JPH09307989A - Excess input detection circuit for voice signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the inexpensive excess input detection circuit by converting a voice input signal into a DC voltage, comparing the voltage with a preset reference voltage and generating a pulse with a prescribed width by means of a one-shot multivibrator even when the DC voltage is higher thereby lighting a light emitting diode. SOLUTION: A voice input signal P1 is given to an absolute value amplifier circuit 1, in which the signal is full-wave rectified and converted into a DC voltage P2 denoting a level of the voice signal and the voltage is compared with a preset reference voltage level PL at a comparison arithmetic circuit 2. The comparison arithmetic circuit 2 provide an output of a pulse signal P3 when the DC voltage P2 is higher than the reference voltage level PL to drive a one-shot multivibrator circuit 3, from which an output pulse P4 with a prescribed pulse width is generated. The output pulse P4 lights a light emitting diode D4 via an LED drive amplifier IC5. Thus, the inexpensive excess input detection circuit is obtained, by which the voice input signal P1 in excess of the maximum rated value is surely detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when an audio signal having a magnitude exceeding the maximum rated value is input to the input portion of an audio signal transmission device such as a karaoke microphone, displays the state by lighting an LED. The present invention relates to a voice signal excessive input detection circuit configured to notify.

[0002]

2. Description of the Related Art Conventionally, when an audio signal having a magnitude exceeding a maximum rated value is input to an input portion of an audio signal transmission device such as a microphone, there is a problem that noise such as howling occurs. As a measure to solve the above-mentioned difficulty, it is possible for the user to visually confirm the excessive input of the audio signal and save the volume of the audio. In this case, in order for the user to recognize the magnitude of the voice signal, it is necessary to measure the magnitude of the voice signal and visually display the magnitude of the voice signal.

By the way, the audio signal is an AC signal having a sinusoidal waveform, and its value changes with time. Therefore, in order to measure the magnitude of the voice signal, it is general to convert the AC signal into a DC that is easy to measure and then measure.
In addition, the AC signal is displayed as the maximum value, average value, effective value, etc.
It is often used to display the level of an AC signal as a value that directly displays the amount of electricity and heat. In order to obtain the true effective value, it is necessary to square the AC signal, average it, and further calculate its square root.

FIG. 3 shows a block diagram of a circuit configuration of a conventional example using an IC device having a function necessary for obtaining a true effective value. In the figure, P1 is a voice signal,
Reference numeral 5 is an input amplifier circuit, 6 is a full-wave rectifier circuit, 7 is an effective value conversion circuit unit configured in a circuit so that square, averaging, and square root calculations are performed. 8 is an output amplifier. The output ripple can be reduced by operating also as an LPF (low-pass filter) having a.

In the circuit thus constructed, the audio signal P1 is full-wave rectified by the full-wave rectifier circuit 6 via the input amplifier circuit 5. The full-wave rectified audio signal P
1 is converted into an effective value in the effective value conversion circuit unit 7, buffered by the output amplifier 8 and output P1A, and the measured value of the audio signal P1 is obtained.

[0006]

By the way, in order to obtain the true effective value of an AC signal having various waveforms such as a voice signal, the effective value conversion section as described above squares and averages the signal. , An arithmetic circuit for square root calculation is required. Therefore, needless to say, when the IC device is not used, the configuration of the arithmetic circuit is considerably complicated.

Further, even when an IC device is used, there is a problem that the obtained circuit becomes expensive.

An object of the present invention is to solve the above-mentioned problems and provide an inexpensive excessive input signal detection circuit for an audio signal which allows a user to recognize an audio signal input having a maximum rated value or more by a simple means. is there.

[0009]

An absolute value amplifying circuit 1 for detecting and amplifying an absolute value of an audio input signal P1 and an output P2 of the absolute value amplifying circuit 1 are inputted, and an output P2 is a preset maximum input. A comparison operation circuit 2 that detects an excessive input signal and outputs a high level signal P3 in a pulse waveform when the value is higher than the reference level PL of the rated value, and a comparison operation circuit 2
The one-shot multivibrator circuit 3 which receives the pulse waveform signal P3 output from the device and which detects the rising edge of the pulse waveform signal P3 and outputs the adjusted pulse width signal P4, and the one-shot multivibrator When the output P4 of the circuit 3 is at a high level, the LED drive circuit 4 that causes the light emitting diode D4 to emit light is provided to configure an excessive input detection circuit for an audio signal.

