Patent Publication Number: US-11043228-B2

Title: Multi-microphone signal processing apparatus, method, and program for wind noise suppression

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage Entry of PCT/JP2016/062021 filed on Apr. 14, 2016, which claims priority from Japanese Patent Application 2015-097716 filed on May 12, 2015, the contents of all of which are incorporated herein by reference, in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a signal processing apparatus, a signal processing method, and a signal processing program. 
     BACKGROUND ART 
     In the above technical field, patent literature 1 describes an apparatus formed by a bidirectional microphone having audio characteristics suitable for picking up wind noise and a nondirectional microphone suitable for picking up speech. 
     CITATION LIST 
     Patent Literature 
     Patent literature 1: Japanese Patent Laid-Open No. 2007-158516 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     In the apparatus described in the above patent literature, however, the nondirectional microphone is readily influenced by wind noise, and it is thus impossible to obtain a speech signal with sufficiently reduced wind noise. 
     The present invention enables to provide a technique of solving the above-described problem. 
     Solution to Problem 
     One aspect of the present invention provides a signal processing apparatus comprising:
         a main microphone that is provided so as to be readily influenced by movement of air outside the signal processing apparatus;   a sub microphone that is provided so as to be hardly influenced by movement of air outside the signal processing apparatus;   a determiner that determines, based on a strength of a main speech signal output from the main microphone, whether the main speech signal includes a predetermined amount of wind noise; and   a selector that receives the main speech signal and a sub speech signal output from the sub microphone, executes, if it is determined that the main speech signal includes the predetermined amount of wind noise, selection processing for outputting the sub speech signal, and executes, if it is determined that the main speech signal includes no predetermined amount of wind noise, selection processing for outputting the main speech signal.       

     Another aspect of the present invention provides a signal processing method of a signal processing apparatus including a main microphone that is provided so as to be readily influenced by movement of air outside the signal processing apparatus and a sub microphone that is provided so as to be hardly influenced by movement of air outside the signal processing apparatus, the method comprising:
         determining, based on a strength of a main speech signal output from the main microphone, whether the main speech signal includes a predetermined amount of wind noise; and   receiving the main speech signal and a sub speech signal output from the sub microphone, executing, if it is determined that the main speech signal includes the predetermined amount of wind noise, selection processing for outputting the sub speech signal, and executing, if it is determined that the main speech signal includes no predetermined amount of wind noise, selection processing for outputting the main speech signal.       

     Still other aspect of the present invention provides a signal processing program of a signal processing apparatus including a main microphone that is provided so as to be readily influenced by movement of air outside the signal processing apparatus and a sub microphone that is provided so as to be hardly influenced by movement of air outside the signal processing apparatus, the program for causing a computer apparatus to execute a method, comprising:
         determining, based on a strength of a main speech signal output from the main microphone, whether the main speech signal includes a predetermined amount of wind noise; and   receiving the main speech signal and a sub speech signal output from the sub microphone, executing, if it is determined that the main speech signal includes the predetermined amount of wind noise, selection processing for outputting the sub speech signal, and executing, if it is determined that the main speech signal includes no predetermined amount of wind noise, selection processing for outputting the main speech signal.       

