HU195047B - Noise suppressing circuit arrangement - Google Patents

Abstract

Noise suppressor, consisting of the operation divider 1, which is connected to the frequency-dependent voltage divider 2 whose first branch is designed as a resistor 3 and whose second branch contains the low-pass 4 and the basic high-pass 5, which are connected in parallel on the input side and are connected to the adder 6, whose output is connected to the branch of the frequency-dependent voltage divider 2, and the series circuit of the additional high-pass filter 7 whose input is connected to the output of the basic high-pass 5, and the Steuerspannungsformer 8 whose input is connected to the control input of the basic high-pass 5 and the additional high-pass filter 7 , Fig. 1

Description

The present invention relates to a noise suppressing circuit arrangement for electronic circuits, such as voltage regulators, in particular for audio amplifiers of HEF-quality tape recorders, turntables and radios, such as for dynamic amplification and / or amplification.

A circuit arrangement for automatic dynamic equalization / expansion is known having a signal channel and a control channel, wherein the signal channel is formed by an inverting amplifier having an output from the inverting amplifier forming an output of the switching arrangement, and a low-pass the control channel is constructed as a control voltage generator. Such apparatus is described in U.S. Pat. DE patent specification.

A disadvantage of the solution is that its noise suppression effect is weak, which is due to the noise modulation effect, which in turn manifests itself in audible changes in the noise level as the useful signal changes.

The closest embodiment of the invention is disclosed in U.S. Pat. SU patent specification. This specification describes a noise suppressor circuit arrangement having an operational amplifier and a frequency dependent voltage divider, wherein one terminal of the frequency dependent voltage divider is connected to the input of the noise suppressor circuit and the other terminal is connected to the output of the operational amplifier, which is also provided. The frequency-dependent voltage divider branch is connected to the inverting input of the operational amplifier.

One branch of the frequency-dependent voltage divider comprises a resistor and the other branch has a low-pass filter and a high-pass filter with parallel input. The circuit arrangement further comprises a second high-pass filter identical to the first and a control voltage generator whose output is connected to the control inputs of the first and second high-pass filters. The first and second high-pass filters are sequentially controlled.

Another disadvantage of this latter solution is that its noise suppression effect is weak, which can be attributed to noise modulation effect.

It is an object of the present invention to overcome the above defect, i.e. to reduce noise modulation.

SUMMARY OF THE INVENTION The object is solved by providing a noise suppressor circuit arrangement having an operational amplifier and a frequency dependent voltage divider, one terminal of the frequency dependent voltage divider serving as the input of the noise suppressor circuit and the other terminal acting as a the branch of the voltage divider connected to the inverting input of the operational amplifier 2, the first branch of the frequency dependent voltage divider being formed as a resistor, the second branch comprising a low-pass filter and a first high-pass filter having has a high-pass filter and a control voltage generator which is a control head the output of the voltage generator is connected to the control inputs of the frequency controlled first and second high pass filters. According to the present invention, in the above switching arrangement, the outputs of the low-pass filter and the high-pass filter of the frequency-dependent voltage divider are connected to one of the sumers of the frequency-dependent voltage divider and the output of the first high-pass filter to the second top.

According to the invention, the voltage source output is connected to a voltage divider input and a low-pass filter input to the output voltage control output, the output of which is connected to a resistor, pulse duration pulse discriminator output, a first comparator output to its input, and an amplitude sensor output to its input; and the discharge switch control unit and a second comparator is connected to his enete.

The invention will now be described with reference to the drawings. In the drawing it is

Fig. 1 is a block diagram of an exemplary embodiment of a noise suppressing circuit arrangement according to the invention for dynamic reduction;

FIG. 2 is a block diagram of an exemplary embodiment of the noise suppression circuitry of the present invention for dynamic amplification.

As shown in the drawing, the operation amplifier 1, the frequency dependent voltage divider 2, the resistor 3 forming the first branch of the voltage divider 2 and the low-pass filter 4, the high-pass filter 5 and the high-pass filter 7 in the second division of the voltage divider has a filter and 8 control voltage generators. The 4 are low-pass

The -2195047 filter input is connected to the input of the high-pass filter 5, while the output of the low-pass filter 4 and the output of the filter 5 is connected to the summing input 6. The output of the first high-pass filter 5 is further connected to the second input of the second high-pass filter 7.

