JPH0371720B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a voice detection method and circuit for determining the presence or absence of a voice signal. (Prior art and its problems) Voice detection circuits are mainly DSI (Digital Speech
It is an abbreviation for Interpolation. ) is incorporated into the device and is used to determine whether an audio signal is present on the input channel to the DSI device. Regarding DSI equipment, for example, see the document "COMSAT TECHNICAL REVIEW" vol.6 No. published in March 1976.
1, pp. 127-158, "Digital Speech Interpolation", please refer to the paper by SJ Campanella. Conventionally, the level detection method is known as a method with simple hardware scale and clear detection logic, but this method detects the signal energy (power and amplitude) of the input signal and then compares it with a threshold. This is to determine the presence or absence of a signal. Furthermore, among voice detectors that use the level detection method, fixed-threshold voice detectors that compare the amplitude of the input signal with a predetermined threshold are the simplest and most reliable voice detectors in terms of hardware scale. known as. Next, the principle of this fixed threshold type voice detector will be explained with reference to the drawings. FIG. 1 is a block diagram showing the principle of a fixed-threshold voice detector, in which there is a signal input terminal 1, an amplitude threshold input terminal 2, an amplitude comparison circuit 3, an accumulation circuit 4, and input signals of +1 and -1 to the accumulation circuit. increase/decrease control lines 5 and 6, flip-flop 7 for voice detection, flip-flop set/reset control lines 8 and 9 for voice detection, voice detection result output terminal 1
Starting from 0. In this case, the accumulation circuit can be replaced with a reversible counter (up-down counter). In the figure, the input signal input from terminal 1 is sent to the amplitude comparator circuit 3 every sampling period, and the input signal is input from terminal 2 to a predetermined amplitude threshold value (THa).
compared to As a result, if the input signal amplitude is greater than the amplitude threshold, the contents of the accumulator circuit 4 are incremented by one using the accumulator increment control line 5. Also,
Conversely, if the input signal amplitude is less than the amplitude threshold, the contents of the accumulator circuit 4 are decremented by one using the accumulator decrement control line 6. However, the contents of the accumulator circuit are designed not to take a negative value. As audio signals arrive and more inputs exceed the amplitude threshold, the contents of the accumulator circuit increase sequentially. Of course, if an input below the amplitude threshold is added during that time,
The contents of the accumulator circuit are decreased by one. In this way, when the contents of the accumulator circuit reach the preset duration threshold (THt), the voice detection flip-flop 7 is set using the voice detection flip-flop set control line 8, and the voice is detected. The result is output from the terminal 10. Also, when no voice is detected, which is indicated by the content of the accumulator circuit 4 becoming 0, for example, the voice detection flip-flop 7 is reset using the voice detection flip-flop reset control line 9; The result is output from terminal 10, but is generally reset after a certain period of time. This is called a hangover, and is created because the ear is sensitive to disconnections between words or phrases during a call.
It is about 250ms. For further understanding, an explanation will be given by taking as an example a case where a signal indicated by 11 in a of FIG. 2 is input to the fixed threshold type voice detector shown in FIG. 1. FIG. 2 shows an input signal 11, an amplitude threshold 12, an accumulation circuit content 13, a duration threshold 14, and a voice detection result output 15. First, when the input signal 11 is input from the terminal 1, it is compared with the amplitude threshold value 12 by the amplitude comparison circuit 3 every sampling period Ts. As can be seen from Figure 2, the amplitude of the input signal becomes larger than the amplitude threshold only at time t _a1 , so the contents of the accumulation circuit 1
3 starts to become 1 at time t _a1 (Fig. 2b), and thereafter increases by 1 until time t _a2 . As a result, at time _tb1 , the content 13 of the accumulator circuit becomes larger than the duration threshold 14, which means that voice has been detected, and the output 15 becomes 1. By the way, at time t _a3 , the amplitude of the input signal 11 becomes smaller than the amplitude threshold 12, so the content 13 of the accumulation circuit decreases by 1 until time t _b2 ,
Since the duration becomes smaller than the threshold value 14, it is determined that the audio signal has disappeared, and a hangover is added for the above-mentioned reason, and after the hangover ends, the output is 1.
