JPH01144808A - Distortion suppression circuit - Google Patents

Abstract

PURPOSE:To eliminate the disagreement feeling of auditory sense by converting an acoustic signal to a direct current level with the aid of a DC conversion circuit, obtaining the difference between the output of the DC conversion circuit and a differential level which is previously set and lowering the gain of an attenuation circuit or an amplification circuit according to that difference. CONSTITUTION:In the amplification circuits 37-40 of which maximum output amplitude levels are specified, the acoustic signals from the circuits 37-40 are converted to the direct current signal by the DC conversion circuits 41 and 42 so as to prevent the sound of speakers FL1, FR1, RL1 and RR1 from being distorted by clipping when excess input over the clip level of the maximum output amplitude level is inputted. Then, only the difference that the DC voltage is over the differential level which is previously set by a level discrimination circuit 54 is fetched and the gain is controlled so as to be lowered in proportion as the difference grows larger. Therefore, the gain is suppressed not to be drastically changed in a moment. Thus, the occurrence of the disagreement feeling of the auditory sense can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to amplifying an acoustic signal using an amplifier circuit to generate sound-W.
Regarding a distortion suppression circuit implemented in connection with an audio device that suffers from high noise, in more detail, when an acoustic signal with an excessive voltage is input to the amplifier circuit, clipping of the sound signal occurs, resulting in so-called sound cracking. This invention relates to a distortion suppression circuit that prevents the occurrence of distortion.

Background technology A typical prior art is shown in FIG.

An acoustic signal is inputted from line 1 and applied to a g-attenuation circuit 3 having a transistor 2, and the output from this attenuation circuit 3 is amplified by an amplifier circuit 4 and applied from line 5 to a speaker. In order to prevent sound cracking, the acoustic signal from line 5 is given to a DC conversion circuit 6, in which the acoustic signal from line 5 is rectified and smoothed via a coupling capacitor, and then passed to line 7. A DC signal is derived. This DC signal is applied via line 7 to the base of transistor 2. This transistor 2 becomes conductive to prevent distortion from occurring when the acoustic signal exceeds a level that causes sound cracking.

In the prior art shown in FIG. 6, the transistor 2 conducts conduction and cutoff, and therefore does not control the amount of attenuation of the audio signal, that is, the gain, by continuously changing it. Therefore, when listening to music, etc., it sounds as if one's body is floating inside, which gives a very uncomfortable feeling to the auditory sense, and is not satisfactory from a practical standpoint.

Another prior art is shown in FIG. The acoustic signal from line 8 is given to a DC voltage controlled amplifier circuit 9 called an electronic volume, etc. The acoustic signal whose gain is controlled here is given to an amplifier circuit 11 from line 10 to be amplified, and from line 12 to a speaker. given to. The acoustic signal derived from the voltage controlled amplifier circuit 9 on line 10 also
It is applied to a control circuit 13 where the gain of the voltage-controlled amplifier circuit 9 can be controlled to be continuously reduced when the acoustic signal on the line 10 exceeds a predetermined discrimination level that causes sound cracking.

Problems to be Solved by the Invention A new problem with the prior art shown in FIG. Therefore, distortion cannot be suppressed.

An object of the present invention is to provide a distortion suppression circuit that can reliably prevent sound cracking without causing an audible discomfort or depending on the characteristics of an amplifier circuit for amplifying an acoustic signal. The goal is to provide the following.

Means for Solving the Problems The present invention provides a direct current converting circuit that rectifies and smoothes an acoustic signal from an amplifier circuit via a coupling capacitor and outputs a direct current signal, and a predetermined discrimination between the output of the direct current converting circuit and the output of the direct current converting circuit. A level discrimination circuit for deriving a signal representing a difference between the levels and a means provided before the amplifier circuit, which responds to the output from the level discrimination circuit, amplifies or attenuates the acoustic signal, and decreases the gain as the difference increases. A distortion suppression circuit characterized by comprising:

In a preferred embodiment, the level discrimination circuit is realized using a single power supply operational amplifier circuit.

Further, in a preferred embodiment, the discrimination level of the level discrimination circuit is obtained by dividing the output voltage of a power source that energizes an amplifier circuit that amplifies an acoustic signal using a voltage dividing resistor.