     Advantageous Effects of Invention 
     According to this example embodiment, it is possible to obtain a speech signal with sufficiently reduced wind noise. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing the overall arrangement of a signal processing apparatus according to the first example embodiment of the present invention; 
         FIG. 2  is a view showing the outer appearance of a smartphone according to the second example embodiment of the present invention; 
         FIG. 3  is a block diagram showing the overall arrangement of a signal processing apparatus according to the second example embodiment of the present invention; 
         FIG. 4  is a block diagram showing the arrangements of a determiner and selector according to the second example embodiment of the present invention; 
         FIG. 5  is a block diagram showing the arrangement of a signal processing apparatus according to the third example embodiment of the present invention; 
         FIG. 6A  is a block diagram showing the arrangement of a signal processing apparatus according to the fourth example embodiment of the present invention; 
         FIG. 6B  is a view showing an example of a smoother in the signal processing apparatus according to the fourth example embodiment of the present invention; 
         FIG. 6C  is a view showing another example of the smoother in the signal processing apparatus according to the fourth example embodiment of the present invention; 
         FIG. 7  is a block diagram showing the arrangement of a signal processing apparatus according to the fifth example embodiment of the present invention; 
         FIG. 8  is a block diagram showing the arrangements of a wind noise determiner and speech signal selector according to the fifth example embodiment of the present invention; 
         FIG. 9  is a block diagram showing the arrangement of a signal processing apparatus according to the sixth example embodiment of the present invention; 
         FIG. 10  is a block diagram showing the arrangement of a signal processing apparatus according to the seventh example embodiment of the present invention; 
         FIG. 11  is a block diagram showing the arrangement of an automatic equalizer according to the seventh example embodiment of the present invention; 
         FIG. 12  is a block diagram showing the arrangement of an automatic equalizer according to the eighth example embodiment of the present invention; 
         FIG. 13  is a block diagram showing the arrangement of a signal processing apparatus according to the ninth example embodiment of the present invention; 
         FIG. 14  is a block diagram showing the arrangement of a signal processing apparatus according to the 10th example embodiment of the present invention; 
         FIG. 15  is a block diagram showing the arrangement of a signal processing apparatus according to the 11th example embodiment of the present invention; 
         FIG. 16  is a block diagram showing the arrangement of a signal processing apparatus according to the 12th example embodiment of the present invention; 
         FIG. 17  is a block diagram showing the arrangement of a signal processing apparatus according to the 13th example embodiment of the present invention; 
         FIG. 18  is a block diagram showing the arrangement of a signal processing apparatus according to the 14th example embodiment of the present invention; 
         FIG. 19  is a block diagram showing the arrangement of a signal processing apparatus according to the 15th example embodiment of the present invention; 
         FIG. 20  is a block diagram showing the arrangement of a signal processing apparatus according to the 16th example embodiment of the present invention; 
         FIG. 21  is a block diagram showing the arrangement of a signal processing apparatus according to the 17th example embodiment of the present invention; 
         FIG. 22A  is a view showing the outer appearance of a smartphone according to the 18th example embodiment of the present invention; 
         FIG. 22B  is a block diagram showing the arrangement of a signal processing apparatus according to the 18th example embodiment of the present invention; 
         FIG. 23  is a block diagram showing the arrangement of a signal processing apparatus according to the 19th example embodiment of the present invention; 
         FIG. 24  is a block diagram showing the arrangement of a signal processing apparatus according to the 20th example embodiment of the present invention; 
         FIG. 25  is a view showing the outer appearance of a multicopter including a signal processing apparatus according to the 21st example embodiment of the present invention; 
         FIG. 26  is a block diagram showing the arrangement of a signal processing apparatus according to the 21st example embodiment of the present invention; 
         FIG. 27  is a view showing the outer appearance of a smartphone according to the 22nd example embodiment of the present invention; 
         FIG. 28  is a view showing the outer appearance of a smartphone according to the 23rd example embodiment of the present invention; and 
         FIG. 29  is a view showing the outer appearance of a smartphone according to the 24th example embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Example embodiments of the present invention will now be described in detail with reference to the drawings. It should be noted that the relative arrangement of the components, the numerical expressions and numerical values set forth in these example embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. Note that “speech signal” in the following explanation indicates a direct electrical change that occurs in accordance with speech or another sound. The speech signal transmits speech or another sound and is not limited to speech. 
     First Example Embodiment 
     A signal processing apparatus  100  according to the first example embodiment of the present invention will be described with reference to the accompanying drawings.  FIG. 1  is a block diagram showing the overall arrangement of the signal processing apparatus  100 . As shown in  FIG. 1 , the signal processing apparatus  100  is an apparatus including a main microphone  102 , a sub microphone  103 , a determiner  104 , and a selector  105 . 
