JPH043360Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a signal detection circuit, for example, by comparing the number of periods of an input audio signal and the number of periods of a reference signal to determine whether the input audio signal matches the reference signal. Used in karaoke machines with a scoring function that scores the percentage of

Prior Art In recent years, karaoke machines with a scoring function have been developed. This method compares the number of periodic pulses corresponding to audio signals sung by amateurs input into a microphone and periodic pulses corresponding to audio signals sung by professional singers within a certain period of time. The quality of an amateur's singing is scored and displayed based on the proportion of the number of periodic pulses by a person and the number of periodic pulses by a professional singer.

Such karaoke equipment is equipped with a signal cycle detection circuit that detects the cycle of the audio signal.
For example, when an impact sound having the same level as the audio signal is generated in the vicinity of a microphone, it is not necessary to detect the period of this impact sound and display a score. Therefore, in general, a signal judgment circuit is provided separately from the signal period detection circuit to judge the presence or absence of a normal input signal, and a score is displayed based on the output of the signal period detection circuit and the output of the signal judgment circuit. .

FIG. 2 shows a circuit diagram of an example of a conventional signal detection circuit that combines a signal period detection circuit and a signal judgment circuit used in such a karaoke apparatus. In the figure, when a single impact sound enters the terminal 1, the impact sound is transmitted through the amplifier 3 of the signal judgment circuit 2 and the DC removal capacitor 4 to the diodes 5 and 6.
It is rectified there, supplied to capacitor 7 to charge it, and supplied to the base of transistor 10 via resistors 8 and 9.

In this case, since it is an impact sound, the charging and discharging of the capacitor 7 takes place far, and the voltage at its terminal does not become large, so the transistor 10 remains off. When transistor 10 is turned off, its collector becomes H.
The output of the inverter 11 is set to L level.

At the same time, a periodic pulse corresponding to the impact sound is detected in the signal period detection circuit 12 and supplied to the AND gate 13. In this case, in the signal period detection circuit 12, the incoming signal is amplified by a high gain amplifier and then compared with a reference voltage by a comparator to detect a zero cross point. Due to the L level output of the inverter 11 and the H level output of the signal period detection circuit 12, the output of the AND gate 13 (output terminal 14) is set to the L level, and no detection signal is taken out.

On the other hand, when a relatively low-level noise signal enters the terminal 1, the transistor 10 remains off, and no detection signal is taken out from the terminal 14, as in the case of the above-mentioned impact sound.

Next, when a normal input signal enters terminal 1, this signal is rectified by diodes 5 and 6 and then supplied to capacitor 7 to charge it. In this case, since the input signal is continuous, the charging of the capacitor 7 is maintained, and the terminal voltage is high.
Transistor 10 is turned on. When transistor 10 is turned on, its collector becomes L level and the output of inverter 11 becomes H level.

At the same time, a periodic pulse corresponding to the input signal is detected in the signal period detection circuit 12 and supplied to the AND gate 13. The output of AND gate 13 (output terminal 14) is set to H level by the H level output of inverter 11 and the H level output of signal period detection circuit 12, and a detection signal is taken out.

Problems to be solved by the invention However, in the conventional circuit with the above configuration, the signal judgment circuit 2
Both the signal period detection circuit 12 (actually composed of a high gain amplifier, a comparator, and a reference voltage power supply) have a relatively large number of parts, and there is a problem that they cannot be constructed at low cost.

Means for Solving the Problems and Their Effects The present invention provides an amplifier that amplifies an AC input signal, a rectifier circuit that flows a rectified current for a period when the output amplitude level of this amplifier is equal to or higher than a predetermined value, and a DC control according to the rectified current. An automatic level control (hereinafter referred to as ALC) circuit consists of a circuit that controls the output of the amplifier so that it does not exceed a certain value depending on the signal, and a circuit that detects the presence or absence of rectified current from the rectifier circuit and controls the output of the AC input signal. A signal output circuit that outputs a signal corresponding to a period, a signal judgment circuit that outputs a signal when the rectified current continues to flow for a predetermined period or more, and an output of the signal output circuit and an output of the signal judgment circuit exist at the same time. The object of the present invention is to provide a signal detection circuit which can be configured easily with a relatively small number of parts and which solves the above problems by configuring a circuit that outputs a detection signal when a detection signal is generated. Hereinafter, one embodiment will be described with reference to FIG. 1.

Embodiment FIG. 1 shows a circuit diagram of an embodiment of the circuit of the present invention, in which the same components as in FIG. 2 are given the same numbers. In the same figure, when a normal input signal enters terminal 1, this signal is transmitted to signal period detection circuit 1.
The voltage is supplied to the transistor 17 via the amplifier 3 of No. 5, the DC removal capacitor 4, and the capacitor charge discharge diode 16. In this case, since the normal input signal has a level above a certain level, a current flows between the base and emitter of the transistor 17, and this current is integrated by an integrator consisting of a resistor 18 and a capacitor 19, and is converted into a DC control signal. be done.

