Howling suppression method and device applied to an ANR earphone

Abstract

The present invention discloses a howling suppression method and device applied to an ANR earphone. The method comprises: collecting signals by using a first microphone and a second microphone; wherein the first microphone is arranged in a position outside an auditory meatus when said ANR earphone is worn, and the second microphone is arranged in a position inside the auditory meatus when the ANR earphone is worn; according to a relation between signals collected by the first microphone and the second microphone, judging whether the current state of said ANR earphone is a state unable to produce a howling or a state able to produce a howling; and when the current state of said ANR earphone is a state able to produce a howling, starting processing for preventing howling production. The technical scheme can achieve that the ANR earphone does not produce a howling all the time.

Claims

1. A howling suppression method applied to an Active Noise Reduction (ANR) earphone before howling occurs, comprising: collecting signals using a first microphone and then a second microphone, wherein the first microphone is arranged in a position outside an auditory meatus when the ANR earphone is worn, and the second microphone is arranged in a position inside the auditory meatus when the ANR earphone is worn; generating a transfer function that relates the collected signals from the first and second microphones; using the transfer function, determining whether a current state of the ANR earphone is a state that is able to produce howling; and suppressing howling when the current state of the ANR earphone is the state able to produce howling.

2. The method according to claim 1, wherein judging the current state of said ANR earphone that is able to produce howling comprises: judging whether the current state of said ANR earphone is a state unable to produce a howling or a state able to produce a howling according to a time-domain characteristic of the transfer function from the first microphone to the second microphone; or, judging whether the current state of said ANR earphone is a state unable to produce a howling or a state able to produce a howling according to a frequency-domain characteristic of the transfer function from the first microphone to the second microphone.

3. The method according to claim 2, wherein judging whether the current state of said ANR earphone is a state unable to produce a howling or a state able to produce a howling according to a time-domain characteristic of the transfer function from the first microphone to the second microphone comprises: making a time-domain judgment statistic as the ratio of quadratic sum of the first M orders to quadratic sum of the first N orders of the time-domain transfer function from the first microphone to the second microphone; wherein N is a natural number, and N is the length of said time-domain transfer function; M is a natural number which is smaller than N; if said time-domain judgment statistic is smaller than a judgment threshold, judging as a state unable to produce a howling; if said time-domain judgment statistic is larger than the judgment threshold, judging as a state able to produce a howling, wherein the judgment threshold varies with structural change of the earphone and is obtained by statistics.

4. The method according to claim 2, wherein judging whether the current state of said ANR earphone is a state unable to produce a howling or a state able to produce a howling according to a frequency-domain characteristic of the transfer function from the first microphone to the second microphone comprises: making a frequency-domain judgment statistic as the ratio of modular quadratic sum of the first M orders to modular quadratic sum of the first M+1 to N/2 orders of the frequency-domain transfer function from the first microphone to the second microphone; N is a natural number, and N is the length of said frequency-domain transfer function; M is a natural number which is smaller than N/2; if said frequency-domain judgment statistic is smaller than the judgment threshold, judging as a state able to produce a howling; if said frequency-domain judgment statistic is larger than the judgment threshold, judging as a state unable to produce a howling, wherein, the judgment threshold varies with structural change of the earphone and is obtained by statistics.

5. The method according to claim 1, wherein processing for preventing howling production comprises: amending ANR parameters or shutting down ANR circuits.

6. The method according to claim 1, wherein, when said ANR earphone is a Feed Forward ANR earphone, said first microphone is a REF MIC demanded to realize the Feed Forward ANR; when said ANR earphone is a Feed Back ANR earphone, said second microphone is an ERR MIC demanded to realize the Feed Back ANR; when said ANR earphone is a Hybrid ANR earphone, said first microphone is a REF MIC demanded to realize the Feed Forward ANR, and said second microphone is an ERR MIC demanded to realize the Feed Back ANR.