     The main microphone  102  is provided in the apparatus  100  so as to be readily influenced by movement of air outside the apparatus. 
     The sub microphone  103  is provided in the apparatus  100  so as to be hardly influenced by movement of air outside the apparatus. 
     Based on the strength of a main speech signal  106  output from the main microphone  102 , the determiner  104  determines whether the main speech signal  106  includes wind noise. 
     The selector  105  receives the main speech signal  106  and a sub speech signal  107  output from the sub microphone  103 . If it is determined that the main speech signal  106  includes a predetermined amount of wind noise, the selector  105  executes selection processing for outputting the sub speech signal  107 ; otherwise, the selector  105  executes selection processing for outputting the main speech signal  106 . 
     With the above arrangement, a speech signal  109  output from the selector  105  is a speech signal including no wind noise. 
     Second Example Embodiment 
     A smartphone  200  as the second example embodiment of a signal processing apparatus according to the present invention will be described with reference to  FIGS. 2 to 4 . 
     Referring to  FIG. 2 , the smartphone  200  includes a case  201 . A main microphone  202  is arranged close to an opening  211  formed in the case  201  so as to be readily influenced by air outside the case  201 . 
     A sub microphone  203  is arranged in the case  201  apart from the opening  211  formed in the case  201  so as to be hardly influenced by air outside the case  201 . The sensitivity of the sub microphone when there is no wind is desirably set to be almost equal to that of the main microphone. 
       FIG. 3  is a block diagram showing a signal processing apparatus provided in the smartphone  200 . As shown in  FIG. 3 , the smartphone  200  includes the main microphone  202 , the sub microphone  203 , a signal processor  301 , and a speech processor  302 . The main microphone  202  and the sub microphone  203  are microphones of the same type having the same characteristics. 
     The signal processor  301  includes a wind noise determiner  311  and a speech signal selector  313 . 
     The wind noise determiner  311  compares the strength of a main speech signal  310  output from the main microphone  202  with a predetermined threshold, and outputs a binary signal  312  to the speech signal selector  313 . 
     The speech signal selector  313  receives the main speech signal  310  output from the main microphone  202  and the sub speech signal  320  output from the sub microphone  203 . Furthermore, if it is determined based on the binary signal  312  that the strength of the main speech signal  310  is smaller than the predetermined threshold, the speech signal selector  313  determines that the main speech signal  310  includes no predetermined amount of wind noise, and outputs the main speech signal  310 . Alternatively, if the strength of the main speech signal  310  is equal to or larger than the threshold, the speech signal selector  313  determines that the main speech signal  310  includes the predetermined amount of wind noise, and outputs a sub speech signal  320 . 
     The speech processor  302  receives a speech signal with suppressed wind noise, and performs processing (for example, recording processing, recognition processing, or the like). 
     &lt;&lt;Arrangements of Wind Noise Determiner and Speech Signal Selector&gt;&gt; 
       FIG. 4  is a block diagram showing examples of the arrangements of the wind noise determiner  311  and speech signal selector  313 . As shown in  FIG. 4 , the wind noise determiner  311  includes a comparator  401 , and causes the comparator  401  to determine whether the strength of the main speech signal  310  is equal to or larger than a threshold  402  and output the binary signal  312 . As a result of the comparison, if the strength of the main speech signal  310  is equal to or larger than the threshold  402 , the comparator  401  outputs 0 as the binary signal  312 ; otherwise, the comparator  401  outputs 1 as the binary signal  312 . Note that the threshold  402  is set to a value which is larger by a predetermined amount than the maximum strength of the main speech signal  310  obtained when no predetermined amount of wind noise is input to the main microphone  202 . By performing comparison in the comparator  401 , when the predetermined amount of wind noise is input to the main microphone  202 , the comparator  401  outputs 0 as the binary signal  312 . 