[0010]

The level of the full-wave rectified audio signal in the absolute value amplifier circuit is compared with the reference level by the comparison operation circuit, and when the input audio signal is higher than the reference level, the comparison operation circuit outputs a pulse signal. At this time, the one-shot multivibrator circuit detects the rising edge of this pulse signal and outputs a high-level signal that is a pulse signal in which the pulse width of this pulse signal is set to a predetermined pulse width. Since the level signal is input to the LED drive circuit to turn on the light emitting diode,
Have the microphone user visually confirm excessive input of the audio signal.

[0011]

The present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of an excessive input signal prevention circuit for an audio signal according to the present invention, and FIG. 2 is an explanatory diagram showing waveforms in a main circuit of FIG. 1, and FIGS. ) And (d) are waveform charts of the main circuits 1, 2, 3, and 4, respectively. In the figure, 1 is an absolute value amplifier circuit, and amplifiers IC1 and IC2
It is composed of diodes D1 and D2 forming a half-wave rectification circuit and resistors R1, R2, R3, R4 and R5. Reference numeral 2 is a comparison operation circuit including an amplifier AIC3, resistors R6 and R7, and a variable resistor VR1, and reference numeral 3 is a one-shot multivibrator including a multivibrator IC4, resistors R8 and R9, a capacitor C1 and a diode D3. In the circuit, 4 is an amplifier IC5, a resistor R10, a light emitting diode D4 and a transistor T.
It is an LED drive circuit composed of R and the like. Further, P1 indicates an audio input signal, P2 indicates the output of the absolute value amplifier circuit 1,
P3 represents the output of the comparison operation circuit 2, and P4 represents the output of the one-shot multivibrator circuit 4, respectively.

The output P2 of the absolute value amplifier circuit 1 is applied to the comparison operation circuit 2, the output P3 of the comparison operation circuit 2 is applied to the one-shot multivibrator circuit 3, and the output P4 of the one-shot multivibrator circuit 3 is applied to the LED drive circuit 4. They are connected in a circuit so that they are input to. Also,
Power supply voltages VEE and VCC are supplied to each circuit as needed.

In the circuit for preventing excessive input of the audio signal according to the present invention having the above-mentioned structure, the signal is inputted to the absolute value amplifying circuit 1 composed of the half-wave rectifying circuit composed of IC1, IC2 and D1, D2. The audio signal P1 is always converted into a positive voltage and output regardless of its polarity. That is, when the audio signal P1 input to the absolute value amplifier circuit 1 is positive (+ V), its output voltage is positive (+ V),
Output voltage is positive (+ V) even when the audio signal is negative (-V)
The audio signal P1 is so-called full-wave rectified.

The purpose of configuring the absolute value amplifier circuit 1 as a full-wave rectification type is that the input of the comparison operation circuit 2 in the next stage is set between the ground level and the positive power supply voltage VCC, and This is because the output of the one-shot multivibrator circuit 3 is fixed at a high level by increasing the number of sampling times in the comparison operation circuit 2 as much as possible even when the input signal exceeds the rated level at a low frequency of several tens Hz.

Further, the comparison operation circuit 2 compares the output P2 of the absolute value amplifier circuit 1 with the reference voltage level PL preset at the test point TP, and the output P2 of the absolute value amplifier circuit 1 is compared with the reference voltage level PL. Only when it is larger than PL, the comparison operation unit IC3 of the comparison operation circuit 2 outputs the high-level output P3.

