Cockpit Audio System Based on Microphone Digital Gain and Its Howling Suppression Method

Abstract

The present invention discloses a cockpit audio system based on digital gain of a microphone and a method for suppressing howling thereof. The present invention belongs to the field of avionics technology. The howling suppression method includes: filtering an input signal of the microphone by calling a corresponding anti-howling filter according to the interval in which the digital gain indicated by a volume knob is located, so as to suppress the generation of howling. The present invention loads different howling suppression filters for different gains of the audio system, and can achieve a good balance between howling suppression and sound quality loss, and ensure the sound quality of the audio system while realizing howling suppression.

Description

Technical Field

[0001] The present invention belongs to the field of avionics technology, and particularly relates to a cockpit audio system based on microphone digital gain and a method for suppressing its howling. Background Art

[0002] The airborne audio processing equipment of civil airliners is a central management device for the audio information of the cockpit speech and communication navigation system. When the cockpit speaker is turned on, the crew speaks through the microphone and the sidetone (self-listening sound) is activated, the microphone, the power amplifier inside the airborne audio processing equipment, and the speaker form a typical sound amplification system. Since the cockpit is a small enclosed space and the speaker is close to the microphone, it is very easy to generate the "howling" phenomenon.

[0003] The closed-loop transfer function of the cockpit sidetone sound amplification system is:

[0004]

[0005] Among them, G is the digital gain of the sound collected by the microphone, which is determined by the position of the volume knob of the airborne audio processing equipment. The open-loop transfer function of the sound amplification system T(z)=G×F(z)×A(z). When the frequency ω satisfies the following conditions, howling will occur:

[0006]

[0007] Some existing howling suppression technologies: for example, measures such as redesigning the position of the cockpit speaker, appropriately reducing the microphone sensitivity and speaker volume, etc., can improve howling to a certain extent but cannot fundamentally suppress it, and at the same time will also reduce the sidetone sound quality and affect the pilot's use experience; the phase shift method has limited ability to suppress howling in the closed and narrow cockpit; the notch filter suppression method has high requirements for the accuracy of howling detection and howling frequency estimation, and high-precision frequency estimation also has high requirements for the performance of the calculation processing unit. Summary of the Invention

[0008] Aiming at the problem that the suppression effect of the existing howling suppression technology is not ideal, the present invention provides a cockpit audio system based on microphone digital gain and a method for suppressing its howling. The present invention divides the digital gain into different intervals, trains different anti-howling filters for different intervals of gain, and can call the corresponding anti-howling filter according to the interval where the gain indicated by the volume knob is located.

[0009] The present invention is realized by the following technical solutions:

[0010] A cockpit audio system based on microphone digital gain and a method for suppressing its howling, comprising:

[0011] Filter the microphone input signal with a corresponding anti-whistling filter according to the interval where the digital gain indicated by the volume knob is located, so as to suppress the generation of whistling.

[0012] The present invention loads different anti-whistling filters for different gains of the audio system, and can achieve a good balance between whistling suppression and sound quality loss, ensuring the sound quality of the audio system while realizing whistling suppression.

[0013] As a preferred embodiment, the anti-whistling filter of the present invention adopts but is not limited to a finite impulse response filter.

[0014] As a preferred embodiment, the training process of the anti-whistling filter of the present invention includes:

[0015] Divide the digital gain into different intervals;

[0016] Train different anti-whistling filters for the gains in different intervals.

[0017] As a preferred embodiment, the present invention trains different anti-whistling filters for the gains in different intervals, specifically including:

[0018] Set the digital gain;

[0019] Load the training sequence, and use the training sequence to train the filter coefficients and save them.

[0020] As a preferred embodiment, the present invention uses the LMS algorithm to iteratively train each filter coefficient vector, and each iterative training process specifically includes:

[0021] Calculate the output of the filter according to the input signal stored in the shift register of the filter;

[0022] Calculate the error signal according to the training sequence and the output of the filter;

[0023] Update the filter coefficients according to the error signal.

[0024] As a preferred embodiment, the present invention filters the microphone input signal with a corresponding anti-whistling filter according to the interval where the digital gain indicated by the volume knob is located, specifically including:

[0025] Read the digital gain corresponding to the position of the volume knob;

[0026] Judge whether the digital gain is lower than the minimum digital gain at which whistling can occur;

[0027] If so, call the default filter to filter the input audio;

[0028] Otherwise, according to the gain interval to which the digital gain belongs, call the corresponding anti-howling filter to filter the input audio.

[0029] As a preferred embodiment, the default filter of the present invention is a band-pass filter with a pass-band start frequency of 300 Hz and a cut-off frequency of 3400 Hz.

[0030] As a preferred embodiment, the present invention filters the input audio by calling the corresponding anti-howling filter according to the gain interval to which the digital gain belongs, specifically:

[0031] Determine the gain interval number to which the digital gain belongs;

[0032] Then call the anti-howling filter corresponding to the gain interval number to filter the input audio.

