JPH07221832A - Telephone set and method for controlling its frequency characteristic - Google Patents

Abstract

PURPOSE:To secure desired articulation by changing a level of a reception frequency spectrum at a border of a lower limit frequency. CONSTITUTION:A level revision discrimination circuit 205 receives a result of comparison between a noise spectrum L and a reception spectrum (f) from a level comparator 203. Then a level revision quantity is decided to increase the reception spectrum to be a level over the noise spectrum at frequencies higher than a frequency Af. A level control signal generator 206 receiving the level revision quantity generates a control signal S1 used to decrease a level of lower frequencies and a control signal S2 used to increase a level of higher frequencies and provides outputs of them to a frequency characteristic revision circuit 207. The frequency characteristic revision circuit 207 changes a filter coefficient of an echo canceller 104 accordingly to increase a high frequency spectrum of a reception acoustic signal to be a noise spectrum level or over and to decrease a low frequency spectrum of the reception acoustic signal to be a noise spectrum level or below.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephone terminal, and more particularly to a method of controlling frequency characteristics of a received sound signal for improving call quality.

[0002]

2. Description of the Related Art In recent years, mobile phones have become widespread with the progress of mobile communication, and it has become possible to easily carry out telephone conversations not only in a limited place such as a telephone box but also anywhere. The point that this call location is not chosen is a major feature of mobile phones, but it is problematic from the viewpoint of call quality.

In a car telephone, there is a case where a speaker and a microphone provided in the car are used for communication without having a handset. For this reason, the sound of the speaker is reflected in the vehicle and input to the microphone, so-called acoustic echo is generated. Further, since the wireless line is used, it is difficult to sufficiently cancel the line echo generated by the hybrid. A circuit configuration that effectively removes both such acoustic echo and line echo is disclosed in Japanese Patent Laid-Open No. 3-29424. This echo canceller circuit will be briefly described with reference to FIG.

In FIG. 4, a voice signal input from a microphone 401 of a car telephone is an acoustic canceller 40.
2 to the wireless device 403, and is transmitted from the wireless device 403 to the base station 404 via a wireless line. Base station 4
The signal received at 04 is transmitted to the partner terminal by hybrid 406 via PSTN public communication network 405. The voice signal of the other party is output from the speaker 408 through the base station 404, the car telephone radio 403, and the line echo canceller 407.

The microphone 401 of the car telephone is
In addition to the voice of the speaker M, the voice of the other party generated from the speaker 407 is also input, but the acoustic echo canceller 402 removes the acoustic echo component. In addition, the line echo component En generated by the hybrid 406
Are removed by the line echo canceller 407. The line echo canceller 407 includes a phase tracking circuit and an adaptive filter. The voice signal of the speaker M of the car telephone is input, the phase tracking circuit generates the voice signal of the speaker M including the compensation components of the frequency offset and the phase jitter, and using this, the adaptive filter uses the line echo signal En. A synchronized line echo cancel signal is generated to effectively remove the line echo signal En. In this way, acoustic echo and line echo can be removed, and high speech quality can be obtained.

[0006]

However, in the conventional telephone, since the echo cancellation processing is always performed with a constant frequency characteristic regardless of the presence or absence of ambient noise,
The reception quality, especially the clarity of the call, was insufficient. For example, when the ambient noise is severe and the reproduction output level of the speaker is limited by the mobile phone standard or the like, the clarity of the received voice is lowered and it becomes difficult to hear the conversation content.

It is an object of the present invention to provide a telephone and a frequency characteristic control method therefor capable of obtaining a sufficient call intelligibility even when the ambient noise level is high.

[0008]

A method of controlling a frequency characteristic of a receiving acoustic signal according to the present invention is a method of calculating a noise frequency spectrum from a noise component of a transmitting acoustic signal output from a transmitter.
The reception frequency spectrum is detected from the reception acoustic signal input to the receiver. Level consisting of at least one of the frequency range below the lower limit frequency and the frequency range above the lower limit frequency required to obtain the desired speech intelligibility based on the level difference in the mask area where the noise frequency spectrum is above the receiving frequency spectrum The change range and the level change amount of the frequency spectrum of the reception acoustic signal are determined, and the level change direction of the frequency spectrum of the reception acoustic signal is determined so that the reception frequency spectrum becomes equal to or higher than the noise frequency spectrum level. The frequency spectrum level of the reception acoustic signal is changed based on the level change range, the level change amount, and the level change direction.