     The speech signal selector  313  includes multipliers  411  and  412 , a subtracter  413 , and a combiner  414 . 
     The multiplier  411  outputs a speech signal  416  obtained by multiplying the main speech signal  310  by the value of the binary signal  312  as a constant. 
     The multiplier  412  outputs a speech signal  418  obtained by multiplying the sub speech signal  320  by, as a constant, a value  417  output from the subtracter  413 . 
     The subtracter  413  outputs the value  417  obtained by subtracting, from 1, the value output from the comparator  401 . 
     The combiner  414  outputs a speech signal  415  obtained by combining the speech signal  416  output from the multiplier  411  with the speech signal  418  output from the multiplier  412 . 
     With the above arrangement, if no wind blows against the main microphone  202 , the main speech signal  310  is output as the output signal  415  of the combiner  414 . If the predetermined amount of wind noise is mixed in the main speech signal  310  of the main microphone  202 , the sub speech signal  320  output from the sub microphone  203  against which no wind blows is output as the output signal of the combiner  414 . At this time, the sub speech signal  320  includes no predetermined amount of wind noise. 
     Therefore, the speech signal  415  output from the combiner  414  is a speech signal with sufficiently reduced wind noise. 
     As described above, when the speech processor  302  performs speech processing, it is possible to obtain a speech signal in which no predetermined amount of wind noise is mixed. That is, if a wind blows against the opening  211  and wind noise is mixed in the main speech signal  310 , the sub speech signal of the sub microphone  203  in which no wind noise is mixed is used. Thus, even if there is a wind, it is possible to always obtain a speech signal in which no predetermined amount of wind noise is mixed. 
     Third Example Embodiment 
     A signal processing apparatus according to the third example embodiment of the present invention will be described next with reference to  FIG. 5 .  FIG. 5  is a block diagram showing the arrangement of a signal processor  501  of the signal processing apparatus according to this example embodiment. The signal processor  501  according to this example embodiment is different from the signal processor according to the above-described second example embodiment in that a wind noise determiner  510  is provided instead of the wind noise determiner  311 . The remaining components and operations are the same as those in the second example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The wind noise determiner  510  includes a comparator  511 , a wind extraction low-pass filter  512 , and a volume calculator  513 . 
     The wind extraction low-pass filter  512  is a low-pass filter, and receives a main speech signal  310 , and extracts and outputs an electrical signal  515  in a frequency domain corresponding to the frequency of wind noise. That is, the wind extraction low-pass filter  512  passes the low frequency domain of the main speech signal. The volume calculator  513  calculates, based on the electrical signal  515  output from the wind extraction low-pass filter  512 , a volume input to a main microphone  202 , and outputs an electrical signal  516  corresponding to the volume. 
     The comparator  511  determines whether the strength of the signal  516  output from the volume calculator  513  is equal to or larger than a threshold  514 , and outputs a binary signal  312 . As a result of the comparison, if the strength of the signal  516  is equal to or larger than the threshold  514 , the comparator  511  outputs 0 as the binary signal  312 ; otherwise, the comparator  511  outputs 1 as the binary signal  312 . Note that the threshold  514  is set to a value larger by the predetermined amount than the maximum strength of the signal  516  obtained when no predetermined amount of wind noise is input to the main microphone  202 . By performing comparison in the comparator  511 , when the predetermined amount of wind noise is input to the main microphone  202 , the comparator  511  outputs 0 as the binary signal. 
     Consequently, if no wind blows against the main microphone  202 , a speech signal selector  313  outputs the main speech signal  310  as an output signal  415  of a combiner  414 . Alternatively, if the predetermined amount of wind noise is mixed in the main speech signal  310  of the main microphone  202 , the sub speech signal  320  output from the sub microphone  203  against which no wind blows is output as the output signal of the combiner  414 . At this time, the sub speech signal  320  includes no predetermined amount of wind noise. Therefore, the speech signal  415  output from the combiner  414  is a speech signal with sufficiently reduced wind noise. 