The control voltage generator 8 has 9 amplitude sensors, 10 and 11 comparators, 12 pulse duration pulse discriminators, 13 timers, 14 positive feedbacks, 15 voltage sources, 16 voltage divertors, 17 output low-pass filters, 18 low-voltage and low-voltage switches, 18 wherein the output of the high-pass filter 7 is connected to the input of the amplitude sensor 9, the output of the amplitude sensor 9 to the input of the comparator 10 and its output is the pulse duration pulse discriminator 12. its output, its output to the time relay 13, and its output to the control input of the controllable voltage divider 16 and to the control input of the pulse duration pulse discriminator 12 via positive feedback 14. The output of the voltage source 15 is connected to the input of the high voltage divider 16 and its output is connected to the input of the low-pass filter 17. The low-pass filter input 17 is further connected in parallel to the discharge switch 18 and to the output of the variable-resistance element 19 in parallel. The control input of the discharge switch 18 is connected to the output of the comparator 11 and to the control input of the variable resistance element 19 to the output of the minimum value limiter 20. The input of the comparator 11 and the minimum value limiter 20 is connected to the output of the amplitude sensor 9.

1, the first branch of the frequency dependent voltage divider - the resistor 3 - is connected to the output of the operational amplifier 1, i.e. the noise suppression circuit arrangement, the terminal of the second branch of the voltage divider 2, i.e. the low pass filter 4 and common input point for high-pass filter - it is the input for the circuit layout.

In the embodiment shown in Fig. 2, the output of the first branch of the frequency-dependent voltage divider 2 is the input of the circuit arrangement, and in the second branch of the voltage divider the coupled input of the low-pass filter 4 and the high-pass filter 5. is connected to its output and the summing output 6 is connected to the inverting input of the operational amplifier 1.

The noise suppression circuitry of the present invention operates as follows:

In the initial state, the working frequency range is divided into two sub-ranges by the high-pass filter 5 and the low-pass filter 4; 1 kHz. The transmission value is set to 1 in the permeability range of the low-pass filter 4 and N times in the permeability range of the high-pass filter 5, so that in case of compression the transmission of the switching arrangement is N times greater in expansion. which is N times less than the transmission of the switching arrangement in the pass region of the low pass filter 4.

The selected N number (~ 10) determines the maximum dynamic reduction or dynamic expansion of the signal components within the transmission range of the high pass filter 5 so that it is independent of the boundary frequency. The change in signal amplification or amplification in the closing region of the high-pass filter 5 occurs by shifting the cut-off frequency, while the frequency range in which the noise reduction occurs is determined by the output throughput range of the high-pass filter 5, and 7 by switching over the high-pass filters to the control inputs.

In the case of compression (Fig. 1), the signal is applied to the input of the circuit arrangement, that is to say the input of the low-pass filter 4 and the high-pass filter 5. From the output of the high-pass filter 5, the signal components in the pass-through region of the high-pass filter 5 are applied to one of the inputs of the totalizer 6 and to the input of the high-pass filter 7. The signal components from the output of the low-pass filter 4 to the pass-through range of the low-pass filter 4 are sent to the other input of the totalizer 6. From the output of the summing 6, the sum of the signal components separated by the low-pass filter 4 and the high-pass filter 5 is applied to an operational amplifier 1 with feedback resistance 3 between its output and its input. For example, the summing device 6 may be constructed of resistors, preferably having the same value as the resistors 3, resulting in a transmission value of 1 between the summing input 6 and the output of the operational amplifier 1, the output of the noise suppression circuitry.

With the arrival of a signal containing mid- and high-frequency signal components, when the mid-frequency and high-frequency signal components are below the threshold level of the comparator 11, the amplitude characteristic of the switching arrangement increases in the high- and mid-frequency range. Based on the increasing characteristic curve, the signal components leave the compressor mounted on the expander input via the transmission channel, but on the expander output the same signal components return to the original level, since the expander characteristic curve is exactly opposite to the compressor. Of course, with the signal components, the transmission channel is the same 3

Noise components in the frequency range of 195C47 are also attenuated.

