JPS6110307A - Automatic sound volume adjusting device - Google Patents

Abstract

PURPOSE:To attain excellent automatic sound volume control in audible sense by applying a detected noise component to a time constant circuit having a time constant different depending on the increase/decrease in noise and controlling the sound volume by the output. CONSTITUTION:A sound in a cabin including noise detected by a microphone 11 is amplified by an amplifier 1, detected by a detector 5 and smoothed into a DC by a time constant circuit 13. Similarly, an audio signal is smoothed by a detector 5' and a time constant circuit 13'. Both the DC signals are subjected to substraction by a subtractor 14, the audio component iseliminated and only the noise component is extracted. The noise component controls an electronic volume 2 via a voltage/current converter 16, a current mirror 15 and a time constant circuit 17. Further, a variable impedance circuit 18 is connected to an output of the current mirror 15 to increase the time constant of the time constant circuit 17 when noise increases and to decrease the time constant when the noise decreases. Thus, the audible sense is improved.

Description

TECHNICAL FIELD The present invention relates to an automatic volume adjustment device, and more particularly to an automatic volume adjustment device for in-vehicle audio equipment.

BACKGROUND ART An example of this type of device is the circuit shown in FIG.
In the figure, reference numeral 11 is a microphone for detecting the sound field facing the vehicle interior and the sound outside the vehicle.
The signal is supplied to a detector 5, which is a half-wave rectifier circuit. This half-wave rectified output is obtained by resistor R1゜R2, transistor Q1
and a constant current charging circuit 6 consisting of a capacitor C2, and charges the capacitor C2 with a constant current. Reference numeral 7 designates a discharge circuit for discharging the charge of the capacitor C2, which is composed of a transistor Q2, r resistors R3 to R6, and a capacitor C6.

The charging output of the capacitor C2 is inputted to a smoothing circuit 6 and an inverter 8 having a smoothing function and a buffer function. This circuit 8
, capacitor C4, resistor R7~”+.

and transistor Q3. Consists of Q4.

On the other hand, is the audio signal from the in-vehicle audio equipment caused by electronic volume 2? The speaker 4 is driven through the wireless LAN controller 3 under ream control. The output of this 3 is connected to the diode D5 through the resistor
．． D6, resistor R1□ and capacitors C5, C6 are detected by the detector 9 having a negative half-wave rectification and smoothing function, and this negative detected output is smoothed by the smoothing circuit 8 via the resistor R11. The output is subtracted. This subtracted output becomes a control signal for the electronic volume 2 via a limit circuit 10 consisting of a diode D4 and a resistor i4. It is a limiter.

In this configuration, the sound containing noise detected by the microphone 11 is amplified by the amplifier 1 and then subjected to positive half-wave rectification by the detector 5. The voltage across the resistor R2 of the constant current charging circuit 6 in the next stage is the VBo (pace) of the transistor Q1.
emitter voltage), R2/V,.

With the constant current in (8), the capacitor C2 is charged with a constant current intermittently according to the half-wave rectified waveform. At the same time, the capacitor C3 of the discharge circuit 7 is also charged, but constant current charging is not performed.

When the sound inside the car decreases, the output of the microphone amplifier also decreases, so the detection output also decreases. At this time, since the capacitor C2 does not have a fixed discharge path, it momentarily maintains the voltage at that point. Since the resistor R3 is connected in parallel to the capacitor C3, the electric charge is quickly discharged by appropriately setting the time constant 03·R3. However, when the noise decreases, the collector potential of the transistor Q2 remains at the potential of the immediately preceding capacitor C2, and the emitter potential decreases. The pace potential of transistor Q2 is determined by the difference between the voltages of power supply element B and capacitor C3, and resistors R5 and R.
By setting the values of R5 and R6 appropriately, if the voltage of capacitor C is higher than that of capacitor C3 only when noise is reduced, transistor Q2 is turned on. Therefore, the charge in the capacitor C2 is quickly discharged through the transistor Q2 and the resistors R4 and R.

When the noise rises, the voltage of capacitor C3 increases
2 is also larger, the transistor Q2 is turned off, and the voltage of the capacitor C2 intermittently rises slowly due to constant current charging. This output voltage is smoothed by a smoothing circuit 8 to become a DC signal. Here, the detector 9 generates a negative half-wave rectification of the audio signal and its smoothed signal, and therefore, at the input of the limit circuit 10, the audio component is subtracted from the sound inside and outside the car detected by the microphone 11. A signal proportional to the noise component will be obtained.

By doing this, when the noise increases, the volume of the audio signal increases due to the electron volume 2, and when the noise decreases, the volume of the audio signal decreases, but due to the action of the limit circuit 10, the audio component is reduced below a certain gain. will no longer decrease.

