JPH0478045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic volume adjustment device, and more particularly to an automatic volume adjustment device for allowing reproduced sound to be heard well in a place where the level of ambient noise is high.

When trying to listen to reproduced musical sounds in a place where there is a lot of ambient noise, the reproduced musical sounds may be masked by the ambient noise. For example, if you try to listen to a car stereo while the car is running, the reproduced musical sound may be masked by the driving noise when the driving noise level increases.

The first solution to this problem is
A gain control device corresponding to the magnitude of ambient noise as shown in the figure has been proposed. This is sensor 1
Ambient noise is converted into an electrical signal, and this electrical signal is supplied to the noise level detection circuit 2 to detect its level. The noise level detected by the noise level detection circuit 2 is multiplied by a predetermined constant K in a constant circuit 4 to generate a gain control signal A.

On the other hand, an external musical tone signal B supplied to the signal input terminal 3 is supplied to a power amplifier 6 via a gain control circuit 5, where it is amplified and then reproduced from a speaker 7. In this case, since the gain control circuit 5 changes the gain in response to the gain control signal A supplied from the constant circuit 4, when the ambient noise level increases, the musical tone reproduced from the speaker 7 increases accordingly. It is also elevated to make listening easier. That is, the relationship between the ambient noise level and the volume in this case shows a characteristic in which the average volume b increases as the ambient noise a increases, as shown in FIG.

However, in the apparatus having the above configuration, the level of the reproduced musical sound is changed only in response to the level of the ambient noise, and is unrelated to the musical sound signal level. Therefore, a sufficient effect can be obtained when the change in signal level is small, but in a symphony, for example, where the change in signal level is large, the low level signal is masked in part D as shown in FIG. 3a. On the other hand, if the gain is increased so that the low level signal c is not masked, Fig. 3b
As shown in FIG. 2, there is a problem in that the volume of the high-level signal e becomes excessive in the portion f, making it sound noisy, and distortion occurs in the speaker or power amplifier.

Therefore, an object of the present invention is to solve the above-mentioned problems in the conventional apparatus by multiplying or adding predetermined coefficients to the ambient noise level and the input musical tone signal level, respectively, to perform gain control. It is an object of the present invention to provide an automatic volume adjustment device that can perform effective volume adjustment even for signals with large changes and can listen to reproduced sound satisfactorily.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The automatic volume adjustment device according to the present invention will be described in detail below with reference to the drawings.

FIG. 4 is a diagram showing the general configuration of the automatic volume adjustment device according to the present invention, and the same parts as in FIG. 1 are denoted by the same symbols, and detailed explanation thereof is omitted.
In the figure, 8 is an input signal level detection circuit that detects the level of the input signal supplied to the signal input terminal 3, and 9 is an input signal that receives the output signal of the ambient noise level detection circuit 2 and the output signal of the input signal level detection circuit 8. This is an arithmetic control circuit that generates a gain control signal A for controlling the gain control circuit 5 by arithmetic operations, and is configured as shown in FIG. 5, for example. In FIG. 5, 10 is the level increase amount (ΔS) of the input signal level supplied from the input signal level detection circuit 8 with respect to the reference signal level (So dBs).
dB) is multiplied by a negative constant α; 11 is an addition circuit that adds a voltage corresponding to a positive constant β to the output of the multiplication circuit 10; 12 is supplied from the ambient noise level detection circuit 2. This is a multiplier circuit that multiplies the output voltage of the adder circuit 11 by the output voltage corresponding to the amount of level increase (ΔN dB) with respect to the reference noise level (No dB(A) SPL).
outputs a voltage proportional to αΔS). 13 is a limiter circuit.

In the device configured in this manner, when the ambient noise level detection circuit 2 inputs the output signal of the sensor 1, a DC voltage proportional to the level increase ΔN dB with respect to the reference noise level No., dB(A) SPL is output. . In this case, the reference noise level No dB(A)
SPL is the lower limit of the ambient noise level that requires volume adjustment, and is generally configured to be fixed or variably set to a value between 40 and 60 dB(A) SPL. Note that the ambient noise level detection circuit 2 includes:
A circuit for separating ambient noise and musical sounds, such as a low-pass filter, is included, so that only the ambient noise level is detected.

