JP2022089106A - Automatic voice adjustment device - Google Patents

Abstract

To provide an automatic voice adjustment device with which it is possible to output a voice signal that is easy to hear without being affected by the skill level of the person who adjusts voice.SOLUTION: The automatic voice adjustment device comprises: a plurality of voice signal input units 1a, 1b-1n; a plurality of voice signal adjustment units 2a, 2b-2n for adjusting the voice signal inputted from each voice signal input unit to a prescribed frequency characteristic; a voice signal mixing unit 3 for mixing the voice signals having been adjusted by each voice signal adjustment unit; and a voice signal output unit 4 for outputting the voice signal having been mixed by the sound signal mixing unit. A frequency analysis arithmetic unit 5 analyzes and compares the frequency characteristic of each of voice signals A-N. When the comparison results are the same or similar, the frequencies f1a, f2a, fna of the first spectra of the compared voice signals are detected, and the center frequency feq of one of the voice signal adjustment units 2a, 2b-2n is moved to become greater than or equal to a preset threshold.SELECTED DRAWING: Figure 1

Description

The present invention relates to an automatic voice adjusting device that adjusts the frequency characteristics of a plurality of voice signals.

Conventionally, in broadcasting studios such as radios and televisions, music recording studios, etc., after adjusting the sound quality and volume of multiple audio signals input from microphones, etc., each audio signal is mixed and output. A voice regulator is used. The audio adjustment device is also called a mixing device, an audio mixing console, a console, a mixing board, a mixer, an audio mixer, an audio adjustment console, an acoustic adjustment console, and the like.

The equalizer mounted on the voice adjustment device includes a parametric equalizer (PEQ) that can finely adjust the frequency characteristics of a voice signal over a plurality of items. This parametric equalizer is used by adjusting setting parameters such as center frequency, equivalent amount, and Q value (Quality Factor) so that the frequency characteristics of the input signal become uniform or musically suitable. do.

The parametric equalizer is operated by a voice coordinator (mixing engineer) who adjusts the sound, and operates various controls such as button switches, adjustment knobs, faders, and a touch panel (volume control device) arranged on the device. It is done by. Therefore, the voice coordinator is required to operate a large number of controls quickly and accurately within a limited time. However, since the voice adjuster operates the voice adjustment device while actually listening to the sound and manually adjusts the mixing balance of each voice signal to be optimal, the voice adjuster adjusts the adjustment. Skills such as technique and experience have a great influence, and the works produced at the production site such as broadcast programs, recordings, and video editing will vary.

In addition, while it takes time to train voice coordinators who are good at operating parametric equalizers, highly skilled voice coordinators will retire due to the aging of the population in recent years, and their skills will disappear. There is concern that the quality of the works made in Japan will deteriorate.

From this point of view, a function that automatically mixes multiple audio signals so that the listener can output audio signals that are not uncomfortable for the listener with simple operations, regardless of the skill level of the audio adjuster. Proposals for an automatic audio regulator equipped with a so-called automixer are shown, for example, in the following patent documents.

Japanese Unexamined Patent Publication No. 2016-111673 Japanese Unexamined Patent Publication No. 2012-10154

However, in Patent Document 1, since the audio signal to be mixed is adjusted only by level control, if the frequency characteristics of the audio signal to be mixed are the same or similar, a plurality of input signals interfere with each other. In some cases, it became difficult to hear each sound. In such a case, the voice adjuster manually adjusts the sound quality by using a parametric equalizer according to the characteristics of each input signal so that it is easy to hear even when each input signal is mixed. The adjustment of the person is very complicated, and the audibility of the adjusted voice depends on the skill level of the voice adjuster. Further, Patent Document 2 has a problem that although it is possible to increase the sound of a specific channel, the sound output of the sound having a small input level is lowered and it becomes difficult to hear.

The present invention has been proposed to solve the above-mentioned problems of the prior art. An object of the present invention is to adjust the parametric equalizer setting so that when a plurality of voices having the same or similar frequency characteristics are input, the peak frequencies are different, so that the skill level of the voice adjuster is not affected. It is an object of the present invention to provide an automatic voice adjusting device capable of outputting an easy-to-hear voice signal.