     Fourth Example Embodiment 
     A signal processing apparatus according to the fourth example embodiment of the present invention will be described next with reference to  FIGS. 6A to 6C .  FIG. 6A  is a block diagram showing the arrangement of a signal processor  601  of the signal processing apparatus according to this example embodiment. The signal processing apparatus according to this example embodiment is different from that according to the third example embodiment in that a speech signal selector  620  is provided instead of the speech signal selector  313 . The remaining components and operations are the same as those in the third example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The difference between the speech signal selectors  313  and  620  is that the speech signal selector  620  includes a smoother (Av)  623  in addition to the components of the speech signal selector  313 . 
     The smoother  623  supplies, to a multiplier  411  and a subtracter  413 , a signal  624  obtained by smoothing a binary signal  312  output from a comparator  511 . 
     By smoothing by the smoother  623 , the binary signal  312  that is instantaneously switched to 0 or 1 is transformed into the signal  624  that gradually changes for a predetermined time. 
     The multiplier  411  outputs a speech signal  416  obtained by multiplying a main speech signal  310  by the amplitude value of the electrical signal  624  as a constant. 
     A multiplier  412  outputs a speech signal  418  obtained by multiplying a sub speech signal  320  by, as a constant, a value  417  output from the subtracter  413 . 
     The subtracter  413  outputs the value 17 obtained by subtracting, from 1, the amplitude value of the signal  624  output from the smoother  623 . 
     A combiner  414  outputs a speech signal  415  obtained by combining the speech signal  416  output from the multiplier  411  with the speech signal  418  output from the multiplier  412 . 
     The circuit of a smoother  630  as an example of the smoother  623  will be described next with reference to  FIG. 6B . 
     The smoother  630  is a leakage integrator, and includes a multiplier  632 , an adder  633 , a delay unit  634 , and a multiplier  635 . The multiplier  632  multiplies, by a leakage coefficient α, a signal input from an input terminal  631 , and outputs the thus obtained signal. In this example, the leakage coefficient a is set to 0.01. 
     The adder  633  outputs a signal obtained by adding the output signal of the multiplier  635  to the output signal of the multiplier  632 . 
     The delay unit  634  receives a signal output from the adder  633 , delays the signal by a predetermined time, and then outputs the signal. 
     The multiplier  635  receives the output signal of the delay unit  634 , multiplies the signal by (1-α) as a leakage coefficient, and outputs the thus obtained signal. 
     With the above arrangement, a signal output from an output terminal  636 , that is, the output signal of the adder  633  is a signal obtained by gradually changing the signal input to the input terminal  631  for a predetermined time. 
     The circuit of a smoother  640  as another example of the smoother  623  will be described with reference to  FIG. 6C . Note that the smoother  640  shown in  FIG. 6C  is different from the smoother  630  shown in  FIG. 6B  in that a comparator  641  is additionally provided. The remaining same components are denoted by the same reference numerals, and a detailed description of the operations thereof will be omitted. 
     The comparator  641  compares the strength of an input signal to an input terminal  631  with that of an output signal from a delay unit  634 , and outputs a comparison result to multipliers  632  and  635  as a binary signal. 
     If the strength of the input signal to the input terminal  631  is equal to or larger than that of the output signal from the delay unit  634 , the comparator  641  outputs 0 as the binary signal; otherwise, the comparator  641  outputs 1 as the binary signal. 
     Each of the multipliers  632  and  635  operates when the binary signal input from the comparator  641  is 1, and stops its operation and is reset when the binary signal is 0. Unlike the multiplier  632  shown in  FIG. 6B , the number of inputs of the multiplier  632  shown in  FIG. 6C  increases, and thus the operation of the multiplier  632  is different. 