When the maximum level difference between the noise frequency spectrum and the receiving frequency spectrum is less than a predetermined limit value, the component level of the receiving frequency spectrum below the required lower limit frequency is increased according to the level change amount. Also,
If the maximum level difference between the noise frequency spectrum and the receiving frequency spectrum exceeds a predetermined limit value,
It is desirable to reduce the level of the receiving frequency spectrum below the required lower limit frequency according to the level change amount, and simultaneously increase the level of the receiving frequency spectrum exceeding the required lower limit frequency according to the level change amount.

[0010]

The reception frequency spectrum is maintained at a level equal to or higher than the noise frequency spectrum by changing the level of the reception frequency spectrum with the lower limit frequency necessary for obtaining the desired speech intelligibility as a boundary. In particular, since the frequency region above the required lower limit frequency of the reception frequency spectrum is above the noise frequency spectrum, the desired clarity can be secured.

Further, when the noise frequency spectrum is at a high level, the intelligibility of the call is ensured by increasing the component level of the reception frequency spectrum exceeding the required lower limit frequency, and the component level of the reception frequency spectrum below the required lower limit frequency is ensured. To reduce power consumption.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a transmitter / receiver section of a mobile telephone according to an embodiment of the present invention. The microphone 101 converts sound into an electric signal and outputs it as a transmission sound signal to the amplifier 102. The acoustic echo of the transmitted acoustic signal amplified by the amplifier 102 is removed by the acoustic adaptive echo canceller 103, and is transmitted to the mobile communication base station by the telephone radio unit (not shown).

The received wave from the base station is demodulated into a baseband signal by the telephone radio unit, and the line echo is removed by the hybrid adaptive echo canceller 104. As will be described later, the filter coefficient of the hybrid adaptive echo canceller 104 has a frequency characteristic changing circuit 207.
The frequency characteristic of the received acoustic signal is changed according to the noise around the telephone to improve the intelligibility. Further, the received sound signal is transmitted to the volume controller 10
It is input to the speaker 108 via 6 and the amplifier 107, and is converted into sound. The volume controller 105 controls the amplitude of the received sound signal so that the received sound signal corresponds to the sound pressure output from the speaker 107. The reception acoustic signal spectrum generator 204 uses the amplitude-controlled reception acoustic signal to generate a reception spectrum. A telephone wireless unit (not shown), acoustic adaptive echo canceller 103, and hybrid adaptive echo canceller 1
04 is well known.

This embodiment further has a circuit for controlling the frequency characteristic of the received acoustic signal according to the noise around the telephone.
The sound around the telephone is collected by the microphone 101, and the noise signal is detected by the noise detector 201 from the transmitted sound signal. Speech and noise are discriminated from each other according to the regressiveness of the transmitted acoustic signal. The noise signal is converted into a level signal for each frequency by the noise spectrum generator 202, and the spectrum signal L is output to the level comparator 203.

On the other hand, the received sound signal whose volume is controlled by the volume controller 105 is the received spectrum generator 20.
4 is output. The volume controller 105 is composed of an electronic volume and outputs to the reception spectrum generator 204 a reception acoustic signal corresponding to the sound pressure output from the speaker 107.

The reception spectrum generator 204 converts the reception sound signal into a level signal for each frequency and outputs the reception spectrum signal f to the level comparator 203. The level comparator 203 compares the noise spectrum signal L with the reception spectrum signal f for each frequency, and outputs the comparison result to the level change determination circuit 205.

The level change determination circuit 205 determines whether or not the maximum level difference between the noise spectrum and the reception spectrum is larger than the level change limit Lth, and determines the level change amount of the reception spectrum signal f. Level change limit Lt
h is the maximum level of the received sound signal in which the received sound signal is not distorted by the volume controller 105.

According to the level change amount, the level control signal generator 206 controls the control signal S1 for controlling the reception spectrum level in the frequency region lower than the required lower limit frequency Af.
And the control signal S2 for controlling the spectrum level in the frequency region higher than the required lower limit frequency Af are output to the frequency characteristic changing circuit 207. The frequency characteristic changing circuit 207 sets the filter coefficient of the hybrid echo canceller 104 to the required lower limit frequency A according to the level control signals S1 and S2.
Change f at the border.

