JP2586847B2 - Electronic telephone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic telephone, and more particularly to an electronic telephone which detects ambient noise and improves speech quality.

[0002]

2. Description of the Related Art In recent years, mobile telephones 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 in any place. The point that the call place is not selected is a great feature of the mobile telephone, but includes a problem that the call quality is degraded when used in a noisy environment.

[0003] Japanese Patent Application Laid-Open No. 63-191447 discloses a telephone having a noise suppressing function. As shown in FIG. 7, a conventional telephone has a microphone 40 and a noise detection circuit 30 for detecting an ambient noise level.
Is provided. The noise detection circuit 30 outputs the noise level signal S20 to the reception circuit 34, the filter circuit 37, and the reception circuit 39, respectively. This noise level signal S20
Accordingly, the gains of the receiving circuit 34 and the receiving circuit 39 are adjusted, and the frequency characteristics of the filter circuit 37 are controlled.

When there is an incoming call to the line terminal 32 through the line, the incoming call circuit 39 generates an incoming call signal S21, whereby the speaker 31 sounds. Since the gain of the incoming circuit 39 is adjusted by the noise level signal S20, the incoming notification sound is automatically adjusted in volume according to the surrounding noise.

When a line is set, the hybrid circuit 3
The signal received through 3 is input to a receiving circuit 34, and the receiving circuit 34 outputs a receiving sound signal S22 to a receiver (that is, a speaker) 38. Since the gain of the receiving circuit 34 is adjusted by the noise level signal S20, the volume of the received voice output from the speaker 38 is automatically controlled according to the surrounding noise level. On the other hand, a microphone (a microphone)
36 outputs the transmission sound signal S23 to the filter circuit 37. The filter circuit 37 is composed of a high-pass filter,
The cutoff frequency changes according to the noise level signal S20. Therefore, the noise frequency component lower than the cutoff frequency is removed from the transmission sound signal S23, and the transmission circuit 3
5 is output. The transmission circuit 35 is a hybrid circuit 3
The transmission signal is transmitted to the line through the line 3.

[0006]

However, in the above-mentioned conventional telephone, it is necessary to separately provide a macrophone for detecting ambient noise, and to separate the microphone from the transmitter 36 in order to collect only the noise. It is necessary to install in the position where it was. For this reason, if the conventional noise suppression system is adopted, it is difficult to reduce the size and weight of the telephone, which is particularly disadvantageous for a mobile telephone.

An object of the present invention is to provide a small-sized electronic telephone capable of obtaining a sufficient communication quality even when the ambient noise level is high.

Another object of the present invention is to provide a small-sized electronic telephone capable of obtaining sufficient call clarity even when the surrounding noise level is high.

[0009]

According to the present invention, there is provided an electronic telephone, comprising: a noise detecting means for detecting a noise component from a transmission sound signal output from a transmitter; and a power level of the noise component and a first threshold value. Noise level determining means for determining the noise level of the noise component by comparing, and noise removing means for removing the noise component from the transmitted audio signal when the noise level is equal to or higher than the first threshold value. Features.

Further, in the electronic telephone according to the present invention, when the noise level is equal to or higher than a second threshold value larger than the first threshold value, it is necessary to obtain a desired call clarity based on the noise level. Level change range consisting of at least one of a frequency range equal to or lower than the lower limit frequency and a frequency range exceeding the required lower limit frequency, the level change amount of the frequency spectrum of the received audio signal, and the frequency spectrum of the received audio signal Level change determining means for determining the level change direction of the frequency spectrum of the received sound signal that is equal to or higher than the level, and changing the frequency spectrum level of the received sound signal based on the level change range, the level change amount, and the level change direction Frequency characteristic changing means.

[0011]

The noise component is detected from the transmitted sound signal, and the noise component is removed from the transmitted sound signal based on the noise level. Further, when the noise level is high, the frequency adjustment of the frequency spectrum of the received audio signal is performed based on the noise level at the required lower limit frequency so as to obtain a predetermined call clarity.

