JPS5841003B2 - automatic volume adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an automatic volume control device that detects ambient noise mainly when the speaker sound is at a relatively low level together with the speaker sound using a microphone, without being affected by the speaker sound at this time. It is an object of the present invention to provide a device that can automatically adjust the volume of a speaker depending on the ambient noise level.

Conventionally, various attempts have been made to automatically adjust the volume in accordance with changes in the level of ambient noise in devices having an audio output stage, such as televisions, radios, tape recorders, and public address systems.

The main methods are: (a) A microphone detects the composite sound of ambient noise and speaker sound, separates and detects only the ambient noise signal component using an electrical signal from the audio signal circuit, and outputs audio using the ambient noise signal component. (b) Detects ambient noise when the speaker is not producing sound, and depending on the level, transfers multiple fixed circuit groups with self-holding functions such as switches to control the volume when the speaker is producing sound. etc.

However, in method (a), separating and detecting only the ambient noise signal component from the composite sound of ambient noise and speaker sound is difficult due to the phase delay of the speaker sound and the frequency characteristics of the speaker and microphone. It is technically difficult to completely cancel out the electrical signal and speaker sound, and even if they can be approximated, when the speaker volume increases to a certain level, the surrounding noise at that time will be masked by the speaker sound. As a result, it becomes difficult for the microphone to detect ambient noise, which prevents the speaker volume from increasing and makes volume adjustment unstable.

In addition, method (0) is not practical in places where ambient noise suddenly or periodically changes while the speaker is producing sound, and especially when the sound source is a continuous sound such as a musical tone, the speaker is not activated. It had drawbacks such as being almost uncontrollable due to the low frequency of pronunciation.

The present invention is intended to eliminate the above-mentioned drawbacks, and one embodiment of the present invention will be described below with reference to the drawings.

The figure shows a circuit of an embodiment of an automatic volume adjustment device according to the invention.

In the figure, reference numeral 1 denotes an audio signal source such as a television, radio, tape recorder, microphone, etc., and the audio signal output from this source passes through a preamplifier 2 to a volume controller 3.
After the volume is adjusted by the power amplifier 4, the sound is converted into sound by the speaker 5 and produced.

A synthesized sound of this speaker sound and the ambient noise component at that time is detected by a microphone 6 installed near the speaker 5, and this detection signal is amplified by a microphone amplifier 7 and then supplied to a rectifier circuit 8 to be negative. It is converted as a DC fluctuation output.

Further, the output audio signal of the power amplifier 4 is supplied to a rectifier circuit 9, where it is converted into a positive DC fluctuation output.

The output of the rectifier circuit 8 is level-adjusted by a level adjuster 10 and then applied to the inverting input of the summing amplifier 17 via a resistor 13, and the output of the rectifier circuit 9 is level-adjusted by a level adjuster 11. It is also applied to the inverting input of the Calorie amplifier 17 via the rear resistor 14.

In addition, the positive DC voltage adjusted by the level regulator 12 connected between the positive DC power supply voltage 1B and the ground is applied to the resistor 1
5 to the inverting input of the summing amplifier 17.

The output of summing amplifier 17 is connected to the inverting input via resistor 16 and to the drain of analog switch 18 .

The output of the summing amplifier 17 has a level adjuster 10.11.1.
An output determined by the sum of the respective outputs of 2 and the amplification degree of the resistors 13, 14, 15 and 16 and the summing amplifier 17 is obtained.

On the other hand, the output of the rectifier circuit 9 is voltage-divided by resistors 19 and 20 and then applied to an inverting input of a level comparator 22 via a resistor 21.

Further, a positive DC voltage is applied to the non-inverting input of the level comparator 22 via a resistor 24 from a comparison voltage regulator 23 connected between the positive DC power supply voltage 1B and ground.

The output of this level comparator 22 is the analog switch 1
It is connected to the gate of B, and also connected to the inverting input of the integrator 27 and the cathode of the diode 26 via the resistor 25.

A capacitor 2B is connected between the inverting input and the output of the integrator 27, and the source and drain of a field effect transistor (hereinafter referred to as FET) 29 are connected, respectively.

The gate of FET 29 is connected to the anode of diode 26 and at the same time is grounded via resistor 30.