This control signal is supplied to a variable impedance circuit composed of transistors 20 and 21, and controls the conduction state of transistors 20 and 21. As a result, the input signal level of the high gain amplifier 3 is lowered and its output level is controlled to be constant. The above ALC operation is conventionally well known.

At the same time, a current (rectified current) flows through the collector of the transistor 17, thereby lowering the base potential of the transistor 22 and turning it on. When the transistor 22 is turned on, a periodic pulse signal is taken out from its collector and supplied to the AND gate 13. This periodic pulse signal is a signal that is extracted at a timing close to outputting its peak value when the level of the input signal is above a certain level.

On the other hand, a part of the rectified current flowing through the transistor 17 is supplied to the transistor 25 via the resistor 24 of the signal judgment circuit 23, turning it on. As a result, the collector of the transistor is set to L level, the output of inverter 11 is set to H level, and is supplied to AND gate 13, and the output to AND gate 13 is set to H level due to the H level output of transistor 22 and the H level output of inverter 11. The detection signal is taken out from the terminal 14.

Next, when a noise signal enters the terminal 1, since its level is low, no current (rectified current) flows through the base and emitter of the transistor 17, so the transistor 22 is turned off, and the output terminal 14 is turned off. No detection signal is extracted.

Further, when an impact sound enters the terminal 1, the level of the impact sound is relatively large, so the transistor 17 is turned on and a charging current flows to the capacitor 19. Since the emitter potential of transistor 17 is approximately zero during a certain period during which this charging current flows, transistor 25 is not base biased and remains off. By the time the charging of the capacitor 19 progresses and the emitter potential of the transistor 17 approaches a predetermined potential, the impact noise has disappeared.As a result, the capacitor 19 is discharged via the resistor 18, and the emitter potential of the transistor 17 is again reduced to a predetermined potential. It becomes almost zero. This causes the transistor 25 to remain off,
Its collector is set at H level, and the output of inverter 11 is set at L level and supplied to AND gate 13.

On the other hand, transistor 22 is turned on by turning on transistor 17, and its H level output is supplied to AND gate 13. and gate 13
is set to the L level by the H level output of the transistor 22 and the L level output of the inverter 11, and no detection signal is taken out from the terminal 14.

Therefore, the circuit of the present invention does not extract the periodic pulse signal when a low-level noise signal or impact sound enters, and as a result, when applied to the above-mentioned karaoke device with a scoring function, it will not result in incorrect scoring like the conventional device. It will never be displayed.

Effects As mentioned above, the signal detection circuit according to the present invention includes an amplifier that amplifies an AC input signal, a rectifier circuit that flows a rectified current for a period when the output amplitude level of this amplifier is equal to or higher than a predetermined value, and a DC control according to this rectified current. An automatic level control circuit consists of a circuit that controls the output of the amplifier so that it does not exceed a certain value depending on the signal, and a signal that detects the presence or absence of rectified current from the rectifier circuit and outputs a signal corresponding to the period of the AC input signal. a signal output circuit that outputs a signal; a signal judgment circuit that outputs a signal when the rectified current continues to flow for a predetermined period or more;
Since it is configured with a circuit that outputs a detection signal when the output of the signal output circuit and the output of the signal judgment circuit are present at the same time, the period detection signal is extracted when a relatively low level noise signal or impact sound comes in. Only when an input signal with a certain level comes in, a periodic signal can be extracted at a timing near its peak value. This makes it possible to reliably detect large periods of the input signal. When applied to a karaoke device with functions, there will be no erroneous scores displayed due to noise signals input to the microphone, and there are comparatively fewer parts compared to conventional circuits, so it can be constructed at a lower cost. has.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the circuit of the present invention;
The figure is a circuit diagram of an example of a conventional circuit. 1... Signal input terminal, 3... High gain amplifier, 1
1...Inverter, 13...And gate, 14
... Signal output terminal, 15 ... Signal period detection circuit,
17, 20, 21, 22, 25...Transistor, 18...Resistor, 19...Capacitor, 23...
...Signal judgment circuit.

Claims (1)

[Scope of utility model registration request] An amplifier that amplifies an AC input signal, a rectifier circuit that flows a rectified current for a period when the output amplitude level of the amplifier is above a predetermined value, and a DC control signal corresponding to the rectified current to control the output of the amplifier so that it does not exceed a certain value. an automatic level control circuit that detects the presence or absence of rectified current from the rectifier circuit and outputs a signal corresponding to the cycle of the AC input signal; A signal detection circuit consisting of a signal judgment circuit that outputs a signal when the above flows continuously, and a circuit that outputs a detection signal when the output of the signal output circuit and the output of the signal judgment circuit exist simultaneously. circuit.