7. A howling suppression device applied to an Active Noise Reduction (ANR) earphone before howling occurs, comprising: a first microphone configured to fit outside an auditory meatus when the ANR earphone is worn; a second microphone configured to fit inside the auditory meatus when the ANR earphone is worn; a state judger configured to generate a transfer function that relates signals firstly collected from the first microphone and then collected from the second microphone and, based on the transfer function, judging whether a current state of the ANR earphone is able to produce howling; a howling processor for preventing howling when the current state of said the ANR earphone outputted by said state judger is able to produce howling.

8. The device according to claim 7, wherein said state judger comprises: a first data cache, for caching digital signals collected by the first microphone; a second data cache, for caching digital signals collected by the second microphone; a transfer function estimator, for obtaining a time-domain transfer function from the first microphone to the second microphone according to data in the first data cache and the second data cache; a judgment statistic calculator, for obtaining a time-domain judgment statistic according to the ratio of quadratic sum of the first M orders to quadratic sum of the first N orders of the time-domain transfer function from the first microphone to the second microphone; wherein, N is a natural number and N is the length of said time-domain transfer function; M is a natural number which is smaller than N; and a state decider, for judging as a state unable to produce a howling when said time-domain judgment statistic is smaller than a judgment threshold; and judging as a state able to produce a howling when said time-domain judgment statistic is larger than the judgment threshold, wherein the judgment threshold varies with structural change of the earphone and is obtained by statistics.

9. The device according to claim 7, wherein said state judger comprises: a first data cache, for caching digital signals collected by the first microphone; a second data cache, for caching digital signals collected by the second microphone; a transfer function estimator, for obtaining a frequency-domain transfer function from the first microphone to the second microphone according to data in the first data cache and the second data cache; a judgment statistic calculator, for obtaining a frequency-domain judgment statistic according to the ratio of modular quadratic sum of the first M orders to modular quadratic sum of the first M+1 to N/2 orders of the frequency-domain transfer function from the first microphone to the second microphone; wherein N is a natural number and is the length of said frequency-domain transfer function; M is a natural number which is smaller than N/2; and a state decider, for judging as a state able to produce a howling when said frequency-domain judgment statistic is smaller than the judgment threshold; and judging as a state unable to produce a howling when said frequency-domain judgment statistic is larger than the judgment threshold, wherein the judgment threshold varies with the structural change of the earphone and is obtained by statistics.

10. The device according to claim 7, wherein when said ANR earphone is a Feed Forward ANR earphone, said first microphone is a REF MIC demanded to realize the Feed Forward ANR; when said ANR earphone is a Feed Back ANR earphone, said second microphone is an ERR MIC demanded to realize the Feed Back ANR; and when said ANR earphone is a Hybrid ANR earphone, said first microphone is a REF MIC demanded to realize the Feed Forward ANR, and said second microphone is an ERR MIC demanded to realize the Feed Back ANR.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a structural diagram of an ANR earphone.

(2) FIG. 2A is a functional block diagram of a FF ANR earphone.

(3) FIG. 2B is a functional block diagram of a FB ANR earphone.

(4) FIG. 2C is a functional block diagram of a Hybrid ANR earphone.

(5) FIG. 3 is a modeling diagram of a howling.

(6) FIG. 4 is a modeling diagram of a howling of a FF ANR earphone.

(7) FIG. 5 is a modeling diagram of a howling of a FB ANR earphone.

(8) FIG. 6 is a flow chart showing a howling suppression method applied to an Active Noise Reduction (ANR) earphone of an embodiment of the invention.

(9) FIG. 7 is a comparison diagram showing an actual measurement result of a time-domain transfer function of a REF MIC to an ERR MIC of embodiments of the invention.

(10) FIG. 8 is a comparison diagram showing an actual measurement result of a frequency-domain transfer function of a REF MIC to an ERR MIC of embodiments of the invention.

(11) FIG. 9 is a structure diagram of a howling suppression device applied to an Active Noise Reduction (ANR) earphone of embodiments of the invention.

(12) FIG. 10 is a structure diagram of a state judger 903 of an embodiment of the invention.