The output of the integrator 27 is sent to a level comparator 34 via a resistor 31.
Also, a positive DC voltage is connected to the non-inverting input of the level comparator 34 via a resistor 32 from a comparison voltage regulator 33 connected between the positive DC power supply voltage 10B and ground. is being applied.

The output of this level comparator 34 is connected to a capacitor 35, and the other end of the capacitor 35 is connected via a resistor 37 to one of the two input NAND circuits (hereinafter referred to as NAND) 38. 36 to the positive DC power supply voltage 10B.

The output of NAND3B is connected to the human power of the inverter 41 via the capacitor 39, and this human power is connected to the resistor 40-
It is connected to the negative DC power supply voltage -B via.

The output of the inverter 41 is connected to the other human power of the NAND 3B, and is also connected to the human power of the inverter 42.

The output of this impark 42 is connected to the gate of an analog switch 43, and the drain and source of this analog switch 43 are connected across the resistor 20.

The source of the analog switch 18 is connected via a resistor 44 to a non-inverting input of a non-inverting amplifier 46, and this non-inverting input is grounded via a capacitor 45.

The inverting input of the non-inverting amplifier 46 is connected to the source of the FET 4B and grounded via a resistor 47, and its output is connected to the gate of the FET 48.

Further, the drain of the FET 4B is connected to the cathode of a light emitting diode 49, and the anode of this light emitting diode 49 is connected to a positive DC power supply voltage 10B.

The light receiving element Cd550 integrated with the light emitting diode 49 is connected in parallel to the resistor 51, one end of which is connected to the output of the preamplifier 2, the other end of which is connected to the input of the power amplifier 4, and the resistor 51 is connected in parallel with the resistor 51. The Cd 550 and the resistors 51 and 52 constitute the volume adjuster 3.

The functions and operations of the circuit having the above configuration will be explained below.

First, considering the case where there is no ambient noise, the audio signal from the audio signal source 1 passes through the preamplifier 2, the volume adjuster 3, and the power amplifier 4, as described above, and is output by the rectifier circuit 9 as a positive DC fluctuation output. converted.

On the other hand, the speaker sound emitted from the speaker 5 is detected by a microphone 6, passes through a microphone amplifier 7, and is converted by a rectifier circuit 8 into a negative DC fluctuation output.

In this 5, the frequency characteristics of the speaker 5 and microphone 6,
Considering the positional relationship between the speaker 5 and microphone 6,
Is the DC output of the rectifier circuit 9 equal to the absolute value of the DC output of the rectifier circuit 8 for frequencies within the audible frequency band?
Alternatively, adjust the level adjusters 10 and 11 so that the level is lower than that, and the negative DC output due to the background noise component output from the rectifier circuit 8 due to background noise when the speaker is not producing sound is equal to the positive DC output. If a DC voltage is applied by the level regulator 12, the sum of the outputs of the level regulators 10, 11, and 12 will be at least approximately zero or a positive potential.

On the other hand, if the comparison voltage of the comparison voltage regulator 23 is higher than the maximum value of the positive DC voltage obtained by dividing the output of the rectifier circuit 9 by the resistors 19 and 20, the output of the level comparator 22 becomes a positive potential. The gate of the analog switch 18 has a positive potential, and the drain and source of the analog switch 18 are electrically connected.

Here, the non-inverting amplifier 46, FET 4B, and resistor 47 form a constant current circuit, and the positive DC voltage applied to the non-inverting input of the non-inverting amplifier 46 and the current proportional to the resistor 47 are its load. The current flows to a certain light emitting diode 49.

Further, a resistor 44 and a capacitor 45 connected to the non-inverting input of the non-inverting amplifier 46 are a time constant circuit for smoothing the fluctuating output of the summing amplifier 17.

However, as described above, since the output of the summing amplifier 17 is approximately zero or negative, the input voltage of the non-inverting amplifier 46 is approximately zero or negative, and no current flows through the light emitting diode 49.

Therefore, there is no resistance change in the Cd550, and the attenuation ratio of the volume adjuster 3 is maintained at its original state.

Next, considering the case where there is relatively low-level frequency noise, a synthesized sound of this ambient noise component and the speaker sound is input to the microphone 6, so the negative DC output of the level adjuster 10 is the ambient noise component. It becomes larger by the amount.

Therefore, the summed voltage input to the summing amplifier 17 becomes a negative voltage due to the ambient noise component.

