A voice adaptive noise reduction circuit suitable for helicopters

Abstract

The present invention discloses a voice-adaptive noise reduction circuit suitable for helicopters, comprising a second-order Chebyshev filter, a rectifier circuit, a voltage comparator electronic switch, and an adder circuit. This circuit is innovative and effectively solves the problem of reducing fixed-frequency noise in helicopter voices, advancing the technology level of domestic intercoms.

Description

Technical Field

[0001] The present invention relates to the field of voice adaptive noise reduction circuits, and more particularly to a voice adaptive noise reduction circuit suitable for helicopters. Background Art

[0002] The intercom is the voice signal terminal on a helicopter. When the helicopter is in flight, a certain amount of rotor fixed-frequency interference will be generated. The currently used digital voice adaptive noise reduction circuit cannot completely eliminate this fixed-frequency interference in the voice. As a result, when the ambient noise is higher than 110dB, whether it is an inter-machine call or an external call, the rotor fixed-frequency interference sound is interspersed in the middle of each sentence and cannot be eliminated. As a result, users are not satisfied with the voice communication effect in the high-noise environment of the helicopter. To eliminate this fixed-frequency interference, this voice adaptive noise reduction circuit is designed.

[0003] By analyzing the power spectrum density of human voice from 300Hz to 7kHz during normal conversations, it was found that the frequency range with the highest power of voice normally emitted through the throat is between 500Hz and 1kHz, followed by 300Hz to 500Hz, and then 1kHz to 2kHz. There is basically no power in the remaining frequency bands.

[0004] At the same time, the fixed-frequency interference sound of the helicopter rotor is analyzed. The rotor interference sound is mainly concentrated between 1kHz and 2kHz, namely 1.2kHz, 1.3kHz, 1.6kHz and 2.3kHz.

[0005] Based on the above analysis, the microphone input speech was divided into two frequency components: the first component was between 500Hz and 1kHz, and the second component was between 1kHz and 2kHz. Voice communication was tested and it was found that when the voice signal only had a component between 500Hz and 1kHz, the voice intelligibility heard through the earphones remained unchanged, with only the sound quality being partially affected, without affecting speech recognition. A voice noise reduction logic was designed using a minimalist circuit: When the power of the voice signal between 1kHz and 2kHz was greater than that between 500Hz and 1kHz, it indicated that the voice was mixed with rotor fixed-frequency interference. In this case, the voice signal between 1kHz and 2kHz was removed, retaining only the voice signal between 500Hz and 1kHz. When the power of the voice signal between 1kHz and 2kHz was less than that between 500Hz and 1kHz, it indicated that the voice was free of rotor fixed-frequency interference. In this case, the signals between 500Hz and 1kHz and 1kHz and 2kHz were combined to maintain the voice frequency response within the appropriate range. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a voice adaptive noise reduction circuit suitable for helicopters.

[0007] The present invention has three purposes:

[0008] 1. Implement narrowband filtering. When the frequency exceeds the cutoff frequency of 200Hz, the voice signal attenuation exceeds 8dB.

[0009] 2. In the passband, the frequency response does not exceed 3dB;

[0010] 3. Bandwidth can be switched automatically.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] A voice adaptive noise reduction circuit suitable for helicopters includes the following five parts: a second-order Chebyshev filter, a rectifier circuit, a voltage comparison circuit, an electronic switch, and an adder, wherein:

[0013] (1) Second-order Chebyshev filter: Two second-order Chebyshev filters are used. Each Chebyshev filter is composed of six resistors (R1, R3, R6, R2, R4, R7), four capacitors (C1, C2, C3, C4), and a dual operational amplifier. Resistors R1, R3, R6, capacitors C1, C3, and an operational amplifier group N1A constitute the first order of the Chebyshev amplifier, and resistors R2, R4, R7, capacitors C2, C4, and another operational amplifier N1B constitute the second order of the Chebyshev amplifier. The cutoff frequencies of the first Chebyshev filter are 520 Hz and 880 Hz, respectively, and the cutoff frequencies of the second Chebyshev filter are 900 Hz and 2 kHz, respectively, thus forming two narrowband filters.

[0014] (2) Rectifier Circuit: The rectifier circuit includes two sub-rectifier circuits, each of which rectifies the output signals of the two Chebyshev filters. Each sub-rectifier circuit is composed of an operational amplifier N2A, a diode V1, a capacitor C5, and two resistors (R5 and R8). The two sub-rectifier circuits convert the AC signals output by the two second-order Chebyshev filters into DC signals.

[0015] (3) Voltage comparison circuit: It is composed of a voltage comparator N4A, three resistors (R22, R19, R20), two capacitors (C16, C15), an NPN transistor V4, and two diodes (V5, V3). This voltage comparison circuit inputs two comparison signals: one input from the first second-order Chebyshev filter and one input from the second second-order Chebyshev filter. These signals are the DC level converted from the low-frequency (500Hz-1kHz) speech signal and the DC level converted from the high-frequency speech signal (1kHz-2kHz). When the DC level converted from the low-frequency (500Hz-1kHz) speech signal is greater than the DC level converted from the high-frequency speech signal (1kHz-2kHz), the voltage comparison circuit outputs a high level; otherwise, it outputs a low level.