In order to achieve the above object, the automatic voice adjusting device of the present invention is characterized by having the following configuration.
(1) Multiple audio signal input units.
(2) A plurality of audio signal adjusting units that adjust the audio signal input from each of the audio signal input units to a predetermined frequency characteristic based on a set center frequency.
(3) A frequency analysis calculation unit that compares the frequency characteristics of a plurality of arbitrarily selected audio signals and performs analysis calculation processing.
(4) An audio signal mixing unit that mixes audio signals that have been adjusted by each of the audio signal adjusting units.
(5) An audio signal output unit that outputs an audio signal mixed by the audio signal mixing unit.
(6) The frequency analysis calculation unit is set to adjust the frequency characteristics of the audio signal for any of the audio signals when the comparison results of the frequency characteristics of the audio signals are the same or similar. The center frequency of the voice signal adjusting unit is moved so as to be equal to or higher than a preset threshold value with respect to the frequency of the first spectrum of the voice signal.

In the present invention, the following configurations can be adopted.
(1) The wave number analysis calculation unit detects the frequency of the second spectrum for each voice signal when the comparison result of the frequency characteristics of each voice signal is the same or similar, and the frequency of the first spectrum and the first. For an audio signal having a large difference in frequency between the two spectra, the center frequency of the audio signal adjusting unit is moved so as to be equal to or higher than a preset threshold value.
(2) The center frequency of the audio signal adjusting unit is moved to the second spectrum side so as to be equal to or higher than a preset threshold value.
(3) The frequency analysis calculation unit is the center of the audio signal adjustment unit set to input the adjusted audio signal output from the audio signal adjustment unit and adjust the frequency characteristics of the audio signal. The frequency is moved so as to be equal to or higher than a preset threshold value with respect to the frequency of the first spectrum of the audio signal.

According to the present invention, when a plurality of voices having the same or similar frequency characteristics are input, the parametric equalizer setting is adjusted so that the peak frequencies are different, so that it is not affected by the skill level of the voice adjuster. It is possible to exert the effect of being able to output an audio signal that is easy to hear.

The block diagram which shows the structure of 1st Embodiment. The flowchart which shows the operation of 1st Embodiment. For the audio signals A and B of the first embodiment, (a) a graph showing the case where the values of the frequencies f1a and f2a of the first spectrum differ by more than a predetermined threshold value, and (b) the frequencies f1a and f2a of the first spectrum. A graph showing the case where the values are the same or close to each other within a predetermined threshold value.

[1. First Embodiment]
[1-1. Configuration of the first embodiment]
Hereinafter, the first embodiment of the present invention will be specifically described with reference to FIG. As shown in FIG. 1, the apparatus of the present embodiment adjusts the audio signals input from the plurality of audio signal input units 1a, 1b, 1n and the respective audio signal input units 1a, 1b, 1n to predetermined frequency characteristics. The audio signal mixing unit 3 that mixes the audio signals that have been adjusted by the plurality of audio signal adjusting units 2a, 2b, 2n, the audio signal adjusting units 2a, 2b, 2n, and the audio signal mixing unit 3 It has an audio signal output unit 4 that outputs a signal.

Audio signals are input from each channel in the audio signal input units 1a, 1b, and 1n. For example, in a broadcasting studio, the voices of male announcers, female announcers, and multiple commentators, and in a recording studio for band performances, the voices of vocals and other musical instruments are the voice signals A and B of each channel. , ..., The voice signal N is input to the voice signal input units 1a, 1b, and 1n, respectively.

The audio signal adjusting units 2a, 2b, 2n adjust the audio signals input from the respective audio signal input units 1a, 1b, 1n to predetermined frequency characteristics. The audio signal adjusting units 2a, 2b, and 2n are so-called parametric equalizers (PEQs) so that the frequency characteristics of the input audio signals A, B, and N become uniform or have a frequency suitable for music. Adjust the setting parameters such as center frequency, equivalent quantity, and Q value (Quality Factor). In particular, in the present embodiment, the audio signal adjusting units 2a, 2b, 2n are input voices based on the center frequencies feqa, pheqb, feqn preset for each of the audio signal adjusting units 2a, 2b, 2n. It adjusts the frequency characteristics of the signals A, B, and N, and it is possible to adjust the frequency gain and Q value of which band of each audio signal by moving the center frequencies feqa, feqb, and feqn. ..

