JPS60182249A - Channel gain control method - Google Patents

Abstract

PURPOSE:To improve the quality of talking by dividing a level change region of a channel gain into plural regions in response to the kind of state changeover of transmission and reception to set respectively the control characteristic of the channel gain at each split region. CONSTITUTION:A transmission attenuation circuit 6 is inserted to a transmission line 1, a reception attenuation circuit 7 is inserted to a reception line 2 and a gain control circuit 8 is connected to both the attenuation circuits 6, 7 so as to constitute a voice switch circuit of the channel gain control system. The control circuit 8 compares the voice level of the transmission line 1 and the voice level of the reception line 2, and the control gain of the channel is formed based on the result of comparison and the result is fed to the attenuation circuits 6, 7. The level change region of the channel gain is split to plural kinds in response to the kind of the state changeover of the transmission and reception. A control characteristic of the channel gain is set respectively to each split region and the talking gain is controlled according to the control characteristic. The increasing characteristic having a large change in the control characteristics is set to a curve projected upward to improve the quality of talking.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a channel gain control method for, for example, a public address telephone device or an echo suppressor.

[Technical background of the invention]

Generally a public address telephone system or echo sabre.

In order to prevent howling caused by the sound from the speaker to the microphone (sound coupling) or the transmitting signal going around to the receiving path (sidetone coupling), an audio switch circuit is installed and calls are made using this circuit. The path gain is controlled. FIG. 1 shows an example of an audio switch circuit.
a transmitting attenuation circuit 4 that varies the channel gain of the transmitting channel 1 in accordance with the comparison output of the comparator 3; and a receiving attenuation circuit 6 that varies the channel gain of the receiving channel 2 in accordance with the comparison output of the comparator 3. It is configured. In this configuration, the channel gain is conventionally controlled as follows. That is, first, when the audio signal level of the sending channel 1 becomes higher than the audio signal level of the receiving channel 2, at that point, the comparator 3 generates an 'O'' level signal. On the one hand, a transistor 41 is connected to a transmitting attenuation circuit 4;
, which turns off transistor 4 and resistor 42.
The amount of attenuation determined by 43 is decreased.

At this time, the change characteristics of this attenuation amount are determined by the time constants of the resistor 44 and the capacitor 45. Further, the output signal "0" of the comparator 3 is led to the reception attenuation circuit 5 on the other hand, and this signal is supplied to the transistor 52 via the inverter b1 to turn on the transistor 52.
The attenuation amount determined by the on-resistance of No. 2, the resistor 53, and the resistor 54 is also increased. At this time, the change characteristics of this attenuation amount are determined by the time constants of the resistor 55 and the capacitor 56.

In this way, a changeover from the receiving state to the transmitting state is made.

On the other hand, if the audio signal level of the receiving channel 2 becomes higher than the audio signal level of the transmitting channel 1, or
When both the audio signal levels of 2 and 2 are below a certain value tj, the comparator 3 outputs a 1" level signal, and this signal increases the amount of attenuation of the transmitting attenuation circuit 4.
The amount of attenuation of the reception attenuation circuit 5 is made small, thereby making the transition from the transmission state to the reception state smooth. Oh,
What about each attenuation circuit 4 and 5 in this case? 5 Attenuation change characteristics are also
Similarly to the 1,300 lines from the receiving state to the sending state, the size is determined by each time constant.

Therefore, with the above method, if the amount of attenuation of each attenuation circuit 4.5 is appropriately selected, it is possible to reliably prevent nodding.

[Problems with background technology]

By the way, in general, when performing the above-mentioned call path gain control in a device having the above-mentioned voice switch, in order to make the call characteristics natural when switching states,
It is considered desirable to determine the switching characteristics so as to satisfy the following conditions. In other words, the conditions are: (1) When switching from the transmitting state to the receiving state, and when the transmitting signal is cut off when there is no receiving signal (low level), the decay time of the transmitting signal is 300 mgee or more.

(11) When switching from the transmitting state to the receiving state, when the level of the receiving signal is high and the transmitting signal becomes lower than the same level, the decay time of the transmitting signal is 100~
300 m5ec.

11ii) Switching from a receiving state to a transmitting state,
When the transmitting signal rises in the absence of the receiving signal, the rising time of the transmitting signal shall be within 'f 15 m5ec.

