JP2658712B2 - Audio signal detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal detection circuit, and more particularly, to an audio signal detection circuit for detecting audio during recording / reproduction in a recording / reproduction apparatus for recording / reproduction of telephone line audio.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing an example of a conventional audio signal detection circuit. In the figure, for example, an input audio signal, which is a reproduction signal of a recording / reproducing apparatus that records an audio signal from a telephone line, is filtered by a filter circuit 21 to remove unnecessary band noises, and then, by a voltage level detection circuit 22, The value is converted to a voltage corresponding to any one of a value, a peak value, and an effective value. This voltage value is held in the time constant circuit 23 for a certain period of time, and is input to the level determination circuit 24. The level determination circuit 24 includes: a preset reference voltage corresponding to a certain level of the audio signal;
Time constant circuit 23 corresponding to the voltage level of the input audio signal
And compare the output voltages. Therefore, when an audio signal of a certain level or more corresponding to the reference voltage is input, an audio detection signal indicating that the audio has been detected is output.

[0003]

However, in the above-mentioned conventional circuit, the presence / absence of an audio signal is determined only by the voltage level of the input signal, so that the signal-to-noise ratio of the input audio signal is less than 20 dB. If the reference voltage is set low so that a low-level audio signal can be detected, noise will be detected as audio.If the reference voltage is set high so that noise will not be erroneously detected as audio, a low-level audio signal will be detected. There is a problem that it cannot be done. Further, there is a problem that noise at the time of telephone line disconnection is erroneously detected as a voice signal.

[0004] The present invention has been made in view of the above, and even if the signal-to-noise ratio of an input audio signal is less than 20 dB,
It is an object of the present invention to provide an audio signal detection circuit which has a low probability of erroneously detecting noise as an audio signal, can correctly detect an audio signal with a high probability, and does not erroneously detect noise at the time of telephone line disconnection as an audio signal. Aim.

[0005]

FIG. 1 is a block diagram showing the principle of the present invention. In the figure, 11 is a filter circuit, Ru passes the signal in a specific band in the input signal. Reference numeral 12 denotes a voltage level detection circuit that detects an output voltage Va that is an average value or an effective value of output voltages of the filter circuit 11. Reference numeral 13 denotes a peak value detection circuit which outputs a peak value of the output voltage of the filter circuit 11.
The voltage Vp is detected. Numeral 14 denotes a level judging means, wherein the output voltage Va of the voltage level detecting circuit 12 is equal to or higher than a preset voltage level reference value, and the output voltage Vp of the peak value detecting circuit 13 is a preset peak value reference. And the output voltage Va of the voltage level detection circuit 12
Of the output voltage Vp of the peak value detection circuit 13 (Vp / V
When a) is equal to or greater than a preset reference value of the ratio between the peak value and the voltage level, a voice detection signal is output.

[0006]

According to the present invention, the input signal is filtered by the filter circuit 11 to remove noise in unnecessary bands,
2, the voltage Va is converted to a voltage Va corresponding to either the average value or the effective value, while the peak value detection circuit 13 converts the voltage to a voltage Vp corresponding to the peak value. Level determination means 1
4 is an output voltage Va of the voltage level detection circuit 12, that is,
The average value or the effective value of the input signal is equal to or higher than the reference value of the voltage level corresponding to the fixed level of the audio signal, and the output voltage Vp of the peak value detection circuit 13, that is, the peak value of the input signal is , Which is equal to or more than a reference value of a peak value corresponding to a certain level of an audio signal, and which is output from the voltage level detection circuit 12.
The ratio (Vp / Va) of the output voltage Vp of the peak value detection circuit 13 to the voltage Va, that is, the peak to the average value of the input signal.
When the ratio of the peak value or the ratio of the peak value to the effective value is equal to or more than the reference value of the ratio of the peak value and the voltage level set in advance, a sound detection signal indicating that the sound has been detected is output. .