[0033] In a second aspect, the present invention provides an airborne audio processing device, which includes an A / D module and an adaptive filtering module;

[0034] The A / D module is used to convert the analog signal input by the microphone into a digital signal;

[0035] The adaptive filtering module calls the corresponding anti-howling filter according to the interval in which the digital gain indicated by the volume knob is located to filter the digital signal, so as to suppress the generation of howling.

[0036] In a third aspect, the present invention provides a cockpit audio system, which includes the above-mentioned airborne audio processing device of the present invention.

[0037] The present invention has the following advantages and beneficial effects:

[0038] 1. By dividing the digital gain into different intervals and training different howling suppression filters for different gain intervals, the present invention can call the corresponding howling suppression filter according to the interval in which the digital gain indicated by the volume knob is located, which can effectively suppress the howling of the cockpit audio system while ensuring the sound quality of the audio system.

[0039] 2. The present invention uses a finite impulse response filter FIR. Compared with the traditional notch filter suppression method, it has low requirements for the corresponding hardware performance, simple implementation method and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0041] Figure 1 It is a schematic diagram of the filter training process of the embodiment of the present invention.

[0042] Figure 2 Schematic diagram of the howling suppression process according to an embodiment of the present invention.

[0043] Figure 3 Principle block diagram of the audio system according to an embodiment of the present invention. Detailed implementation manners

[0044] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0045] Embodiment:

[0046] Existing howling suppression technologies mainly include: (1) measures such as redesigning the position of the cockpit speaker, appropriately reducing the microphone sensitivity and speaker volume, etc., which can improve howling to a certain extent but cannot fundamentally suppress it, and at the same time will also reduce the sidetone volume and affect the pilot's usage experience; (2) the phase shift method, which has limited ability to suppress howling in a closed and narrow cockpit; (3) the notch filter suppression method, which has high requirements for the accuracy of howling detection and howling frequency estimation, and high-precision frequency estimation also has high requirements for the performance of the computing and processing unit. In summary, the existing howling suppression technologies have unsatisfactory effects in the cockpit environment of civil airliners. Based on this, this embodiment proposes a howling suppression method for the cockpit audio system based on microphone digital gain.

[0047] The method proposed in this embodiment includes the following steps:

[0048] Step 1, filter the microphone input signal by calling the corresponding anti-howling filter according to the interval where the digital gain indicated by the volume knob is located, so as to suppress the generation of howling.

[0049] Through research, it is found that the digital gain G has an impact on the characteristics of the howling sound. A larger digital gain G requires a greater degree of suppression of the input audio signal, which also means greater damage to the sound quality. Therefore, in this embodiment, the digital gain is divided into different intervals, and different anti-howling filters are trained for different intervals of digital gain during ground maintenance, and then the corresponding anti-howling filter is called according to the interval where the gain indicated by the volume knob is located during flight.

[0050] The anti-howling filter in this embodiment can be but is not limited to a finite impulse response filter (FIR).

[0051] An optional implementation manner, let G min be the smallest digital gain that can cause howling, and G max be the digital gain when the volume knob is fully deflected. Divide G min by Gmax is evenly divided into K segments, and the distance between each segment is G0 = (G max - G min ) / K. The maximum gain of each segment is G k = G min + k × G0, where k = 1, 2,..., K. For the digital gain G k-1 < G ≤ G k , the filter coefficient is FIR(k).

[0052] Therefore, a total of K + 1 different anti-whistling filters are required to achieve whistling suppression, namely FIR(0), FIR(1),..., FIR(K). The length of each filter is L. The default filter FIR(0) is used to filter and reduce noise of the input voice when the digital gain is not sufficient to trigger whistling. A band-pass filter with a passband start frequency of 300 Hz and a cut-off frequency of 3400 Hz can be designed according to the Kaiser window method; the remaining K filters need to be trained according to the Figure 1 shown process during ground maintenance. The filter training process during ground maintenance includes K cycles of filter training. The k-th cycle performs the following operations:

[0053] Step 11, set the digital gain G = G k ;

[0054] Step 12, load the training sequence, train the adaptive filter coefficient FIR(k) using the training sequence and save it.

[0055] In this embodiment, the LMS algorithm is used to perform T iterations on each filter coefficient vector . Let s(t) represent the t-th value of the training sequence, and the column vector with a length of L represents the input signal stored in the shift register of the filter at the t-th moment. Then the steps for updating the filter at the t-th moment are as follows:

[0056] (1) Calculate the output of the filter:

[0057]

[0058] (2) Calculate the error:

[0059] e(t) = s(t) - y(t)

[0060] (3) Calculate the filter coefficient at the t + 1 moment:

[0061]

[0062] where μ represents the step size for updating the filter coefficient. In this embodiment, μ = 0.001 is taken.