EMBODIMENTS OF THE INVENTION

(13) Different from aforesaid method of detecting a howling by using the frequency-domain feature of a signal usually adopted by prior arts, in the present patent application the state of the ANR earphone can be divided into state able to produce a howling (Howling) and state unable to produce a howling (noHowling). If the state of an earphone at present can be distinguished, then whether or not the earphone is able to produce a howling at present can be known, that is, it is needed to distinguish that the ANR earphone is in a state of being able to produce a howling or in a state of being unable to produce a howling. If it is in the state of being able to produce a howling, directly perform the howling processing. If it is in the state of being unable to produce a howling, do not perform processing. The earphone may not immediately produce a howling after the earphone is in the state able to produce a howling, for howling production need to satisfy the condition of producing a howling. But in the present application, the howling processing is performed immediately if the earphone being in the state able to produce a howling is detected. That is, if the current state of the earphone is a state able to produce a howling, perform processing without exception as the howling is produced regardless of whether or not the condition of producing howling is satisfied. Therefore, the technical scheme of the patent application performs processing without the need to wait until the howling is produced, and thus can achieve that the ANR earphone does not produce a howling all the time.

(14) To make the purpose, technical scheme and advantages of the invention clearer, the embodiments of the invention will be described in further detail with reference to the drawings.

(15) FIG. 6 is a flow chart showing a howling suppression method applied to an Active Noise Reduction (ANR) earphone of an embodiment of the invention. As is shown in FIG. 6, the method comprises:

(16) Step S601, collecting signals by using a first microphone and a second microphone; wherein the first microphone is arranged in a position outside an auditory meatus when said ANR earphone is worn, and the second microphone is arranged in a position inside the auditory meatus when said ANR earphone is worn.

(17) In an embodiment of the invention, when the ANR earphone is a Feed Forward ANR earphone, the first microphone can be a Reference Microphone (REF MIC) demanded to realize the Feed Forward ANR. When the ANR earphone is a Feed Back ANR earphone, the second microphone can be an Error Microphone (ERR MIC) demanded to realize the Feed Back ANR. When the ANR earphone is a Hybrid ANR earphone, the first microphone can be a Reference Microphone (REF MIC) demanded to realize the Feed Forward ANR, and the second microphone can be an Error Microphone (ERR MIC) demanded to realize the Feed Back ANR.

(18) Of course, the first microphone is not necessarily a REF MIC. It can also be a specialized microphone. The second microphone is not necessarily an ERR MIC. It can also be a specialized microphone. However, the cost will increase.

(19) Step S602, according to a relation between signals collected by the first microphone and the second microphone, judging whether the current state of said ANR earphone is a state unable to produce a howling or a state able to produce a howling.

(20) In a state unable to produce a howling and in a state able to produce a howling of the ANR earphone, the relation between signals collected by the first microphone and the second microphone will have certain difference. In the present invention, based on this difference the ANR earphone's state of being unable to produce a howling and the state of being able to produce a howling of can be distinguished.

(21) Step S603, when the current state of said ANR earphone is a state able to produce a howling, starting processing to prevent howling production.

(22) In the step, the specific technology which can be adopted to perform processing to prevent howling production comprises amending ANR parameters to break the condition of producing howling or directly shutting down the ANR circuit, etc.

(23) The method shown in FIG. 6 can judge whether or not the ANR earphone is in a state able to produce a howling and can perform howling processing when judging that the ANR earphone is in a state able to produce a howling, and thus can prevent howling production when the ANR earphone is in a state able to produce a howling. The method can perform howling suppression processing before a howling is produced instead of waiting until the howling has been produced.

(24) As is mentioned before, in Step S602 the ANR earphone's state of being unable to produce a howling and the state of being able to produce a howling can be distinguished according to a relation between signals collected by the first microphone and the second microphone. Specifically, calculating the transfer function from the first microphone to the second microphone according to the signals collected by the first microphone and the second microphone; judging whether the state of the ANR earphone is a state unable to produce a howling or a state able to produce a howling according to time-domain characteristics of the transfer function from the first microphone to the second microphone; or, judging whether the state of the ANR earphone is a state unable to produce a howling or a state able to produce a howling according to frequency-domain characteristics of the transfer function from the first microphone to the second microphone.