[0007]

FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. 2, the filter circuit 11 includes a bandpass filter 15 and a bandpass filter 16. The input terminal of the bandpass filter 15 is connected to the input terminal 1, and the output terminal is connected to the input terminal of the average value detection circuit 12. The input terminal of the bandpass filter 16 is connected to the input terminal 1, and the output terminal is connected to the input terminal of the peak value detection circuit 13.

The average value detection circuit 12 is a known circuit and includes an absolute value circuit and an integration circuit, and detects and outputs the average value of the input voltage.

The peak value detection circuit 13 is a known circuit, detects a peak value of the input voltage, and holds and outputs this voltage value for a predetermined time.

Reference numeral 14 denotes a level judging means. The output terminal of the average value detecting circuit 12 is connected to the input terminal IN1 of the level judging means 14.
The output terminal of the peak value detection circuit 13 is connected to the input terminal IN2 of the level determination circuit 14.

The configuration of each section of the level determining means 14 will be described below. The non-inverting input terminal of the comparator A5 is connected to the input terminal IN1 of the level determining means 14, and the inverting input terminal is connected to a resistor R8 for generating a reference voltage Vref1.
And a resistor R9, and an output terminal thereof is connected to the anode of the diode D5. The cathode of the diode D5 is connected to the input terminal of the buffer amplifier 17, and is grounded via a parallel circuit of a resistor R10 and a capacitor C3.

The non-inverting input terminal of the comparator A6 is connected to the input terminal IN2 of the level judging means 14, the inverting input terminal is connected to the connection point between the resistor R11 and the resistor R12 for generating the reference voltage Vref2, and the output terminal thereof. Connected to the anode of diode D6. The cathode of the diode D6 is connected to the input terminal of the buffer amplifier 18, and is grounded via a parallel circuit of a resistor R13 and a capacitor C4.

The inverting input terminal of the comparator A7 is a resistor R
16 is connected to the input terminal IN1 of the level judging means 14 and its non-inverting input terminal is connected to the input terminal IN2 of the level judging means 14 via the resistor R14, and is grounded via the resistor R15. Connected to the output terminal of comparator A7 via resistor R17. An output terminal of the comparator A7 is connected to an input terminal of the buffer amplifier 19 via a resistor R18. In addition, buffer amplifier 1
The input terminal 9 is grounded via a parallel circuit of a resistor R19 and a capacitor C5.

The NAND circuit 20 has three input terminals. One of the input terminals is connected to the output terminal of the buffer amplifier 17, and the other input terminal is connected to the buffer amplifier 1.
8 and one of the other input terminals is connected to the output terminal of the buffer amplifier 19. Also, NAND
The output terminal of the circuit 20 is connected to the output terminal 2.

In the circuit having the above-described configuration, the bandpass filter 15 and the bandpass filter 16 pass only the voice band component of the input signal and remove noise in unnecessary bands. It is configured by combining a high-pass filter and a high-pass filter. When the recorded signal is reproduced at a normal speed, the band is set to, for example, 300 Hz to 2 kHz. When the recording signal is reproduced at a high speed, approximately (the band of the normal speed) × (the reproduction speed) Magnification). In the present embodiment, the frequency is set to about 10 kHz to 60 kHz in accordance with the reproduction at 32 times speed. The characteristics of the bandpass filter 15 are set to the characteristics optimal for the average value detection circuit 12, and the characteristics of the bandpass filter 16 are set to the characteristics optimal for the peak value detection circuit 13.

The average value detection circuit 12 includes a bandpass filter 15
And outputs the average value of the output voltages. This output voltage is defined as Va. The average time of this circuit is determined by the resistor R5 and the capacitor C1, and is set to an optimum value in the range of several tens ms to 2s.