[0016] (IV) Electronic switch: It is composed of an electronic switch N5A and two capacitors (C12 and C14). The electronic switch inputs a high-frequency voice signal (1kHz to 2kHz). When the voltage comparator circuit outputs a high level, the electronic switch is turned on and the high-frequency voice signal is output. When the voltage comparator circuit outputs a low level, the electronic switch is turned off and the high-frequency voice signal (1kHz to 2kHz) is turned off.

[0017] (5) Adder: It is composed of an operational amplifier circuit N6, three resistors (R17, R18, R21), and a capacitor C14. R18 inputs low-frequency (500Hz~1kHz) voice signals, and R21 inputs high-frequency (1kHz~2kHz) voice signals. This adder mainly adds these two frequency signals. Under normal conditions, low-frequency (500Hz~1kHz) voice signals and high-frequency (1kHz~2kHz) voice signals are input at the same time. At this time, full-band voice signals can be heard. When helicopter rotor fixed-frequency interference appears in the voice, the high-frequency voice signal is automatically cut off. At this time, only low-frequency voice signals exist in the voice, which can ensure clear voice and unchanged voice recognition. At the same time, there is no rotor fixed-frequency interference in the voice.

[0018] In the rectifier circuit, the operational amplifier forms an emitter follower to improve the load capacity of the second-order Chebyshev filter. The diode V1 and the capacitor C5 form a rectifier circuit. The resistors (R5, R8) are mainly used to adjust the output voltage amplitude.

[0019] Technical effects and advantages of the present invention:

[0020] The adaptive noise reduction circuit for helicopter voices reduces the fixed-frequency noise of helicopter rotors in voices. When the helicopter rotors are not turned on, the fixed-frequency noise is not affected. When the helicopter rotors are turned on, the fixed-frequency noise in the voice is automatically reduced, improving voice quality and comfort. The main technical breakthroughs are as follows:

[0021] 1. The overall circuit structure is simple, the cost is low, and the indicators are fully adaptable to the use requirements;

[0022] 2. Use the frequency characteristics of voice to suppress noise without affecting the overall voice quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the second-order Chebyshev filter circuit;

[0024] Figure 2 is a schematic diagram of a rectifier circuit;

[0025] Figure 3 is a schematic diagram of a voltage comparator circuit;

[0026] Figure 4 is a schematic diagram of an electronic switch circuit;

[0027] Figure 5 This is the schematic diagram of the adder circuit. DETAILED DESCRIPTION

[0028] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0029] Example 1

[0030] A voice adaptive noise reduction circuit suitable for helicopters includes the following five parts: a second-order Chebyshev filter, a rectifier circuit, a voltage comparison circuit, an electronic switch, and an adder, wherein:

[0031] (1) Second-order Chebyshev filter: Two second-order Chebyshev filters are used. Each Chebyshev filter is composed of six resistors (R1, R3, R6, R2, R4, R7), four capacitors (C1, C2, C3, C4), and a dual operational amplifier. Resistors R1, R3, R6, capacitors C1, C3, and an operational amplifier group N1A constitute the first order of the Chebyshev amplifier, and resistors R2, R4, R7, capacitors C2, C4, and another operational amplifier N1B constitute the second order of the Chebyshev amplifier. The cutoff frequencies of the first Chebyshev filter are 520 Hz and 880 Hz, respectively, and the cutoff frequencies of the second Chebyshev filter are 900 Hz and 2 kHz, respectively, thus forming two narrowband filters.

[0032] (2) Rectifier circuit: The rectifier circuit includes two sub-rectifier circuits, which rectify the signals output by the two Chebyshev filters respectively. Each sub-rectifier circuit is composed of an operational amplifier N2A, a diode V1, a capacitor C5, and two resistors (R5 and R8). The two sub-rectifier circuits convert the AC signals output by the two second-order Chebyshev filters into DC signals respectively. The operational amplifier forms an emitter follower whose main function is to improve the load capacity of the second-order Chebyshev filter. The diode V1 and capacitor C5 form the rectifier circuit. The resistors (R5 and R8) are mainly used to adjust the output voltage amplitude.

[0033] (3) Voltage comparison circuit: It is composed of a voltage comparator N4A, three resistors (R22, R19, R20), two capacitors (C16, C15), an NPN transistor V4, and two diodes (V5, V3). This voltage comparison circuit inputs two comparison signals: one input from the first second-order Chebyshev filter and one input from the second second-order Chebyshev filter. These signals are the DC level converted from low-frequency (500Hz-1kHz) speech and the DC level converted from high-frequency speech signals (1kHz-2kHz). When the DC level converted from the low-frequency (500Hz-1kHz) speech is greater than the DC level converted from the high-frequency speech signal (1kHz-2kHz), the voltage comparison circuit outputs a high level; otherwise, it outputs a low level.