(25) This is because, when the ANR earphone is in a state of being unable to produce a howling, the signal picked up by the two microphones is characterized in that: the environmental noise always first reaches the first microphone and then reaches the second microphone, thus it can be judged by causality of the transfer function between the first microphone and the second microphone; the environmental noise will be blocked by earphone cover and auricle before being picked up by the second microphone, which is equivalent to passing through a filter, and the high frequency part of the filter decays more than the low frequency part. When the ANR earphone is in a state of being able to produce a howling, the signal picked up by the two microphones is characterized in that: sequence of the environmental noise reaching the first microphone and the second microphone is not fixed, and sound wave has no obvious obstacle between the first microphone and the second microphone, thus there is no obvious filtering effect.

(26) The environmental noise first reaches the first microphone and then reaches the second microphone and is blocked by earphone cover and auricle before being picked up by the second microphone, which is equivalent to passing through a filter. As can be known from the condition of producing howling, a howling can be produced only when positive feedback is created. In the state the signal amplitude is decayed and has filtering effect, thus the condition of producing howling is not satisfied and the howling will not be produced. The sequence of the environmental noise reaching the first microphone and the second microphone is not fixed, and sound wave has no obvious obstacle between the first microphone and the second microphone, thus there is no obvious filtering effect. As can be known from the condition of producing howling, the state is easy to satisfy the condition of producing howling, and hence will produce a howling.

(27) It will be described in detail by taking Hybrid ANR earphone as an example below. In the embodiment, the first microphone is the REF MIC of the Hybrid ANR earphone, and the second microphone is the ERR MIC of the Hybrid ANR earphone. In the state that the earphone is normal and unable to produce a howling, the environmental noise always first reaches the REF MIC and then reaches the ERR MIC, thus it can be judged by causality of the transfer function between the REF MIC and the ERR MIC.

(28) FIG. 7 is a comparison diagram showing an actual measurement result of time-domain transfer function from a REF MIC to an ERR MIC of embodiments of the invention. Seeing FIG. 7, the dotted line represents the time-domain transfer function from the REF MIC to ERR MIC in the state of being able to produce a howling (Howling), and the full line represents the time-domain transfer function from the REF MIC to ERR MIC in the state of being unable to produce a howling (noHowling). The maximum value point of the time-domain transfer function denotes the group delay of the sound wave. As can be seen in FIG. 7, the group delay in Howling state is 0, and the group delay in noHowling state is a positive value which is greater than 0. That is, the Howling state and noHowling state can be distinguished through characteristics of time delay of the transfer function from REF MIC to ERR MIC.

(29) FIG. 8 is a comparison diagram showing an actual measurement result of frequency-domain transfer function from a REF MIC to an ERR MIC of embodiments of the invention. Seeing FIG. 8, the dotted line represents the frequency-domain transfer function from the REF MIC to ERR MIC in the state of being able to produce howling (Howling), and the full line represents the frequency-domain transfer function from the REF MIC to ERR MIC in the state of being unable to produce howling (noHowling). As can be seen in FIG. 8, the amplitude-frequency characteristic of the transfer function in Howling state is similar to an all-pass filter, and the amplitude-frequency characteristic of the transfer function in noHowling state is similar to a low-pass filter. That is, the amplitude-frequency characteristic of the transfer function from REF MIC to ERR MIC can also distinguish the noHowling state and the Howling state.

(30) As can be seen, in the embodiment of the invention, after calculating the transfer function from the REF MIC to the ERR MIC, the ANR earphone's state of being able to produce howling can be judged by the time-domain characteristic of the transfer function, and also the ANR earphone's state of being unable to produce howling can be judged by the frequency-domain characteristic of the transfer function.