(IV) When switching from the receiving state to the transmitting state, when the transmitting signal becomes larger than the same level while the receiving signal is present, the amplification characteristic of the transmitting signal is set to 100 m5ec.
~300 m5ec.

If the above conditions are violated, when transitioning from transmitting to receiving, the ending of the transmitting speech may be cut off, the beginning of the receiving speech may be cut off, or the intelligibility may be reduced; 5. Cutting off speech and receiving speech: Cutting off the end of a sentence or lowering intelligibility is likely to occur, which is not ideal.

However, in the conventional channel gain control method using the voice switch circuit, each attenuation circuit 4.5 is provided with a time constant circuit, and the attenuation amount is determined according to the change mode of the only type 1 furnace, which is determined by the time constant. Therefore, the only way to set the change characteristics of the relative attenuation is to adjust the time constant. For this reason, problems such as not being able to obtain appropriate change quality and change time and unnecessarily long change times often occur, which tends to impair the naturalness of the speech characteristics.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a call path gain control method that enables smooth switching within an appropriate time without impairing the naturalness of a call, and improves call quality.

[Summary of the invention]

In order to achieve the above object, the present invention changes the level change range of the channel gain to six types of state switching between transmitting and receiving, for example, when transmitting and receiving in a state where voice signals are present on both the transmitting and receiving channels. When changing the state of the communication channel, or when inputting an audio signal to one channel from a state where there is no audio signal on both the transmitting and receiving channels, and switching to the receiving or transmitting state (startup), multiple The system is divided into regions, and control characteristics of the channel gain are set for each of these divided regions, and variable control of the channel gain is performed in accordance with these control characteristics.

[Embodiments of the invention]

FIG. 2 is a block diagram of a voice switch circuit used to implement the channel gain control method in one embodiment of the present invention. This audio switch circuit includes a transmitting attenuation circuit 6 inserted in the transmitting channel 1, a receiving attenuating circuit 7 inserted in the receiving channel 2, an audio signal level in the transmitting channel 1, and an audio signal level in the receiving channel 2. are compared with each other, and control information for channel gain is created based on the comparison results, and each of the above-mentioned attenuation circuits 6
, 7.

Each of the transmitting and receiving attenuation circuits 6 and 7 is a so-called digital attenuator, each consisting of, for example, a digital-to-analog converter (D/A converter) and a variable attenuator that performs Q operation based on the converted output.

On the other hand, the gain control circuit 8 includes an analog-to-digital converter (A/D converter) for converting an audio signal input into a digital signal, and a microprocessor (CPU) as a main control section.
), and this CPU compares the input audio signal levels and creates gain control information based on the comparison results. The flowchart shown in FIG. 3 shows the operation of creating this gain control information.

Note that the value of the control information output from the gain control circuit 8 is set so as to be proportional to the logarithm value of the amount of attenuation in each attenuation circuit 6, 7.

Next, the channel gain control method of this embodiment will be explained based on the above configuration.

In general, when changing the transmitting/receiving state of a device with a voice switch, in order to maintain the naturalness of the 5-phone call, in other words, to reduce the sense of sudden disappearance of the voice signal in the attenuated communication path and maintain the presence of the ending of the word. For this reason, it is desirable to change the channel gain gradually in the range from the initial state to 6 dB, and even if the channel gain is changed rapidly in the range 10 dBυ beyond the above 6 dB. It is known that it does not significantly impair the naturalness of hearing.

Furthermore, when switching the state when voice signals are present on both the transmitting and receiving channels, the switching time must be relatively long, for example, about 200 m5ea. When an audio signal is input to the channel, it is necessary to start the signal in a shorter time, for example, 1710 or less, than when the audio signal is present, in order to prevent the beginning of a word from being cut off.

In this embodiment, the channel gain is controlled as follows, focusing on the upper point. That is, first, when switching from the transmitting state to the receiving state with a voice signal present in the transmitting/receiving path 1.2, the change in the level of the gain of the communication path 1.2 occurs, for example, as shown in FIG. 6 dB from the initial level The first area in the deaf ■ and 6 dB
The final level is the level t just before Q2.25dB.
It is divided into a second area @ at 1''! and a third area θ from the level t1 to the final level θ.