The reference voltage level of the test point TP can be set by adjusting the variable resistor VR1, and the inverting amplifier when the maximum rated signal of the audio signal input to the absolute value amplification circuit 1 is input. Output P2 of IC2
It is possible to compare the signal input to the comparator / calculator IC3 of the comparator / calculator circuit 2 with the signal at the maximum rating by setting the maximum value of

Here, the comparison operation unit IC of the comparison operation circuit 2
Since the signal input to 3 is a full-wave rectified waveform signal,
In particular, when the signal level is slightly higher than the reference voltage level PL of the test point TP, the output P3 of the comparison operator IC3 is a pulse waveform signal with a large duty ratio. Therefore, the LED drive circuit 4 can be operated by using the pulse waveform signal having the large duty ratio as it is. However, in this case, the light emitting diode D
Since the display brightness of No. 4 was small, it was extremely difficult to identify whether the light emitting diode D4 was turned on.

Therefore, in order to obtain a signal with a small duty ratio, the one-shot multivibrator circuit 3 is used, and the pulse width of the output P3 from the comparison calculator IC3 is adjusted in advance by the capacitor C1 and the resistor R9. There is. That is, the one-shot multivibrator circuit 3
Then, the IC4 of the CMOS functions to detect the rising edge of the input pulse signal and use a pulse signal having a preset predetermined pulse width as its output P4. The pulse width (TW) set in this way is determined by the constant (R) of the resistor R9 and the constant (C) of the capacitor C1, and the pulse width (TW), the resistor R9, and the capacitor C1. There is the following relational expression between the constants of. TW = RC Here, the value of TW is 1 which is the minimum cycle of the input audio signal.
By setting the R and C constants in advance to be ½ or more (several tens of meters), a pulse waveform signal with a large duty ratio can be used in a one-shot multivibrator IC.
4, the output P4 of the one-shot multivibrator IC4 is stably set to the high level, so that sufficient display brightness can be obtained when the light emitting diode D4 is turned on.

On the other hand, when the voice input signal does not exceed the maximum rated input, the one-shot multivibrator IC4
Does not work, so one-shot multi-vibrator I
The output P4 of C4 is always low level. Therefore, LE
When the input to the LED driving IC 5 is at a high level, the D drive circuit 4 causes a current to flow through the light emitting diode D4 to cause the light emitting diode D4 to emit light. It works to turn off.

[0016]

According to the present invention, when the input audio signal exceeds the maximum rated input even for an instant, the LED is turned on, so that the excessive input of the audio signal can be visually and surely confirmed. Further, even when compared with a circuit having a conventional configuration that detects an excessive input of an audio signal from the effective value of the audio signal, an inexpensive excessive input signal detection circuit having a simple circuit configuration can be obtained. The practical effect is large.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an excessive input detection circuit for an audio signal according to the present invention.

FIG. 2 is an explanatory diagram showing waveforms of a main part of FIG. 1, and FIGS. 2 (a), (b), (c), and (d) are waveform diagrams of the main parts.

FIG. 3 is an explanatory diagram showing a circuit configuration of a conventional example.

[Explanation of symbols]

1 Absolute value amplification circuit 2 Comparison arithmetic circuit 3 One-shot multivibrator circuit 4 LED drive circuit R1, R2, R3, R4, R5, R6, R7, R8, R
9, R10 resistor VR1 variable resistor D1, D2, D3 diode D4 light emitting diode IC1 absolute value amplifier IC2 inverting amplifier IC3 comparison calculator IC4 one-shot multivibrator IC5 LED drive amplifier VEE, VCC power supply voltage

Claims (1)

[Claims] 1. An absolute value amplifying circuit 1 for detecting and amplifying an absolute value of an audio input signal P1, and an output P2 of the absolute value amplifying circuit 1 being inputted and a maximum input rated value preset by the output P2. When it is larger than the reference level PL of, a comparison operation circuit 2 which detects an excessive input signal and outputs a high level signal P3 with a pulse waveform
And a pulse waveform signal P output from the comparison operation circuit 2.
3 is input and a one-shot multivibrator circuit 3 which detects a rising edge of the pulse waveform signal P3 and outputs a pulse width signal P4 adjusted and set.
And the output P4 of the one-shot multivibrator circuit 3
Is a high level, the LED drive circuit 4 for causing the light emitting diode D4 to emit light is provided.