JPH04119708A - Automatic noise suppression method for amplifier and automatic noise suppression device - Google Patents

Abstract

PURPOSE:To improve the S/N and to obtain a pleasant audible sense by amplifying an input electric signal with an amplifier and feeding back part of the amplified electric signal to an input side via an attenuation circuit including a nonlinear resistive element and a filter circuit. CONSTITUTION:An electric signal fed to an input terminal 1 is amplified by a recording amplifier 3 via a feedback voltage summing point 2 and recorded on a magnetic tape 5 by a magnetic recording head 4. Part of an output voltage of the amplifier 3 passes through an attenuation circuit 8 comprising a resistor 6 and a nonlinear resistive element 7 and fed back negatively to the feedback voltage summing point 2 via a low pass filter 11. The effective resistance of the nonlinear resistive element 7 is momentarily reduced when the applied voltage thereto is increased momentarily and conversely the effective resistance of the nonlinear resistive element 7 is momentarily increased when the applied voltage thereto is decreased momentarily. Thus, an undesired signal component such as hum or motor vibration noise at a low frequency region at application of a small input electric signal is suppressed and limited to improve the S/N and to realize a satisfactory high sense of listening effect.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is applied to automatic audio frequency band amplifiers used in video tape recorders, audio tape recorders, digital tape recorders, etc. used for consumer use, broadcasting, etc. The present invention relates to a noise suppression method and an automatic noise suppression device.

2. Description of the Related Art Conventionally, audio frequency electrical signals are amplified through various mechanical-electrical converters such as microphones and big-ups, and are recorded and played back on magnetic tape. When the input electrical signal is small, hum noise, motor vibration noise, etc. reach the speaker and are unpleasant to the ears.

In such cases, there is no device that can automatically change the gain in the bass region where hum noise and motor vibration noise are present in accordance with the input electrical signal to provide a comfortable hearing sensation, and there is no device that can provide a comfortable hearing sensation as shown in Figure 4. , a device has been used that manually changes the cutoff frequency continuously or stepwise to adjust the frequency characteristics of low frequency ranges such as noise.

The device shown in FIG. 4 has a bypass filter 13 between the input terminal 12 and the final stage amplifier 14, the cut-off frequency of which can be manually changed continuously or in steps according to the input electrical signal, thereby improving the bass range. The noise is removed by attenuating the noise, and the sound is generated from the speaker 15.

Problems to be Solved by the Invention When noise suppression is performed using a bypass filter such as the one described above, the cutoff frequency does not immediately follow changes in the input electrical signal, resulting in a time delay and insufficient noise suppression. It is difficult to create a bypass filter, and the bypass filter also has the drawback of requiring an extremely complicated circuit configuration. Furthermore, bypass
If the cutoff frequency of the filter is fixed, there will be a drawback that the sound sensation and fidelity will be impaired.

The present invention automatically and instantaneously follows changes in the input electrical signal and attenuates the frequency range where hum noise and vibration noise are mixed, improving the S/N ratio without causing a time delay and providing comfortable sound. It is an object of the present invention to provide an automatic noise suppression method and device for an amplifier that provides auditory sensation.

Means for Solving the Problems In order to achieve the above object, the present invention amplifies an input electrical signal using an amplifier, and further converts a part of the amplified electrical signal into a part whose effective resistance value is instantaneous with respect to an instantaneous applied voltage. It is composed of an attenuation circuit that includes a nonlinear resistance element with a property that changes over time, and feedback to the input side via a filter circuit.

Effect: With the configuration of the present invention, the gain in the frequency domain determined by the characteristics of the filter circuit changes according to changes in the input electrical signal, even for signal levels that change drastically over time, so noise can be suppressed without causing a time delay. oppressed.

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

First, Fig. 1 is an electrical wiring diagram showing one embodiment of the automatic noise suppression device of the present invention, Fig. 2 is a gain versus frequency characteristic diagram of the same device, and Fig. 3 is a diagram of the nonlinear resistance element used in the present invention. The voltage-current operating characteristic diagram, FIG. 4, is an electrical wiring diagram of the device in the conventional method.

In Fig. 1, 1 is an input terminal, and the electrical signal applied to this input terminal 1 passes through a feedback voltage addition point 2 to a recording amplifier 3.
The signal is amplified by the magnetic recording head 4 and recorded on the magnetic tape 5. A part of the output voltage of the amplifier 3 is connected to a resistor 6.
The voltage passes through an attenuation circuit 8 made up of a nonlinear resistance element 7 and then passes through a low-pass filter 11 made up of a resistor 9 and a capacitor 10 to be negatively fed back to the feedback voltage addition point 2.

Now, K is the gain of the amplifier before applying feedback, β is the attenuation amount of the attenuation circuit, and ωO is the cut-off angular frequency of the low-pass filter (
1/R9・CIO However, R9 is the resistance value of resistor 9, C1
0 indicates the capacitance value of the capacitor 10) and S is the complex frequency, the gain G(s) of the amplifier system after feedback is given by the following equation.