Such conventional circuits have the following drawbacks. First, since the charging circuit 6 uses a constant current charging method using the BE of the transistor Q, the rate of increase in audio volume remains constant regardless of the amount of increase in noise. From an auditory perspective, it is desirable that the sound volume also increases in proportion to the amount of increase in noise.

Also, according to experiments, it is desirable for the audio volume to drop quickly when the noise decreases, but in conventional circuits, the threshold for discharging capacitor C2 depends on the saturation level of rank name Q2. However, due to the negative feedback effect of the resistors R4 and R3, prompt discharge is difficult.

Furthermore, the charging/discharging circuits 6 and 7 are originally required to have an effect on noise signals, but since the charging/discharging circuits are connected to the microphone output, the entire interior sound including audio components, as well as noise, is It will be related to the charge/discharge circuit. Therefore, for example, when the audio volume suddenly increases at a certain point, the output of the smoothing circuit 8 will gradually increase due to constant current charging, but the output of the audio detector 9 will increase faster, and therefore the control signal will be This changes the audio volume in a direction that lowers it, causing unnecessary level fluctuations.

This is due to the fact that the time constants in the circuits 6 and 7 and the time constant of the detector 9 do not match with respect to the audio component.

Furthermore, since transistors are used in the charging/discharging circuits 6 and 7, the nonlinearity caused by the VBliiK of the transistors affects at a very small level and reduces the overall system range.

SUMMARY OF THE INVENTION The present invention has been made to eliminate the drawbacks of the above-mentioned conventional devices, and its purpose is to increase the audio volume in accordance with the rate of rise of noise when the noise rises in the sound field; To provide an automatic volume adjustment device capable of adjusting the volume with good hearing sensation by quickly lowering the volume when descending.

The automatic volume adjustment device according to the present invention includes: a microphone that detects sounds inside and outside a sound field; a means for extracting a noise component by excluding an audio component from an audio device from the sound detected by the microphone; A time constant means configured to have a different time constant when the component increases and when it decreases, and a control means for controlling the volume of the audio signal of the audio equipment by the output of the time constant means. It is a feature.

Example The present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram of one embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same symbols.

In the figure, the detection signal from the microphone 11 is
1, it receives positive half-wave rectification at a detector 5, and then becomes an input to a time constant circuit 13 having a time constant τ.

On the other hand, the electronic volume 2HfC signal of the audio signal is amplified by the amplifier 12 and then subjected to half-wave rectification to the detector 5'.
It is received at the time constant τ and becomes the input to the time constant circuit head which also has the time constant τ. The smoothed output from the constant constant circuits 13, x, 4 is subtracted by a subtracter 14 to separate and extract only the noise component inside the vehicle. This noise component is the resistance R,,te and f
The signal is input to a voltage/current converter 16 consisting of OP1 and a transistor Q5 cuff, and is converted into a current. This current 11 is passed through the current mirror 10 to a current proportional to the current 2, which is connected to the capacitor C8 and the resistor.
It becomes the charging input of the time constant circuit 17 consisting of 18. A variable impedance circuit 18 is provided equimetrically in parallel with this capacitor C8, and this circuit 18 includes an amplifier OP2, resistors R1, .
Consists of D8. The output vrL3 of the time constant circuit 17 and the emitter output vrL2 of the transistor Q5 of the current conversion circuit 16 are applied to a pair of inputs of the operational amplifier OP2. The output Vns of this time constant circuit 17 controls the electronic g-stream 2.

In this configuration, in-vehicle sound including noise detected by the microphone 11 is amplified to an appropriate level by the amplifier 1, then detected by the detector 5, and DC smoothed by the time constant circuit 13. Similarly, the audio signal is also DC smoothed by the detector 5' and the time constant circuit 13. Both DC signals are subtracted by the subtracter 14, thereby removing the audio component and extracting only the noise component. If the predetermined number τ of the time constant circuit 13 is appropriately selected, the subtraction output can quickly follow the noise components inside the vehicle.

As mentioned above, it has been experimentally determined that when noise decreases, it is desirable that the audio component decreases quickly, and when noise increases, it is desirable that the audio component increases slowly. Therefore, there is a need for a circuit that generates an output signal that increases slowly when the subtracted output increases and quickly decreases when it decreases. be.

The current conversion circuit 16 includes an operational amplifier OP1 and a transistor Q.
5, and V3.5 of this transistor Q5. .

