JPH0748618B2 - Distortion suppression circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a distortion suppressing circuit implemented in association with an audio device that amplifies an audio signal by an amplifier circuit to make it acoustic.
More specifically, the present invention relates to a distortion suppressing circuit that prevents a so-called sound crack from occurring when an acoustic signal having an excessive voltage is input to the amplifier circuit and the acoustic signal is clipped.

BACKGROUND ART A typical prior art is shown in FIG. The acoustic signal is input from the line 1 and is given to the attenuating circuit 3 including the transistor 2. The output from the attenuating circuit 3 is amplified by the amplifying circuit 4 and given to the speaker from the line 5. In order to prevent sound cracking, the acoustic signal from the line 5 is supplied to the DC conversion circuit 6, in which the acoustic signal from the line 5 is rectified and smoothed via a coupling capacitor, and the line 7 is converted. A DC signal is derived at. This DC signal is applied to the base of the transistor 2 via the line 7. This transistor 2
When the acoustic signal exceeds the level that causes sound cracking, it conducts to prevent distortion.

In the prior art shown in FIG. 6 as described above, the transistor 2 conducts and cuts off, and accordingly, the attenuation amount, that is, the gain of the audio signal is not continuously changed and controlled. Therefore, when listening to music etc., it feels as if the body is floating inside, and there is a great sense of discomfort in hearing, which is not satisfactory in practice.

Another prior art is shown in FIG. The acoustic signal from the line 8 is given to a DC voltage control amplifier circuit 9 called an electronic volume or the like, and the acoustic signal whose gain is controlled here is given to the amplifier circuit 11 from the line 10 and amplified,
It is given to the speaker from line 12. The acoustic signal derived from the voltage controlled amplifier circuit 9 on the line 10 is also
The gain of the voltage controlled amplifier circuit 9 can be continuously controlled to be controlled when the acoustic signal of the line 10 exceeds a predetermined discrimination level which causes sound cracking.

Problems to be Solved by the Invention The new problem of the prior art shown in FIG. 7 is that the characteristics of the amplifier circuit 11 vary, and
If the gain of 11 is too large, it will not be possible to prevent sound cracking,
It becomes impossible to suppress distortion.

An object of the present invention is to provide a distortion suppressing circuit capable of surely preventing sound cracking without causing a feeling of strangeness in hearing and without depending on characteristics of an amplifier circuit for amplifying an acoustic signal. Is to provide.

Means for Solving the Problems The present invention is directed to a DC conversion circuit that rectifies and smoothes an acoustic signal from an amplification circuit via a coupling capacitor to output a DC signal, and a predetermined discrimination from the output of the DC conversion circuit. A level discriminating circuit for deriving a signal representing the difference from the level, and means for amplifying or attenuating the acoustic signal in response to the output from the level discriminating circuit, which is provided in front of the amplifying circuit, and which reduces the gain as the difference becomes larger. A distortion suppression circuit characterized by including and.

In a preferred embodiment, the level discrimination circuit is realized by using an operational amplifier circuit for a single power source.

In a preferred embodiment, the discriminating level of the level discriminating circuit is obtained by dividing the output voltage of a power source for energizing an amplifier circuit for amplifying an acoustic signal by a voltage dividing resistor.

According to the present invention, the acoustic signal is converted into a direct current level by the direct current conversion circuit, the difference between the output of the direct current conversion circuit and a predetermined discrimination level is obtained, and the attenuation circuit or the amplification circuit is determined according to the difference. Since the gain of is reduced, it is possible to eliminate the uncomfortable feeling in hearing.

Further, the direct-current converting circuit converts the acoustic signal from the amplifier circuit into direct current, so that even if the gain of the amplifier circuit varies, the gain of the gain changing means provided in the preceding stage of the amplifier circuit is changed. By changing it, it becomes possible to surely prevent the sound crack.