(31) In an embodiment of the invention, according to the time-domain characteristic of the transfer function from the first microphone to the second microphone, judging the ANR earphone's state of being unable to produce howling specifically can be: making the time-domain judgment statistic as the ratio of quadratic sum of the first M orders to quadratic sum of the first N orders of the time-domain transfer function from the first microphone to the second microphone; N is a natural number, and N is the length of the time-domain transfer function; M is a natural number smaller than N; if the time-domain judgment statistic is smaller than judgment threshold, judging as the state unable to produce a howling; if the time-domain judgment statistic is larger than judgment threshold, judging as the state able to produce a howling. Wherein, the judgment threshold varies with the structural change of the earphone and is obtained by statistics. A specific compute mode of the method will not be explained here for the time being to avoid repetition, and please see the follow-up description corresponding to FIG. 10.

(32) In another embodiment of the invention, according to the frequency-domain characteristic of the transfer function from the first microphone to the second microphone, judging whether the state of the ANR earphone is a state unable to produce a howling or a state able to produce a howling specifically can be: making the frequency-domain judgment statistic as the ratio of modular quadratic sum of the first M orders to modular quadratic sum of the first M+1 to N/2 orders of the frequency-domain transfer function from the first microphone to the second microphone; N is a natural number, and N is the length of the frequency-domain transfer function; M is a natural number smaller than N/2; if the frequency-domain judgment statistic is smaller than judgment threshold, judging as the state able to produce a howling; if the frequency-domain judgment statistic is larger than judgment threshold, judging as the state unable to produce a howling. Wherein, the judgment threshold varies with the structural change of the earphone and is obtained by statistics. A specific compute mode of the method will not be explained here for the time being to avoid repetition, and please see the follow-up description corresponding to FIG. 10.

(33) FIG. 9 is a structure diagram of a howling suppression device applied to an Active Noise Reduction (ANR) earphone of embodiments of the invention. As is shown in FIG. 9, the device comprises:

(34) a first microphone 901, which is arranged in a position outside an auditory meatus when the ANR earphone is worn;

(35) a second microphone 902, which is arranged in a position inside the auditory meatus when the ANR earphone is worn;

(36) a state judger 903, according to a relation between signals collected by the first microphone 901 and the second microphone 902, judging whether the current state of the ANR earphone is a state unable to produce a howling or a state able to produce a howling;

(37) a howling processor 904, when the current state of the ANR earphone outputted by the state judger 903 is a state able to produce a howling, starting processing to prevent howling production.

(38) In an embodiment of the invention, when the ANR earphone is a Feed Forward ANR earphone, the first microphone 901 can be a Reference Microphone (REF MIC) demanded to realize the Feed Forward ANR; or, when the ANR earphone is a Feed Back ANR earphone, the second microphone 902 can be an Error Microphone (ERR MIC) demanded to realize the Feed Back ANR; or, when the ANR earphone is a Hybrid ANR earphone, the first microphone 901 can be a Reference Microphone (REF MIC) demanded to realize the Feed Forward ANR, and the second microphone 902 can be an Error Microphone (ERR MIC) demanded to realize the Feed Back ANR.

(39) In an embodiment of the invention, the state judger 903 is for calculating the transfer function from the first microphone 901 to the second microphone 902 according to the signals collected by the first microphone 901 and the second microphone 902; and judging whether the state of the ANR earphone is a state unable to produce a howling or a state able to produce a howling according to the time-domain characteristics of the transfer function from the first microphone 901 to the second microphone 902, or judging whether the state of the ANR earphone is a state unable to produce a howling or a state able to produce a howling according to the frequency-domain characteristics of the transfer function from the first microphone 901 to the second microphone 902.

(40) The device shown in FIG. 9 can judge whether or not the ANR earphone is in a state able to produce a howling and can perform howling processing when judging that the ANR earphone is in a state able to produce a howling, and thus can prevent howling production when the ANR earphone is in a state able to produce a howling.