     With the above arrangement, if no predetermined amount of wind blows against a main microphone  202 , that is, if no predetermined amount of wind noise is mixed in the main speech signal  310 , the main speech signal  310  is output as the output signal  415  of the combiner  414 . Alternatively, if the predetermined amount of wind noise is mixed in the main speech signal  310 , the ratio of the main speech signal  310  in the speech signal  415  of the combiner  414  gradually decreases, and the ratio of the sub speech signal  320  gradually increases. Then, after a predetermined time, the sub speech signal  320  output from a sub microphone  203  against which no predetermined amount of wind blows is output as the output signal of the combiner  414 . At this time, the sub speech signal  320  includes no predetermined amount of wind noise. If the amount of wind noise mixed in the main speech signal  310  becomes smaller than the predetermined amount, the ratio of the main speech signal  310  in the output signal  415  of the combiner  414  gradually increases, and the ratio of the sub speech signal  320  gradually decreases. Thus, after the predetermined time, the main speech signal  310  output from the main microphone  202  is output as the output signal of the combiner  414 . At this time, the main speech signal  310  is a signal with sufficiently reduced wind noise. 
     Note that the time from when the predetermined amount of wind noise is mixed in the main speech signal  310  until the components of the speech signal  415  output from the combiner  414  are completely switched from the main speech signal  310  to the sub speech signal  320  is determined based on the time constant of the smoother  623 . 
     Consequently, the speech signal  415  output from the combiner  414  is a signal with sufficiently reduced wind noise. 
     Fifth Example Embodiment 
     A signal processing apparatus according to the fifth example embodiment of the present invention will be described next with reference to  FIG. 7 .  FIG. 7  is a block diagram showing the overall arrangement of a signal processing apparatus  700 . As shown in  FIG. 7 , the signal processing apparatus  700  includes a main microphone  202 , a sub microphone  203 , a signal processor  710 , and a speech processor  302 . The signal processing apparatus  700  according to this example embodiment is different from that according to the above-described third example embodiment in that the signal processor  701  is provided instead of the signal processor  501 . The remaining components and operations are the same as those in the third example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The signal processor  701  includes a wind noise determiner  711  and a speech signal selector  313 . 
     The wind noise determiner  711  compares the strength of a main speech signal  310  output from the main microphone  202  with that of a sub speech signal  320  output from the sub microphone  203 . The wind noise determiner  711  then outputs a binary signal  712  indicating whether the main speech signal  310  includes a predetermined amount of wind noise. The speech signal selector  313  receives this binary signal  712 . 
     &lt;&lt;Arrangement of Wind Noise Determiner&gt;&gt; 
       FIG. 8  is a block diagram showing examples of the arrangements of the wind noise determiner  711  and speech signal selector  313 . As shown in  FIG. 8 , the wind noise determiner  711  includes a comparator  811 , volume calculators  812  and  813 , and a multiplier  814 . 
     The volume calculator  812  calculates, based on the sub speech signal  320 , a volume input to the sub microphone  203 , and outputs an electrical signal  815  corresponding to this volume. 
     The volume calculator  813  calculates, based on the main speech signal  310 , a volume input to the main microphone  202 , and outputs an electrical signal  816  corresponding to this volume. 
     The multiplier  814  outputs a signal  818  obtained by multiplying the electrical signal  816  output from the volume calculator  813  by a predetermined constant  817 . 
     The comparator  811  receives the signal  815  output from the volume calculator  812  and the signal  818  output from the multiplier  814 , compares these signals, determines whether the strength of the signal  818  is equal to or larger than that of the signal  815 , and then outputs a binary signal  312 . As a result of the comparison, if the strength of the signal  818  is equal to or larger than that of the signal  815 , the comparator  811  outputs 0 as the binary signal  312 ; otherwise, the comparator  811  outputs 1 as the binary signal  312 . Note that the constant  817  set in the multiplier  814  is set to a value that makes the maximum strength of the signal  818 , obtained when no predetermined amount of wind noise is input to the main microphone  202 , smaller by a predetermined amount than the strength of the signal  815 . Thus, by performing comparison in the comparator  811 , when the predetermined amount of wind noise is input to the main microphone  202 , the comparator  811  outputs 0 as the binary signal  312 . 