Embodiment FIG. 1 is an overall block diagram of an embodiment of the present invention. The left (L) channel acoustic signal from the acoustic signal generating circuit 20 such as a radio receiver or a magnetic medium reproducing device is from the line 21, and the right (R) channel acoustic signal is from the line 22.
Derived for stereo playback from buffer circuit 2
It is given to the voltage control amplifier circuit 25 called an electronic volume or the like via 3, 24. The voltage control amplifier circuit 25 has input terminals 26 and 27, and correspondingly to the voltage applied to the input terminal 27, the gains of the audio signals of the L channel and the R channel are changed in conjunction, and the L Channel and R
The acoustic signals of the channel are derived on lines 28 and 29, respectively. Acoustic signals from lines 28 and 29 are provided to fader 30.

FIG. 2 is a simplified plan view of the automobile 31. Automobile
In the passenger compartment 32 of 31, the speakers FL1 and FR1 are arranged on the left and right sides of the front part, and the speakers RL1 and RR1 are arranged on the left and right sides of the rear part, respectively. Thus, stereo reproduction can be performed using a total of four speakers. it can.

The fader 30 derives the acoustic signals FL, FR, RL, and RR to be reproduced in these speakers FL1, FR1, RL1, and RR1, respectively, and supplies them to the amplifier circuits 37 to 40 via the buffers 33 to 36, respectively. . The outputs of the amplifier circuits 37-40 are speaker FL1,
Acoustic signals are controlled by being applied to FR1, RL1, and RR1, respectively.

The present invention is implemented in order to prevent an audio signal having an excessive level from being input to the amplifier circuits 37 to 40 to cause a clip and a sound crack. The outputs of the amplifier circuits 37-40 are
It is given to the DC conversion circuits 41 and 42. One DC circuit 41
Has coupling circuits 43 and 44, and a rectifying / smoothing circuit 45 to which their outputs are given. Coupling circuit 43
To the front left speaker FL1, and to the other coupling circuit 44, the sound signal to be given to the front right speaker FR1.
These coupling circuits 43 and 44 have coupling capacitors C1 and C2 and resistors R1 and R2, respectively. The outputs of the coupling circuits 43 and 44 are given to the rectification / smoothing circuit 45 via the line 46. This rectifying / smoothing circuit 45
It has diodes D1 and D3, a capacitor C5, and a resistor R5, and performs double voltage rectification together with the capacitors C1 and C2 for smoothing, whereby the level of the acoustic signal of the front left and front right speakers FL1, FR1 is changed. A DC voltage having a level corresponding to the sum is led to the line 47.

The other DC conversion circuit 42 has a configuration similar to that of the DC conversion circuit 41 described above, and the acoustic signals to be given to the rear left speaker RL1 and the rear right speaker RR1 are coupled to each other by the coupling circuits 48, 49.
Given to each of these coupling circuits 48,49
The output of the sum of is supplied to the rectifying / smoothing circuit 51 from the line 50. The coupling circuits 48 and 49 include capacitors C3 and C4,
The rectifying / smoothing circuit 51 includes resistors R3 and R4, respectively, and has diodes D2 and D4, a capacitor C6, and a resistor R5, and performs voltage doubler rectification to smooth the voltage. The DC output of the rectifying / smoothing circuit 51 is led to the line 52.

The DC voltage from lines 47 and 52 is applied to line 53 via diodes D5 and D6. This allows line 53 to
The higher of the output voltage levels on lines 47, 52 is derived.

In DC converters 41, 42, time constants R1, C1, R2, C2, R3, C
3, R4 and C4 set the attack time τA and the time constant
Release times τR are set for R5, C5, R6, and C6, and the attack time τA is set to 2 to 3 msec and the release time τR is set to 200 msec to 2 sec in terms of hearing. In this DC conversion circuit 41, 42, double voltage rectification is performed,
Therefore, although the direct-current voltage introduced to the lines 47 and 52 can be increased and a preferable result is obtained from the viewpoint of hearing, the rectification may be performed by other configurations.

The signal of the DC voltage from the line 53 is the non-inverting input terminal 55a of the operational amplifier circuit Q1 for single power source in the level discrimination circuit 54.
Is divided by resistors R10 and R12 and given. At the inverting input terminal 55b of the operational amplifier circuit Q1, the voltage divided by the voltage dividing resistors R7 and R8 and the variable resistor R19 is applied to the line 56
It is given as a discrimination level from the resistor R9. resistance
R7 is connected to a DC power supply 58 via line 57. The power source 58 includes an acoustic signal generation circuit 20, a voltage control amplifier circuit 25,
The fader 30, the amplifier circuits 37 to 40, and other electric circuits are energized, so that the discrimination level given to the operational amplifier circuit Q1 changes depending on the voltage of the power supply 58.