[0012]

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

FIG. 1 is a block diagram showing a portable telephone according to one embodiment of the present invention. The receiver of the present embodiment includes an antenna 101, a receiver 102, and a digital signal processor (D
SP) 103, receivers 104 to 107, D / A converter 1
08, a volume controller 109, an amplifier 110, and a speaker 111. The transmitting unit includes a microphone 112, an amplifier 113, an A / D converter 114, a DSP
It comprises 103 transmitting units 115 to 117 and a transmitting unit 118.

The main operation of this embodiment is executed by the DSP 103 using the control software stored in the memory 119. The receiving unit of the DSP 103 includes a channel decoder 104, a speech decoder 105, a frequency characteristic control unit 106, and a side tone removing unit 107, and the transmitting unit includes a noise removing circuit 115, a speech coder 116, and a channel coder 117.

The receiving section 102 receives radio waves through the antenna 101 and outputs a digital reception signal D 6 to the channel decoder 104. The digital reception signal D6 is decoded by the channel decoder 104, and further decoded by the speech decoder 105 into a digital audio signal D7. The digital audio signal D7 is output to the speech decoder 105
To the frequency characteristic control unit 106, where the frequency characteristic of the digital sound signal D7 is
It is changed according to 2. Output signal D8 of frequency characteristic control section 106 and side tone suppression signal D3 from noise removal circuit 115
And the sidetone removing unit 107 outputs the digital sound signal D8
From the digital sound signal D9,
/ A converter 108. The digital sound signal D9 is converted into an analog sound signal A2 by the D / A converter 108, and further, the sound volume controller 109 and the amplifier 11
0 is output to the speaker 111.

On the other hand, the microphone 112
The analog audio signal A1 output from the A / D converter is amplified by the amplifier 113, and further converted by the A / D converter 114 into a digital audio signal D1. This digital sound signal D
As described later, the noise elimination circuit 115 determines the noise level and further removes a noise component from the digital audio signal D1. The noise elimination circuit 115 outputs the noise level determination signal D2 to the frequency characteristic control unit 106 and the side sound signal D3 to the side sound elimination unit 107, respectively.
The digital audio signal D4 from which the noise component has been removed is encoded by the speech coder 116 and the channel coder 117, respectively, and the encoded signal D5 is transmitted by the transmitting unit 118.
Wirelessly transmitted through the antenna 101.

The noise removal circuit 115 FIG. 2 is a block diagram showing the configuration of the noise elimination circuit in this embodiment. As shown in FIG.
5 is a regression determining circuit 210, a noise level determining circuit 2
02, buffer 203, and controllable difference circuit 204
Consists of The regression determining circuit 201 compares the current sound signal with the previous sound signal to obtain the digital sound signal D.
One repetition is detected. When repetition occurs in the digital sound signal D1, the regression determination circuit 201 outputs a noise detection signal to the noise level determination circuit 202.

When a noise detection signal is input from the regression determination circuit 201, the noise level determination circuit 202 inputs the digital sound signal D1 at that time as a noise signal.
The power level (hereinafter referred to as a noise level) is determined. Here, the noise level is determined in four stages: low, medium, high, and very high. For example, three thresholds are set in advance in the noise level determination circuit 202, and when the noise power is smaller than the low threshold, the noise level is set to “small”, and when the noise power is equal to or higher than the low threshold, the noise level is set to be higher than the high threshold. If it is small, it is "medium", and the level limit Lt is over the high threshold.
If it is smaller than h, it is determined as "large", and if it is equal to or more than the level limit Lth, it is determined as "very large". Level limit Lth
Is the maximum level of the received sound signal at which no sound distortion occurs in the volume controller 109. Such a noise level determination signal D2 is output from the noise level determination circuit 202 to the buffer 203, the controllable difference circuit 204, and the frequency characteristic control unit 106.

The write / read control of the buffer 203 is performed by an input / output control unit (not shown). In this case, the noise level determination signal D2 indicates one of “medium”, “large”, and “very large”. Only when indicated, the digital audio signal D1 is stored. In other words, when the noise level is equal to or higher than the low threshold, the buffer 203 always stores and updates the noise signal.