G (s)=K (S+(L)0)/S+ (1+βk
) ωO (1) Here, assuming that S=jω, the relationship between the absolute value Gjω1 of the gain and the angular frequency is shown in FIG. 2.

As is clear from this figure, the lower bending point of the frequency characteristic is the cut-off angular frequency ω0 of the low-pass filter 11, while the upper bending point is expressed as (1+β)ω0, and the attenuation amount β of the attenuation circuit 8 It is a function of

Note that the attenuation amount β is expressed by the following equation.

β-R1/ (R7+R6) (2) However, R7: Effective resistance of the nonlinear resistance element 7 R6: Resistance value of the resistor 6 Therefore, the voltage vs. current as the nonlinear resistance element 7 as shown in FIG. A nonlinear resistance element that has operating characteristics, that is, when the applied voltage momentarily increases, the effective resistance value instantaneously decreases, and conversely, when the applied voltage momentarily decreases, the effective resistance value instantaneously increases. For example, when the input signal is small as shown in curve A shown in Fig. 2, the output voltage of the amplifier 3 is also small, and therefore the effective resistance value of the nonlinear resistance element 7 is large. The attenuation amount β becomes small, and the effect of the low-pass filter 11 becomes large, so that the attenuation in the bass region becomes large. Conversely, when the input signal is large as shown in the curve shown in FIG. Since the effect of is small, there is little attenuation in the bass region, and the frequency distribution becomes almost flat.

In this way, unnecessary signal components such as hum noise and motor vibration noise in the low frequency region when a small input electrical signal is suppressed and limited, and the S/H is improved.Furthermore, the filter after the attenuation circuit is It is also possible to effectively suppress high frequency distortion generated in the above.

Furthermore, in the embodiment of the present invention described above, a low-pass filter stage is constructed using a resistor R and a capacitor C, but depending on the frequency component of the noise, multiple stages of low-pass filters, bypass filters, or band-pass filters can be used. A filter may be used, and an inductance L and a capacitor C may further constitute a filter circuit. In this case, since the steep characteristics of the LC resonance circuit can be utilized, by selecting a resonance point at a noise frequency in a specific narrow frequency range that exists in the audio frequency band, the noise can be effectively removed.

Effects of the Invention With the configuration of the present invention, unnecessary signal components such as hum noise and motor vibration noise are suppressed and limited in the audio frequency region when a small input electrical signal is input, and temporal changes in signal level are suppressed, as is the case with music. Even with intense signals, there is almost no time delay, so a highly satisfying auditory effect can be obtained.

In particular, the present invention uses a part of the output voltage of the amplifier as a feedback voltage, so compared to the case where a magnetic or mechanical-electrical converter is added to the magnetic recording head or speaker and the voltage from the converter is used. It goes without saying that such a special and expensive structure is not required at all; for example, this device can be added to a sound reinforcement system to terminate multiple loudspeakers (without mechanical-electrical converters). By simply connecting them directly to the output side of the stage amplifier, all sounds from those speakers can be heard as noise automatically adjusted.
It has various excellent advantages.

[Brief explanation of drawings]

Fig. 1 is an electrical connection diagram of the automatic noise suppression device of the present invention, Fig. 2 is a gain versus frequency characteristic diagram of the same device, Fig. 3 is a voltage-current operation characteristic diagram of the nonlinear resistance element used in the present invention, FIG. 4 is an electrical wiring diagram of the device in the conventional method. 1... Input terminal, 2... Feedback voltage addition point, 3... Recording amplifier, 4... Magnetic recording head, 5...・Magnetic recording tape, 6...
...Resistance, 7...Nonlinear resistance element, 8...
...Attenuation circuit, 9...Resistor, 10...
・Capacitor, 11...Low pass filter,
12...Input terminal, 13...Bypass filter, 14...Final stage amplifier, 15...
...Speaker. Name of agent: Patent attorney Haruaki Ogata Funeral map of two idiots!・Roppo T&Ki Fu Qihe Tape. lp-thumbs filter

Claims (2)

[Claims] (1) A part of the signal amplified by the amplifier is input to an attenuation circuit including a non-linear resistance element whose resistance value changes depending on the instantaneous applied voltage, and the output of the attenuation circuit is passed through the filter circuit to the amplifier. An automatic noise suppression method for an amplifier, characterized by feedback to the input of the amplifier. (2) an attenuation circuit that includes a nonlinear resistance element whose resistance value changes depending on the instantaneous applied voltage and inputs a portion of the output of the amplifier; and an attenuation circuit that inputs the output of the attenuation circuit and outputs it to the input side of the amplifier. and one or more filter circuits arranged to suppress noise.