The peak value detection circuit 13 includes a bandpass filter 16
The peak value of the output voltage is detected and output. This output voltage is defined as Vp. The attack time of this circuit is determined by the resistor R6 and the capacitor C2, and is set to an optimum value in about several ms. The hold time of this circuit is determined by the resistor R7 and the capacitor C2, and is set to an optimum value in about several hundred ms.

The level determining means 14 determines that the input voltage Va of the input terminal IN1 is higher than the reference voltage Vref1, the input voltage Vp of the input terminal IN2 is higher than the reference voltage Vref2, and the input voltage Vp of the input terminal IN2 is equal to the input voltage Vp. Terminal I
When the ratio (Vp / Va) of N1 to the input voltage Va is equal to or higher than a preset reference value, a low-level sound detection signal is output. In this embodiment, the reference voltage Vref1,
The reference voltage Vref2 is set to about 100 mV corresponding to a fixed level of the audio signal.

By the way, as shown by a general speech voice signal on a telephone line in FIG. 3, a normal voice signal has a ratio of a peak value to an average value of 3 to 4. In the general speech voice signal on the telephone line of FIG. 3, the average value is 150 mV with respect to the peak value of 600 mV, and this ratio is 4. On the other hand, the line noise at the time of no signal recording on the telephone line of FIG.
As shown by the noise when the telephone line is disconnected, the ratio between the peak value and the average value of the noise other than the voice signal is smaller than 3. In the line noise at the time of no signal recording in the telephone line of FIG. 4, the average value is 30 mV with respect to the peak value of 55 mV, and this ratio is smaller than 3. In the noise at the time of disconnection of the telephone line in FIG. 5, the average value is 500 mV with respect to the peak value of 600 mV, and this ratio is smaller than 3.
From this, in order to detect only the audio signal, the input voltage Vp of the input terminal IN2 and the input voltage V
The reference value of the ratio with respect to a (Vp / Va) is set to 4. The reference value of this ratio is determined by (R14 + R15) / R15.

In the following, the operation of each circuit of the level determination circuit 14 will be described. The reference voltage Vref1 is generated by dividing a DC voltage by the resistors R8 and R9. The comparator A5 has a reference voltage Vref set in advance.
1 is compared with the input voltage Va of the input terminal IN1. When the input voltage Va of the input terminal IN1 is smaller than the reference voltage Vref1, the voltage is low (hereinafter referred to as "L"). H ”). When the output voltage of the comparator A5 is "L", the diode D5 is turned off, and after a lapse of a predetermined time determined by the resistor R10 and the capacitor C3, the input voltage of the buffer amplifier 17 becomes "L".
The input voltages of the two input terminals become “L”. When the output voltage of the comparator A5 is “H”, the diode D5 is turned on, C3 is charged, the input voltage of the buffer amplifier 17 becomes “H”, and the input voltage of one input terminal of the NAND circuit 20 becomes “H”. H ”. Once comparator A
When the output voltage of the buffer amplifier 17 becomes "H", the input voltage of the buffer amplifier 17 is maintained at "H" for a certain time determined by the resistor R10 and the capacitor C3.

The reference voltage Vref2 is generated by dividing a DC voltage by the resistors R11 and R12. The comparator A6 compares the preset reference voltage Vref2 with the input voltage Vp of the input terminal IN2. When the input voltage Vp of the input terminal IN2 is smaller than the reference voltage Vref2, the comparator A6 is "L". H ”is output. When the output voltage of the comparator A6 is "L", the diode D6 is turned off, and after a certain time determined by the resistor R13 and the capacitor C4, the buffer amplifier 18
Becomes "L", and the input voltage of one input terminal of the NAND circuit 20 becomes "L". Comparator A
6 is "H", the diode D6 is turned on, C4 is charged, the input voltage of the buffer amplifier 18 becomes "H", and the input voltage of one input terminal of the NAND circuit 20 becomes "H". ". Once the output voltage of the comparator A6 becomes "H", the resistor R13 and the capacitor C
The input voltage of the buffer amplifier 18 is maintained at "H" for a certain time determined by the step (4).