The frequency characteristics of a plurality of audio signals A, B, N arbitrarily selected by the audio adjuster are compared between the audio signal input units 1a, 1b, 1n and the audio signal adjusting units 2a, 2b, 2n, and an analysis calculation is performed. A frequency analysis calculation unit 5 for processing is connected. In the present embodiment, the frequency analysis calculation unit 5 inputs each audio signal after the gain and the like output from the audio signal adjusting units 2a, 2b, and 2n have been adjusted, and analyzes the frequency characteristics thereof. That is, the adjusted audio signals output from the respective audio signal adjusting units 2a, 2b, and 2n are mixed by the audio signal mixing unit 3 and then output from the audio signal output unit 4, but a plurality of audios interfere with each other. It is due to the adjusted audio signal that it becomes difficult to hear. Therefore, in the present embodiment, by analyzing the adjusted voice signal, it is possible to prevent voice interference and difficulty in hearing.

The frequency analysis calculation unit 5 includes an input frequency analysis unit 51, an input frequency comparison unit 52, a spectrum interval comparison unit 53, and a center frequency setting unit 54.

The frequency analysis calculation unit 5 analyzes the frequency characteristics of the audio signals A, B, and N, and compares the characteristics. When the comparison results are the same or similar, the frequencies f1a, f2a, fna of the first spectrum of each audio signal A, B, N are detected, and the center frequencies feqa, pheqb, of the audio signal adjusting units 2a, 2b, 2n, The frequency is moved so as to be equal to or higher than a preset threshold value. Therefore, the output side of the frequency analysis calculation unit 5 is connected to the audio signal adjustment units 2a, 2b, 2n, and each audio signal adjustment unit 2a, 2b, 2n adjusts the gain of the audio signal based on the center frequency after movement. Is configured to run.

The input frequency analysis unit 51 analyzes a plurality of arbitrarily selected voice signals, for example, voice signals A and B by FFT (Fast Fourier Transform), and analyzes each frequency.

The input frequency comparison unit 52 compares whether or not the frequency spectra of the audio signals A and B analyzed by the input frequency analysis unit 51 are the same or similar. That is, as shown in FIG. 3A, the frequencies f1a and f2a of the first spectrum of the audio signals A and B and the frequencies f1b and f2b of the second spectrum are detected and these frequencies are compared.

The spectrum interval comparison unit 53 compares the difference between the frequencies f1a and f2a of the first spectrum and the frequencies f1b and f2b of the second spectrum for each of the audio signals A and B. For example, as shown in FIG. 3B, the distance L1 between the frequency f1a of the first spectrum and the frequency f1b of the second spectrum in the voice signal A, the frequency f2a of the first spectrum and the frequency of the second spectrum in the voice signal B. Compare with the distance L2 of f2b. In FIG. 3B, since L1 <L2, in the present embodiment, the frequency difference between the frequency f1 of the first spectrum and the frequency f2 of the second spectrum of the audio signal B is large.

The center frequency setting unit 54 sets the values of the center frequencies feqa, pheqb, and feqn to be output to the respective audio signal adjustment units 2a, 2b, and 2n according to the comparison results of the input frequency comparison unit 52 and the spectral interval comparison unit 53. In this case, for example, for the audio signals A and B, when the values of the frequencies f1a and f2a in the first spectrum are separated by more than a certain threshold value, the values of the respective center frequencies feqa and feqb are set to the frequencies of the first spectrum. Match the values of f1a and f2a.

On the other hand, regarding the audio signals A and B, when the values of the frequencies f1a and f2a of the first spectrum are the same or close to each other within a certain threshold value, the audio signal adjusting units 2a and 2b that adjust one of the audio signals, Move the center frequency of 2n. For example, as shown in FIG. 3B, when the audio signal A and the audio signal B are compared, the audio signal B having a large difference in frequency between the frequency f2a of the first spectrum and the frequency f2b of the second spectrum is the audio. The center frequency pheqb of the signal adjusting unit 2b is moved to the second spectrum side f2b so as to be equal to or higher than a preset threshold value. Here, the threshold value is a value at which the frequencies that become mutual peaks have an arbitrary level difference, and is a level difference to the extent that the listener does not feel uncomfortable.

The audio signal mixing unit 3 mixes the audio signals that have been adjusted by the audio signal adjusting units 2a, 2b, and 2n. The audio signal output unit 4 outputs the audio signal mixed by the audio signal mixing unit 3.