(41) FIG. 10 is a structure diagram of a state judger 903 of an embodiment of the invention. As is shown in FIG. 10, the state judger 903 comprises:

(42) a first data cache 1001, for caching digital signals collected by a first microphone 901;

(43) a second data cache 1002, for caching digital signals collected by a second microphone 902;

(44) a transfer function estimator 1003, for calculating the time-domain transfer function from the first microphone 901 to the second microphone 902 according to the data in the first data cache 1001 and the second data cache 1002;

(45) a judgment statistic calculator 1004, for obtaining the time-domain judgment statistic according to the ratio of quadratic sum of the first M orders to quadratic sum of the first N orders of the time-domain transfer function from the first microphone to the second microphone; wherein N is a natural number and is the length of the time-domain transfer function; M is a natural number smaller than N;

(46) and, a state decider 1005, for judging as the state unable to produce a howling when the time-domain judgment statistic is smaller than judgment threshold; and judging as the state able to produce a howling when the time-domain judgment statistic is larger than judgment threshold, wherein the judgment threshold varies with the structural change of the earphone and is obtained by statistics.

(47) Still taking the Hybrid ANR earphone as an example, the first microphone 901 is the REF MIC of the Hybrid ANR earphone, and the second microphone 902 is the ERR MIC of the Hybrid ANR earphone. First the transfer function from the REF MIC to the ERR MIC is calculated. The digital signal x.sub.Ref [n] of the REF MIC and the digital signal x.sub.Err [n] of the ERR MIC enter into the first data cache 1001 and the second data cache 1002 respectively, forming data frames {tilde over (x)}.sub.Ref [n] and {tilde over (x)}.sub.Err[n]:
{tilde over (x)}.sub.Ref[n]=(x.sub.Ref[n−L+1] . . . x.sub.Ref[n−1]x.sub.Ref[n])
{tilde over (x)}.sub.Err[n]=(x.sub.Err[n−L+1] . . . x.sub.Err[n−1]x.sub.Err[n])

(48) Wherein L is the data frame length.

(49) The data frames {tilde over (x)}.sub.Ref[n] and {tilde over (x)}.sub.Err [n] enter into the transfer function estimator 1003, calculating the transfer function h.sub.ref.sub._.sub.err [n] from the REF MIC to the ERR MIC. The compute mode of the transfer function can adopt the mode of dividing the auto-power spectrum by the cross-power spectrum: making {tilde over (X)}.sub.Ref [k] the frequency-domain form of {tilde over (x)}.sub.Ref [n]; {tilde over (X)}.sub.Err [k] the frequency-domain form of {tilde over (x)}.sub.Err [n]; H.sub.ref.sub._.sub.err [k] the frequency-domain form of the transfer function h.sub.ref.sub._.sub.err [n], thus the calculation formula is:

(50) $H_{{\mathrm{ref}}_{—}\mathrm{err}}\left[k\right]=\frac{E\left({\tilde{X}}_{\mathrm{Err}}^{*}\left[k\right]{\tilde{X}}_{\mathrm{Err}}\left[k\right]\right)}{E\left({\tilde{X}}_{\mathrm{Err}}^{*}\left[k\right]{\tilde{X}}_{\mathrm{Ref}}\left[k\right]\right)}$$h_{{\mathrm{ref}}_{—}\mathrm{err}}\left[n\right]=\mathrm{ifft}\left(H_{{\mathrm{ref}}_{—}\mathrm{err}}\left[k\right]\right)$

(51) wherein {tilde over (X)}*.sub.Err [k] is the conjugate of {tilde over (X)}.sub.Err [k]. E(.) represents requesting expectation operation, and ifft represents inverse Fourier transform.