[0034] (IV) Electronic switch: It is composed of an electronic switch N5A and two capacitors (C12 and C14). The electronic switch inputs a high-frequency voice signal (1kHz to 2kHz). When the voltage comparator circuit outputs a high level, the electronic switch is turned on and the high-frequency voice signal is output. When the voltage comparator circuit outputs a low level, the electronic switch is turned off and the high-frequency voice signal (1kHz to 2kHz) is turned off.

[0035] (5) Adder: It is composed of an operational amplifier circuit N6, three resistors (R17, R18, R21), and a capacitor C14. R18 inputs low-frequency (500Hz~1kHz) voice signals, and R21 inputs high-frequency (1kHz~2kHz) voice signals. This adder mainly adds these two frequency signals. Under normal conditions, low-frequency (500Hz~1kHz) voice signals and high-frequency (1kHz~2kHz) voice signals are input at the same time. At this time, full-band voice signals can be heard. When helicopter rotor fixed-frequency interference appears in the voice, the high-frequency voice signal is automatically cut off. At this time, only low-frequency voice signals exist in the voice, which can ensure clear voice and unchanged voice recognition. At the same time, there is no rotor fixed-frequency interference in the voice.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A voice adaptive noise reduction circuit suitable for helicopters, characterized by: It includes the following five parts: second-order Chebyshev filter, rectifier circuit, voltage comparison circuit, electronic switch, adder, among which: (1) Second-order Chebyshev filter: Two second-order Chebyshev filters are used. Each Chebyshev filter is composed of six resistors R1, R3, R6, R2, R4, and R7, four capacitors C1, C2, C3, and C4, and a dual operational amplifier. Resistors R1, R3, R6, capacitors C1, C3, and an operational amplifier group N1A constitute the first order of the Chebyshev amplifier, and resistors R2, R4, R7, capacitors C2, C4, and another operational amplifier N1B constitute the second order of the Chebyshev amplifier. The cutoff frequencies of the first Chebyshev filter are 520 Hz and 880 Hz, respectively, and the cutoff frequencies of the second Chebyshev filter are 900 Hz and 2 kHz, respectively, forming two narrowband filters. (2) Rectifier circuit: The rectifier circuit includes two sub-rectifier circuits, each of which rectifies the signals output by the two Chebyshev filters. Each sub-rectifier circuit is composed of an operational amplifier N2A, a diode V1, a capacitor C5, and two resistors R5 and R8. The two sub-rectifier circuits convert the AC signals output by the two second-order Chebyshev filters into DC signals. (3) Voltage comparison circuit: It is composed of a voltage comparator N4A, three resistors R22, R19, and R20, two capacitors C16 and C15, an NPN transistor V4, and two diodes V5 and V3. This voltage comparison circuit inputs two comparison signals, one from the first second-order Chebyshev filter and the other from the second second-order Chebyshev filter, which are respectively the DC level converted from a low-frequency speech signal with a frequency of 500 Hz to 1 kHz and the DC level converted from a high-frequency speech signal with a frequency of 1 kHz to 2 kHz. When the DC level converted from the low-frequency speech signal with a frequency of 500 Hz to 1 kHz is greater than the DC level converted from the high-frequency speech signal with a frequency of 1 kHz to 2 kHz, the voltage comparison circuit outputs a high level; otherwise, it outputs a low level. (4) Electronic switch: It is composed of an electronic switch N5A and two capacitors C12 and C14. The electronic switch inputs a high-frequency voice signal with a frequency of 1kHz to 2kHz. When the voltage comparator circuit outputs a high level, the electronic switch is turned on and the high-frequency voice signal is output. When the voltage comparator circuit outputs a low level, the electronic switch is turned off and the high-frequency voice signal with a frequency of 1kHz to 2kHz is turned off. (5) Adder: It is composed of an operational amplifier circuit N6, three resistors R17, R18, R21, and a capacitor C14. R18 inputs a low-frequency voice signal with a frequency of 500Hz to 1kHz, and R21 inputs a high-frequency voice signal with a frequency of 1kHz to 2kHz. This adder mainly adds these two frequency signals. Under normal conditions, the low-frequency voice signal with a frequency of 500Hz to 1kHz and the high-frequency voice signal with a frequency of 1kHz to 2kHz are input at the same time. At this time, the full-band voice signal can be heard. When the helicopter rotor fixed-frequency interference appears in the voice, the high-frequency voice signal is automatically cut off. At this time, only the low-frequency voice signal exists in the voice, which can ensure the clarity of the voice and the unchanged voice recognition. At the same time, there is no rotor fixed-frequency interference in the voice.

2. The voice adaptive noise reduction circuit suitable for a helicopter according to claim 1, characterized in that: In the rectifier circuit, the operational amplifier forms an emitter follower mainly to improve the load capacity of the second-order Chebyshev filter, the diode V1 and the capacitor C5 form a rectifier circuit, and the resistors R5 and R8 are mainly used to adjust the output voltage amplitude.

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