JPS5841004B2 - automatic volume adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic volume adjustment device for an audio device, which automatically adjusts the volume of the speaker according to ambient noise, regardless of whether the audio level of the speaker of the audio device is high or low. The purpose is to provide an automatic volume adjustment device that automatically adjusts the volume according to changes in ambient noise level in audio equipment such as televisions, radios, tape recorders, and public address systems. Various methods have been considered, but most of them detect the ambient noise component from a composite sound of the output audio signal of the audio device, speaker sound, and ambient noise, and adjust the volume of the audio device using the ambient noise component. It's just something to try to adjust.

With these methods, when the speaker sound reaches a high level, the ambient noise is masked by the speaker sound, making it difficult for the microphone to detect the ambient noise, and the ambient noise level is relatively reduced. The disadvantage is that the volume is reduced when the

Therefore, ambient noise is detected only when the speaker audio level is low, and when the speaker audio level is high, the ambient noise is detected only when the speaker audio level is low.
One possible method is to maintain the volume at a level raised by ambient noise when the speaker audio level is low, but if the sound source is a continuous sound such as a musical tone and there are almost no low-level periods, the volume will be lower even if there is an ambient noise level adjuster. The drawback is that the volume remains at a constant level and does not change in response to changes in the ambient noise level.

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.

FIG. 1 is a block diagram of an embodiment of an automatic volume adjustment device according to the present invention, and FIG. 2 is a circuit diagram of an embodiment based on FIG. 1. Parts are numbered the same.

In FIG. 1 or 2, reference numeral 1 denotes an audio signal source such as a television, radio, tape recorder, microphone, etc. The audio signal outputted from this source is supplied to a volume controller 3 via a preamplifier 2. After the volume is adjusted in this step, the sound is converted into sound by the speaker 5 via the power amplifier 4 and then produced.

The synthesized sound of this speaker sound and the ambient noise at that time is detected by the microphone 6, and this detection signal is amplified by the microphone amplifier 1 and then supplied to the rectifier circuit 9 via the level adjuster 8, for example, a negative signal. Converted as DC fluctuating output.

Further, the output audio signal of the power amplifier 4 is supplied to a rectifier circuit 11 via a level adjuster 10, where it is converted into, for example, a positive DC fluctuation output.

The output of this rectifier circuit 11 is connected to a non-inverting input of a buffer 12 and is also grounded via a resistor 13.
The output of this buffer 12 is connected to the inverting input of the buffer 12 and is also connected to an inverting summing amplifier 15 via a resistor 14.
connected to the inverting input of

Further, the output of the rectifier circuit 9 is connected to the non-inverting input of the buffer 16 and grounded via the resistor 11, and the output of the buffer 16 is connected to the inverting input of the buffer 16 and is grounded via the resistor 18. The above inverting summing amplifier 1
Connected to the inverting input of 5.

The output of this inverting summing amplifier 15 is connected to this inverting input via a resistor 19 and to the drain of an analog switch 21 .

These buffers 12, 16, inverting summing amplifier 15, resistors 13, 14, 17, 18, 19, etc. make up the subtracting circuit 2.
It constitutes 0.

In addition, inverters 22, 23, resistors 24, 25, 26,
The output of the unstable multi-by break composed of the diode 2γ and the capacitor 28 is connected to the gate of the analog switch 21, and the gate circuit 29 is connected to the gate circuit 29 by the unstable multi-by break and the analog switch 21.
It consists of

The source of the analog switch 21 is connected to a non-inverting input of a buffer 32 via a resistor 30 and a diode 31, and is also connected to a non-inverting input of the buffer 32 via a resistor 33.

Also, the non-inverting input of this buffer 32 is connected to a capacitor 34.
These resistors 30, 33, diode 31, and capacitor 34 constitute an integrator 35 having a time constant determined by their values.