[1-2. Action of the first embodiment]
FIG. 2 is a flowchart illustrating the operation of the first embodiment having the above configuration. As shown in FIG. 2, in step S01, the audio signals A, B, and N of each channel are input to the audio signal input units 1a, 1b, and 1n.

In step S02, the voice is responded to various requests of the voice adjuster, such as when a plurality of voices are covered and difficult to hear, or when it is desired to perform amplification processing for frequencies having different voice peaks such as a male announcer and a female announcer. When the adjuster operates the voice signal adjusting units 2a, 2b, 2n, the voice signals A, B, N of any channel for performing the voice adjustment are selected, and the voice signals A, B, N are adjusted. To. In this case, instead of manually performing the voice adjustment by the voice adjuster, an automatic voice adjustment device as shown in the prior art, for example, the voice signal adjustment unit 2a, automatically according to the mode of the input voice signal, 2b, 2n may perform the adjustment.

In step S03, the frequency characteristics of the channel selected by the voice coordinator are analyzed and compared. That is, each audio signal A, B, N output from each audio signal input unit 1a, 1b, 1n is input to the frequency analysis calculation unit 5, and FFT analysis is performed by the input frequency analysis unit 51.

Further, in step S03, the analysis results of the voice signals A, B, and N analyzed by the input frequency analysis unit 51 are output to the input frequency comparison unit 52, and the voice signals A, B, respectively in the input frequency comparison unit 52. The frequency characteristics of N are compared. When the frequency characteristics of the compared audio signals differ by more than a predetermined threshold value (YES in step S04), that is, when the audio signals A and B are compared, for example, as shown in FIG. 3A. When the frequencies f1a and f2a of the first spectrum differ from each other by a predetermined threshold value or more (f1a ≠ f2a), the center frequency is matched with the frequencies f1a and f2a of the first spectrum of the audio signals A and B. The setting unit 54 determines the center frequencies feqa and feqb of the audio signal adjusting units 2a and 2b.

The center frequencies feqa and feqb determined by the center frequency setting unit 54 are output to the respective audio signal adjustment units 2a and 2b, and the respective audio signal adjustment units 2a and 2b are based on the center frequencies feqa and feqb. With respect to the audio signals A and B input from 1a and 1b, audio adjustment is performed according to the parameters input by the audio adjuster and the parameters determined by the automatic audio adjustment device (step S06).

In step S06, the audio signal adjusted by the audio signal adjusting units 2a and 2b is mixed by the audio signal mixing unit 3 provided in the subsequent stage (step S07), and then the mixed audio signal is generated. It is output from the audio signal output unit 4 to an external device such as a speaker or a recording device (step S08).

When the frequency characteristics of the voice signals compared in step S03 are the same or similar (NO in step S04), that is, when the voice signals A and B are compared, for example, as shown in FIG. 3 (b), they. When the frequencies f1a and f2a of the first spectrum of the above are the same or close to each other within a certain threshold value (f1a≈f2a), the frequency of the first spectrum is used for the respective voice signals A and B in the spectrum interval comparison unit 53. The difference between f1a and f2a and the frequencies f1b and f2b of the second spectrum are compared (step S09). In FIG. 3B, the difference L1 between the frequency f1a of the first spectrum and the frequency f1b of the second spectrum of the voice signal A, and the difference L2 between the frequency f2a of the first spectrum and the frequency f2b of the second spectrum of the voice signal B. Then, L2> L1.

In the next step S10, the center frequency setting unit 54 sets the center frequency pheqb of the audio signal adjusting unit 2b of the audio signal B having a large difference between the frequency f2a of the first spectrum and the frequency f2b of the second spectrum to the audio signal having a small difference. The center frequency feqa of the audio signal adjusting unit 2a of A is moved so as to be equal to or higher than a preset threshold value. The direction of movement may be any, but in the present embodiment, the center frequency feqb of the audio signal adjusting unit 2b of the audio signal B having a large difference can be obtained from the center frequency feqa of the audio signal adjusting unit 2a of the audio signal A having a small difference. It is moved to the frequency f2b side of the second spectrum so as to be separated by a preset threshold value or more.