On the other hand, the level of the input signal supplied to the signal input terminal 3 is detected by the input signal level detection circuit 8, and a DC voltage proportional to the increase ΔS dB with respect to the reference signal level So dBs is output. In this case, it is desirable to set the reference signal level So dBs to the average value of the input signal level. Furthermore, when the input signal has two channels, it is sufficient to detect the sum of the signal levels of both channels. An embodiment of the time constant circuit portions of the noise level detection circuit 2 and the signal level detection circuit 8 are shown in FIGS. 14 and 15, respectively. The time constant τn is determined by the resistor R ₁ and the capacitor C ₁ , the time constant τγ is determined by the resistor R ₂ and the capacitor C ₂ , and the time constant τf is determined by the resistor R ₃ and the capacitor C ₂ . In addition, D is a diode for backflow prevention, A ₁
is an amplifier. The detection time constant in the signal level detection circuit 8 is the time constant τγ for level rise.
The time constant τf(s) for the level decrease is larger than (s), and both of these are
It is desirable to set it smaller than the detection time constant τn(s) in . Since the gain is controlled to be large when the musical tone signal is at a low level, unless the time constant τγ is kept small, there is a risk that a sudden increase in level will be reproduced as an extremely high level. Natural reproduced sound can be obtained by making the constant τγ smaller than the time constant τf. Furthermore, the level change of the musical tone level signal is generally faster than the noise level change, and the time constant τγ, τf
is made smaller than the time constant τn to be able to follow sudden changes. The output signal of the input signal level detection circuit 8 detected in this way is output to the multiplication circuit 1.
0 is multiplied by a negative coefficient α. α is a constant that determines the rate of increase in the degree of compression of the signal level with respect to the increase in the ambient noise level, and is generally −0.04<
The user can arbitrarily set the value α≦0. Then, a voltage corresponding to the positive coefficient β is added to the output of the multiplier circuit 10 by an adder circuit 11. In this case, β is a constant that determines the gain increase rate for the reference level input signal with respect to an increase in the ambient noise level, and generally 0≦β<
The user can arbitrarily set the value to 1. A multiplication circuit 12 multiplies the output of the ambient noise level detection circuit 2 and the output of the addition circuit 11, and its output voltage is proportional to ΔN (β+αΔS). Note that a two-quadrant multiplier is used as the multiplier circuit 12, and the output of the ambient noise level detection circuit 2 is connected to the positive input terminal, and the adder circuit 1 is connected to the bipolar input terminal.
By connecting the output of 1, when the ambient noise level is below the reference noise level, that is, when ΔN≦0, the output can be set to 0 so that no volume adjustment is performed. The output signal of the multiplier circuit 12 obtained in this way is the output signal of the limiter circuit 1
3 to the gain control circuit 5 as a gain control signal A. In this case, since the gain control circuit 5 is a variable gain circuit composed of a voltage control amplifier or the like whose gain can be logarithmically and linearly controlled, its control sensitivity and the output voltage sensitivity of the multiplier circuit 12 are By matching these, the gain △G for the input signal supplied from the signal input terminal 3
dβ can be controlled so as to satisfy the following equation: ΔG=ΔN(β+αΔS) (1).