The inverting input of the buffer 32 is a field effect transistor (
It is connected to 36 sources (hereinafter referred to as FET), and
It is grounded via a resistor 31, and the output of this buffer 32 is connected to the gate of FETa6.

Further, the drain of the FETa6 is connected to the cand of the light emitting diode 38, and the anode of the light emitting diode 38 is connected to the positive DC power source 1B.

A light receiving element Cd5 integrated with this light emitting diode 38
Reference numeral 39 constitutes a volume adjuster 3 with resistors 40 and 41.

In addition, the buffers 12, 16, 32 and the inverting summing amplifier 1
5. Power for the inverters 22, 23 and the analog switch 21 is supplied from the positive DC power supply 1B and the negative DC power supply -B.

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

As mentioned above, the audio signal from the audio signal source 1 passes through the preamplifier 2, the volume adjuster 3, and the power amplifier 4, and then is level-adjusted by the level adjuster 10, and then output by the rectifier circuit 11 as a positive DC fluctuation output. On the other hand, the speaker sound emitted from the speaker 5 is detected together with ambient noise by the microphone 6, passes through the microphone amplifier γ and the level adjuster 8, and is converted by the rectifier circuit 9 as a negative DC fluctuation output.

Here, the frequency characteristics of speaker 5 and microphone 6,
Considering the positional relationship between the speaker 5 and the microphone 6, etc., the level adjusters 8 and 1 are adjusted so that the absolute values of the DC outputs of the rectifier circuits 9 and 11 are equal to each other when there is no ambient noise.
0 and the rectifier circuit 9. Adjust the smoothing circuit of 11, etc.

The DC outputs obtained from the rectifier circuits 9 and 11 are input to buffers 16 and 12, respectively.
An output with the same polarity as each input is obtained at the output terminal.

An output determined by the sum of these outputs and the amplification degree of the resistors 14, 18, 19 and the inverting summing amplifier 15 is obtained as the output of the inverting summing amplifier 15, that is, the output of the subtracting circuit 20.

However, as mentioned above, in the case of the negative DC output of the rectifier circuit 9 and the positive DC output of the rectifier circuit 11, when there is no ambient noise, the absolute values of each rectified output are equal to z, so the input of the inverting summing amplifier 15 The sum total becomes a negative voltage due to the ambient noise component, and therefore, a positive DC voltage proportional to the ambient noise component is obtained at the output of the inverting summing amplifier 15, that is, the output of the subtracting circuit 20.

On the other hand) inverters 22, 23, resistors 24, 25゜26,
An oscillation pulse waveform as shown in FIG. 3 is obtained at the output of the astable multi-by-break composed of the diode 21 and the capacitor 28, and this pulse is applied to the gate of the analog switch 21.

During the period when the pulse is at a positive potential, the analog switch 21
The train and source of the circuit are electrically conductive and non-conductive during the period of negative potential, and this operation is repeated.

This is set so that the pulse width at which the pulse becomes a negative potential is sufficiently larger than the pulse width at which the pulse becomes a positive potential.

In addition, the resistor 30 is selected such that the forward resistance value of the diode 31 in the integrator 35 can be ignored with respect to the resistance value of the resistor 30, and the resistance value of the resistor 33 is selected to be Since it is selected to be sufficiently large, the charging time constant for charging across the capacitor 34 is approximately determined by the resistor 30 and the capacitor 34, and the discharging time constant is determined by the extremely high reverse resistance value of the diode 31. It is approximately determined by the resistor 33 and capacitor 34.

Therefore, the charging time constant of the integrating circuit 35 is sufficiently smaller than the discharging time constant.

Regarding the relationship between the pulse width of the above pressure and the charging time constant and the discharging time constant, the ratio between the pulse width of the above pressure and the charging time constant should be appropriately selected, and the discharge should be performed with respect to the positive pulse width. The time constant is selected to be sufficiently large.