The controllable difference circuit 204 removes the noise signal stored in the buffer 203 from the digital sound signal D1 according to the noise level determination signal D2. Specifically, when the noise level determination signal D2 is “medium”, “large” or “very large”, a difference operation of subtracting the noise signal from the digital sound signal D1 is performed, and the noise level determination signal D2 Is small, the differential operation is not performed. Output signal D4 of controllable difference circuit 204
Is output to the speech coder 116 as a transmission sound signal, and further output to the side-tone removing unit 107 as a side-tone suppression signal D3.

The frequency characteristic control unit 106 FIG. 3 is a block diagram of a frequency characteristic control unit in the present embodiment. As shown in FIG.
Comprises a frequency spectrum level control unit 301, a coefficient control unit 302, and a digital filter 303. The frequency spectrum level control unit 301 includes a noise removal circuit 115
Input the noise level determination signal D2. According to the noise level determination signal D2, the frequency characteristic control unit 106
Outputs to the coefficient control unit 302 a control signal SC1 for controlling the reception spectrum level in a frequency region lower than the required lower limit frequency Af and a control signal SC2 for controlling the spectrum level in a frequency region higher than the required lower limit frequency Af.
The coefficient control unit 302 controls the level control signals SC1 and SC2
, The filter coefficient of the digital filter 303 is changed at the required lower limit frequency Af (see FIG. 6).

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

FIG. 4 is a flowchart showing the operation of this embodiment. When noise is detected in the digital acoustic signal D1 by the regression determination circuit 201 (S501), the noise level determination circuit 202 measures the noise power level at that time (S502) and outputs the above-described noise level determination signal D2. (S503).

When the noise level is "small", the frequency spectrum level control section 301 sends the control signals SC1 and SC2 to the coefficient control section 302 so that the received sound signal D8 maintains a flat spectrum S3 (see FIG. 6). It outputs (S504). Further, the controllable difference circuit 204 does not perform a difference operation on the digital sound signal D1 and outputs the digital sound signal D1 to the speech coder 116 as it is.

When the noise level is "medium", the frequency spectrum level control unit 301 also receives the received sound signal D8.
Is controlled so as to obtain a flat spectrum S3 (S505), but the controllable difference circuit 204 performs a difference operation of removing a noise component stored in the buffer 203 from the digital audio signal D1 (S506).

When the noise level is "high" or "very high", the frequency spectrum level control unit 301 performs spectrum control described later (S507), and the controllable difference circuit 204 outputs the buffer 2 from the digital audio signal D1.
Then, a difference operation for removing the noise component stored in No. 03 is performed (S508).

Next, the frequency characteristic control (S507) will be specifically described with reference to FIG.

FIG. 5 is a flowchart showing the frequency characteristic control in this embodiment. When the noise level is determined to be “large” (S601), the frequency spectrum level control unit 301 causes the received sound signal D7 to be higher than the noise level in a frequency region (low band) lower than the necessary lower limit frequency Af. To determine the level increase amount (S6
02), a level increase control signal SC1 in a frequency region lower than the necessary lower limit frequency Af is generated (S603).
In accordance with the control signal SC1, the coefficient control unit 302 changes the filter coefficient of the digital filter 303, and in the frequency domain lower than the necessary lower limit frequency Af, the reception sound signal D
8 is raised above the noise spectrum level, and is not changed in a frequency region (high band) higher than the necessary lower limit frequency Af (S604).

On the other hand, if the noise level is very high (S601), the frequency spectrum level control unit 301 determines that the increase in the low-frequency level cannot cope with it, gives up the voice basic formant area, and secures a predetermined intelligibility. For this purpose, the level of the received sound signal D7 in the high frequency range equal to or higher than the frequency Af is increased. That is, the frequency spectrum level control unit 301 determines the level change amount so as to raise the reception spectrum to a level higher than the noise spectrum in a frequency higher than the frequency Af (S605). This level change amount is also used as a decrease amount of the received spectrum level in the low frequency band. According to this level change amount,
The frequency spectrum level control unit 301 generates a control signal SC1 for lowering the low frequency level and a control signal SC2 for increasing the high frequency level, and outputs them to the coefficient control unit 302 (S606). Accordingly, the coefficient control unit 302
Changes the filter coefficient of the digital filter 303 to raise the high-band spectral level of the received sound signal D7 to the noise spectral level or higher, and lower the low-band spectral level by the same level (S607).