In this level discrimination circuit 54, R9 = R10 = R11 = R12 (1) Therefore, the voltage V01 derived from the operational amplifier circuit Q1 to the line 60 is input to the non-inverting input terminal 55a of the operational amplifier circuit Q1. When the applied voltage is V (+) and the discrimination level input to the inverting input terminal 55b is V (-), the arithmetic operation is performed as shown by the second equation.

V01 = V (+)-V (-) (2) The operational amplifier circuit Q1 is an operational amplifier circuit for a single power source, and therefore the voltage V (+) given to the non-inverting input terminal 55a is an inverting input. The voltage V01 on the line 60 is zero when it is below the discrimination level V (-) applied to the terminal 55b. If the operational amplifier circuit Q1 is an operational amplifier circuit for both power supplies,
When the voltage V (+) applied to the non-inverting input terminal 55a is below the discrimination level (-) applied to the inverting input terminal 55b, a residual voltage of about 0.2 to 0.4 V is output to the output line 60, and Although the circuit may malfunction, the operational amplifier circuit Q1 is for a single power source in the above-described embodiment, and such a problem is solved.

In order to adjust the sound output from the speakers FL1, FR1, RL1, RR1, the variable resistor 61 is connected to the input terminal 26 of the voltage control amplifier circuit 25, and the displacement of the brush 62 is manually adjusted. In the arithmetic control circuit 63, the output from the brush 62 of the variable resistor 61 is divided by the resistors R16 and R15, and the arithmetic amplification circuit Q
2 is provided to the non-inverting input terminal 64. The output from the level discrimination circuit 54 is applied to the inverting input terminal 65 of the operational amplifier circuit Q2 via the line 60 and the resistor R13. A resistor R14 is connected to the operational amplifier circuit Q2. The output from the output terminal 66 of the operational amplifier circuit Q2 is given to the input terminal 27 of the voltage controlled amplifier circuit 25 via the line 67. The voltage V0 at the output terminal 66 of the operational amplifier Q2 is the voltage VC derived from the brush 62 of the variable resistor 61 and the output voltage V0 from the level discrimination circuit 54.
It is the difference from 1.

V0 = VC-V01 (3) The capacitor C7 in the level discrimination circuit 54 and the capacitor C8 in the arithmetic control circuit 63 are for noise absorption.
The operational amplifier circuit Q2 of the operational control circuit 63 is the level discrimination circuit 54
It is an operational amplifier circuit for a single power supply for the same reason as the operational amplifier circuit Q1 used in.

The operation of the embodiment shown in FIGS. 1 and 2 will be described with reference to FIG. Lines 21 and 2 of the acoustic signal generation circuit 20
The acoustic signal as shown in Fig. 3 (1) is derived from Fig. 2, and the acoustic levels before and after the passenger compartment 32 are changed to the fader 30.
Are adjusted differently according to the
Reference lines V (+) 1 in FIG. 3 (2) are provided on lines 47 and 52 of 41 and 42.
Suppose that and V (+) 2 are derived. The discrimination level of the level discrimination circuit 54 is indicated by reference numeral V (−) in FIG. 3 (2), and this discrimination level is a value appropriately determined from the viewpoint of hearing. In FIG. 3 (2), V (+) 1 <V (+) 2 (4), and therefore, the larger direct current in the line 53 as shown in FIG. 3 (3). The output V (+) 2 is derived.

By the level discriminating circuit 54, a difference V01 between the larger DC level V (+) 2 and the discriminating level V (-) shown in FIG. 3 (4) is derived from the line 60. Variable resistor 6
When the voltage VC shown in FIG. 3 (5) is derived by the brush 62 of 1, the operational amplifier circuit Q2 of the operational control circuit 63
From the output terminal 66 of the voltage control amplifier circuit 25 via the line 67
The voltage V0 shown in FIG. 3 (6) is derived from the input terminal 27 of the.