[0063] An optional implementation. When it is detected that the crew turns the volume knob during flight, the process shown in Figure 2 is executed to suppress howling. The specific process is as follows:

[0064] Step 21, read the digital gain G corresponding to the position of the volume knob;

[0065] Step 22, determine whether G is lower than the minimum digital gain G min at which howling can occur; if so, call the default filter FIR(0) to filter the input audio; if not, then:

[0066] a) First, determine the serial number of the gain interval where G is located according to the following formula, where is the ceiling function of x

[0067]

[0068] b) Then call the filter FIR(k) to filter the input audio.

[0069] This embodiment also proposes an airborne audio processing device for executing the above method of this embodiment.

[0070] The airborne audio processing device of this embodiment includes an A / D module and an adaptive filtering module;

[0071] Among them, the A / D module is used to convert the analog signal input by the microphone into a digital signal;

[0072] The adaptive filtering module is used to call the corresponding anti-howling filter according to the interval where the digital gain indicated by the volume knob is located to filter the digital signal input by the microphone to suppress the generation of howling.

[0073] The airborne audio processing device of this embodiment further includes a digital gain control module, a D / A module, and a power amplifier module;

[0074] Among them, the digital gain control module is used to adjust the digital gain of the filtered signal according to the digital gain indicated by the volume knob;

[0075] The D / A module is used to convert the adjusted digital signal into an analog signal;

[0076] The power amplifier module is used to amplify the analog signal output by the D / A module and then input it to the speaker.

[0077] This embodiment also proposes a cockpit audio system, specifically as shown in Figure 3 . This audio system includes the above-mentioned airborne audio processing device, a microphone, and a speaker;

[0078] Among them, the microphone signal is filtered by the airborne audio processing device and then sent to the speaker for output. The signal output by the speaker is collected by the microphone after passing through the cockpit sound field.

[0079] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0080] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the flows and / or blocks in the flowchart and / or block diagram can also be implemented. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the specified functions in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0081] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means implements the specified functions in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0082] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the specified functions in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0083] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for suppressing howling in a cockpit audio system based on digital gain of a microphone, characterized in that, Including: Filter the microphone input signal with a corresponding anti-howling filter according to the interval where the digital gain indicated by the volume knob is located to suppress the generation of howling. The anti-howling filter uses a finite impulse response filter. The training process of the anti-howling filter includes: Divide the digital gain into different intervals. Train different anti-howling filters for the gains in different intervals; specifically for training different anti-howling filters for the gains in different intervals, it includes: Set the digital gain. Load the training sequence, train the filter coefficients with the training sequence and save them; use the LMS algorithm to iteratively train each filter coefficient vector. Each iterative training process specifically includes: Calculate the output of the filter according to the input signal stored in the shift register of the filter. Calculate the error signal according to the training sequence and the output of the filter. Update the filter coefficients according to the error signal; filter the microphone input signal with a corresponding anti-howling filter according to the interval where the digital gain indicated by the volume knob is located, specifically including: Read the digital gain corresponding to the position of the volume knob. Judge whether the digital gain is lower than the minimum digital gain at which howling can occur. If so, call the default filter to filter the input audio. Otherwise, filter the input audio with a corresponding anti-howling filter according to the gain interval to which the digital gain belongs.

2. The method for suppressing howling in a cockpit audio system based on digital gain of a microphone according to claim 1, characterized in that, The default filter is a band-pass filter with a passband start frequency of 300 Hz and a cut-off frequency of 3400 Hz.

3. The method for suppressing howling in a cockpit audio system based on digital gain of a microphone according to claim 1, characterized in that, Filter the input audio with a corresponding anti-howling filter according to the gain interval to which the digital gain belongs, specifically: Determine the gain interval serial number where the digital gain is located. Then call the anti-howling filter corresponding to the gain interval serial number to filter the input audio.

4. An airborne audio processing device, characterized in that, The device includes an A / D module and an adaptive filtering module. The A / D module is used to convert the analog signal input by the microphone into a digital signal. The adaptive filtering module filters the digital signal with a corresponding anti-howling filter according to the interval where the digital gain indicated by the volume knob is located to suppress the generation of howling. The anti-howling filter uses a finite impulse response filter. The training process of the anti-howling filter includes: Divide the digital gain into different intervals. Train different anti-howling filters for the gains in different intervals. Specifically for training different anti-howling filters for the gains in different intervals, it includes: Set the digital gain. Load the training sequence, train the filter coefficients with the training sequence and save them. Use the LMS algorithm to iteratively train each filter coefficient vector. Each iterative training process specifically includes: Calculate the output of the filter according to the input signal stored in the shift register of the filter. Calculate the error signal according to the training sequence and the output of the filter. Update the filter coefficients according to the error signal. Filter the microphone input signal with a corresponding anti-howling filter according to the interval where the digital gain indicated by the volume knob is located, specifically including: Read the digital gain corresponding to the position of the volume knob. Determine whether the digital gain is lower than the minimum digital gain at which howling can occur; If so, call the default filter to filter the input audio; Otherwise, according to the gain range to which the digital gain belongs, call the corresponding anti-howling filter to filter the input audio.

5. A cockpit audio system, characterized in that, The audio system includes the airborne audio processing device described in claim 4.

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