JPH08265805A - Speech quality compensation control system for subscriber circuit - Google Patents

Abstract

PURPOSE: To attain speech quality compensation with high reliability by avoiding duplicate measurement result of noise onto a line characteristic so as to reduce the error of the measurement result of the line characteristic. CONSTITUTION: The speech quality compensation control system for a subscriber circuit having at least a subscriber line characteristic measurement circuit 4 measuring the line characteristic of a subscriber line and a speech quality compensation control circuit 15 controlling optimizingly the characteristic giving the effect on the speech quality of the subscriber line suitably for the subscriber line is provided with a compensation operation suppression section (loop detection circuit 5 a DC supply circuit 6 and a measurement control circuit 17) which detects the occurrence of noise being a cause to an error of the measurement result of the characteristic measurement circuit 4 on the occurrence of noise to suppress the operation of the speech quality compensation control circuit 15 based on the measurement result of the characteristic measurement circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber circuit of a digital electronic exchange, and more particularly to a call quality compensation control system for a subscriber circuit suitable for efficiently performing a call quality compensation control of the subscriber circuit. Is.

[0002]

2. Description of the Related Art Digital electronic exchanges include, for example, "Electronic Information Handbook" (1988) edited by The Institute of Electronics, Information and Communication Engineers.
(Issued by Ohmsha, Inc.), page 2163, as a function of supplying a call current to a telephone terminal (battery feed) in correspondence with a subscriber line, and a two-line subscriber line
Subscriber having "BORSCHT" function such as 2-wire to 4-wire conversion function (hybrid function; Hybrid) for converting and connecting relay lines of wires and CODEC function for converting analog signals and digital signals to each other An operator circuit is provided.

Under the normal installation conditions of a digital electronic exchange, the subscriber line connecting the telephone terminal and the subscriber circuit is used within a range of "0 to 7 km", but depending on the line length condition, the telephone terminal is Since the call quality characteristics such as the receiving volume and the sidetone change, the best call quality is not always ensured. In order to solve this problem, in recent years, attempts have been made to optimize the call quality by setting the amplifier gain of the speech path inside the subscriber circuit, the balancing network constant of the hybrid circuit, etc. to optimum values according to the line conditions. ing.

For example, at a certain moment before the start of a call, line characteristics (for example, loop resistance) are measured to calculate the line length, and as a result, optimum gain and balancing network constant are set to compensate for the call quality. The method of doing has been often used. However, with such technology,
If noise such as voice, dial pulse, or polarity reversal signal happens to be duplicated at the moment of measuring the line characteristics, a large error will occur in the measurement result, and as a result, there will be a problem that optimal call quality compensation cannot be performed. is there.

[0005]

The problem to be solved by the prior art is that the conventional techniques cannot prevent noise such as voice, dial pulse, or polarity inversion signal from overlapping the measurement result of the line characteristics. It is a point. An object of the present invention is to solve these problems of the prior art and to provide a speech quality compensation control system for a subscriber circuit that reduces error in the measurement result of line characteristics and enables highly reliable speech quality compensation. Is.

[0006]