In the amplifier circuits 37 to 40 in which the maximum output amplitude level is specified in this way, when an excessive input exceeding the clip level is input, the sound of the speakers FL1, FR1, RL1, RR1 is prevented from being clipped and distorted. For this purpose, the acoustic signals from the amplifier circuits 37-40 are converted into DC signals by the DC conversion circuits 41, 42, and the DC voltage thereof exceeds the discrimination level V (-) predetermined in the level discrimination circuit 54. The gain of the voltage control amplifier circuit 25 is controlled so that the gain decreases as the difference increases, thereby suppressing a large change in gain as instantaneously as possible. Is prevented from occurring. Moreover, in such an embodiment, since the gain of the voltage control amplifier circuit 25 is controlled by the output of the amplifier circuits 37 to 40, the gain of the amplifier circuits 37 to 40, and hence the clip level is the amplifier circuit 37 to 40. Even if it is different for each 40, it is possible to surely prevent the distortion due to the sound input from being generated due to the excessive input.

In the above-described embodiment, the common DC conversion circuit 4 is also used in the first group of speakers FL1 and FR1 arranged in front of the passenger compartment 32.
The outputs of the amplifier circuits 37, 38 are given to 1, and in the second group of speakers RL1, RR1 arranged after the passenger compartment 32,
The acoustic signals from the amplifier circuits 39 and 40 are commonly given to the DC conversion circuit 42. The outputs from the DC conversion circuits 41 and 42 are given to the line 53 from the lines 47 and 52 through the diodes D5 and D6, and thus the higher level of the outputs of the DC conversion circuits 41 and 42 is selectively supplied to the line 53. Be derived to. As a result, the sound crack preventing operation is achieved as described above.

A person in the passenger compartment 32 of the car 31 operates the fader 30,
(A) Only the front FL1 and FR1 loudspeakers of the first group are sonicated, and at this time the second loudspeaker RL of the second group
When the sound is not output from the first and the RR1, the sound is not output from the speaker FL1 and the FR1 of the first group of the front and the reverse of the speaker RL1 of the second group of the RL1 and the rear of the first group.
In any of the cases (a) and (b) in which sound is output only from RR1, the sound cracking prevention function is achieved.

To explain this reason in more detail, in the coupling circuits 43 and 44 of FIG. 1, the output level of the acoustic signal of the amplifier circuit 37 is VFL, and the output level of the acoustic signal from the amplifier circuit 38 is VFL.
FR, the output impedance Z of the amplifier circuits 37 and 38 is set to zero, and the output of the coupling circuits 43 and 44 is connected to line 4
When the impedance when the side of the rectifying / smoothing circuit 45 is viewed from 6 is Rin and the voltage level of this line 46 is VF, the fifth equation is satisfied.

Here, R2Rin represents the parallel impedance of the resistor R2 and the impedance Rin.

Here, if Rin >> R1, R2 (6), the signal level VF shown in the fifth equation becomes the value VF1 shown in the seventh equation.

Here, if R1 = R2 (8) is established, the value VF1 expressed by the equation 7 is expressed by VF2 of the equation 9.

For example, when VFL = VFR (10), the signal level VF3 of the line 46 is as shown in the equation 11 from the equation 9.

Therefore, the first group of speakers FL1, in front of the passenger compartment 32,
Even if the fader 30 is operated so that sound output is obtained only from FR1 and no sound is generated from the second group of speakers RL1 and RR1, the line 46 as shown in Equation 11 is used. As the output level of, the acoustic output level VFL of the amplifier circuit 37 is obtained on the line 46. Therefore, the gain of the voltage control amplifier circuit 25 is controlled by the signal level VFL of this line 46 so that the acoustic signals input to the amplifier circuits 37 and 38 do not reach the clip levels of those amplifier circuits 37 and 38. The excellent effect that it can be suppressed to the above is achieved.

The same applies to the loudspeaker FL of the first group in front of the passenger compartment 32.
Even when the sound output from 1 and FR1 is set to zero and the sound is output only from the speakers RL1 and RR1 of the second group later, the operation of preventing sound cracking is achieved.