First, in the first region (3), the gain control circuit 8 issues control information (io reciprocal) to linearly decrease the logarithm of the attenuation amount of the reception attenuation circuit 7, as shown in FIG. According to this control information, the channel gain of the receiving channel 2 is changed so as to form a downwardly convex curve as shown in FIG. 5, 6). At this time, the CPU of the gain control circuit 8 sets the time interval ΔTi for changing the amount of attenuation (loss) as Tt, as shown in 5TIP 1 in the flowchart of FIG. emit control information to change and attenuate.

Control is performed until the total of l reaches 6 dB. FIG. 4 shows the gain change characteristics due to the above control.

10- After the profit control in the first region (■) (characteristic A in FIG. 4) is completed, in the second region @, the gain control circuit 8 receives a call as shown in FIG. The attenuation amount of the attenuation circuit 7 generates control information @ which is determined to be a quadratic convex curve in the downward direction, and this control information causes the channel gain of the receiving channel 2 to change in the upward direction as shown in FIG. 6(b). control so that the curve is convex. At this time, the CPU of the gain control circuit 8 is
In order to make the control information convex downward in a quadratic logarithm, first set the time interval ΔTi of attenuation amount (loss) change, as shown in 5TeP 2 in Figure 3, and attenuate every time this ΔTi elapses. The amount change range ΔLi is determined and this calculated value is output as control information.

Here, the time width ΔLl and time interval ΔT of the above attenuation amount
i, the initial value of the attenuation amount is Ls, the current value of the attenuation amount Li, and the final value of the attenuation amount. Then, ΔLI (logarithm value) is +
(Ll (logarithmic value) - Lx (versus medullary)). If set in this way, the following can be obtained, so that the communication path value can be made upwardly convex. However, K+ * K2 a Km represents a constant. FIG. 7 shows the above control operation.

After the control in the second region @ (characteristic B in FIG. 4) is completed, the gain control circuit 8 receives the signal as shown in FIG. Attenuation (logarithmic value) 'f of attenuation circuit 7: Generates control information that linearly decreases, and uses this control information to lower the channel gain of receiving channel 2 as shown in FIG. 5(b). Change it so that it becomes a convex curve on the side.

At this time, the CPU of the gain control circuit 8 is 5Te in FIG.
As shown in P 3, the time interval ΔTl of attenuation change is set as Ta, and the attenuation ΔLi is set every time this Ta elapses,
The above control operation is performed by outputting this attenuation amount ΔLi as control information. FIG. 4C shows its control robustness.

In this way, a series of gain controls are completed when switching from transmitting to receiving in a state where an audio signal is present on the transmitting/receiving channel. Although the attenuation open control of the receiving attenuation circuit 7 has been described in the above description, the attenuation amount control of the transmitting attenuation circuit 6 is performed in a manner contrary to the control on the receiving side.

On the other hand, when there is no audio signal on the transmission/reception channels 1 and 2,
When an audio signal enters the transmitting path, for example, when switching from the receiving state to the transmitting state, that is, when the transmitting state starts, the gain change range is 2 from the initial value to the final value as shown in Figure 9.
．． It is divided into a first region (2) up to the level tI which is 25 dB earlier, and a second region (2) from the level tI to the final value. First, in the first region O, the change characteristics of the transmitted voice attenuation sound are determined from the gain control circuit 8 as shown in FIG.
), the control information is set and output so that it is convex downward with the logarithm of the square, and this control information is used to make the channel gain convex upward as shown in Figure 9. Control.

Then, in the second region, control information is set so that the attenuation amount of the transmitting attenuation circuit 6 decreases linearly 13- as shown in FIG. The transmitting path gain is expressed by a downward convex curve (Δ
Since ΔLi is small with respect to Ti, it is controlled so that it becomes a substantially straight line. In addition, in the above control, the CPU of the gain control circuit 8 is operated by the 5Te shown in FIG. 3 in the first region.
The control operation shown in P2 is performed, and in the second region, the control shown in 5TeP3 in FIG. 3 is performed.