In order to achieve the above object, a speech quality compensation control system for a subscriber circuit according to the present invention comprises:
(1) A characteristic measuring unit (subscriber line characteristic measuring circuit 4) for measuring the line characteristic of the connected subscriber line 2 and a measurement result by the subscriber line characteristic measuring circuit 4 are input, and the measurement result is used as a basis. And a compensation control unit (speech quality compensation control circuit 15) for optimally controlling the characteristics that affect the speech quality of the subscriber line 2 including at least the speech gain and the balancing network constant according to the subscriber line 2. In the speech quality compensation control system of at least the subscriber circuit, the generation of noise that causes an error in the measurement result of the line characteristic by the subscriber line characteristic measuring circuit 4 is detected, and at the time of detecting this noise generation,
A compensation operation suppressing unit (loop detection circuit 5, DC power supply circuit 6, measurement control circuit 17) for suppressing the operation of the speech quality compensation control circuit 15 based on the measurement result of the subscriber line characteristic measuring circuit 4 is provided. . (2) In the communication quality compensation control system for the subscriber circuit according to (1) above,
The compensation operation inhibiting unit detects the subscriber line 2 in a loop-on state or a loop-off state by a loop detection circuit 5
When the loop detection circuit 5 detects a loop-off state, the measurement control circuit 1 suppresses the operation of the speech quality compensation control circuit 15 based on the measurement result of the subscriber line characteristic measurement circuit 4.
And at least 7. Also,
(3) In the call quality compensation control system for a subscriber circuit as described in (1) above, the compensating operation inhibiting unit is a subscriber line characteristic when the supply of the call current to the telephone terminal connected to the subscriber line 2 is stopped. At least a measurement control circuit 17 for suppressing the operation of the speech quality compensation control circuit 15 based on the measurement result of the measurement circuit 4 is provided. (4) In the communication quality compensation control system for a subscriber circuit according to (1) above, the compensation operation suppressing unit detects a loop detection circuit for detecting whether the subscriber line 2 is in a loop-on state or a loop-off state. 5 and at least one of detection of a loop-off state by the loop detection circuit 5 and stop of supply of call current to the telephone terminal connected to the subscriber line 2, it is detected as noise, and the subscriber line is detected. Characteristic measurement circuit 4
And a measurement control circuit 17 for suppressing the operation of the speech quality compensation control circuit 15 based on the measurement result of 1. (5) In the speech quality compensation control system for a subscriber circuit according to any one of (1) to (4), a timer 10 that counts a preset fixed time period.
Is provided, and the compensating operation suppressing unit sets the timer 10 after the noise disappears.
It is characterized in that the operation suppression state of the speech quality compensation control circuit 15 based on the measurement result of the subscriber line characteristic measuring circuit 4 is continued for a certain period of time counted in (4). (6) In the speech quality compensation control system for a subscriber circuit according to any one of (1) to (5) above, the compensation operation suppressing unit of the subscriber line characteristic measuring circuit 4 detects the occurrence of noise. It is characterized in that the input of the measurement result to the speech quality compensation control circuit 15 is stopped and the compensation control operation of the speech quality compensation control circuit 15 based on the measurement result is suppressed. Also, (7) above (6)
In the speech quality compensation control system for a subscriber circuit as described in [1], the compensation operation suppressing unit stops the operation of the subscriber line characteristic measuring circuit 4 when the occurrence of noise is detected, and the measurement result of the subscriber line characteristic measuring circuit 4 is measured. The input to the speech quality compensation control circuit 15 is stopped. Also, (8) above (1)
In the speech quality compensation control system for a subscriber circuit according to any one of (1) to (5), the compensation operation inhibiting unit stops the operation of the speech quality compensation control circuit 15 when detecting the occurrence of noise, and measures the subscriber line characteristic. It is characterized in that the operation of the speech quality compensation control circuit 15 based on the measurement result of the circuit 4 is suppressed. Further, (9) the subscriber line characteristic measuring circuit 4 for measuring the line characteristic of the connected subscriber line 2 and the measurement result by the subscriber line characteristic measuring circuit 4 are inputted, and based on the measurement result, at least The characteristics that affect the call quality of the subscriber line 2, including call gain and balancing network constants,
In a speech quality compensation control system for a subscriber circuit having at least a speech quality compensation control circuit 15 for optimally controlling the subscriber line 2, a timer 10 for counting a preset fixed time and a subscriber line 2 A loop detection circuit 5 for detecting whether the loop is in a loop-on state or a loop-off state, a loop-on state detected by the loop detection circuit 5, and a call current supply state to a telephone terminal connected to the subscriber line 2. It has at least a measurement control circuit 17 which permits the operation of the speech quality compensation control circuit 15 based on the measurement result of the subscriber line characteristic measurement circuit 4 only when it continues for a preset fixed time. Also,
(10) In the communication quality compensation control system for a subscriber circuit according to any one of (1) to (9), the measurement result of the subscriber line characteristic measuring circuit 4 is continuously input a plurality of times,
A weighted measurement result calculation circuit 20 that weights each measurement result is provided, and the speech quality compensation control circuit 15 uses the weighted measurement result calculation circuit 20 to weight the measurement results.
It is characterized in that characteristics including at least a call gain and a balancing network constant are optimally controlled according to the subscriber line 2.

[0007]

In the present invention, the compensating operation suppressing unit detects the characteristic measuring circuit when, for example, one of the non-loop-on state (loop-off state) of the subscriber line and the stop state of DC power supply to the telephone terminal is detected. Judging that noise that causes an error in the measurement results of the line characteristics due to
The measurement operation of the line characteristic of the characteristic measurement circuit, the input of the measurement result to the compensation control circuit, or the operation of the compensation control circuit itself is stopped. As a result, it is possible to prevent inaccurate speech quality compensation due to measurement results with duplicated errors.

