the input signal level at this time is determined by the first hold section 30.
The input signal level at the immediately preceding time t(is) is set in the second hold unit 31, and both signal levels are compared in the comparison unit 32, and the signal level changes from negative to positive. , it is detected that the input signal level at time t(15) is a minimum value. Since the minimum value thus detected is larger than the noise signal level, a slow rise time constant of, for example, 1 dB/sec is applied, and the noise signal level is calculated by the calculation unit 3351 and set in the storage unit 34.

Then, the noise signal level is taken into the calculation unit 33 and continues to rise so as to asymptotically approach the minimum value at time t(15).
When the second minimum value at time t(18) is detected, 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, when the U sound signal level exceeds the input signal level at time t (25), this is detected by the comparator 32, and a fast falling time constant of, for example, -2 dB/sec is applied, and the noise signal level is calculated by the calculator 33. is calculated and stored in the storage unit 34. Then, the noise signal level continues to fall so as to approach the input signal level, but at time t (2
When the third minimum value of 7) is detected, this minimum value is taken into the calculation section as a noise signal level, and is set in the storage section 34 as it is, and this value is maintained. Next, when the fourth minimum value at time t (38) 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 level has returned to the initial no-signal level.

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

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 sharply decreases, and accordingly Accurate S/N ratio can be obtained even if the transmitted voice is degraded. Since it is impossible for the noise signal level to exceed the detected input signal level or this minimum value, the falling time constant is set small. Also, the minimum value at time t (1) (27) (44) is detected as a noise signal level, but at time t (15)
(18) If the minimum value in (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 false 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. Note that when a steady signal such as a beep is input, a constant continuous lowest level is detected as a noise signal level, similar to the minimum value when there is no signal in FIG.

<Effects of the Invention> As described above, according to the present invention, the S/N ratio between the audio signal included in the transmitting/receiving signal and the ambient noise is compared and the transmitting/receiving signal is determined.
By switching the receiving state, even 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 implementing the present invention; Fig. 2 is a circuit block diagram of the same S/N ratio detection device;
FIG. 3 is a waveform diagram for explaining the operation. 10...Audio switch device, 11...Talking signal path,
12, 13... Audio switch section, 14... Receiving signal path, 16... S/N ratio detection device, 19... Comparing section,
20... Switching control section, 30, 31... Sampling/holding section, 32... Comparison section, 33... Noise level 31 part, 34... Noise level storage section, 35...
- Audio signal level detection section, 36... S/N ratio calculation section, 38... Time constant control section. Figure 2

Claims (2)

[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 detecting device for detecting the S/N ratio of the receiving signal. An S/N ratio detection device that detects the N ratio, a comparison unit that compares the S/N ratio of the received signal and the transmitted signal, and a signal path with a higher S/N ratio based on the comparison result. It is equipped with a switching control section that switches the inserted audio switch section to the closed state and also switches the inserted audio switch section in the signal path with the smaller S/N ratio to the open state. A voice switching device characterized in that the transmitting/receiving state is switched based on the magnitude relationship of the /N ratio. (2) The audio switching device according to claim 1, wherein the S/N ratio detecting device detects the minimum value of the level of the transmitting/receiving signal as the ambient noise level.