5 becomes 0. T _H in c of FIG. 2 indicates the hangover time. Although the fixed-threshold sound detector described above does have a simple hardware scale, it has the drawback that once the threshold is set, it will detect even noise as long as it is at a level above the threshold. (Object of the Invention) The object of the present invention is to provide a variable threshold type that has a threshold that changes depending on the noise power contained in the input signal, reduces the frequency of false detection of noise, and improves the voice detection ability. The purpose of the present invention is to provide a voice detector. (Structure of the Invention) According to the present invention, the magnitude determination results between the audio signal input at each sample time and the first and second thresholds that vary depending on the silent section noise level of the audio signal are accumulated, The signal level of the input signal is determined by comparing the cumulative value with a third threshold value, and when the determination result changes from a high signal level to a low signal level, a predetermined time period is added to the determination result. In the voice detection method, a predetermined high-level threshold and a low-level threshold determined according to the noise level are prepared as the third threshold, and the voice detection output is determined as a voice. A low level threshold is used to notify the presence of a signal, and a high level threshold is used to perform voice detection when the voice detection output indicates no voice signal, and even in the added sound section, the low level is determined depending on the noise. A voice detection method is obtained which is characterized by using a threshold value of . Further, according to the present invention, there is provided a noise power calculation circuit that calculates a silent section noise level of an input signal inputted at each sample time, and a first and second threshold value that fluctuates according to the output of the noise power calculation circuit. a first threshold generation circuit that generates a first threshold, a level detection circuit that determines the magnitude of the input signal and the first and second thresholds and outputs the result, and an accumulation circuit that accumulates the output of the level detection circuit; The second threshold output from the first threshold generation circuit is input, and one of a plurality of predetermined low-level thresholds is selected and output according to the level of the second threshold. A selection circuit, a threshold value outputted from the selection circuit, and a predetermined high level threshold value are inputted, and when the output of an output holding circuit, which will be described later, indicates the presence of an audio signal, the low level outputted from the selection circuit is inputted. a second threshold value, and when the output of the output holding circuit indicates that there is no audio signal, the predetermined high level threshold value is selected and outputted as a third threshold value;
a threshold generation circuit; a determination circuit that determines the presence or absence of an audio signal by comparing the output of the accumulation circuit with a third threshold output from the second threshold generation circuit; an output holding circuit that adds a predetermined time as a sound interval to the output of the determination circuit when the sound signal changes from presence to absence; A voice detection circuit characterized in that the third threshold value used in the sound interval is varied according to the noise level is obtained. (Embodiment) The present invention has the above-described configuration, and adaptively changes the amplitude thresholds (first and second thresholds) and the third threshold (TH3L) used in the sound section according to the noise level. This improves voice detection ability without increasing false detections due to noise. The present invention will be explained in detail with reference to the drawings.
FIG. 3 shows an embodiment of the present invention, in which the input terminal 2
0, even bit inversion circuit 21, code conversion circuit 2
2. Rectifier circuit 23, power calculation circuit 24, first threshold generation circuit 25, level detection circuit 26, accumulation circuit 27, comparison circuit 28, second threshold generation circuit 29,
It is composed of a reversible counter 30, a counter setting circuit 31, a determination circuit 32, an output terminal 33, and a selection circuit 34. For example, the International Telegraph and Telephone Consultative Committee, (CCITT;
Comite´ C onsultatif I nternational T ´
elegraphaique et T´ele´phonique ), and is non-linearly encoded based on recommendation G.711 from
See pp409-410. ) is input from the input terminal 20 as an example. A-Law, which is usually transmitted over telephone lines.
Since the even-numbered bits of the code signal are inverted when viewed from the MSB (abbreviation for Most Significant Bit ) side, the even-numbered bits of the input signal are inverted by the even-numbered bit inversion circuit 21, and the input signal is converted into a signal before being transmitted. The original signal is returned. The returned A-Law code signal is sent to the code conversion circuit 22, and as shown in FIG. 4, for the positive A-Law code signal, only the MSB,
For negative A-Law code signals, all bits are inverted and an 8-bit two's complement number is used.