The required lower limit frequency Af is the lower limit frequency of the frequency band required for obtaining the clarity of 70% or more,
In this embodiment, Af = 1 kHz is set. The required lower limit frequency Af can be set to 1 kHz in many cases, but it may be set higher or lower than 1 kHz in order to secure a predetermined intelligibility depending on the degree of ambient noise and frequency characteristics.

Next, the frequency characteristic control of this embodiment will be specifically described with reference to FIGS. 2 and 3.

FIG. 2 is a flow chart showing an embodiment of the frequency characteristic control method according to the present invention. First, the level change determination circuit 205 inputs the comparison result of the noise spectrum L and the reception spectrum f from the level comparator 203 (S301), and determines whether or not there is a mask region in which the noise spectrum is larger than the reception spectrum. (S30
2). If the mask area exists, it is determined whether or not the level difference between the noise spectrum and the reception spectrum in the mask area is larger than the level change limit Lth (S3).
03). If the level difference is equal to or less than Lth (N in S303)
o), it is determined that this can be dealt with by changing the reception spectrum level, and the level increase amount is determined so as to increase the reception spectrum to a level equal to or higher than the noise spectrum in the lower frequency range than the frequency Af (S304). The level increase amount is output to the level control signal generator 206.

Inputting the level increase amount, the level control signal generator 206 generates a level increase control signal S1 in a frequency range lower than the frequency Af and outputs it to the frequency characteristic changing circuit 207 (S305). According to this, the frequency characteristic changing circuit 2
07 raises the low-frequency spectrum level of the reception acoustic signal to the noise spectrum level or higher, and does not change the high-frequency spectrum level (S306).

On the other hand, the level difference in the mask area is Lt.
If it is larger than h (Yes in S303), it is determined that it cannot be dealt with by increasing the level in the low frequency range, the voice basic formant area is abandoned, and the level in the high frequency range above the frequency Af required to secure the predetermined intelligibility is increased. . That is, the level change amount is determined so as to raise the reception spectrum to a level equal to or higher than the noise spectrum in the frequency range higher than the frequency Af (S307). This level change amount is also used as the amount of decrease in the received spectrum level in the low frequency range. This level change amount is output to the level control signal generator 206.

When the level change amount is input, the level control signal generator 206 controls the control signal S for lowering the level in the low frequency range.
1 and a control signal S2 for increasing the level of the high frequency band are generated and output to the frequency characteristic changing circuit 207 (S30).
8). Accordingly, the frequency characteristic changing circuit 207 changes the filter coefficient of the echo canceller 104 to raise the high-frequency spectrum level of the reception acoustic signal to the noise spectrum level or more and reduce the low-frequency spectrum level by the same level (S309). ).

As described above, by raising the level of the reception spectrum in the higher frequency range than the required lower limit frequency Af and lowering the level of the reception spectrum in the lower frequency range than the frequency Af, the power consumption can be ensured while ensuring the clarity. The increase can be suppressed.

Next, the specific control of this embodiment will be described with reference to FIG.

FIG. 3 is a graph showing the amplitude distribution of the reception spectrum and the noise spectrum in this embodiment.
Curves L1 to L5 in the figure are general spectral distributions of 1 / f noise, and the noise level increases from the curve L1 to the curve L5. Curves f1 to f5 are spectrum distributions of the reception acoustic signal, and the curve f3 represents the reception spectrum before the frequency characteristic control, and the other curves represent the reception spectrum after the frequency characteristic control. However, here, the frequency bandwidth is set to 300 Hz to 3.4 kHz.

The frequency characteristic control of this embodiment adjusts the reception spectrum so as to improve the clarity of the reception sound. Therefore, it is important to adjust the frequency characteristic so that the reception spectrum f becomes the noise spectrum L or more in the high frequency band of 1 kHz or more required for obtaining the predetermined clarity.

First, when the spectrum distribution of the noise spectrum signal L is the curve L3, the mask area determination circuit 20
5 determines that the low frequency band of 1 kHz or less is masked by the noise spectrum L3. That is, the level of the reception spectrum f3 is higher than the noise spectrum L3 in the frequency range of 1 kHz to 3.4 kHz related to the predetermined intelligibility, but is low in the frequency range of 300 to 1 kHz. Since the maximum level difference between the noise spectrum L3 and the reception spectrum f3 is smaller than the level change limit Lth, the reception spectrum f up to the noise level at the lowest frequency 300 Hz of the predetermined frequency band as shown by the curve f1.
Increase the level of 3 (for example, the level increase amount 10d
B).