(52) The time-domain judgment statistic r.sub.ref.sub._.sub.err calculated by the judgment statistic calculator 1004 is:

(53) $r_{{\mathrm{ref}}_{—}\mathrm{err}}=\frac{\underset{n=0}{\overset{M}{.Math.}}{\left(h_{{\mathrm{ref}}_{—}\mathrm{err}}\left[n\right]\right)}^2}{\underset{n=0}{\overset{N}{.Math.}}{\left(h_{{\mathrm{ref}}_{—}\mathrm{err}}\left[n\right]\right)}^2}$

(54) wherein, N is the length of the transfer function and is a natural number. That is, the time-domain judgment statistic r.sub.ref.sub._.sub.err is the ratio of the quadratic sum of the first M order of the transfer function to the quadratic sum of the whole transfer function. The time-domain judgment statistic r.sub.ref.sub._.sub.err reflects the time delay characteristic between REF MIC signals to ERR MIC signals, i.e. causality. The smaller the time delay, the larger the r.sub.ref.sub._.sub.err, the closer to the state of being able to produce howling. M is a natural number which is smaller than N. Generally, M is 1, 2 or 3. The judgment threshold varies with the structural change of the earphone and is obtained by statistics. The judgment statistic in Howling state is larger than that in noHowling state. If r.sub.ref.sub._.sub.err is larger than the threshold, judging as the state able to produce a howling, otherwise judging as the state unable to produce a howling.

(55) That is, the estimated value h.sub.ref.sub._.sub.err [n] of the transfer function obtained by the transfer function estimator 1003 enters into the judgment statistic calculator 1004, and the judgment statistic calculator 1004 calculates the time-domain judgment statistic r.sub.ref.sub._.sub.err. The time-domain judgment statistic r.sub.ref.sub._.sub.err enters into the state decider 1005 to judge the current state of the earphone (a state unable to produce howling or a state able to produce howling) and to output it. The state decider 1005 judges the state as a state unable to produce a howling when the time-domain judgment statistic is smaller than the judgment threshold, and judges the state as a state able to produce a howling when the time-domain judgment statistic is larger than the judgment threshold.

(56) In aforesaid embodiment, the state judger 903 judges the state of the ANR earphone according to the time-domain transfer function from the first microphone to the second microphone. In another embodiment of the invention, the state judger 903 also can judge the state of the ANR earphone according to the frequency-domain transfer function from the first microphone to the second microphone, specifically:

(57) a first data cache 1001, for caching digital signals collected by the first microphone 901;

(58) a second data cache 1002, for caching digital signals collected by the second microphone 902;

(59) a transfer function estimator 1003, for calculating the frequency-domain transfer function from the first microphone 901 to the second microphone 902 according to the data in the first data cache 1001 and the second data cache 1002;

(60) a judgment statistic calculator 1004, for obtaining a frequency-domain judgment statistic according to the ratio of modular quadratic sum of the first M orders to modular quadratic sum of the first M+1 to N/2 orders of the frequency-domain transfer function from the first microphone to the second microphone; wherein N is a natural number and N is the length of the frequency-domain transfer function; M is a natural number smaller than N/2;

(61) a state decider 1005, for judging as the state able to produce a howling when the frequency-domain judgment statistic is smaller than the judgment threshold; and judging as the state unable to produce a howling when the frequency-domain judgment statistic is larger than the judgment threshold, wherein the judgment threshold varies with the structural change of the earphone and is obtained by statistics.

(62) Still taking the Hybrid ANR earphone as an example, the first microphone 901 is the REF MIC of the Hybrid ANR earphone, and the second microphone 902 is the ERR MIC of the Hybrid ANR earphone. First the transfer function from the REF MIC to the ERR MIC is calculated. The digital signal x.sub.Ref [n] of the REF MIC and the digital signal x.sub.Err [n] of the ERR MIC enter into the first data cache 1001 and the second data cache 1002 respectively, forming data frames {tilde over (x)}.sub.Ref [n] and {tilde over (x)}.sub.Err [n]:
{tilde over (x)}.sub.Ref[n]=(x.sub.Ref[n−L+1] . . . x.sub.Ref[n−1]x.sub.Ref[n])
{tilde over (x)}.sub.Err(x.sub.Err[n−L+1] . . . x.sub.Err[n−1]x.sub.Err[n])

(63) Wherein L is the data frame length.