It is converted into a code signal and input to the rectifier circuit 23. The rectifier circuit 23 converts this input signal into an absolute value signal (signal representing only the magnitude), one of which is sent to the power calculation circuit 24 and the other to the level detection circuit 26. The power calculation circuit 24 extracts the noise contained in the input signal and calculates the effective value of the noise. Specifically, when no audio is detected (e.g.
(When the output of the comparison circuit 28 described below is 0), all input signals are considered as noise, and even when voice is detected (for example, when the output of the comparison circuit 28 described later is 1), the predetermined A signal below this level is considered to be noise, and this noise is input to a low-pass filter to calculate the effective value of the noise, and the result is sent to the first threshold generation circuit 25. Therefore, the audio signals that are excluded when calculating the effective value of noise are those signals in which the output of a comparison circuit, which will be described later, is 1 and which has a signal level equal to or higher than a predetermined level. First threshold generation circuit 25
Now, by multiplying the output from the power calculation circuit 24 by a constant, the first threshold (TH1) used in the level detection circuit 26 and the second threshold (TH2) are set at a location 6 dB higher than the first threshold. is set and sent to the level detection circuit 26. The level detection circuit 26 uses the output of the rectification circuit 23 and the first
The threshold value and the second threshold value are compared, and since there is a high probability that the input signal is an audio signal where the output of the rectifier circuit is larger than the second threshold value, +2 is added between the first threshold value and the second threshold value. , the probability that the input signal is a voice signal and the probability that it is noise are approximately equal, or the former is slightly higher, so
If it is smaller than the first threshold, there is a high probability that the input signal is noise, so -1 is output. Accumulation circuit 2
7, the output of the level detection circuit 26 is accumulated and the accumulated value is sent to the comparison circuit 28. The comparison circuit 28 compares a third threshold (TH3) output from a second threshold generation circuit 29, which will be described later, with the cumulative value, and if the latter is larger than the former, the input signal is an audio signal. It is determined that +1 is given, and
If the former is larger than the latter, the input is determined to be noise and 0 is output. The selection circuit 34 selects and outputs one of a plurality of predetermined low-level thresholds according to the level of the second threshold (TH2) output from the first threshold generation circuit described above. do. The second threshold generation circuit 29 generates a low level threshold (TH3L) output from the selection circuit and a predetermined high level threshold (TH3H).
is input, and when the output of the determination circuit 32 described later is 0 (when there is no sound), the predetermined high level threshold is selected, and the determination circuit 32 described later
When the output is 1 (when there is a sound), the low level threshold outputted from the selection circuit is selected and outputted as the third threshold used by the comparison circuit 28. The reversible counter 30 inputs the output of the comparison circuit 28, and when the input signal is 1, the contents of the counter are increased by 1, and when the input signal is 0, the contents of the counter are decreased by 1, and the output of the comparison circuit is accumulated. ing. Further, the counter setting circuit 31 monitors the output of the comparison circuit, detects the point in time when the output changes from 1 to 0, and sets the contents of the reversible counter 30 to a predetermined value at that point. . In the determination circuit 32, the contents of the reversible counter 30 are set to a predetermined value (usually 0 is used).
1 if an audio signal is detected.
is output to the outside via the output terminal 33. Of course, if it is small, 0 is output, but doing so will also result in the above-mentioned hangover. The circuit shown in FIG. 5 can be used as the power calculation circuit 24 and the first threshold generation circuit 25 in FIG. unit 53, OR circuit 54, multipliers 55, 56,
57, 58, multiplicand input terminals 59, 60, 61,
62, 63, a multiplicand selector 64, an adder 65, limiters 66, 67, a memory 68, a first threshold output terminal 69, and a second threshold output terminal 70. Absolute value input signal is input terminal 50
One is sent to the multiplier 55 and the other is sent to the comparator 53. The comparator 53 compares the input signal with the noise judgment level input from the input terminal 51, and outputs 0 if the former is larger than the latter, and +1 if it is smaller.