In order to eliminate the nonlinearity of the transistor Q5, the base and emitter of the transistor Q5 are inserted into the negative feedback section of the operational amplifier OP1. As a result, when the noise voltage Vn is applied to the positive phase input of the transistor Q
5 emitter output vy12FiVn2-vn1,
The collector of transistor Q5 has ■1=Vtz2/R
17=Vn, /R1,7)E flow. Noise voltage VTh
, the current 11 proportional to 'Jn becomes a current 2 similarly proportional to 'Jn' by the current mirror 15, and the time constant circuit 17
The capacitor C8 is charged. The time constant of this time constant circuit 17 is 18·C8, which is sufficiently larger than the time constant circuit 13 and x time (τ).

Now, assuming that there is no variable impedance circuit 18, the output VT'L3 of the time constant circuit 17 with respect to the noise input voltage VrL1 has a large time constant 08.
In other words, when noise is input, Vn2 quickly follows the noise, and VW3 follows the noise slowly. When the noise increases, the electronic volume control signal Vns gradually slows down. This is desirable because it meets the above requirements, but it is desirable for Vn3 to quickly follow this noise when the noise decreases.

Here, the diode D7. The circuit with D8 and resistor "191 R20 becomes a positive phase input"
When Jn 2 is lower than Vn s, which is the negative phase input (1
It has a gain of 10"20/Jt, 9), and conversely, Vn
2) It has a gain of 1 when Vns. Therefore, considering the output section of the output of the operational amplifier OP2 through the diode D8, and considering the impedance Z seen from the output section (Vn 3) of the time constant circuit 17 to the resistor "21 side, Vn
When 2≧Vn s, Vn a =Vn s and Z
becomes infinite. On the other hand, when Vn2<Vn3, VW, :(V7L2-VW3) (1-12o/R,,
)+Vn2=■n2(2+R2o/R1,)-■rL3
(l+R2Q//R49) Z””’2+”’J/(”3Vyi4)=R2,・Vn
The following relationship holds true: 3/(VW3-Vn1).(2+R2o/R19).

That is, when the noise rises, Vn 2 rises following the noise, and Vn s rises slowly, so Vn2≧Vn s
Therefore, the resistor R21 has an apparently high intensity (nearly infinite), and the time constant circuit 17 has its own large time constant 08.
- R18 remains as it is, so the control signal Vn3 rises slowly.

On the other hand, when the noise decreases, VW2 quickly descends and VW
3 falls slowly, so VW2<vrL3, and the resistor R21 has an apparently low impedance and decreases in proportion to (Vn s Vn 1), so the actual time constant of the time constant circuit 17 is (" 3 ”'1)
, and the control signal VrL3 also becomes small accordingly. In other words, when the noise increases, the audio signal increases, and when the noise decreases, it quickly decreases according to the amount of decrease, thereby achieving the objective. In addition, if R2o/R1 is made sufficiently large, or R2
If 1 is made small, Vn3 can be decreased following the groaning Vyzz when the noise decreases.

In the above example, the method for extracting the noise component is to subtract the audio signal component from the microphone output. However, another method is to subtract the audio signal component from the microphone output, but as shown in FIG. The object of the present invention can be achieved in a similar manner even with a configuration in which only the above components are excluded.

Effects of the Invention As shown above, according to the present invention, since a time constant circuit having different time constants is used when the noise rises and when the noise falls, when the noise rises, the audio volume also increases according to the speed of rise. Furthermore, when the noise level decreases, the volume can be quickly reduced, making it possible to perform automatic volume control with good audibility.

Furthermore, since the non-linear regions of the transistor Q5 and the diodes D, D8 are absorbed by being provided in the feedback loop of the amplifier, operation from a minute level is possible, and the range of the entire system is expanded.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional automatic volume adjustment device, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a partial block diagram of another embodiment of the present invention. Explanation of symbols of main parts 2...Electronic volume 4...Speaker 1
1...Microphone 13.13.17...Time constant circuit 16...Current conversion circuit

Claims (2)

[Claims] (1) A microphone that detects sounds inside and outside the sound field, a noise extraction means that extracts a noise component by excluding the audio component from the audio equipment from the sound detected by the microphone, and a noise extraction means that uses this noise component as input and when this component increases. An automatic volume control device comprising: a time constant means configured to have a different time constant when the time constant is lowered and when the volume is decreased; and a control means configured to control the volume of the audio signal of the audio equipment by the output of the time constant means. Adjustment device. (2) The time constant means includes a time constant circuit charged by a current according to the extracted output by the noise extracting means, and a variable impedance circuit provided in parallel with the time constant circuit, and Claim 1, characterized in that the impedance of the variable impedance circuit is controlled according to a level difference with the output of the time constant circuit, so that the output of the time constant circuit is used as a volume control signal. Automatic volume adjustment device as described.