Since this summing amplifier 17 is an inverting amplifier, a negative DC voltage due to the ambient noise component and a positive DC voltage determined by the amplification degree of the summing amplifier 17 and the resistance 13°14.15.16 are obtained as the output of the summing amplifier 17. .

If the analog switch 18 is conducting here,
The positive output voltage of the summing amplifier 17 passes through the analog switch 18, is smoothed by a resistor 44 and a capacitor 45, and is applied to the input of a non-inverting amplifier 46.

A direct current corresponding to this input voltage and the resistor 47 flows through the light emitting diode 49, and the resistance value of the Cd 550 decreases in accordance with this current, and the attenuation ratio of the volume adjuster 3 decreases.

As a result, the input level of the power amplifier 4 increases, its output level increases, and the volume of the speaker 5 increases.

Of course, when the volume of the speaker 5 increases, the microphone 6
The speaker sound input to the input signal increases.

Correspondingly, the negative DC output level of the level adjuster 10 increases by the amount that the speaker sound increases, but at the same time, the positive DC output level of the level adjuster 11 also increases by the amount that the speaker sound increases. The sound component becomes approximately zero, and the volume of the speaker 5 is maintained at the volume due to the ambient noise component.

In this state, when the ambient noise disappears, the summing amplifier 1
Since the output of 7 becomes approximately zero, when the analog switch 18 is conductive, the charge across the capacitor 45 is discharged through the resistor 44 and becomes zero potential, and the original volume is restored.

Next, high-level ambient noise is input to the microphone 6, and as a result, the speaker volume increases significantly, and the output level of the rectifier circuit 9 increases accordingly, causing the inverted input level of the level comparator 22 to become extremely high. Considering the case where the inverted input level is exceeded, the output of the level comparator 22 is inverted from a positive potential to a negative potential.

Therefore, the gate of the analog switch 18 becomes a negative potential, the analog switch 18 becomes non-conductive, and the capacitor 4
5 is maintained at a voltage corresponding to the output voltage of the summing amplifier 17 immediately before the analog switch 18 becomes non-conductive,
The volume of the speaker 5 is maintained at a high level according to the voltage.

If there is no analog switch 18 here and the output of the summing amplifier 17 and the resistor 44 are directly connected and the speaker sound becomes high level, the microphone 6 will mask the ambient noise by the high level speaker sound. This makes it difficult to detect ambient noise5, and as a result, at that level, it is the same as when there is relatively no ambient noise, so the level decreases to a level where the ambient noise is not masked by the speaker sound. However, since the ambient noise is detected again and the volume increases repeatedly, the volume increases and decreases rapidly, making it extremely difficult to hear.

The analog switch 18 is provided to eliminate such a drawback that volume adjustment becomes unstable.

However, due to the high level of volume, the analog switch 18
If it continues to maintain a non-conducting state, even if the ambient noise level decreases and the output voltage of the summing amplifier 17 decreases, the output of the summing amplifier 17 will not be input to the non-inverting amplifier 46, so the volume of the speaker will decrease. It will not decrease.

The circuits provided after the output of the level comparator 22 are intended to eliminate the above-mentioned drawbacks, and these circuits will be explained next.

When the output of the level comparator 22 is reversed from a positive potential to a negative potential due to the inverted input voltage of the level comparator 22 being higher than the non-inverted input voltage, the integrator 27 starts integrating with a time constant provided by the capacitor 28 and the resistor 25. As a result, the output of the integrator 27 rises from negative potential to positive potential.

When the output voltage of the integrator 27 exceeds the positive comparison voltage of the level comparator 34, the output of the level comparator 34 is inverted from a positive potential to a negative potential.

At this falling edge, a trigger pulse is generated by capacitor 35 and resistors 36 and 37 and applied to the input of NAND 38.

NAND 3B, Impark 41, 42, resistor 40, and capacitor 39 constitute a multi-vibration brake, and the above-mentioned tri-pulse is used as manual power to resistor 40 and capacitor 3.
A positive pulse with a pulse width determined by 9 is obtained at the output of the inverter 42.

Since this positive pulse is applied to the gate of the analog switch 43, while the pulse is at a positive potential, the analog switch 4
3 conducts and short-circuits the resistor 20.

Here, the value of the resistor 19 is selected so that the output of the rectifier circuit 9 will not be affected even if the resistor 20 is short-circuited.