Then, the output signal of the comparator 53 and the inverted signal of the output signal from the comparison circuit 28 are logically summed, and when at least one of them is +1, the output signal is +1.
is output, and serves as a control signal for the multiplier 56 and a selection control signal for the multiplicand selector 64. In the multiplicand selector 64, when the selection control signal is +1, the multiplicand input from the multiplicand input terminal 59 is selected, and when it is 0, the multiplicand input from the multiplicand input terminal 60 is selected (currently 0 is used). ) is selected and becomes the multiplicand of the multiplier 55. Further, in the multiplier 55, the product of the absolute value input signal and the multiplicand selected as described above is calculated and sent to the adder 65. On the other hand, multiplier 56 multiplies the multiplicand input from multiplicand input terminal 61 and the contents of memory 68 and sends the product to adder 65 . However, when the output of the OR circuit 54 is 0, this multiplication is not performed and the contents of the memory 68 are output as they are. Then, in the adder 65, the multiplier 55 described above
The output of the multiplier 56 is added to the output of the multiplier 56, and the result is stored in the memory 68 via the limiter 66. At the same time, limiter 66
The output of is sent to the multiplicand input terminal 62 by the multiplier 57.
The multiplicand inputted from the multiplicand is multiplied by the multiplicand, which becomes equal to the effective value (σ) of the noise, and is outputted from the output terminal 69 via the limiter 67 as the first threshold value (TH1). Further, the output of the limiter 67 is multiplied by the multiplicand (currently 2 is used) inputted from the multiplicand input terminal 63 in a multiplier 58, and the product is determined as a second threshold value (TH2) at the output terminal 70. It is output from Here, the limiters 66 and 67 are used to quickly adjust the threshold value by limiting the contents of the memory 68 and the variable range of the threshold value (TH1), and to limit the reception sensitivity and emotional level range of the audio detector. This is to ensure immunity against noise. Note that the power calculation circuit 24 calculates the noise level by passing the absolute value signal through a first-order low-pass filter as described above, but this is because the amplitude distribution is
The power P obtained by taking the absolute value of noise with a Gaussian distribution and a variance of σ ² and passing it through a first-order low-pass filter is approximately equal to the standard deviation (also called the effective value, with σ This is because the value is proportional to 5, which is expressed as 5. Here, ∫ ^∞ ₀ x exp{−x ² /(2σ ² )}dx (If x ² =y, 2xdx=dy) ∫ ^∞ ₀ 1/2exp{−y/(2σ ² )}dy = σ ² Therefore, equation (1) becomes as follows. Therefore, by performing the above processing, a value approximately proportional to the standard deviation σ of the noise amplitude can be obtained at the output of the first-order low-pass filter, and if this value is multiplied by a constant, the standard deviation of the noise amplitude (the effective value σ ) will be obtained. The reversible counter 30, counter setting circuit 31, and determination circuit 32 used in FIG.
The circuit shown in the figure can be used, including an input terminal 71, a one-sample delay circuit 72, an AND circuit 73, a counter setting value input terminal 74, a reversible counter 75, and a comparison circuit 7.
6, a threshold input terminal 77 and an output terminal 78, and 30, 31, and 32 surrounded by broken lines indicate a reversible counter, a counter setting circuit, and a determination circuit shown in FIG. 3, respectively. One side of the input signal input from the input terminal 71 is sent to the reversible counter 75.
and the other one is sent to a one-sample delay circuit 72 and an AND circuit 73. The AND circuit 73 multiplies the signal obtained by inverting the current input signal and the input signal one sample time ago.
The result is sent to the reversible counter 75. The reversible counter 75 increases the contents of the counter by 1 when the input signal is 1, and decreases the contents of the counter by 1 when the input signal is 0. 1
When the value changes from 0 to 0, the contents of the counter are forcibly set to a predetermined value input from the counter setting value input terminal 74. The comparator 76 compares the threshold value input from the threshold input terminal 77 (actually, 0 is used) with the content of the counter output from the reversible counter 75, and outputs 1 if the content of the counter is larger. It is output to the outside via the terminal 78. Further, as shown in FIG. 3, a second threshold generation circuit 29 is provided to generate a third threshold (TH3) used in the comparison circuit 28.