According to the present invention, an acoustic signal is converted to a DC level by a DC conversion circuit, the difference between the output of the DC conversion circuit and a predetermined discrimination level is determined, and the gain of the attenuation circuit or amplifier circuit is adjusted according to this difference. Since the sound quality is reduced, it becomes possible to eliminate the sense of discomfort in the auditory sense.

In addition, the DC converting circuit converts the acoustic signal from the amplifier circuit into DC current, so even if there is variation in the gain of this amplifier circuit, the gain of the gain changing means provided at the front stage of the amplifier circuit is changed. This makes it possible to reliably prevent sound cracking.

Embodiment FIG. 1 is an overall block diagram of an embodiment of the present invention. A left (L>channel) audio signal from an audio signal generation circuit 20 such as a radio receiver or a magnetic media reproducing device is output from line 21, and a right (R) channel audio signal is output from line 22 for stereo reproduction. The voltage control amplifier circuit 25 has input terminals 26 and 27, and is supplied via buffer circuits 23 and 24 to a voltage control amplifier circuit 25, which is called an electronic volume.
The gains of the L channel and R channel acoustic signals are changed in response to the voltage applied to the line 28, and the L channel and R channel acoustic signals after the change are transferred to the line 28.
, 2.9, respectively. The audio signals from lines 28, 29 are applied to fader 30.

The second (21) is a simplified plan view of the automobile 31.

In the cabin 32 of the automobile 31, speakers FLL and FRI are arranged on the left and right sides of the front part, and speakers RL 1 and Rr (1) are arranged on the left and right parts of the rear part, respectively.In this way, a total of four speakers are used to create a stereo system. Can be played.

The fader 30 is connected to these speakers FLL, FR1, R.
At LI and RRI, the acoustic signals FL, FR, RL, and RR to be reproduced are derived and sent to buffers 33 to 33.
36 to amplifier circuits 37 to 40, respectively. The outputs of the amplifier circuits 37 to 40 are sent to speakers FLL, FRI,
The acoustic signals are controlled by being applied to RLI and RR1, respectively.

Sound having an excessive level in the amplifier circuits 37-40.

The present invention is implemented in order to prevent sound signals from being input and causing clipping and sound cracking.

The outputs of the amplifier circuits 37 to 40 are applied to DC converting circuits 41 and 42. One of the DC converting circuits 41 includes coupling circuits 43 and 44, and a rectification/smoothing circuit 45 to which the outputs of the coupling circuits 43 and 44 are supplied. The coupling circuit 43 is given an acoustic signal to be given to the front left speaker FL1,
Another coupling circuit 411 is supplied with an acoustic signal to be supplied to the front right speaker FRI. These coupling circuits f143, 44 have coupling capacitors C1, C2 and resistors R, 1, R2, respectively. The outputs of the coupling circuits 43 and 44 are:
It is applied to a rectifier/smoothing circuit 45 via a line 46.

This rectifier/smoothing circuit 45 includes diodes Di, D3,
It has a capacitor C5 and a resistor R5, and the capacitor C1
, C2 to perform voltage double rectification and smoothing, thereby leading to a line 47 a DC voltage having a level corresponding to the sum of the levels of the acoustic signals of the front left and front right speakers FLL and FRI.

Another direct current converting circuit 42 has a configuration similar to the above-described direct current converting circuit 41, and audio signals to be provided to the rear left speaker RL1 and rear right speaker RRI are provided to coupling circuits 48 and 49, respectively. The phase outputs of these coupling circuits 48 and 49 are given to a rectifier/smoothing circuit 51 from a line 50. Coupling circuit 48.
49 includes capacitors C3 and C4 and resistors R3 and R4, respectively, and the rectifier/smoothing circuit 51 includes a diode D.
2. D4, a capacitor C6, and a resistor R5, and performs voltage double rectification and smoothing. The DC output of the rectifier/smoothing circuit 51 is led out to a line 52.

The DC voltage from line 47.52 is connected to diode D5.
It is applied to line 53 via D6.

This causes line 53 to have the greater of the output voltage levels on lines 47 and 52.