FIG. 4 is an electric circuit diagram of still another embodiment of the present invention. In this embodiment, the woofer 68 is disposed at the center position on the left and right in front of or behind the passenger compartment 32 of the automobile 31, so-called
It realizes a 3D system. The acoustic signal from the buffer 69a given to the woofer 68 via the amplifier circuit 69 is added (= L + R) to the left and right acoustic signals and given to the coupling circuit 70 of the DC conversion circuit 72, and further from the rectification / smoothing circuit 71. The output of the DC conversion circuit 72, which is led out through the diode D7, is given to the line 53. DC conversion circuit
72 has the same configuration as the DC conversion circuits 41 and 42.

As still another embodiment of the present invention, a sound field control signal used in a surround system or the like instead of the woofer 68, for example, a signal (L-
The present invention can be similarly implemented by converting R), (RL), etc. into a direct current and supplying it to the line 53.

FIG. 5 is an electric circuit diagram of still another embodiment of the present invention. In this embodiment, the passenger compartment 32 of the automobile 31 is provided with left and right speakers FL1 and FR1 only, and instead of the rear speakers RL1 and RR1 in the above-described embodiment, a woofer 6 is placed after the passenger compartment 32.
Equipped with 8. The parts corresponding to those in the above-described embodiment are designated by the same reference numerals. Even in such an embodiment, the fader
Operate 30 to operate the first group of speakers FL in front of the passenger compartment 32.
It is possible to achieve sound crack prevention even when sound is output only from FR1 and the sound signal from the woofer 68 of the second group after the passenger compartment 32 is set to zero, and vice versa. it can. Instead of the embodiment shown in FIG.
It is placed in front of 32 and behind the passenger compartment 32 left and right speakers RL1, RR1
May be arranged to form a 3D system.

The resistors R7, R8, R19 for setting the discrimination level V (−) given to the non-inverting input terminal 55a of the operational amplifier circuit Q1 in the level discrimination circuit 54 are connected to the DC power source 58,
The DC power source 58 powers the entire audio device of the present invention. This power supply 58 is mounted on the automobile 31 and is a battery, and varies greatly, for example, in the range of 10.5V to 16V, and thus the clip level that causes the sound cracking of the amplifier circuits 37 to 40 also varies. As described above, the discrimination level V (−) also follows the fluctuation of the voltage of the power source 58, so that there is an advantage that the optimum maximum distortion-free output can be obtained.

Instead of changing the gain of the voltage control circuit 25, the attenuation rate of the attenuating circuit and hence the gain may be changed.

Effects As described above, according to the present invention, it is possible to reliably prevent the generation of distortion due to sound cracking without causing an uncomfortable feeling in hearing and even when the gain of the amplifier circuit varies. .

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of an embodiment of the present invention, FIG. 2 is a schematic view of a passenger compartment 32 of an automobile 31, and FIG. 3 is an embodiment of the embodiment shown in FIGS. FIG. 4 is a waveform diagram for explaining the operation, FIG. 4 is an electric circuit diagram of another embodiment of the present invention, FIG. 5 is an electric circuit diagram of yet another embodiment of the present invention, and FIG. Circuit diagram, FIG. 7 is another prior art electrical circuit diagram. 20 ... Acoustic signal generation circuit, 25 ... Voltage control amplification circuit, 30 ... Fader, 37-40 ... Amplification circuit, FL1, FR1, RL1, RR1 ... Speaker, 41, 42, 72 ... DC conversion circuit, 43, 44, 48 , 49,70 ... Coupling circuit, 45,51,71 ... Rectification / smoothing circuit, 54 ... Level discrimination circuit, 63 ... Operation control circuit

Claims (3)

[Claims] 1. A DC conversion circuit for rectifying and smoothing an acoustic signal from an amplification circuit through a coupling capacitor to output a DC signal, and a signal representing the difference between the output of the DC conversion circuit and a predetermined discrimination level. And a means provided in front of the amplifier circuit for amplifying or attenuating the acoustic signal in response to the output from the level discriminating circuit, and decreasing the gain as the difference increases. Distortion suppression circuit. 2. The distortion suppressing circuit according to claim 1, wherein the level discriminating circuit is realized by using an operational amplifier circuit for a single power source. 3. The discrimination level of the level discrimination circuit is obtained by dividing the output voltage of a power source for energizing an amplifier circuit for amplifying an acoustic signal by a voltage dividing resistor. The distortion suppression circuit according to the first or second range.