As described above, the channel gain control method of this embodiment provides the following effects. That is, first, the transmitting/receiving channel 1
, 2, when the state is switched in a state where an audio signal is present in , 2, the first region (■) up to 6 dB from the control start point is changed so that it becomes a downwardly convex gain change curve in the case of receiving channel gain. Since the characteristics are set, the gain can be changed relatively slowly, and as a result, clear and natural switching can be performed without causing the end of the transmitted voice to be cut off. Also,
In the second region @, the gain change curve is convex upward, so
The gain can be changed quickly, and as a result, the switching can be completed within an appropriate time without unnecessarily lengthening the switching time. Although the level of the transmitted voice signal decreases rapidly due to the above-mentioned high-speed gain change, the naturalness of the conversation is not impaired because the gain has already been attenuated by 6 dB. Furthermore, the level of the received voice signal increases rapidly due to the above-mentioned high-speed gain change, but since the received voice level is originally small and changes upwardly with respect to time, it changes gradually as the level increases. This does not result in loss of naturalness of the call. Furthermore, in this second region @, since the gain change characteristic is upwardly convex as described above, it is possible to smoothly reduce the change in each gain of the receiving path and the sending path, and in this respect as well. Switching can be performed without impairing the naturalness of the call. In addition, since the third region θ is provided and the gain is made to reach the final gain approximately linearly in this region, compared to the case where the final gain is reached while maintaining the characteristics of the second region @, Switching can be completed in a short time without unnecessarily lengthening the switching time.

On the other hand, when starting to send or receive a call when there is no audio signal in sending or receiving path 1 or receiving path 2, the start-up is performed immediately and at high speed from the initial state, so there is no interruption at the beginning of the word. A clear start-up can be performed. After the above-mentioned high-speed start-up, the gain is made to reach the final gain in a substantially linear manner in the second region near the final gain, so the switching time is not unnecessarily lengthened. . Note that when switching from the receiving state to the transmitting state due to the above-mentioned rapid start-up, the gain of the receiving path will decrease rapidly, but since there is no receiving audio signal in the case of this transmitting start-up, this will cause It does not impair the naturalness of the call.

Note that the present invention is not limited to the above embodiments.

For example, in the above embodiment, when switching when an audio signal is present, the total gain change area is divided into three areas and gain control characteristics are set for each area, but if more precise control is required, the gain control characteristics are set for each area. Gain control may be performed separately for each. This also applies at startup when no audio signal is present.

Furthermore, the form of the control characteristic of each divided region, the configuration of the circuit for setting this characteristic, the configuration of the attenuation circuit, etc. can be modified in various ways without departing from the gist of the present invention.

〔Effect of the invention〕

As described in detail above, the present invention divides the level change area of the channel gain into a plurality of areas according to the transition of the transmitting and receiving states, and changes the level of the channel gain for each of these divided areas. Control characteristics are set respectively, and the channel gain is variable controlled in accordance with these control characteristics.

Therefore, according to the present invention, it is possible to provide a call path gain control method that can perform smooth switching within an appropriate time without impairing the naturalness of a call, and can improve call quality.

17-

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a voice switch circuit for implementing a conventional channel gain control method, and FIGS. 2 to 9 are for explaining an embodiment of the present invention. FIG. 3 is a flowchart showing the control operation of the circuit, FIG. 4 and FIG. 9 are diagrams showing the gain control circuit, and FIG. a), (b), Fig. 6 (a), (
b), Figures 7 and 8 (a), (b) lt
FIG. 7 is a diagram showing attenuation/change severity and gain control characteristics in the nominal side region, respectively. DESCRIPTION OF SYMBOLS 1... Sending line, 2... Receiving line 56... Sending line attenuation circuit, 7... Receiving line attenuating circuit, 8... Gain control circuit. Applicant's agent Patent attorney Takehiko Suzue 18-;

Claims (2)

[Claims] (1) By mutually comparing the audio signal levels of the sending path and the receiving path, and reciprocally controlling the gain of each of the speaking paths and the receiving path according to the comparison result, the state of the sending and receiving calls can be controlled. In a channel gain control method that performs switching, the channel gain level change region is divided into a plurality of regions according to the type of switching between transmitting and receiving states, and the channel gain is adjusted for each of these divided regions. 1. A communication path gain control method characterized in that control characteristics are set and the communication path gain is variably controlled in accordance with these control characteristics. (2) Among the control characteristics of the channel gain, the increasing characteristic with a large amount of change is set to be an upwardly convex curve with respect to the time axis. The channel gain control method described.