As described above, the level of the spectrum of the received sound signal D7 is raised in the frequency range higher than the necessary lower limit frequency Af and lowered in the frequency range lower than the frequency Af, thereby increasing the power consumption while maintaining the clarity. Can be suppressed.

Next, a specific example of frequency characteristic control in this embodiment will be described with reference to FIG.

FIG. 6 is a graph showing the spectral amplitude distribution of the received audio signal and the noise in the present embodiment when the noise level is "very large" and "very large". Symbols f1 to f5 in the figure indicate a general spectrum distribution of 1 / f noise, and the noise level decreases in the direction from the symbol f1 to f5. Symbols S1 to S5 are reception sound signals D8.
The symbol S3 is a flattened spectrum distribution serving as a reference, and the other symbols represent the spectrum distribution of the received audio signal D8 whose spectrum is controlled. However, here, the frequency bandwidth is 300 Hz to 3.4 kHz.
z.

The frequency characteristic control of this embodiment adjusts the spectral distribution of the received sound signal D7 so as to improve the clarity of the received sound. Therefore, it is important to adjust the frequency characteristics so that the reception spectrum S is equal to or higher than the noise spectrum f in a high frequency band of 1 kHz or more necessary for obtaining a predetermined clarity.

First, when the noise spectrum has the spectrum distribution f3, the low band of 1 kHz or less is masked by the noise spectrum f3. That is, in the frequency range of 1 kHz to 3.4 kHz related to the predetermined clarity, the level of the reception spectrum S3 is higher than the noise spectrum f3, but lower in the frequency range of 300 to 1 kHz. The noise spectrum f3 and the reception spectrum S3
Is smaller than the level change limit Lth, and as shown by the curve S5, the reception spectrum S up to the noise level at the lowest frequency 300 Hz in the predetermined frequency band.
3 (for example, a level increase amount 10d)
B).

In accordance with the level increase, the frequency spectrum level control section 301 outputs the level control signal SC1 to the coefficient control section 302, and obtains the reception spectrum distribution shown by the curve S5. That is, by the level control signal SC1, 3
The reception spectrum in the frequency range of 00 to 1 kHz is 10
dB rises above the noise spectrum and becomes 1 kHz ~
The reception spectrum in the high band of 3.4 kHz does not change (S604 in FIG. 5).

When the noise level decreases and becomes the noise spectrum distribution shown by the curve f4, only a part of the low band of the reception spectrum S3 is masked. Therefore,
The frequency spectrum level control unit 301 raises the reception spectrum S3 to the noise level at the lowest frequency of 300 Hz (for example, the level increase amount is 5 dB), and obtains the reception spectrum distribution indicated by the curve S4, similarly to the control described above.

When the ambient noise exceeds a certain level, for example, when the maximum level difference between the noise spectrum f2 and the reception spectrum S3 exceeds the level change limit Lth, the frequency spectrum level control unit 301 changes the frequency spectrum from 1 kHz to 3.4 kHz.
The reception spectrum in the high frequency range of
The reception spectrum in the low band of 00 to 1 kHz is lowered by the same level. The level change amount is determined so that the reception spectrum becomes higher than or equal to the noise spectrum f2 in the high frequency range. Specifically, the level difference between the noise spectrum f2 at the frequency of 1 kHz and the reception spectrum S3 is set as the level change amount. Noise spectrum f2
In the case of, the level change amount is about 5 dB,
The frequency is raised by dB, and the low frequency is lowered by 5 dB. Thus, the reception spectrum is 1 kHz as shown in the curve S2.
The spectrum distribution has a slope around z. Similarly, in the case of the noise spectrum f1, a level change amount of about 10 dB is determined, and the reception spectrum has the spectrum distribution shown by the curve S1 (S607 in FIG. 5).

As described above, when the surrounding noise level becomes higher than the limit as shown by symbols f2 and f1, the low-frequency component level below the necessary lower limit frequency Af is reduced and the high-frequency component level is raised. Energy can be concentrated on ensuring clarity. Therefore, even in a high-noise environment, a call can be made with sufficient clarity, and power consumption can be suppressed.