Since it takes time for the loop-on state and the DC power feeding state of the subscriber line after the operation of invalidating the measurement result to become stable, the subscriber line for a predetermined time corresponding to the stable time is required. The call quality compensation control is performed only when the loop-on state and the DC power feeding state continue. In this way, the result of the subscriber line characteristic measurement is validated only when the noise is detected and the noise-free period continues for a predetermined time. As a result, the call quality compensation control can be performed based on the accurate measurement result. Also, the compensation control circuit is
Input the measurement results from the characteristic measurement circuit multiple times in succession,
The speech quality compensation control is performed based on the result of weighting the measurement results of the multiple times. As a result, the measurement error of the characteristic measuring circuit can be further reduced.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a configuration according to the present invention of a speech quality compensation control system for a subscriber circuit of the present invention. In the figure, 1 is a subscriber circuit for performing speech quality compensation control according to the present invention, 2 is a subscriber line composed of two-line analog metallic lines, 3 is a telephone terminal,
The subscriber circuit 1 is connected to a telephone terminal 3 via a subscriber line 2. The subscriber circuit 1 includes a subscriber line characteristic measurement circuit 4, a loop detection circuit 5, a DC power supply circuit 6, and a hybrid function circuit 7 (in the figure, which will be described below).
HYB), balancing network 8 (in the figure,
BNW), timer 10, codec function circuit 11
(Indicated as CODEC in the figure), transmitter amplifier 12, receiver amplifier 14, speech quality compensation control circuit 15, measurement control circuit 1
7 and each circuit element of the weighted measurement result calculation circuit 20.

The subscriber line characteristic measuring circuit 4 is a circuit for measuring the characteristic of the subscriber line 2, and more specifically, is a circuit for measuring the signal attenuation characteristic of the line or the characteristic such as loop resistance. As an example, a case where the loop resistance measuring circuit is used will be described as a specific example. When the telephone terminal 3 is off-hook, that is, when the subscriber line 2 is in the loop-on state, the DC current flowing through the subscriber line 2 and The loop resistance is calculated by measuring the DC voltage between the lines. It should be noted that this technology is existing (known) and its detailed description is omitted here.

The loop detection circuit 5 is in accordance with the present invention, and when the telephone terminal 3 goes off-hook and the subscriber line 2 goes into the loop-on state, the direct current becomes a predetermined value or more. Is detected and its output line 16
It is a circuit that outputs "on" information. DC power supply circuit 6
Supplies a direct current necessary for its operation to the telephone terminal 3 via the loop detection circuit 5, the subscriber line characteristic measuring circuit 4 and the subscriber line 2. Then, while the call current is being supplied to the telephone terminal 3, the “on” information is output to the output line 19.

The hybrid function circuit 7 is a 2-wire to 4-wire conversion circuit for mutually converting the 2-wire signal of the subscriber line 2 and the 4-wire signal connected to the upper switching device. The balancing network 8 is a network circuit for realizing an impedance that is balanced with the characteristics of the subscriber line 2 necessary for 2-line to 4-line conversion. The codec function circuit 11 converts the transmission (uplink) signal 9 converted into four lines by the hybrid function circuit 7 from an analog signal to a digital signal, and
The received (downstream) signal 13 from the host switching device is converted from a digital signal to an analog signal.

The transmission amplifier 12 is a codec function circuit 1
The digital signal converted in 1 is amplified and sent to the host switching device. The reception amplifier 14 amplifies the digital reception (downstream) signal 13 from the upper switching device and sends it to the codec function circuit 11. The transmitter amplifier 12, the receiver amplifier 14, and the balancing network 8 are functional blocks that affect the call quality, and set their impedance and gain to optimum values according to the characteristics (line length) of the subscriber line 2. There is a need to. Speech quality compensation control circuit 1
Reference numeral 5 is a circuit for setting these values according to the characteristics of the subscriber line 2 measured by the subscriber line characteristic measuring circuit 4.

The measurement control circuit 17 is related to the present invention, and based on the respective outputs of the loop detection circuit 5 and the DC power supply circuit 6 which are input via the output lines 16 and 19, the measurement control circuit 17 is output via the output line 18. The subscriber line characteristic measuring circuit 4 is started and stopped. The timer 10 has a preset time (Δ
In this embodiment, the time from when the output line 16 of the loop detection circuit 5 is in the "on state" until it stabilizes, and the DC current fed by the DC feed circuit 6 are stable. Whichever is longer, (Δ
t) is set. The weighted measurement result calculation circuit 20 continuously inputs a plurality of measurement results from the subscriber line characteristic measurement circuit 4, weights the respective measurement results, and outputs the weighted measurement results to the speech quality compensation control circuit. Send to 15.