The voltage Va is input to the inverting input terminal of the comparator A7, and Vp · R is input to its non-inverting input terminal.
A voltage of 15 / (R14 + R15) is input. Therefore, when Vp / Va is smaller than the value of (R14 + R15) / R15, the comparator A7 is "L" and Vp / V
When a is equal to or more than the value of (R14 + R15) / R15,
Outputs the voltage of “H”. When the output voltage of the comparator A7 is "L", the resistors R18 and R19 and the capacitor C
After a lapse of a predetermined time determined by 5, the input voltage of the buffer amplifier 19 becomes “L”, and the input voltage of one input terminal of the NAND circuit 20 becomes “L”. When the output voltage of the comparator A7 is "H", after a certain time determined by the resistors R18 and R19 and the capacitor C5, the buffer amplifier 1
9 becomes “H”, and the input voltage of one input terminal of the NAND circuit 20 becomes “H”.

The NAND circuit 20 outputs an "L" output voltage (voice detection signal) to the output terminal 2 when all the input voltages of the three input terminals are "H".

Therefore, the audio signal detection circuit of the present embodiment
The average value of the signal input to the input terminal 1 is equal to the reference value of the voltage level defined by Vref1 (about 100 in this embodiment).
mV) or more, and the peak value of the signal input to the input terminal 1 is not less than the reference value of the peak value defined by Vref2 (about 100 mV in this embodiment) and the peak value of the input signal. And the ratio (Vp / Va) of the average value is (R14 + R15)
When the ratio between the peak value and the voltage level determined by / R15 is equal to or greater than the reference value (in this embodiment, it is set to 4), an "L" sound detection signal indicating that sound has been detected is output to the terminal 2.

Next, the operation of this embodiment with respect to actual telephone line signals shown in FIGS. 3 to 5 will be described. FIG. 3 shows a general conversation voice signal on a telephone line. The signal shown in FIG.
2, a voltage of 150 mV is output as an average value. Further, when this signal is input to the peak value detection circuit 13 through the bandpass filter 16, the peak value becomes 60
A voltage of 0 mV is output. The average voltage Va and the peak voltage Vp are respectively input to the input terminal IN of the level determination unit 14.
1 and input to the input terminal IN2, and the comparator A5, the comparator A6, and the comparator A7 make a determination.

The comparator A5 compares the average voltage Va with the reference voltage Vref1 as described above. Assuming that the reference voltage Vref1 of the comparator A5 is set to 100 mV, 150 mV of the average voltage Va is 10 mV.
Since the output voltage exceeds 0 mv, the output voltage of the comparator A5 becomes “H”, and one input terminal of the NAND circuit 20 becomes “H” via the buffer amplifier 17.

The comparator A6 compares the peak voltage Vp with the reference voltage Vref2 as described above. Assuming that the reference voltage Vref2 of the comparator A6 is set to 100 mV, 600 mV of the peak voltage Vp is 10 mV.
Since it exceeds 0 mv, the output voltage of the comparator A6 becomes “H”, and one input terminal of the NAND circuit 20 becomes “H” via the buffer amplifier 18.

The comparator A7 compares the ratio between the peak voltage Vp and the average voltage Va (Vp / Va) with a reference value of the ratio between the peak value and the average value. Assuming that the reference value of the ratio between the peak value and the average value is set to 4, the peak voltage Vp is 6
Since 00 mV is four times the average voltage Va 150 mV, the output voltage of the comparator A7 becomes “H”, and one input terminal of the NAND circuit 20 becomes “H” via the buffer amplifier 19.

Accordingly, the voltages of all the input terminals of the NAND circuit 20 become “H”, and the “L” sound detection signal is output to the output terminal 2.