In the DC converting circuit 41.42, time constant R1・C1,R
2.C2, R3.C3, and R4.C4 set the attack time τA, and the time constants R5.C5 and R6.C6 are
The release time τR is set, and the attack time τA is determined to be 2 to 3 seconds per ear, and the release time τR is set to 200 seconds to 2 seconds.
stipulated in c. This DC converting circuit 41, 42 performs voltage double rectification, and therefore the DC voltage led out to the line 47, 52 can be increased, and a desirable result from an aural perspective is obtained. You may also do so.

The DC voltage signal from line 53 is passed through level discriminator l8
The voltage is divided by resistors R40 and R12 and applied to the non-inverting input terminal 55a of the single power supply operational amplifier circuit Q1 at 54. A voltage divided by voltage dividing resistors R7, R8 and variable resistor R19 is applied to the inverting input terminal 55b of the operational amplifier circuit Q1 as a discrimination level via a line 56 and a resistor R9. Resistor R7 is connected to DC power supply 58 via line 57. This power source 58 is connected to the acoustic signal generating circuit 20. Voltage controlled amplifier circuit 25, fader 30, amplifier circuits 37-4o and other electric circuits are energized with power, and therefore the discrimination level given to operational amplifier circuit Q1 changes depending on the voltage of power supply 58.

In this level discrimination circuit 54, R9=R10=R11=R12-(1) Therefore, the voltage VOI derived from the operational amplifier circuit Q1 to the line 6°
When the voltage input to the non-inverting input terminal 55a of the operational amplifier circuit Q1 is (+) and the discrimination level input to the inverting input terminal 55b is V (-), the subtraction operation is expressed by the second equation. Do as shown.

VO1=V (+) -V (-)
(2) The operational amplifier circuit Q1 is a single power supply operational amplifier circuit, and therefore the non-inverting input terminal 55
When the voltage (+) applied to a is less than the discrimination level V (-) applied to the inverting input terminal 55b, the voltage V01 on the line 60 is zero. Moshiro operational amplifier circuit Q1
is an operational amplifier circuit for dual power supplies, the voltage V(+) applied to the non-inverting input terminal 55a is the voltage V(+) applied to the inverting input terminal 55.
When the voltage is below the discrimination level (-) given to b, a residual voltage of about 0.2 to 0.4 V is output to the output line 60, which may cause malfunction of the subsequent circuit. In this case, the operational amplifier circuit Q1 is for a single power supply and solves such a problem.

In order to adjust the acoustic output from the speakers FLL, FRI, RLI, and RRI, a 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 voltage-divided by resistors R16 and R15, and is applied to the non-inverting input terminal 64 of the operational amplifier circuit Q2. The output from the level discrimination circuit 54 is applied to the inverting input terminal 65 of the operational amplifier circuit Q2 via a line 60 and a resistor R13. A resistor R14 is connected to this operational amplifier circuit Q2.

The output from the output terminal 66 of the operational amplifier circuit Q2 is applied to the input terminal 27 of the voltage controlled amplifier circuit 25 via a line 67. Voltage VO at output terminal 66 of operational amplifier circuit Q2
is the voltage V derived from the brush 62 of the variable resistor 61
This is the difference between C and the output voltage VOI from the level discrimination circuit 54.

VO=VC-VO1 (3) Note that 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 a single power supply operational amplifier circuit for the same reason as the operational amplifier circuit Q1 used in the level discrimination circuit 54.

The operation of the embodiment shown in FIGS. 1 and 2 will now be described with reference to 3.m. An acoustic signal as shown in FIG. 3 (1) is derived from the lines 21 and 22 of the acoustic signal generation circuit 20, and the acoustic levels before and after the vehicle interior 32 are adjusted to be different by the fader 30, and therefore the DC conversion is performed. Figure 3 (
Assume that the reference mark V(+>1 and V (+) 2) in 2) is derived. This discrimination level is a value determined as appropriate based on listening comprehension.In Fig. 3 (2), at v(+)1, V(+>2...
(4), and therefore line 53 has a
) as shown by the larger DC output V (+) 2
is derived.