As such, the output of the determination circuit 32 is used as a selection signal, and when the selection signal is 1, a low level third threshold (TH3L) is selected, and when it is 0, a high level third threshold (TH3H) is selected and used. However, this is to avoid excessive ON/OFF of the speech detector by providing hysteresis in the output of the comparator circuit 28, and as will be described below, drop-offs and endings of words are reduced. For example, the audio signal (waveform 130
and 131. ) is input. If a waveform 130 arrives and is compared with the first and second threshold values in the level detection circuit 26, and as a result, an output like the waveform 132 shown in FIG. 7b is obtained as the output of the accumulation circuit 27, the comparison circuit At step 28, the output waveform 132 of the accumulation circuit 27 is compared with a third threshold value indicated by the changing waveform 134. As shown in FIG. 7b, until time T ₁ , the third threshold change waveform 134 is larger than the output waveform 132 of the accumulator 27, so no audio signal is detected, but at time T ₁ , the latter is larger. Since the value increases, the output waveform 135 of the comparison circuit 28 becomes 1, and the content waveform 137 of the reversible output holding counter 30 also begins to increase. Therefore, the output waveform 138 of the output terminal 33 also becomes 1, indicating that an audio signal has been detected. By the way, since the output of the output terminal 33 is 0 until time T ₁ , a high-level third threshold (TH ₃ H) is selected as the third threshold;
After T ₁ , the output of the output terminal 33 becomes 1, so
A third threshold (TH ₃ L) at a lower level is selected as shown by the changing waveform 134 in FIG. 7b. Thereafter, the amplitude of the input waveform 130 shown in _FIG . 7
It becomes 0 as shown in Figure c. However, as shown in FIG. 7c, the content waveform 137 of the reversible counter 30 does not immediately become 0, and data for hangover is set by the data setting circuit 31. A hangover is added to the output waveform. Therefore, when the waveform 131 shown in FIG. 7a arrives at the input terminal 20 when a hangover is added, the output waveform 133 of the accumulation circuit 27 reaches the second threshold value at time T ₃ as shown in FIG. 7b. Generation circuit 29
28 output waveform 13 of the comparator circuit is larger than the change waveform 134 indicating the third threshold outputted by
6 becomes 1 as shown in FIG. 7c, and the content 137 of the output holding reversible counter 30 increases again. Then, as shown in FIG. 7b, when the output waveform 133 of the accumulator circuit 27 becomes smaller than the changing waveform 134 indicating the third threshold at time _T4 , the output waveform 136 of the comparator circuit 28 becomes as shown in FIG. 7c. becomes 0, data for hangover is set in the reversible counter 30 as described above, and hangover is added. Then, at time _T5 , the hangover ends, so the output waveform 138 of the output terminal 33 (FIG. 7d) becomes 0, and the third threshold, which is at a high level, is selected again. Become. In this way, by selectively using the third threshold value as a high level third threshold value (TH3H) and a low level third threshold value (TH3L) depending on the output of the output terminal 33, the sound interval (output terminal When the output of 33 is 1), it becomes possible to detect low level audio signals (waveform 131 shown in FIG. 7a).
Word dropouts and word endings are reduced. Further, in the present invention, the TH3L selection circuit 34 inputs the second threshold value (TH2) output from the first threshold value generation circuit 25, as shown in the graph of FIG.
A predetermined value is selected according to the threshold value and outputted to the second threshold generation circuit 29 as TH3L. Therefore, since the threshold TH2 is a value determined according to the noise level included in the input signal, TH3L
is also a value determined according to the noise level included in the input signal. Note that, as shown in FIG. 8, the smaller the second threshold value (TH2), the smaller the value used as TH3L. This is because when a hangover is added, the smaller the noise level is, the smaller the time average value of the cumulative value becomes, so the distance between the cumulative value and the third threshold (TH3L) is kept constant. By keeping this distance constant regardless of the noise level, a constant detection ability is guaranteed, and therefore a constant operating time rate can be obtained regardless of the noise level. Therefore, if the third threshold value is used differently in the sound section and the silent section, and the third threshold value (TH3L) used in the sound section is made variable according to the noise level as shown in Fig. 8, then It is possible to reduce erroneous detection due to noise that occurs when a hangover is added, and also to reduce dropouts in the middle of words and dropouts at the end of words, and it is possible to realize a speech detector that has a constant and good operating time rate independent of the noise level. In addition, in this embodiment, as the output signal of the selection circuit 34 of the third threshold value (TH3L) used in the sound section,
Although the threshold value TH2 is used, even if the threshold value _TH1 or the output of the power calculation circuit 24 is changed, a TH3L that varies depending on the noise level can be obtained, and the same effect as the present invention can be obtained, and therefore it is included in the present invention. Note that the selection circuit 34 used in the present invention includes:
Since it can be configured using only ROM ( Read Only Memory ), only a simple addition of hardware is required. Furthermore, TH3H used in the silent section is also 1 of TH3L.