The moved center frequency pheqb set by the center frequency setting unit 54 in this way is sent to the audio signal adjusting unit 2b of the corresponding audio signal B. On the other hand, for the voice signals A and N for which the center frequencies feqa and feqn were not moved by the frequency analysis calculation unit 5, the center frequencies feqa and feqn preset in the voice signal adjustment units 2a and 2n were used. The gain adjustment and the like are executed according to the parameters set by the voice adjuster and the automatic voice adjustment device (step S06).

In step S06, the audio signal adjusted by the audio signal adjusting units 2a and 2b is mixed by the audio signal mixing unit 3 provided in the subsequent stage (step S07), and then the mixed audio signal is generated. It is output from the audio signal output unit 4 to an external device such as a speaker or a recording device (step S08).

[1-3. Effect of the first embodiment]
(1) According to the automatic voice adjusting device in the present embodiment, the voice signal adjusting units 2a, 2b, 2n are set so that the peak frequencies are different when a plurality of voices having the same or similar frequency characteristics are input. Therefore, it is possible to output an easy-to-hear voice signal regardless of the skill level of the voice adjuster.

(2) According to the automatic voice adjusting device in the present embodiment, the center frequency feqb of the voice signal adjusting unit 2b of the voice signal B having a large difference is derived from the center frequency feqa of the voice signal adjusting unit 2a of the voice signal A having a small difference. Since the audio signals are moved so as to be separated by a preset threshold value or more, even when a plurality of audio signals having the same or similar frequency characteristics are input, they can output audio signals that are easy to hear without interfering with each other.

(3) According to the automatic voice adjusting device in the present embodiment, the center frequency feqb of the voice signal adjusting unit 2b of the voice signal B having a large difference is derived from the center frequency feqa of the voice signal adjusting unit 2a of the voice signal A having a small difference. Since it is moved to the frequency f2b side of the second spectrum so as to be separated by a preset threshold value or more, the emphasized spectrum and the second spectrum are close to each other, so that there is no discomfort and an audio signal that is easier to hear is output. It becomes possible.

(4) According to the automatic voice adjustment device in the present embodiment, the frequency analysis calculation unit 5 inputs each gain-adjusted voice signal output from the voice signal adjustment units 2a, 2b, 2n, and inputs the frequency thereof. Since the characteristics are analyzed, the settings of the audio signal adjusting units 2a, 2b, and 2n are moved so that the peak frequencies are different even when a plurality of voices having the same or similar frequency characteristics are input. Therefore, in the state before the audio signals are mixed by the audio signal mixing unit 3, the peak frequencies of the respective audio signals A, B, and N are adjusted to be different, which makes it difficult for each audio to interfere or be heard. It can be prevented from becoming.

[2. Second Embodiment]
[2-1. Configuration of the second embodiment]
Hereinafter, a second embodiment of the present invention will be described. The configuration of the second embodiment is different from the configuration of the first embodiment in the following points, and is the same in other points. The difference is that the frequency analysis calculation unit 5 does not compare the frequency characteristics of a plurality of arbitrarily selected audio signals A, B, N, but has the maximum gain among the plurality of audio signals A, B, N. The point is that the audio signal of No. 1 and the audio signal having the second largest gain are automatically selected, the frequency characteristics are compared, and the analysis calculation process is performed.

[2-2. Action effect of the second embodiment]
According to the present embodiment, the voice signal having the maximum gain and the voice signal having the second largest gain are automatically selected and the frequency characteristics are adjusted without the voice adjuster making any selection. The voice can be easily adjusted, and an easy-to-hear voice signal can be output regardless of the skill level of the voice adjuster.

[3. Other embodiments]
The present invention is not limited to the above embodiment as it is, and at the implementation stage, the components can be modified and embodied within a range that does not deviate from the gist thereof. In addition, various inventions can be formed by an appropriate combination of the plurality of components disclosed in the above-described embodiment. For example, some components may be removed from all the components shown in the embodiments. Furthermore, components over different embodiments may be combined as appropriate. The following is an example.

(1) The frequency analysis calculation unit detects the frequency of the second spectrum of each voice signal when the comparison results of the frequencies of the frequency characteristics of each voice signal are the same or similar, and the frequency of the first spectrum and the second spectrum. For an audio signal having a small difference in frequency, the center frequency of the audio signal adjusting unit can be moved so as to be equal to or higher than a preset threshold value. In that case, the center frequency of the audio signal adjusting unit that processes the audio signal having the smaller difference may be moved to the side opposite to the second spectrum.