Upon arriving at the compressor input of the high frequency signal components higher than the threshold of comparator 11 and the high frequency signal components below the threshold of comparator 11, the capacitor of the low-pass filter 17 of the output low-pass filter is discharged through the a voltage drop occurs. The cut-off frequency of the high-pass filter 5 and 7 is consequently increased, which results in a deterioration of the mid-frequency transmission of the compressor, while the high-frequency transmission remains unchanged, thus maximizing the reduction at high frequencies.

In the expander, the high frequency signal components will be attenuated along with the noise components of the transmission channel, and in the high frequency range this attenuation is maximum, which corresponds to maximum dynamic amplification. The capacitance and resistance of the capacitor of the output lowpass filter 17 determines the system set-up time when the input signal level of the noise suppression circuit is increased.

If the level of the mid and high frequency signal components exceeds the threshold level of comparator 11, the cut-off frequency of the high-pass filters 5 and 7 is shifted above the cut-off frequency of the working range. In this case, the compressor amplitude-frequency curve is determined by the low-pass filter 4, so the high-frequency transmission of the compressor drops below 1 so that the high-frequency signal components continue to weaken after leaving the compressor and do not overload the transmission channel. The same signal components are amplified as they pass through the expander to the output level (compressor input level), while the noise components of the transmission channel are amplified. However, due to the psychoacoustic effect of the stronger sound level, which suppresses the weaker sound level, these noise components cannot be detected.

For smaller input signal levels that are just above the threshold level of comparator 11, the system ripple time is aligned with the discharge time of the low pass filter capacitor 17 of the output and takes a maximum value. When the input signal level is rapidly increased such that the input signal level exceeds the threshold of the minimum value limiter 20, the signal is applied to the control input of the variable resistor element 19. As a result, the resistance of the minimum value limiter 20 is reduced and as a result, the discharge circuit of the low-pass filter capacitor 17 is bridged, thereby accelerating the discharge of the capacitor and reducing the system ripple time. The greater the signal level exceeds the threshold value of the minimum threshold 20, the lower the ripple time. As the capacitor discharges, the output voltage of the control voltage generator 8 is reduced, so that the control inputs of the high-pass filters 5 and 7 are also lowered, which causes the high-pass filter limit frequency 5 and 7 to be shifted in high frequency direction. at the input of the comparator drops to its threshold level.

When the signal level drops below the threshold of comparator 11, comparator 11 returns to the initial state, the discharge switch 18 opens, the minimum value limiter 20 is reset, thus increasing the resistance of the variable resistor 19 and the capacitor of the low-pass filter 17 it is charged, that is, when the input signal level decreases, the ripple time increases, so that short-term small changes in the signal level and short pulse disturbances do not affect the transmission and do not cause a noticeable noise modulation even when the useful signal is lost.

After a rapid decrease in the useful signal level following a rapid increase, it returns to its former value after a recovery time defined by the capacitor charge time of the low-pass filter 17 output.

Given that the threshold level of the comparator 10 is slightly lower, preferably about 2 dB, than the threshold level of the comparator 11, the comparator 11 changes its state due to signals that exceed its threshold level. However, if the pulse duration generated by the signal from the output of the amplitude sensor 9 via comparator 11 does not exceed the discriminating threshold of the pulse duration pulse discriminator 12, the pulse duration pulse discriminator 12 will not allow pulse time 13. The time relay 13 is a monostable circuit that changes its output state contrary to the appearance of a pulse arriving at its input and returns to its initial state after a certain delay after the pulse has stopped.

The time relay 13 can also be designed as a serial connection of a sawtooth voltage generator and a comparator, wherein the sawtooth voltage generator can be implemented as a parallel connection of a power source, a capacitor and a switch in the closed state.

The time relay 13 thus remains in the initial state and the controlled voltage divider 16 provides good transmission, thereby providing a smaller recovery time, which is adapted to the charge time of the capacitor of the output low-pass filter 17.