Considering the selection circuit 34 and the second threshold generation circuit 29 as a single selection circuit (for example, by using a ROM or the like), almost no additional hardware is required. (Effects of the Invention) As described above, in the variable threshold type voice detection circuit of the present invention, by performing signal processing using PCM codes, the hardware size does not increase, and the first and second Since the threshold value of 2 is varied, immunity to noise is strong. By specifying the maximum and minimum values of the threshold value, the reception sensitivity and emotional level range can be set arbitrarily. By using the third threshold values at different levels, it is possible to achieve constant good voice detection characteristics independent of the noise level.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional voice detector.
2 is a diagram showing the waveforms of each part in FIG. 1, FIG. 3 is a block diagram showing the speech detector of the present invention, FIG. 4 is a diagram showing the code conversion method, and FIGS. Block diagram showing details of a part of the components in Fig. 3, No. 7
The figure is a diagram for explaining the operation of the voice detection circuit of the present invention, and Figure 8 shows the second and third threshold values in the present invention.
FIG. In the figure, 20 is an input terminal, 21 is an even bit inversion circuit, 22 is a code conversion circuit, 23 is a rectifier circuit, 24 is a power calculation circuit, 25 is a first threshold generation circuit, 26 is a level detection circuit, and 27 is an accumulation circuit. circuit,
28 is a comparison circuit, 29 is a second threshold generation circuit, 3
0 is a reversible counter, 31 is a counter setting circuit, 3
2 is a determination circuit, 33 is an output terminal, and 34 is a selection circuit.

Claims (1)

[Claims] 1. A first signal that varies depending on the audio signal input at each sample time and the noise level of the silent section of the audio signal.
and a second threshold value, the result of the magnitude determination is digitized and accumulated, and the cumulative value is compared with the third threshold value to determine the presence or absence of an audio signal, and when the determination result changes from the presence of an audio signal to the absence of an audio signal. In a voice detection method for obtaining a voice detection output by adding a predetermined time to the determination result as a sound interval, the third threshold is determined according to a high level predetermined threshold and a noise level. A low level threshold is prepared, and the low level threshold is used when the voice detection output indicates the presence of a voice signal, and the high level threshold is used when the voice detection output indicates the absence of a voice signal. A voice detection method characterized in that a low level threshold determined according to noise is used even in an added voiced section. 2. A noise power calculation circuit that calculates the noise level of the silent period specified by the output of the below-mentioned determination circuit of the input signal input at each sample time, and a first threshold generation circuit that generates a second threshold, a level detection circuit that determines the magnitude of the input signal and the first and second thresholds, converts the result into a numerical value, and outputs the result; and an output of the level detection circuit. an accumulation circuit that accumulates the threshold value, and the second threshold value outputted from the first threshold value generation circuit, and selects one from among a plurality of predetermined low-level threshold values according to the second threshold level. A selection circuit that selects and outputs one, a threshold output from the selection circuit and a predetermined high level threshold are input, and when the output of an output holding circuit, which will be described later, indicates the presence of an audio signal, the selection circuit outputs an audio signal. a second threshold generation circuit that selects a low level threshold to be set, and selects the predetermined high level threshold and outputs it as a third threshold when the output of the output holding circuit indicates that there is no audio signal; a determination circuit that determines the presence or absence of an audio signal by comparing the output of the accumulation circuit and a third threshold output from the second threshold generation circuit; and an output of the determination circuit that changes from presence of audio signal to absence of audio signal. an output holding circuit that adds a predetermined time as a sound interval to the output of the determination circuit when the change occurs; A voice detection circuit characterized in that a threshold value of No. 3 is varied according to a noise level.