FIG. 4 shows the line noise when no signal is recorded on the telephone line. When this signal is input to the average detection circuit 12 through the bandpass filter 15, a voltage of about 30 mV is output as an average. When this signal is input to the peak value detection circuit 13 through the bandpass filter 16, a voltage of about 55 mV is output as the peak value.

The comparator A5 compares the average voltage Va with the reference voltage. Reference voltage Vr of comparator A5
Assuming that ef1 is set to 100 mV, 30 mV of the average voltage Va is smaller than 100 mv, so that the output voltage of the comparator A5 becomes "L" and one input terminal of the NAND circuit 20 via the buffer amplifier 17 becomes "L". L ”.

The comparator A6 compares the peak voltage Vp with the reference voltage Vref2. Assuming that the reference voltage Vref2 of the comparator A6 is set to 100 mV, the peak voltage Vp of 55 mV is smaller than 100 mv, so that the output voltage of the comparator A6 becomes "L", One input terminal becomes “L”.

The comparator A7 compares the ratio between the peak voltage Vp and the average voltage Va (Vp / Va) with a reference value of the ratio between the peak value and the average value. If the reference value of the ratio between the peak value and the average value is set to 4, the peak voltage Vp of 55
Since mV is less than four times the average voltage Va30mV, the output voltage of the comparator A7 becomes "L", and one input terminal of the NAND circuit 20 becomes "L" via the buffer amplifier 19.

Therefore, the voltages of all the input terminals of the NAND circuit 20 become "L", and the output voltage of the NAND circuit becomes
It becomes "H", and no audio detection signal is output to the output terminal 2.

FIG. 5 shows noise when the telephone line is disconnected. When this signal is input to the average value detection circuit 12 through the bandpass filter 15, a voltage of about 500 mV is output as an average value. When this signal is input to the peak value detection circuit 13 through the bandpass filter 16, a voltage of about 600 mV is output as the peak value.

The comparator A5 compares the average voltage Va with the reference voltage Vref1. Assuming that the reference voltage Vref1 of the comparator A5 is set to 100 mV, the output voltage of the comparator A5 becomes "H" because the average voltage Va of 500 mV exceeds 100 mV. One of the input terminals becomes “H”.

The comparator A6 compares the peak voltage Vp with the reference voltage Vref2. Assuming that the reference voltage Vref2 of the comparator A6 is set to 100 mV, the peak voltage Vp of 600 mV exceeds 100 mV, so that the output voltage of the comparator A6 becomes "H", One input terminal becomes “H”.

The comparator A7 compares the ratio between the peak voltage Vp and the average voltage Va (Vp / Va) with a reference value of the ratio between the peak value and the average value. Assuming that the reference value of the ratio between the peak value and the average value is set to 4, the peak voltage Vp is 6
Since 00 mV is less than four times the average voltage Va 500 mV, the output voltage of the comparator A7 becomes “L”, and one input terminal of the NAND circuit 20 becomes “L” via the buffer amplifier 19.

Accordingly, the voltage of one input terminal of the NAND circuit 20 becomes "L", the output voltage of the NAND circuit 20 becomes "H", and no sound detection signal is output to the output terminal 2.

As described above, when a general conversation voice signal on the telephone line shown in FIG. 3 is input, a voice detection signal is output, but no signal is recorded on the telephone line shown in FIG. No sound detection signal is output for the noise at the time and the noise at the time of disconnection of the telephone line shown in FIG.

As described above, in this embodiment, when the signal-to-noise ratio of the input speech signal is less than 20 dB, the probability of erroneously detecting noise as speech is extremely low, and the speech signal is correctly detected with high probability. In addition, it is possible to prevent noise at the time of telephone line disconnection from being erroneously detected as a voice signal.