(64) The data frames {tilde over (x)}.sub.Ref [n] and {tilde over (x)}.sub.Err [n] enter into the transfer function estimator 1003, calculating the frequency-domain transfer function H.sub.ref.sub._.sub.err [k] of the REF MIC to the ERR MIC. The compute mode of the transfer function can adopt the mode of dividing auto-power spectrum by the cross-power spectrum: making {tilde over (X)}.sub.Ref [k] the frequency domain form of {tilde over (x)}.sub.Ref [n]; {tilde over (X)}.sub.Err [k] the frequency domain form of {tilde over (x)}.sub.Err[n]; H.sub.ref.sub._.sub.err [k] the frequency domain form of the transfer function h.sub.ref.sub._.sub.err [n], thus the calculation formula is:

(65) $H_{{\mathrm{ref}}_{—}\mathrm{err}}\left[k\right]=\frac{E\left({\tilde{X}}_{\mathrm{Err}}^{*}\left[k\right]{\tilde{X}}_{\mathrm{Err}}\left[k\right]\right)}{E\left({\tilde{X}}_{\mathrm{Err}}^{*}\left[k\right]{\tilde{X}}_{\mathrm{Ref}}\left[k\right]\right)}$

(66) wherein {tilde over (X)}*.sub.Err[k] is the conjugate of {tilde over (X)}.sub.Err [k]. E(.) represents requesting expectation operation.

(67) The frequency-domain judgment statistic R.sub.ref.sub._.sub.err calculated by the judgment statistic calculator 1004 is:

(68) $R_{{\mathrm{ref}}_{—}\mathrm{err}}=\frac{\underset{k=0}{\overset{M}{.Math.}}|H_{{\mathrm{ref}}_{—}\mathrm{err}}\left[k\right]{|}^2}{\underset{k=M+1}{\overset{N\text{/}2}{.Math.}}|H_{{\mathrm{ref}}_{—}\mathrm{err}}\left[k\right]{|}^2}$

(69) wherein, N is the length of the transfer function. That is, the frequency-domain judgment statistic R.sub.ref.sub._.sub.err is the ratio of the modular quadratic sum of the first M order of the frequency-domain transfer function to the modular quadratic sum of the M+1 to N/2 order of the frequency-domain transfer function. The judgment statistic reflects the low-pass filter property of the transfer function. The larger the R.sub.ref.sub._.sub.err, the better the low-pass filter property, the closer to the state of being unable to produce a howling. The judgment threshold varies with the structural change of the earphone and is obtained by statistics. If the judgment statistic R.sub.ref.sub._.sub.err is larger than the threshold, judging as the state unable to produce a howling, otherwise judging as the state able to produce a howling.

(70) The estimated value H.sub.ref.sub._.sub.err [k] of the transfer function obtained by the transfer function estimator 1003 enters into the judgment statistic calculator 1004, and the judgment statistic calculator 1004 calculates the frequency-domain judgment statistic R.sub.ref.sub._.sub.err. The frequency-domain judgment statistic R.sub.ref.sub._.sub.err enters into the state decider 1005 to judge the current state of the earphone.

(71) In an embodiment of the invention, when the current state of the earphone is noHowling, starting ANR; when the current state of the earphone is Howling, shutting down ANR, thus the howling suppression is achieved.

(72) In summary, the technical scheme of the present invention uses the relation between signals collected by the first microphone which is arranged in a position outside an auditory meatus when an ANR earphone is worn and the second microphone which is arranged in a position inside the auditory meatus when the ANR earphone is worn to judge whether the current state of the ANR earphone is a state unable to produce a howling or a state able to produce a howling, and starts processing to prevent howling production when the current state of the ANR earphone is a state able to produce a howling, which can judge whether or not the ANR earphone is in a state of being able to produce a howling and can perform a howling processing when judging that the ANR earphone is in a state of being able to produce a howling, thus howling production can be prevented when the ANR earphone is in a state of being able to produce a howling. And then it can achieve that the ANR earphone does not produce a howling all the time, and thus can avoid damaging device and reduce users' discomfort.

(73) The foregoing descriptions merely show preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall fall into the protection scope of the present invention.