-4195047

If the duration of the pulse generated by the comparator 10 exceeds the discriminator threshold of the pulse duration pulse discriminator 12, the pulse duration pulse discriminator 12 releases the pulse to the input of the time relay 13, which changes its state and thus controls the control. Since the time relay 13 returns to its initial state after the input pulse has stopped, the recovery time will be longer within the overall delay time. The low frequency signal components present in the signal of the control voltage generator 8 thus provide a high transmission recovery time while lowering the level of the same signal components after a level increase. When the spectrum of the input signal is widened to a certain extent, the cut-off frequency of the high-pass filters 5 and 7 is shifted to the upper cut-off during operation of the noise suppression circuitry, resulting in a decrease The high-pass filters 5 and 7, respectively, fall within the instantaneous pass range. In this way, in the event of a decrease in the level of the high frequency signal components after a level increase, a short recovery time of the noise suppression circuit arrangement is provided.

The control voltage displayed at the output of the control voltage generator 8 can be expressed as:

Ü2 = [Ki U ₅ 'K ₇ - (F, U ₂ ) -K ₉ - U _R J (1) where

K, i all comparator transfer

U _{5 is} the output voltage of the high-pass filter 5

K ₇ (F, U ₂ ) transmission of high pass filter 7 as a function of frequency and control voltage

K _{9 is} the transmission of the amplitude sensor 9 and

Unn is the threshold of 11 comparators.

The high-pass filter 7 R ₇ (M, U ₂₎ transmission of highlighting the equations (1) to transmit the high-pass filter 7, the following relationship is obtained:

UU ₂

K ₇ (F, U ₂ ) = ------ + --------- (2)

U ₅ 'K-5 ΚιΓ Us'Kg

Equation (2) above takes the following form for Κ ,, ^ - co:

^U mi

K ₇ (F, U ₂ ) ------- (3) κ ₅ · u ₉

The voltage U _{5 of} the high-pass filter ₅ can be expressed as:

U ₅ ^{= U} on <* ^K 5 ^(F 'U ₂ ⁾ (4) where

U /, _{fS is} the input of the high-pass filter 5

K ₅ (F, U ₂ ) Transmits the high pass filter 5 as a function of frequency and control voltage.

Since the high-pass filters 5 and 7 are designed as a single circuit element and their cut-off frequency is similarly dependent on the control voltage,

Ks (F, U ₂ ) = k ₇ (f, u ₂ ) ₍₅₎

Substituting equations (3) and (5) into equation (4) gives the following equation:

U ₅ = U, · K ₇ (F, U ₂ ) = DG 5 = u.

be 5 from where

U _s · K ₉

U ₅ = U.

without ⁵ i / 2 (6) (7)

K ₉

Given that —A ¹ ′ = K = cons K tans, equation (7) can be written as follows:

U ₅ = (K'U.) ^1/2 without 5 (8)

It follows from Equation (8) that the output voltage of the high-pass filter 5 is proportional to the square root of its input voltage, and that when Equation (5) is fulfilled, it does not depend on the characteristic of the high-pass filter 5 itself.

Assuming that the transmission from the summing input 6 to the output of the noise suppressor switching arrangement in the case of dynamic reduction (compression) 1 and taking into account equation (8), the output voltage of the compressor can be expressed as follows:

^ off comp. = 115 + 1 (4 = (Κ · υ ^ θ 5) ¹ + + Ü4 - (KU _{in comp} .) + Uu (9) where

U _{4 is} the output voltage of the low pass filter 4,

Uh, _e k _om p. and the compressor input voltage.

The output voltage of the expander can be written as follows:

U.

who exp.

= U, · K be exp. exp.

GK - ^U be exp.T7K ₂ +5 'where

Ui, _e exp is the expander input voltage, Kexp is the expander transmission,

K _{2 is} the transmission of the operational amplifier 1 and

U5 + Ua (11)

GK U,.

..ki exp.

transmission of the negative feedback loop.

-5195047

Substituting equation (8) into equation (11) gives the following equation:

«• u ₅ > ^{l / 2 + u} ' ^b gk" ú "----------- ^{(, 2)} ki exp.

and considering that in the expander

Ufceg = Ufc / exp gives the following relationship:

(KU,) ^{l / z} + u ₄ ^b gk = -4 ”“ ^Ελ --------- · ⁽¹³⁾ ki exp.