As described above, in this embodiment, in addition to the subscriber line characteristic measuring circuit 4, the loop detecting circuit 5, the DC power feeding circuit 6, and the measurement control circuit 17 are provided. Then, the loop detection circuit 5 and the DC power supply circuit 6 are connected to the subscriber line 2 based on the output state of the loop detection circuit 5 and the operation of the DC power supply circuit 6.
Monitor the track condition of. Based on these monitoring results, the measurement control circuit 17 determines the reliability of the measurement result of the channel state of the subscriber line 2 by the subscriber line characteristic measuring circuit 4. That is, the output of the loop detection circuit 5 continues a stable loop-on state for a predetermined time (Δt), and the DC power supply circuit 6
It is determined that the subscriber line characteristic measuring circuit 4 can perform the correct line characteristic measurement without noise duplication, only when the stable power feeding state continues for a predetermined time (Δt).

The measurement control circuit 17 permits the result of the measurement of the subscriber line characteristic measuring circuit 4 to be input to the speech quality compensation control circuit 15 based on the result of the determination as correct. If the measurement control circuit 17 determines that it is not correct,
The operation of the subscriber line characteristic measuring circuit 4 is stopped, or the output of the measurement result is stopped to prevent the measurement result having a possibility that noise is duplicated from being input to the speech quality compensation control circuit 15. In this way, the measurement result to the speech quality compensation control circuit 15 can be made accurate at all times, and as a result, the speech quality compensation control circuit 15 can always perform accurate speech quality compensation. Further, in the present embodiment, the measurement result of the subscriber line characteristic measuring circuit 4 is weighted by the weighting measurement result calculating circuit 20 and sent to the speech quality compensation control circuit 15. As a result, the error in the measurement result can be further reduced, and as a result, more optimal call quality compensation control can be performed.

Next, the operation relating to such speech quality compensation control will be described with reference to FIG. FIG. 2 is a time chart showing an operation example according to the present invention of the speech quality compensation control system for the subscriber circuit in FIG. In FIG. 2, 2
1 is the output waveform of the loop detection circuit 5 of FIG. 1, 22 is the output waveform of the DC power supply circuit 6 of FIG. 1, and the telephone terminal 3 of FIG.
Is off-hooked to send a dial pulse, and thereafter, a DC signal feeding circuit 6 of FIG. 1 sends a reversal signal (revers pulse).

In a normal sequence from outgoing / incoming calls to a call, even after the subscriber line 2 in FIG. 1 is in the loop-on state, dial pulses, hooking and polarization signals, etc. are output as shown by output waveforms 21 and 22. The loop state may be momentarily unstable due to a change in the DC voltage (or current) on the subscriber line. The measurement control circuit 17 of FIG.
As shown by the output waveform 25, the output is turned off and the measurement operation of the subscriber line characteristic measurement circuit 4 in FIG. 1 is stopped only during the period of instability.

In this control, for example, as shown by the output waveform 24, after both the loop detection circuit output (output waveform 21) and the DC power supply circuit output (output waveform 22) are turned on or changed to other states, The output is turned on only for a fixed time (Δt), and again both the loop detection circuit output (output waveform 21) and the DC power supply circuit output (output waveform 22) are turned on or not during the fixed time (Δt). If it changes to the state of
This can be realized by providing a function of turning on the output only for t). Specifically, for example, a re-trigger type monostable multivibrator (MMV) that uses a logical product result of the loop detection circuit output (output waveform 21) and the DC power supply circuit output (output waveform 22) as a trigger signal input is used. Can be easily achieved with.

The output waveform 25 is the measurement control circuit 17 of FIG.
Of the output waveform of the output waveform 21 and the output waveform 22
It can be created by taking the logical product of the output waveform 23 which is the logical product of the above and the inverted waveform of the output waveform 24. The output waveform 25 is constant after the subscriber line 2 of FIG. 1 is in the loop-on state, the DC power supply circuit 6 of FIG. 1 is in the power supply state, and the output waveform 21 and the output waveform 22 are changed. Only the stable period excluding the unstable period of time (Δt) is on. The measurement control circuit 17 of FIG. 1 controls so that the subscriber line characteristic measurement circuit 4 of FIG. 1 performs the measurement operation only during this stable period. Subscriber line characteristic measuring circuit 4 of FIG.
During this period, by continuously measuring and outputting the measurement result, dial pulse, hooking,
Stable measurement results that are not affected by sudden changes in DC voltage (or DC current) such as polarity inversion signals can be obtained.