The positive DC output of the subtraction circuit 20 is charged across the capacitor 34 with a time constant determined by the resistor 30 and the capacitor 34 when the analog switch 21 is conductive, and is charged across the capacitor 34 with a time constant determined by the resistor 30 and the capacitor 34 when the analog switch 21 is conductive. - Since the impedance between the sources and the input impedance of the buffer 32 are very high, the potential across the capacitor 34 is held at the potential immediately before the analog switch 21 becomes non-conductive.

In this way, the positive DC output of the subtraction circuit 20 is applied to the capacitor 34 with a charging time determined by the resistor 30 and the capacitor 34 each time the analog switch 21 is turned on.
to charge.

Here, as described above, since the time for full charging of the capacitor 34 with respect to the output of the subtraction circuit 20 is appropriately accelerated, the potential across the capacitor 34 increases in accordance with the rise of the ambient noise.

The positive DC voltage obtained across the capacitor 34 is applied to the non-inverting input of the buffer 32;
2. Since the FET 36 and the resistor 31 constitute a constant current circuit with the light emitting diode 38 as a load, the buffer 32
A current proportional to the positive DC voltage applied to the input of the light emitting diode 38 and the resistor 31 flows through the light emitting diode 38 .

Therefore, the resistance value of the Cd539 integrated with the light emitting diode 38 becomes smaller in accordance with the current flowing through the light emitting diode 38, and the attenuation ratio of the volume adjuster 3 becomes smaller.

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

When the volume of the speaker 5 increases, the speaker sound input to the microphone 6 increases, and the negative DC output level of the rectifier circuit 9 increases by the increased speaker sound, but at the same time, the positive DC output level of the rectifier circuit 11 increases. The output level also increases by the amount that the speaker sound increases.

However, when there is no ambient noise, the absolute values of the DC outputs of the rectifier circuits 9 and 11 are equal, so the speaker sound component appearing in the output of the subtraction circuit 20 is approximately zero, and as a result,
The volume of the speaker 5 is maintained at the level of the ambient noise component at that time.

In this state, when the ambient noise disappears, the subtraction circuit 2
The output of 0 is approximately zero.

At this time, the charge across the capacitor 34 is discharged through the resistor 33 while the analog switch 21 is turned on.

However, as described above, the time constant formed by the resistor 33 and the capacitor 34 is smaller than the positive pulse width, and
Since the positive pulse width is smaller than the negative pulse width, the charge across the capacitor 34 is not discharged suddenly but gradually.

Therefore, the volume of the speaker 5 gradually returns to the original volume.

Also, if the speaker volume becomes very high (due to high level of ambient noise), the high level of speaker sound masks the ambient noise, making it difficult to detect the ambient noise, and the ambient noise level decreases. The volume of the speaker tends to decrease as it becomes equal, but as mentioned above,
Since the discharge time constant consisting of the resistor 33 and the capacitor 34 is sufficiently large compared to the on time of the analog switch 21, and the off time of the analog switch 21 is sufficiently large relative to the on time, the ambient noise level is equivalently reduced. Even if the voltage decreases, the potential across the capacitor 34 does not drop suddenly.

In addition, the charging time constant consisting of the resistor 30 and the capacitor 34 is appropriately selected with respect to the ON time of the analog switch 21, and generally, even if the audio signal source is a continuous sound such as a musical tone, it is possible to maintain a constant charge for a long period of time. It is rare for the level to remain high, and there is always a period, even for a short time, when the speaker sound reaches a level that does not mask the surrounding noise.

Since the ambient noise component equivalently rises during this period, if the analog switch 21 is conductive at this time, the ambient noise component will charge the recharging capacitor 34 within a short time and reduce its potential. as a result, the speaker volume increases to its original level.

Therefore, even when the speaker sound is at a low level, the masking phenomenon can be alleviated, and the volume adjustment will not be unnatural.