Substituting equation (13) into equation (10) gives the following equation:

_________ ^ be exp ._________ ki exp.

/ 1 \. «'V exp. ^{) l / 2} ' ^U \ ^K 2 / S _{fci exp} . _{(| s)}

Equation (14) for K ₂ - * co is simplified as follows:

(U, -u ²

U ₌ -------. (15) ki exp. K where

K = a constant.

Given that Uz, e " _p . = U" _exp ., Equation (15) can be written as:

U ^(U ki exp ^U * ^{) 2} ki exp. -------- -------- 1. (16)

Substituting equation (9) into equation (16) gives the following equation:

(κ · υ,. y! ² + Uu - u ² without comp.) ki exp. It follows from Equation KA (17) that for compression and expansion expansion, the signal at the output of the expander corresponds to the signal at the compressor input.

The effect of the Mayak noise suppression system is as follows:

Dynamic smoothing and reverse dynamic amplification, as well as proper noise reduction in the transmission channel in the pass-through filter, have a controlled cut-off frequency that can be automatically adjusted as a function of the signal spectrum, allowing for noise modulation and noise suppression. maintaining a quadratic relation between the output signal and the input signal of the high-pass filter, which is not influenced by the control characteristic of the controllable high-pass filter, which results in stable dynamic reduction and amplification characteristics that are independent of external interference effects of the filter elements. It is also advantageous that the slope of the control channel damping curve doubles the signal components in the range below the cut-off frequency of the high pass filters, thereby reducing their influence on adjusting the high pass filters, thereby increasing the noise modulation and it is low and increases in signal tone by ¹⁰ , so that low-level transient pulse disturbances or short-term small changes in the useful signal do not cause a change in the transmission of the system, and thus no audible change in the noise level. In the noise suppressor switching arrangement, the recovery time varies as a function of the frequency of the signal components of the control voltage generator 8. In the presence of the ² θ components of the control voltage generator 8 low frequency signal, the forgetting time is shifted by the cut-off frequency of the high-pass filters as the signal spectrum is curved, thereby weakening the low frequency signal components. The high-frequency signal components that cause a downward change in the value of the recovery time constant in the control voltage generator ^{25 of the} controller 8 are retained, which causes the high-frequency signal components to decrease in level after a level increase when the transmission is reset. The same effect occurs for transient pulse disturbances, which also reduces noise modulation.

Claims (2)

PATENT CLAIMS 1. Noise suppression switching arrangement, 40 consisting of an operational amplifier (1), a frequency-dependent voltage divider (2) and a control voltage generator (8), wherein the input of the switching arrangement is one of the terminals of the voltage divider (2) and the output of the switching arrangement. further, the other terminal of the voltage divider (2) is connected to the output of the operational amplifier (1) and its branch to the inverting input of the operational amplifier (1), wherein the first branch of the voltage divider (2) is formed as a resistor (3). comprising a low-pass filter (4) and a first high-pass filter (5), wherein the first high-pass filter (5) is connected to the control voltage generator (8) via a high-through filter (7), characterized in that the control voltage generator (8) The output is frequency controlled first and second high pass filters 60 (5, 7), and in order to reduce noise modulation, the outputs of the low pass filter (4) and the first high pass filter (5) in the second section of the frequency dependent voltage divider (2) are summed They are connected to 65 (6) inputs, which output is for branching the voltage divider (2) -6195047, and the output of the first high-pass filter (5) is connected to the inlet of the second high-pass filter (7). Noise suppression circuit arrangement according to claim 1, characterized in that in the control voltage generator (8) the output of the voltage source (15) is connected to the input of a voltage divider (16) and its output is connected to the input of a low-pass filter (17). 18), a variable resistor element (19) is connected to its output, and an output of a relay timer (13) which can be restarted to the control input of the voltage divider (16), an output of a pulse duration pulse discriminator (12) and a first comparator (10). the input of which is connected to the output of the amplitude sensor (9), the output of the time relay (13) is connected via the positive feedback (14) to the control input of the pulse duration pulse discriminator (12) and the output (9) of the amplitude a second comparator (11) is connected between a control input of a minimum value (20) and an output of the amity sensor (9) and a control switch (18) of the discharge switch (18).