In accordance with the level increase amount, the level control signal generator 206 outputs the level control signal S1 to the frequency characteristic changing circuit 207 to obtain the reception spectrum distribution shown by the curve f1. That is, 300 to 1 depending on the level control signal S1.
The reception spectrum in the frequency range of kHz is increased by 10 dB and becomes equal to or higher than the noise spectrum, and 1 kHz to 3.4 kHz.
The reception spectrum in the high range of Hz does not change.

When the noise level is lowered to the noise spectrum distribution shown by the curve L2, only a part of the low frequency band of the reception spectrum f3 is masked. Therefore,
The level change determination circuit 205, similar to the control described above,
The reception spectrum f3 is increased to the noise level at the lowest frequency of 300 Hz (for example, the level increase amount is 5 dB),
The reception spectrum distribution shown by the curve f2 is obtained.

When the ambient noise exceeds a certain level and, for example, the maximum level difference between the noise spectrum L4 and the reception spectrum f3 exceeds the level change limit Lth, the level change determination circuit 205 causes the high range of 1 kHz to 3.4 kHz. Increases the reception spectrum, and conversely 300 to 1k
The reception spectrum in the low frequency range of Hz is reduced by the same level. This level change amount is determined so that the reception spectrum becomes equal to or higher than the noise spectrum L4 in the high frequency band. Specifically, the level difference between the noise spectrum L4 at the frequency of 1 kHz and the reception spectrum f3 is set as the level change amount. In the case of the noise spectrum L4, the level change amount is about 5 dB, and the high range is increased by 5 dB and the low range is decreased by 5 dB. Thus, the reception spectrum has a spectrum distribution having a slope around 1 kHz as shown by the curve f4. Similarly, in the case of the noise spectrum L5, the level change amount of about 10 dB is determined, and the reception spectrum has the spectrum distribution shown by the curve f5.

As shown in the curves L4 and L5, when the ambient noise level becomes higher than the limit, the low-frequency component level below the required lower limit frequency Af is lowered and the high-frequency component level is raised to increase the energy level. Can be focused on ensuring clarity. Therefore, even in a high noise environment, it is possible to talk with sufficient clarity and to suppress power consumption.

[0035]

As described above in detail, in the frequency characteristic control method for a telephone according to the present invention, the level of the reception frequency spectrum is changed at the lower limit frequency necessary for obtaining the desired speech intelligibility. This maintains the reception frequency spectrum at a level above the noise frequency spectrum. In particular, since the frequency region above the required lower limit frequency of the reception frequency spectrum is above the noise frequency spectrum, the desired intelligibility can be ensured even when there is a limit to the noise around the telephone or the voice output of the telephone.

Even when the bass is masked by noise, the sound quality deterioration can be prevented because the level of the reception frequency spectrum in the bass increases according to the noise level.

Further, when the noise frequency spectrum is at a high level, the intelligibility of the call can be secured by increasing the component level of the reception frequency spectrum exceeding the required lower limit frequency. At the same time, by lowering the component level of the reception frequency spectrum below the required lower limit frequency, power consumption can be suppressed while ensuring clarity.

[Brief description of drawings]

FIG. 1 is a block diagram showing a transmission / reception unit of a mobile phone according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an embodiment of a frequency characteristic control method according to the present invention.

FIG. 3 is a graph showing amplitude distributions of a reception spectrum and a noise spectrum in the present embodiment.

FIG. 4 is a block diagram showing an example of a conventional telephone.