[0039]

As described above in detail, according to the present invention, a noise component is detected from a transmission audio signal, and when the noise level is higher than a certain value, the noise component is transmitted. If the noise level is removed from the signal and the noise level is larger than a certain level limit, the low-band spectrum level of the received sound signal is reduced and the high-band spectrum level is raised. As a result, it is possible to communicate with sufficient clarity even in an environment where the surrounding noise level is high. In addition, a microphone for noise detection is separately installed to detect noise from the transmitted sound signal, remove noise components from the transmitted sound signal according to the level thereof, and perform spectrum control of the received sound signal. There is no need, and the telephone can be downsized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a mobile telephone according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a noise removal circuit according to the present embodiment.

FIG. 3 is a block diagram illustrating a configuration of a frequency characteristic control unit according to the embodiment.

FIG. 4 is a flowchart illustrating the operation of the present embodiment.

FIG. 5 is a flowchart showing a spectrum control routine in FIG. 4;

FIG. 6 is a graph showing a spectral amplitude distribution of a received audio signal and noise in the present embodiment.

FIG. 7 is a block diagram showing an example of a conventional telephone.

[Explanation of symbols]

 Reference Signs List 101 antenna 102 receiving unit 103 DSP 104 channel decoder 105 speech decoder 106 frequency characteristic control unit 107 side sound removing unit 108 D / A converter 109 volume controller 110 amplifier 111 speaker 112 microphone 113 amplifier 114 A / D converter 115 noise removing circuit 116 Speech coder 117 Channel coder 118 Transmitter 119 DSP control software memory 201 Recursiveness determination circuit 202 Noise level determination circuit 203 Buffer 204 Controllable difference circuit 301 Frequency spectrum level control unit 302 Coefficient control unit 303 Digital filter Lth level change limit value Af Lower limit frequency required for ensuring intelligibility S1-S5 Frequency spectrum distribution of received sound signal f1-f5 Noise frequency spectrum

Claims (6)

(57) [Claims] 1. An electronic telephone comprising a transmitter for outputting a transmission sound signal and a receiver for inputting a reception sound signal, a noise detection means for detecting a noise component from the transmission sound signal, and a power of the noise component. A noise level determining unit that determines a noise level of the noise component by comparing a level with a first threshold value; and when the noise level is equal to or greater than the first threshold value, An electronic telephone, comprising: noise removing means for removing a noise component. 2. The electronic telephone according to claim 1, wherein said noise detecting means comprises recursiveness detecting means for detecting occurrence of repetition of said transmission sound signal. 3. The noise elimination unit includes: a storage unit configured to store the noise component when the noise level is equal to or higher than the first threshold; and a storage unit configured to store the noise component when the noise level is equal to or higher than the first threshold. 3. The electronic telephone according to claim 1, further comprising: a difference unit configured to subtract the noise component stored in the storage unit from the transmission audio signal. 4. When the noise level is equal to or higher than a second threshold value that is higher than the first threshold value, a frequency equal to or lower than a lower limit frequency required to obtain a desired call clarity based on the noise level. A level change range comprising at least one of a range and a frequency range exceeding the necessary lower limit frequency, a level change amount of a frequency spectrum of the received sound signal, and a frequency spectrum of the received sound signal is equal to or higher than a frequency spectrum of the noise component. Level change determining means for determining a level change direction of a frequency spectrum of the received sound signal, and a frequency spectrum of the received sound signal based on the level change range, the level change amount, and the level change direction. 2. A frequency characteristic changing means for changing a level, further comprising: Child phone. 5. The frequency characteristic changing means comprises a digital filter having a variable filter coefficient, wherein the filter coefficient is changed based on the level change range, the level change amount, and the level change direction. The electronic telephone according to claim 4, wherein 6. The apparatus according to claim 1, further comprising a side sound removing unit that uses a transmission sound signal output from the noise removing unit as a side sound suppression signal and removes a side sound from the received sound signal. The electronic telephone according to 1 or 4.