Figure 6 shows the volume adjustment effect of the above device. In the figure, the maximum value of the input signal level is So + ΔSmax dB, and the minimum value is So + ΔSmin.
dB (ΔSmax>0, ΔSmin<0), and the vertical axis represents the sum of the input signal level and gain to correspond to the volume.
It is shown in dB. Also, the horizontal axis shows the ambient noise level in dB. When the ambient noise level is below the reference noise level No dB(A) SPL (indicated by a in the figure), the volume is not adjusted.
ΔG=0. Next, when the ambient noise level increases, the volume is adjusted according to equation (1) above. Here, for the amount of increase ΔN dB (indicated by b in the figure), the gain ΔG ₁ with respect to the average signal level (So dBs) becomes ΔG ₁ =ΔNβ according to (1) above.
Similarly, if the increase in gain with respect to the maximum signal level (So + ΔSmax) and the minimum signal level (So + ΔSmin) is ΔG ₂ and ΔG ₃ dB, respectively, then ΔG ₂ = ΔN (β + αΔSmax) ΔG ₂ = ΔN (β + αΔSmin). Here, ΔN≧0, β≧0, α≦0,
Since ΔSmax>0 and ΔSmin<0, ΔG ₂ ≦
ΔG ₁ ≦ΔG ₃ . That is, the volume is adjusted so that the smaller the signal level is, the larger the gain is, and the larger the signal level is, the smaller the gain is. Therefore, appropriate volume adjustment is performed so that low-level input signals are not masked by the ambient noise level and high-level signals are not made excessively loud. Further, when the ambient noise level is sufficiently low (ΔN≦0), since ΔG=0, the state is automatically returned to a state in which no volume adjustment is performed.

Next, the relationship between the reference volume setting and its effects when using such a device will be described.
Here, the reference volume refers to the overall volume depending on individual preference, and corresponds to the overall volume when the ambient noise is sufficiently small (ΔN≦0). In the signal level detection circuit 8, the reference value for level detection is normally fixed. Therefore, the adjustment effect differs depending on whether this reference volume setting is performed before or after signal level detection. When the control constants α and β are the same as shown in Fig. 7a, the reference volume is set before being input to the device by the volume of the tape deck, tuner, etc. (input to terminal 3 in Fig. 4). Fig. 7b shows the adjustment effect when the reference volume is set within or after the signal level is detected (when setting the signal level of the gain control circuit 5 in Fig. 4). This shows the adjustment effect when the level is set at the input end or output end of Therefore, the former shown in FIG. 7a is more preferable than the latter in terms of adjustment effect.

Next, the setting range of the control constant α will be described.
According to this device, as the ambient noise level rises, the degree of compression of the signal level increases as the value of α increases, but when |α| is large and ΔN is large, as shown in FIG. An inversion phenomenon occurs in the volume relationship. Two different signal levels ΔS ₁ , ΔS ₂
(where ΔS ₁ >ΔS ₂ ), the gains are ΔG ₁ =ΔN (β+αΔS ₁ ) and ΔG ₂ =ΔN (β+αΔS ₂ ), respectively, according to the above equation (1). The condition that the volume relationship is not reversed is ΔS ₁ +ΔG ₁ ≧ΔS ₂ +ΔG ₂ .

Therefore, from these equations, the range of α is −(1/ΔN)≦α≦0, and the larger ΔN is, the smaller the setting range of α is.

In this device, the maximum value of ΔN is 25 (dB), and -
0.04≦α≦0.

Next, we will discuss the phenomenon of gain reduction as the ambient noise level increases and how to prevent it. As is clear from the above equation (1), when β is small and both |α| and ΔS are large, the gain ΔG may become negative as shown in FIG. 9. To prevent this phenomenon,
In this device, it is desirable to prevent ΔG<0 by using a limiter circuit 13 having diode characteristics. Of course limiter circuit 13
may be provided at the input stage of the multiplication circuit 12. That is, the multiplication circuit 12 may be configured as a one-quadrant multiplier that produces an output only when both inputs are positive.

FIG. 10 shows another embodiment of the automatic volume adjustment device according to the present invention, in which the same parts as in FIG. 5 are designated by the same symbols. In the figure, 10' is a multiplication circuit that multiplies the output of the ambient noise level detection circuit 2 by a constant β, 14 is a switch provided on the output side of the multiplication circuit 10, and the addition circuit 11 is a multiplier circuit that multiplies the output of the ambient noise level detection circuit 2 by a constant β.
and the output of the multiplier circuit 10 supplied via the switch 14 are added, and the resulting output is supplied to the gain control circuit 5.