The factors that adversely affect the measurement result of the subscriber line characteristic measuring circuit 4 of FIG. 1 are, in addition to the abrupt change of the DC signal described above, "0.3 to 3.4 kHz.
The influence of AC signals such as voice, dial tone, ring back tone, and PB signal (signal of push button diamond) used in the transmission band of "z" can be considered. These AC signals are
Since the subscriber line characteristic measuring circuit 4 of FIG. 1 also exists during a call in which measurement is being performed, the weighted measurement result calculation circuit 20 of FIG. 1 is provided in order to suppress the influence on the measurement accuracy. , As many measurements as possible over a long time,
It is effective to weight the result. Less than,
Such a processing operation will be described with reference to FIG.

In FIG. 1, the weighted measurement result calculation circuit 20 is shown.
Receives the measurement result of the subscriber line characteristic measuring circuit 4, and during the measurement operation period, the measurement result is continuously taken in a plurality of times at a constant time and weighting processing is performed. As a concrete method of the weighting process, for example, various types such as simple average, central value process, majority vote process by frequency distribution, etc. can be applied, and depending on the type and nature of noise (voice etc.) affecting the measurement, Optimal design method is adopted. By these processes, the line characteristic measurement result is determined, and the speech quality compensation control circuit 15 determines the constant of the balancing network 8, the gain of the transmitting amplifier 12, the receiving amplifier 1 based on the values.
The gain of 4 is set to the optimum value.

As described above with reference to FIGS. 1 and 2, in the speech quality compensation control system for the subscriber circuit of this embodiment, the loop detection circuit 5, the DC power supply circuit 6, the measurement control circuit 17, and the subscriber. By combining the line characteristic measuring circuit 4, it becomes possible to measure the line characteristic without being affected by a sudden change in the DC voltage (or current) of the subscriber line 2 such as dial pulse. Further, the weighting process of the speech quality compensation control circuit 15 alleviates the influence of AC noise in the transmission band such as voice, and enables more accurate line characteristic measurement. Therefore, the balancing network 8 corresponding to the line state and the characteristics such as the amplifier gain can be set accurately, and the optimum call quality compensation can be performed.

The present invention is not limited to the embodiment described with reference to FIGS. 1 and 2, and various modifications can be made without departing from the scope of the invention. For example, the subscriber line characteristic measuring circuit 4 may have characteristics other than the loop resistance, and the control target for performing speech quality compensation is something other than the balancing network 8, the transmission amplifier 12, and the reception amplifier 14, for example, Codec function circuit 1
1 may be used, or control such as a time delay amount or the like not shown in FIG. 1 or control such as a signal bandwidth or a dynamic range may be performed. Further, although FIG. 1 shows an example in which the transmitter amplifier 12 and the receiver amplifier 14 are installed in the digital processing unit on the higher side of the codec function circuit 11, they may be installed on the analog side of the circuit side. good.

[0025]

According to the present invention, noise such as voice, dial pulse, or polarity inversion signal can be prevented from overlapping the measurement result of the line characteristic, the error of the measurement result of the line characteristic can be reduced, and the reliability can be improved. It is possible to perform high quality call quality compensation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a configuration according to the present invention of a speech quality compensation control system for a subscriber circuit of the present invention.

FIG. 2 is a time chart showing an operation example according to the present invention of the speech quality compensation control system for the subscriber circuit in FIG.

[Explanation of symbols]

1: Subscriber circuit, 2: Subscriber line, 3: Telephone terminal, 4:
Subscriber line characteristic measurement circuit, 5: loop detection circuit, 6: DC power supply circuit, 7: hybrid function circuit, 8: balancing network, 9: transmission (upstream) signal, 10: timer, 11: codec function circuit, 12 : Transmitting amplifier, 1
3: reception (downstream) signal, 14: reception amplifier, 15: speech quality compensation control circuit, 16: output line, 17: measurement control circuit, 18, 19: output line, 20: weighted measurement result calculation circuit, 21 to 21 25: Output waveform

Claims (10)