The level discrimination circuit 54 derives the difference VOI between the larger DC level V(+)2 and the discrimination level V(-) shown in FIG. 3(4) on a line 60. When the voltage VC shown in FIG. 3 (5) is derived by the brush 62 of the variable resistor 61, the output terminal 66 of the operational amplifier circuit Q2 of the operational control circuit 63 is connected to the voltage control amplifier circuit 25 via the line 67. The third [2I(
The voltage ■0 shown in 6) is derived.

In the amplifier circuits 37 to 40 whose output maximum amplitude levels are defined in this way, when an excessive input exceeding the clip level is input, the speakers FL1, FRI, RLI,
In order to prevent the sound of the RRI from being clipped and distorted, the sound signals from the amplifier circuits 37 to 40 are converted to a DC circuit 41.
．． 42 into a DC signal, and the DC voltage is converted into a DC signal by a level discrimination circuit 54 at a predetermined discrimination level V(-).
The gain of the voltage-controlled amplifier circuit 25 is controlled so that as the difference increases, the gain decreases, thereby suppressing the instantaneous large change in gain as much as possible. This prevents the discomfort described above from occurring. Moreover, in such an embodiment, since the gain of the voltage-controlled amplifier circuit 25 is controlled by the output of the amplifier circuits 37-40, the gain of the amplifier circuits 37-40, and hence the clip level, differs for each amplifier circuit 37-40. Even if the input signal is too high, the sound cracking and distortion caused by excessive input can be reliably prevented.

In the above-described embodiment, in the first group of speakers FLL and FRI arranged in front of the vehicle compartment 32, the outputs of the amplifier circuits 37 and 38 are given to the common DC conversion circuit 41,
In addition, the speakers RLI and R arranged after the vehicle compartment 32
In the second group of RIs, the acoustic signals from the amplifier circuits 39 and 40 are commonly supplied to the DC converter circuit 42. The output from the DC conversion circuit 41.42 is routed from line 47.52 to diode D5. It is applied to line 53 via D6, and the higher level of the outputs of the DC conversion circuits 41 and 42 is selectively led out to line 53. This achieves the sound cracking prevention operation as described above.

A person inside the cabin 32 of the car 31 operates the fader 30 to (a) listen to the first group of speakers FLL, I'' in front;
Sound (hi) is performed only on R1, and at this time the second group of barley
When the sound is not output from the first speaker R, L 1 and RR1, (b) and vice versa, when the previous first speaker
No sound is output from the speakers FLL and FBI of the group, and the speakers RL 1 and RR1 of the second group
Any place where you want to output sound only from #
Also in (a) and (b), the sound cracking prevention function is achieved.

To explain this reason in more detail, in the coupling circuits 43 and 44 of FIG. The output impedance Z of 37.38 is set to zero, and the coupling circuits 43, -4
The rectifier/smoothing circuit il is connected to the line 46 to which the output of 4 is connected.
! When the impedance when looking at the 845 side is Rin, and the voltage level of this line 46 is VF, then the fifth
The formula holds true.

... (5) Here, R27Rin is the resistance R2 and impedance R
Let i represent the parallel impedance of in.

Here, if Ri rr > R, 11, R2・ (6),
The signal level VF shown by the fifth equation becomes the value VFI shown by the seventh equation.

, where, R1=R2...<8), the value VF1 shown by the seventh formula is equal to the value VF1 of the ninth formula
Indicated by F2.

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

(11) Therefore, the first group of speakers F in front of the vehicle compartment 32
Even if the fader 30 is operated so that acoustic output is obtained only from LY and FRI, and no sound is produced from the speakers RLI and FCO R1 of the second group of f&,
As shown in Equation 11, as the output level of line 46, the acoustic output level VFL of the amplifier circuit 37 is the output level of line 46.
It becomes two things that can be obtained. Therefore, the gain of the voltage-controlled amplifier circuit 25 is controlled by the signal level VFL of this line 46, and the acoustic signals input to the amplifier circuits 37 and 38 are suppressed so as not to reach the clip level of those amplifier circuits 37 and 38. The excellent effect that it is possible to achieve is achieved.

Similarly, the fff output from the first group of speakers FLL and I''R1 in front of the vehicle compartment 32 is set to zero, and the second group in the rear
Group speaker RL1. Even when sound is output only from RR,1, the sound cracking prevention operation is achieved.