In addition, as volume regulators, there are all types of volume regulators that can vary the input audio signal by voltage, such as photocouplers that are composed of a light emitter such as a light emitting diode and a photoreceptor such as CdS, as well as transistors, etc. Needless to say, you can use .

Furthermore, FIGS. 4 and 5 show other embodiments based on FIG. 1 or 2, in which at the moment when the speaker voice changes from non-producing to producing, the ambient noise at the time when the speaker voice is not producing This is an embodiment in which a function is added to prevent the volume of the speaker from becoming temporarily louder than necessary.

These will be briefly explained below.

Common parts in the figures are given the same numbers.

In FIG. 4, analog switches 42 and 4 are connected between the outputs of rectifier circuits 9 and 11 and the input of subtraction circuit 20, respectively.
On the other hand, a level comparator 4 is provided at the output of the rectifier circuit 11.
4 is provided, and when the output of the rectifier circuit 11 is approximately zero, the analog switches 42 and 43 are rendered non-conductive by the output of the level comparator 44, and the outputs of the rectifier circuits 9 and 11 are prevented from being input to the subtraction circuit 20. It was designed to prevent this.

Further, in FIG. 5, the input side audio signal of the volume adjuster 3 is rectified by a rectifier circuit 45, and the level comparator 44 is operated by this output, and when the output of the rectifier circuit 45 is approximately zero, the analog switch 42 is .43 is non-conductive,
The outputs of the rectifying circuits 9 and 11 are prevented from being input to the subtracting circuit 20.

As described above, the automatic volume adjustment device according to the present invention includes a circuit that subtracts a signal converted from the output side audio signal of the volume adjustment device and a signal converted from a synthesized sound consisting of speaker sound and ambient noise, and a circuit that subtracts a signal converted from the output side audio signal of the volume adjustment device and a signal converted from the synthesized sound consisting of the speaker sound and ambient noise, and A repeating gate circuit with a constant period of time, an integrator that integrates the subtracted output with a time constant whose charging time constant is smaller than the discharging time constant when the gate circuit is on, and an integrator that integrates the subtracted output with a time constant whose charging time constant is smaller than the discharging time constant when the gate circuit is on. It consists of a circuit that stores and holds the output, and the volume adjuster is adjusted by the output of this integrator.

Therefore, the speaker volume is automatically adjusted according to the ambient noise level, and even if the speaker audio level becomes high, the speaker sound will not mask the ambient noise and the volume will not become unstable. Since the speaker sound does not temporarily become excessive due to ambient noise, a reliable automatic volume adjustment device can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an automatic volume adjustment device according to the present invention, FIG. 2 is a circuit diagram of an embodiment based on FIG. 1, FIG. 3 is an oscillation waveform of an unstable multivib break,
5 and 5 are other embodiments based on FIG. 1 or FIG. 2. 1...Audio signal source, 2...#J equipment amplifier, 3...Volume adjuster, 4...Power amplifier, 5...・Speaker, 6...Microphone, γ...Microphone amplifier, a, io
...Rehe #adjuster, 9, 11, 45...
... Rectifier circuit, 12, 16.32 ... Buffer, 15, ... Inverting summing amplifier, 20 ...
・Subtraction circuit, 21゜42.43... Analog switch, 22, 23..., Inverter, 29...
...Gate circuit, 35...Integrator, 36.
... FET, 38 ... Light emitting diode,
39...CdS, 44...Level comparator.

Claims (1)

[Claims] 1 A circuit that subtracts the signal converted from the output side audio signal of the volume adjuster and the signal converted from the synthesized sound consisting of the speaker sound and ambient noise, and the off time is longer than the on time = fixed period repeating gate circuit and an integrator that integrates the subtracted output with a time constant whose charging time constant is smaller than the discharging time constant when the gate circuit is on, and a circuit that stores and holds the output of the integrator when the gate circuit is off. death,
An automatic volume adjustment device characterized in that the volume controller is adjusted by the output of the integrator.