[Claims] 1. A characteristic measuring unit for measuring a line characteristic of a connected subscriber line and a measurement result by the characteristic measuring unit are inputted, and based on the measurement result, at least a call gain and a balancing network constant are included. In a speech quality compensation control system for a subscriber circuit, which has at least a compensation control means for optimally controlling a characteristic affecting the speech quality of the subscriber line according to the subscriber line, the line characteristic by the characteristic measuring means. And a compensation operation inhibiting means for inhibiting the operation of the compensation control means based on the measurement result of the characteristic measuring means when detecting the occurrence of noise that causes an error in the measurement result. A subscriber circuit speech quality compensation control system. 2. The communication quality compensation control system for a subscriber circuit according to claim 1, wherein the compensation operation suppressing means is
Loop detection means for detecting whether the subscriber line is in a loop-on state or a loop-off state, and operation of the compensation control means based on the measurement result of the characteristic measuring means when the loop detection state is detected by the loop detection means. A call quality compensation control system for a subscriber circuit, comprising: 3. The communication quality compensation control system for a subscriber circuit according to claim 1, wherein the compensating operation suppressing means comprises:
A subscriber having at least measurement control means for suppressing the operation of the compensation control means based on the measurement result of the characteristic measurement means when the supply of the call current to the telephone terminal connected to the subscriber line is stopped. Circuit speech quality compensation control system. 4. The communication quality compensation control system for a subscriber circuit according to claim 1, wherein the compensating operation suppressing means comprises:
Loop detecting means for detecting whether the subscriber line is in a loop-on state or a loop-off state, detecting the loop-off state by the loop detecting means, and stopping the supply of the call current to the telephone terminal connected to the subscriber line. A subscriber having at least one of a state and a measurement control unit for detecting the occurrence of the noise and suppressing the operation of the compensation control unit based on the measurement result of the characteristic measuring unit. Circuit speech quality compensation control system. 5. The call quality compensation control system for a subscriber circuit according to any one of claims 1 to 4, further comprising timer means for counting a preset fixed time, and said compensation operation inhibiting means, After the noise disappears, the speech quality compensation of the subscriber circuit is continued for a certain period of time counted by the timer means, in which the operation of the compensation control means based on the measurement result of the characteristic measuring means is continued. Control system. 6. The communication quality compensation control system for a subscriber circuit according to claim 1, wherein the compensation operation suppressing unit measures the measurement result of the characteristic measuring unit when the occurrence of the noise is detected. (4) A speech quality compensation control system for a subscriber circuit, characterized in that the input to said compensation control means is stopped to suppress the compensation control operation of said compensation control means based on said measurement result. 7. The communication quality compensation control system for a subscriber circuit according to claim 6, wherein the compensation operation inhibiting means is
A speech quality compensation control system for a subscriber circuit, which stops the operation of the characteristic measuring means and stops the input of the measurement result of the characteristic measuring means to the compensation control means when the occurrence of the noise is detected. 8. The speech quality compensation control system for a subscriber circuit according to any one of claims 1 to 5, wherein the compensating operation suppressing means operates the compensating controlling means when the occurrence of the noise is detected. A speech quality compensation control system for a subscriber circuit, which is stopped to suppress the operation of the compensation control means based on the measurement result of the characteristic measurement means. 9. A characteristic measuring unit for measuring a line characteristic of a connected subscriber line and a measurement result by the characteristic measuring unit are inputted, and based on the measurement result, at least a call gain and a balancing network constant are included. In a call quality compensation control system for a subscriber circuit, which has at least a compensation control means for optimally controlling a characteristic affecting the call quality of the subscriber line according to the subscriber line, counting a preset fixed time. Timer means, loop detecting means for detecting whether the subscriber line is in a loop-on state or a loop-off state, detection of the loop-on state by the loop detecting means, and a telephone terminal connected to the subscriber line. Only when the power supply state of the call current continues for a preset period of time, the compensation control means based on the measurement result of the characteristic measurement means A call quality compensation control system for a subscriber circuit, comprising at least a measurement control means for permitting operation. 10. A speech quality compensation control system for a subscriber circuit according to claim 1, wherein:
A weighted measurement result calculation means for weighting each measurement result by continuously inputting the measurement results of the characteristic measurement means a plurality of times is provided, and the compensation control means is weighted by the weighted measurement result calculation means. A call quality compensation control system for a subscriber circuit, which optimally controls the characteristics including at least the call gain and the balancing network constant based on the measured result according to the subscriber line.