4th [2I] is an electric circuit diagram of still another embodiment of the present invention. In this embodiment, a woofer 68 is disposed at the center position of the left and right sides of the vehicle compartment 32 of the automobile 31, in front or at the rear, to realize a so-called 3D system. The sound signals from the buffer 69a provided to the woofer 68 through the six amplifier circuits are such that the left and right sound signals are each added g (
=L+R) and is applied to the coupling circuit 70 of the DC conversion circuit 72, and further led out from the rectification/smoothing circuit 71 via the diode D7, and the output of the DC conversion circuit 72 is applied to the line 53. The DC conversion circuit 72 has a similar configuration to the DC conversion circuits 41 and 42.

As yet another embodiment of the present invention, a sound field control signal used in a surround system etc. in place of the woofer 68, for example, a signal of the difference between the left signal R and the right signal R (L-
The present invention can be implemented in the same manner by converting R), (R-L), etc. into direct current and supplying it to the line 53.

FIG. 5 is an electrical circuit diagram of still another embodiment of the present invention. In this embodiment, only the left and right speakers FLL and FRI are provided in the vehicle interior 32 of the automobile 31, and a woofer 68 is provided behind the vehicle interior 32 in place of the rear speakers RL1 and RRI in the previous embodiment. Parts corresponding to the previous embodiments are given the same reference numerals. In this embodiment as well, by operating the fader 30, the sound is output only from the first group of speakers FLL and FRI in front of the vehicle compartment 32, and the sound is output from the second group of speakers FLL and FRI in front of the vehicle compartment 32. Even when the acoustic output of the speaker is set to zero, and vice versa, it is possible to achieve a dynamic range that prevents sound cracking. Instead of the embodiment shown in FIG. 5, the woofer 68 may be placed in front of the vehicle compartment 32, and the left and right speakers RLI and RRI may be located after the vehicle compartment 32 to configure a 3D system.

Resistors R7, R8, and R19 for setting the discrimination level (-) applied 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 supply 58. The entire audio device is energized by power. This power source 58 is mounted on the automobile 31 and is a battery, for example, 1
Although the clip level, which fluctuates greatly in the range of 0.5 V to 16 V and causes sound cracking in the amplifier circuits 37 to 40, also fluctuates, as described above, the discrimination level V (
-) also follows the fluctuations in the voltage of the power supply 58, which has the advantage of making it possible to obtain the optimum maximum undistorted output.

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

Effects As described above, according to the present invention, it is possible to reliably prevent the occurrence of distortion due to sound cracking, without causing any audible discomfort, and even if there are variations in the gain of the amplifier circuit. Become.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of an embodiment of the present invention, FIG. 2 is a simplified diagram showing the cabin 32 of an automobile 31, and FIG. 3113 is an operation of the embodiment shown in FIGS. 1 and 2. FIG. 4 is an electric circuit diagram of an embodiment of the present invention, FIG. 5 is an electric circuit diagram of yet another embodiment of the present invention, and FIG. 6 is an electric circuit of the prior art. FIG. 7 is an electrical circuit diagram of another prior art. 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 converter circuit, 4
3,44.48゜49.70...coupling circuit,
45,51.71... Rectification/smoothing circuit, 54... Level discrimination circuit, 63... Arithmetic control circuit Agent Patent attorney Number of strokes Keiichi Figure 2) () (132t-) (1 Figure 3

Claims (3)

[Claims] (1) Derive a DC converter circuit that rectifies and smoothes the acoustic signal from the amplifier circuit via a coupling capacitor and outputs a DC signal, and a signal that represents the difference between the output of the DC converter circuit and a predetermined discrimination level. and means provided before the amplifier circuit to amplify or attenuate the acoustic signal in response to the output from the level discrimination circuit, and to reduce the gain as the difference becomes larger. suppression circuit. (2) The level discrimination circuit is realized using a single power supply operational amplifier circuit.
Distortion suppression circuit described in section. (3) The discrimination level of the level discrimination circuit is obtained by dividing the output voltage of a power source that energizes an amplifier circuit that amplifies an acoustic signal using a voltage dividing resistor. The distortion suppression circuit according to item 1 or 2.