(2) As each audio signal to be input to the frequency analysis calculation unit, adjustment from the audio signal input units 1a, 1b, 1n instead of the adjusted audio signal that has passed through the audio signal adjustment units 2a, 2b, 2n. The previous audio signal can be used.

(3) The audio signal input unit and the audio signal adjustment unit can be increased or decreased as appropriate according to the number of input channels.

(4) The configuration of the frequency analysis calculation unit is not limited to that shown in the figure, and a frequency analysis calculation unit can be provided in each audio signal adjustment unit. Further, in the illustrated embodiment, the frequency characteristics of the audio signal input by the frequency analysis calculation unit are compared, but the frequency characteristics are compared by the audio signal adjustment unit, and the frequency analysis calculation unit compares the frequency characteristics according to the result. The center frequency of the processing unit may be moved so as to be equal to or higher than a preset threshold value.

(5) The threshold value setting unit can be set in advance by a program in addition to being manually set by the voice coordinator. For example, the processing of the present invention may be applied only to a time zone in which a plurality of performers appear in the broadcast content, and the processing of the present invention may not be performed in a time zone in which the announcer is speaking alone. It is also possible to set a program for changing the threshold in advance so that the threshold is automatically changed according to the characteristics of the performer even in the time zone of the main body in which the performer appears.

(6) When the voice signal differs depending on the gender and the number of people, for example, the inverse number of the hearing correction filter is multiplied by the manually set threshold value to determine the corrected threshold value. By setting a set threshold, it is possible to make it easier to hear the thick voice of men and the high voice of women.

(7) The threshold value can be set to a different value for each audio signal input unit. For example, in the first embodiment, by setting the threshold value of the voice signal A to a value that becomes background noise, it is possible to eliminate the influence of noise caused by a large voice suddenly generated in the voice signal A, and the voice signal B can be eliminated. , Background noise can be efficiently masked with respect to the voice of the voice signal N.

A, B, N ... Audio signals 1a, 1b, 1n ... Audio signal input units 2a, 2b, 2n ... Audio signal adjustment unit 3 ... Audio signal mixing unit 4 ... Audio signal output unit 5 ... Frequency analysis calculation unit 51 ... Input frequency Analysis unit 52 ... Input frequency comparison unit 53 ... Spectral interval comparison unit 54 ... Center frequency setting unit

Claims (4)

With multiple audio signal input units,
A plurality of audio signal adjusting units that adjust the audio signal input from each audio signal input unit to a predetermined frequency characteristic based on a set center frequency, and
A frequency analysis calculation unit that compares the frequency characteristics of a plurality of arbitrarily selected audio signals and performs analysis calculation processing, and a frequency analysis calculation unit.
An audio signal mixing unit that mixes audio signals that have been adjusted by each audio signal adjusting unit,
An audio signal output unit that outputs an audio signal mixed by the audio signal mixing unit, and an audio signal output unit.
Equipped with
The frequency analysis calculation unit is set to adjust the frequency characteristics of the audio signal for any of the audio signals when the comparison results of the frequency characteristics of the audio signals are the same or similar. An automatic voice adjustment device characterized in that the center frequency of the adjustment unit is moved so as to be equal to or higher than a preset threshold value with respect to the frequency of the first spectrum of the voice signal. The wave number analysis calculation unit detects the frequency of the second spectrum for each voice signal when the comparison result of the frequency characteristics of each voice signal is the same or similar, and the frequency of the first spectrum and the frequency of the second spectrum. The automatic voice adjusting device according to claim 1, wherein the center frequency of the voice signal adjusting unit is moved so as to be equal to or higher than a preset threshold value for a voice signal having a large frequency difference. The automatic voice adjustment device according to claim 2, wherein the center frequency of the voice signal adjustment unit is moved to the second spectrum side so as to be equal to or higher than a preset threshold value. The wave number analysis calculation unit inputs the adjusted audio signal output from the audio signal adjustment unit, and sets the center frequency of the audio signal adjustment unit set to adjust the frequency characteristics of the audio signal. The automatic audio adjustment device according to any one of claims 1 to 3, wherein the frequency of the first spectrum of the audio signal is moved so as to be equal to or higher than a preset threshold value.

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