Further, since the band-pass filter 15 for the average value detection circuit 12 and the band-pass filter 16 for the peak value detection circuit 13 are independently provided and have optimum characteristics, the detection probability of the audio signal can be further increased. . Also, the bandpass filter 15 and the bandpass filter 1
By setting the characteristic of No. 6, an audio signal can be correctly detected with a high probability regardless of the reproduction speed. Also,
The reference voltage Vref1 and the reference voltage V
By changing ref2, the present invention can be applied to audio signal detection circuits of various magnetic recording / reproducing apparatuses using a magnetic tape.

In the present embodiment, the low-potential-side power supply voltage of the signal is set to 0 V (ground), but it is not necessarily required to be 0 V.

The present invention is not limited to this embodiment, but may be configured so that the band-pass filter 16 is omitted and the signal from the band-pass filter 15 is also input to the peak value detection circuit 13.

An effective value detection circuit may be used instead of the average value detection circuit 12. At this time, the reference value of the ratio between the peak value and the voltage level in the comparison by the comparator A7 is an optimum value when the effective value detection circuit is used.

The peak value detection circuit 13 may use a simplified quasi-peak value detection circuit composed of one operational amplifier. At this time, in the comparison by the comparator A7,
The reference value of the ratio between the peak value and the voltage level is an optimum value when a simplified quasi-peak value detection circuit is used.

The NAND circuit 20 may be replaced with another logic circuit. Further, the right side portion of the dashed line of the level determination means in FIG. 2 may be a combination of an A / D converter and a central processing unit (CPU), and the level determination may be performed by software.

[0048]

As described above, according to the present invention, the average value or the effective value of the input signal and the peak value of the input signal are compared with the respective reference values, and the average value or the effective value of the input signal is compared. versus
The ratio of the peak value of the input signal to be
It is compared with a reference value of the voltage level ratio, and it is determined whether or not the signal is an audio signal based on the result of the above comparison. For this reason, according to the present invention, when the signal-to-noise ratio of the input audio signal is less than 20 dB, the probability that noise is erroneously detected as audio or a low-level audio signal cannot be detected is extremely low, An audio signal can be correctly detected with a high probability, and noise at the time of telephone line disconnection can be prevented from being erroneously detected as an audio signal. Also, at this time, the voice detection determination process only needs to calculate the ratio between the peak value and the average value and compare it with the reference value. It has features such as realization.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a circuit diagram of one embodiment of the present invention.

FIG. 3 is a diagram showing a general conversation voice signal on a telephone line.

FIG. 4 is a diagram showing line noise when no signal is recorded on a telephone line.

FIG. 5 is a diagram showing noise when a telephone line is disconnected.

FIG. 6 is a configuration diagram of an example of a conventional audio signal detection circuit.

[Description of Signs] 11 Filter circuit 12 Voltage level detection circuit 13 Peak value detection circuit 14 Level determination means

Claims (2)

(57) [Claims] 1. The method of claim 1, whereinLet the signal in a specific band pass
Filter circuit(11)And the filter circuit(11)Average or effective value of outputIs
Output voltage VaVoltage level detection circuit(12)
And the filter circuit(11)Output peak valueOutput voltage V
pValue detection circuit that detects(13)And a voltage level detection circuit(12)Output voltage Va is preset
Voltage level is equal to or higher than the reference value and the peak value is detected.
circuit(13)Output voltage Vp is based on a preset peak value.
Is equal to or higher than the standard value, andOf the voltage level detection circuit (12)
The output voltage of the peak value detection circuit (13) with respect to the output voltage Va
Pressure VpThe ratio (Vp / Va) of the peak value and the power
When the pressure level ratio exceeds the reference value, the sound detection signal
And a level determining means (14) for outputting
Voice signal detection circuit. 2. The filter circuit according to claim 1, wherein the filter circuit includes:
A signal of a first specific band is passed, and a voltage level detection circuit is provided.
A first filter circuit (15) for supplying to (12); Pass a signal of a second specific band in the input signal, and obtain a peak value
The second filter circuit (1
6. The voice signal according to claim 1, comprising:
Signal detection circuit.