[Explanation of symbols]

 101 Microphone 102 Amplifier 103 Acoustic Adaptive Echo Canceller 104 Hybrid Adaptive Echo Canceller 105 Volume Controller 106 Amplifier 107 Speaker 201 Background Noise Detector 202 Noise Spectrum Generator 203 Level Comparator 204 Received Acoustic Signal Spectrum Generator 205 Level Change Judgment Circuit 206 Level Control Signal generator 207 Frequency characteristic change circuit Lth level change limit value Af Lower limit frequency necessary for ensuring intelligibility f1-f5 Received frequency spectrum distribution L1-L5 Noise frequency spectrum distribution

Claims (11)

[Claims] 1. A method for controlling a frequency characteristic of a reception acoustic signal in a telephone comprising a transmitter and a receiver, wherein a noise frequency spectrum is detected from a noise component of the transmission acoustic signal output from the transmitter, Detecting the receiving frequency spectrum from the input receiving acoustic signal, based on the level difference in the mask region where the noise frequency spectrum is equal to or higher than the receiving frequency spectrum,
Determine a level change range consisting of at least one of a frequency range below the lower limit frequency necessary to obtain a desired speech intelligibility and a frequency range above the required lower limit frequency, and a level change amount of the frequency spectrum of the received acoustic signal. Then, based on the level difference in the mask region, the reception frequency spectrum is equal to or higher than the level of the noise frequency spectrum, the level change direction of the frequency spectrum of the reception acoustic signal is determined, the level change range, the A frequency characteristic control method, wherein the frequency spectrum level of the received acoustic signal is changed based on the level change amount and the level change direction. 2. When the maximum level difference between the noise frequency spectrum and the receiving frequency spectrum is less than or equal to a predetermined limit value, the level of the frequency spectrum of the receiving acoustic signal in a frequency range below the required lower limit frequency is set. The frequency characteristic control method according to claim 1, wherein the frequency characteristic is increased according to the level change amount. 3. The level of the frequency spectrum of the received acoustic signal in a frequency range that exceeds at least the required lower limit frequency when the maximum level difference between the noise frequency spectrum and the received frequency spectrum exceeds a predetermined limit value. 3. The frequency characteristic control method according to claim 1 or 2, wherein is increased in accordance with the level change amount. 4. The level of the frequency spectrum of the received acoustic signal in the frequency range lower than the required lower limit frequency is reduced according to the level change amount, and the frequency spectrum of the received acoustic signal is exceeded in the frequency range exceeding the required lower limit frequency. 4. The frequency characteristic control method according to claim 3, wherein the level is increased according to the level change amount. 5. The frequency characteristic control method according to claim 1, wherein the required minimum frequency is 1 KHz. 6. A telephone comprising a transmitter and a receiver, a noise spectrum detecting means for detecting a noise frequency spectrum from a noise component of a transmitting acoustic signal, and a receiving spectrum detecting means for detecting a receiving frequency spectrum from the receiving acoustic signal. By comparing the noise frequency spectrum with the receiving frequency spectrum, the determining unit for determining a range in which the receiving frequency spectrum is masked by the noise frequency spectrum, and the noise frequency spectrum is more than the receiving frequency spectrum. Based on the level difference in the mask area
A level change range consisting of at least one of a frequency range equal to or lower than a lower limit frequency necessary to obtain a desired call intelligibility and a frequency range exceeding the necessary lower limit frequency, a level change amount of a frequency spectrum of the received acoustic signal, and Level change determination means for determining a level change direction of the frequency spectrum of the received acoustic signal so that the received frequency spectrum is equal to or higher than the level of the noise frequency spectrum, the level change range, the level change amount, and the level And a frequency characteristic changing means for changing the frequency spectrum level of the received acoustic signal based on the changing direction. 7. The level change determination means, when the maximum level difference between the noise frequency spectrum and the reception frequency spectrum is equal to or less than a predetermined limit value, the level change range is a frequency range equal to or less than the required lower limit frequency. 7. The telephone set according to claim 6, wherein the level change amount is determined to be the maximum level difference. 8. The level change determination means, if the maximum level difference between the noise frequency spectrum and the reception frequency spectrum exceeds a predetermined limit value, exceeds the level change range at least the required lower limit frequency. The telephone according to claim 6 or 7, wherein a frequency range is determined, and the level change amount is determined as a level difference between the noise frequency spectrum and the reception frequency spectrum at the required lower limit frequency. 9. The level change determination means determines a level falling range to be a frequency range equal to or lower than the required lower limit frequency,
9. The telephone according to claim 8, wherein the level increase range is determined to be a frequency range exceeding the required lower limit frequency. 10. The telephone according to claim 6, wherein the frequency characteristic changing means comprises a filter having a variable filter coefficient. 11. The telephone according to claim 10, wherein the frequency characteristic changing means comprises an echo canceller for removing an echo component from the received acoustic signal.