In the circuit configured in this way, the degree of signal compression is kept constant regardless of the ambient noise level. Therefore, by opening the switching switch 14 for a signal with a small level change and closing the switching switch 14 for a signal with a large level change, the adjustment effect shown in FIG. 11 can be obtained. . The control equations in this case are: ΔG=βΔN (when the switch 14 is off) ΔG=βΔN+αΔS (when the switch 14 is on) However, β≧0, −1≦α≦0.

FIG. 12 is a circuit diagram showing still another embodiment of the present invention, in which the same parts as in FIG. 10 are indicated using the same symbols. In the figure, adder circuit 1
1 adds the voltage corresponding to the negative constant ΔSΤ and the output of the multiplier circuit 10' and outputs the result. Also 15
is a subtraction circuit that subtracts the output of the adder circuit 11 from the output of the signal level detection circuit 8, and a multiplier circuit 10 that multiplies by a multiplier α is provided on the output side of the subtraction circuit, and the output is The signal is supplied to the gain control circuit 5.

In the circuit configured in this way, an operation is performed to gradually increase the volume from a low signal level so as not to be masked in response to an increase in ambient noise. And the control equation in this case is γ=
Assuming ΔS-βΔN-ΔSΤ, when γ<0, ΔG=α·γ, and when γ≧0, ΔG=0, and the control characteristics are as shown in FIG.

However, β≧0, −1≦α<0, and ΔS T is the upper limit of the signal level at which the gain is increased when ΔN=0, and is fixed or variable.

As explained above, according to the present invention, gain control is automatically performed not only for the ambient noise level but also for the input signal level. Even for musical sound signals with large level changes, the volume can be effectively adjusted without masking at low levels or excessive volume at high levels, so the generated sounds can be heard in an optimal state.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional automatic volume adjustment device, FIGS. 2 and 3 a and b are characteristic diagrams of FIG. 1, FIG. 4 is a diagram showing the general configuration of the present invention, and FIG. 5 6, 7a and 7b, 8 and 9 are circuit diagrams showing one embodiment of the automatic volume adjustment device according to the present invention.
The figures are characteristic diagrams of Figures 4 and 5, Figure 10 is a circuit diagram showing another embodiment, Figure 11 is a characteristic diagram of Figure 10, and Figure 12 is a circuit diagram showing still another embodiment. , FIG. 13 is a characteristic diagram of FIG. 12, FIG. 14 is a circuit diagram showing an embodiment of the noise level detection circuit, and FIG. 15 is a circuit diagram showing an embodiment of the signal level detection circuit. 1...sensor, 2...noise level detection circuit,
5...gain control circuit, 6...power amplifier, 7...
...Speaker, 8...Signal level detection circuit, 9...
Arithmetic control circuit, 10, 10'...Multiplication circuit, 11
... Addition circuit, 12 ... Multiplier circuit, 13 ... Limiter circuit, 14 ... Switch, 15 ... Subtraction circuit.

Claims (1)

[Claims] 1. In a device that amplifies and reproduces a musical tone signal in a place with surrounding noise, an increment ΔN of the noise from a predetermined reference level is detected, and an increment ΔS of the musical tone signal from a predetermined reference level is detected. is detected, and the change ΔG in the amplification gain of the musical tone signal is controlled by a control signal containing a component corresponding to the sum signal of the product of the negative coefficient α and the increment ΔS and the product of the positive coefficient β and the increment ΔN. An automatic volume adjustment device characterized by: 2. Only when the change range of the increment ΔS is relatively large, the change ΔG is controlled by the sum signal, and when the change range of the increment ΔS is relatively small, it corresponds to the product of the increment ΔN and the coefficient β. 2. The automatic volume adjustment device according to claim 1, wherein said change amount ΔG is controlled by adjusting the amount of change ΔG. 3. The automatic volume adjustment device according to claim 1 or 2, wherein at least one of the coefficients α and β can be arbitrarily set by a user. 4. The automatic volume adjustment device according to claim 1, wherein a detection time constant for detecting the increment ΔN is larger than a detection time constant for detecting the increment ΔS. 5. The automatic volume adjustment device according to claim 4, wherein the detection time constant for detecting the increment ΔS is larger when the musical tone signal decreases than when the musical tone signal increases.