When the resistor 20 is short-circuited, the inverting input of the level comparator 22 becomes zero potential, so the output of the level comparator 22 is inverted from a negative potential to a positive potential.

Therefore, the analog switch 1B is conductive while the pulse is at a positive potential.

Furthermore, when the output of the level comparator 22 is reversed from a negative potential to a positive potential, the diode 26 is reverse biased and becomes non-conductive, so the gate voltage of the FET 29 changes from a negative potential to zero potential, and the drain-source voltage of the FET 29 changes from a negative potential to a zero potential. The period changes from a non-conducting state to a conducting state.

Therefore, the charge on the capacitor 28 is discharged through the drain and source of the FET 29, the output of the integrator 27 becomes a negative potential, and the integrator 27 is reset.

The above operation is repeated periodically when the inverted input voltage of the level comparator 22 is higher than the non-inverted input voltage.

The pulse width is set to be sufficiently small for this repetition period.

Since the analog switch 18 becomes conductive every time the above-mentioned pulse is generated, the state of the output of the summing amplifier 17 is repeatedly monitored for a short period of time at regular intervals. The setting current circuit is controlled accordingly.

Further, since the pulse width of the pulse is set to be sufficiently smaller than the time constant formed by the resistor 44 and the capacitor 45, the potential across the capacitor 45 does not change suddenly.

Therefore, the light emitting diode 4, which is the load of the constant current circuit,
Since the current flowing through the volume controller 9 does not change abruptly, the volume adjuster 3 changes gradually, and the masking phenomenon can be alleviated, resulting in no unnatural sound volume adjustment.

In addition, as a volume regulator, any volume regulator that can vary the input audio signal by voltage, such as a transistor, can be used, in addition to photocoupler, which consists of a light emitter such as a light emitting diode and a light receiving element such as CdS. Needless to say.

As described above, the automatic volume adjustment device according to the present invention subtracts the DC fluctuation output converted from the output side audio signal of the volume adjuster and the DC fluctuation output converted from the synthesized sound consisting of the speaker sound and ambient noise, respectively, to generate the speaker sound. The volume of the audio signal is adjusted by the subtracted output, with the component set to approximately zero, and the level of the DC fluctuation output converted from the output side audio signal of the volume adjuster is compared by a level comparator,
When the DC fluctuation output is at a certain level, the level comparator memorizes and retains the subtraction output, and at the same time cancels the memory retention function repeatedly for a certain period of time, and adjusts the volume of the audio signal using the subtraction output. It was designed to do so.

Therefore, according to the present invention, it is possible to obtain a highly reliable automatic volume adjustment device that does not have the drawback that the ambient noise is masked by the speaker sound not only when the ambient noise component is at a low level but also when the level is high. It will be highly practical.

[Brief explanation of the drawing]

The figure is a circuit diagram of an embodiment of an automatic volume adjustment device according to the present invention. DESCRIPTION OF SYMBOLS 1... Audio signal source, 2... Preamplifier, 3... Volume adjuster, 4... Power amplifier, 5... Speaker, 6
...Microphone, 7...Microphone amplifier, 8
, 9... Rectifier circuit, 10, 11.12... Level adjuster, 17... Summing amplifier, 18.43... Analog switch, 22.34... Level comparator, 23,
33... Comparison voltage regulator, 26... Diode, 2
7... Integrator, 29, 48... Field effect transistor (FET), 38... AND NAND circuit (NAND
), 41.42... Impark, 49... Light emitting diode, 50... CdS.

Claims (1)

[Claims] 1. In a device that automatically adjusts the volume of sound produced by a speaker according to the ambient noise level, there is a difference between a signal converted from the output side audio signal of the volume adjuster and a signal converted from a synthesized sound consisting of the speaker sound and ambient noise. subtracting means for obtaining a subtracted output with a speaker sound component substantially zero by performing subtraction, means for comparing the level of a signal converted from the output side audio signal of the volume adjuster, and a means for comparing the level of a signal converted from the audio signal on the output side of the volume adjuster; means for storing and retaining the output of the subtracting means using the output of the level comparing means when the signal is at a high level; and means for storing and retaining the output of the subtracting means by using the output of the level comparing means when the signal is at a high level; An automatic volume adjustment device comprising: means for canceling the subtraction means; and means for adjusting the volume of the audio signal based on the output of the subtraction means.