     According to this example embodiment as well, it is possible to obtain the same effect as in the first to fourth example embodiments. A speech signal  415  output from a combiner  414  is a speech signal with sufficiently reduced wind noise. 
     Sixth Example Embodiment 
     The signal processor of a signal processing apparatus according to the sixth example embodiment of the present invention will be described next with reference to  FIG. 9 .  FIG. 9  is a block diagram showing the arrangement of a signal processor  910  of the signal processing apparatus according to this example embodiment. The signal processor according to this example embodiment is different from that according to the above-described fifth example embodiment in that a speech signal selector  620  described in the fourth example embodiment is provided instead of the speech signal selector  313 . The remaining components and operations are the same as those in the fifth example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     According to this example embodiment as well, it is possible to obtain the same effect as in the above-described fourth example embodiment. A speech signal  415  output from a combiner  414  is a signal with sufficiently reduced wind noise. 
     Seventh Example Embodiment 
     A signal processing apparatus according to the seventh example embodiment of the present invention will be described next with reference to  FIG. 10 .  FIG. 10  is a block diagram showing the arrangement of a signal processing apparatus  1000  according to this example embodiment. 
     The signal processing apparatus  1000  according to this example embodiment is different from that according to the above-described fifth example embodiment in that a signal processor  1010  including an automatic equalizer (AEQ)  1011  is provided. The remaining components and operations are the same as those in the fifth example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     In the signal processing apparatus  1000  according to this example embodiment, a main speech signal  310  is input to the automatic equalizer  1011 , a wind noise determiner  711 , and a speech signal selector  313 . A sub speech signal  320  is input to the automatic equalizer  1011 . 
     The automatic equalizer  1011  outputs a speech signal  1012  obtained by correcting the frequency characteristic of the sub speech signal  320  based on the main speech signal  310 . At this time, the automatic equalizer  1011  corrects the sub speech signal  320  so that the difference between the frequency characteristic of the main speech signal  310  and that of the sub speech signal  320  falls within a predetermined range. 
     The automatic equalizer  1011  corrects the sub speech signal  320  in this way. Thus, when wind noise is generated, the speech signal  1012  obtained by improving the quality of the sub speech signal  320  can be used instead of the main speech signal  310 . 
     &lt;&lt;Arrangement of Automatic Equalizer&gt;&gt; 
       FIG. 11  is a block diagram showing the arrangement of the automatic equalizer  1011 . As shown in  FIG. 11 , the automatic equalizer  1011  includes absolute value calculators  1021  and  1022 , a multiplier  1023 , a status determiner  1024 , and an equalizer coefficient updater  1025 . 
     The absolute value calculator  1021  receives the main speech signal  310 , and outputs an absolute value signal  1026  corresponding to the absolute value of the strength of the main speech signal  310 . 
     The absolute value calculator  1022  receives the sub speech signal  320 , and outputs an absolute value signal  1027  corresponding to the absolute value of the strength of the sub speech signal  320 . 
     The multiplier  1023  receives a correction coefficient signal  1038  output from the equalizer coefficient updater  1025 , and outputs a signal  1029  obtained by multiplying the sub speech signal  320  by a correction coefficient represented by the correction coefficient signal  1038 . 
     The status determiner  1024  receives the absolute value signals  1026  and  1027  and the signal  1029 , and outputs an update enable/disable signal  1028  based on these signals. That is, if it is determined using the absolute value signals  1026  and  1027  and the signal  1029  that no wind noise is mixed in the main speech signal  310 , the status determiner  1024  generates the update enable/disable signal  1028  representing that update is possible, and outputs the signal. 
     The equalizer coefficient updater  1025  includes smoothers (Avs)  1031  and  1032 , a divider (Div)  1033 , and a correction coefficient updater  1034 . 
     The smoother  1031  receives the absolute value signal  1026 , and outputs a smoothed signal  1035  obtained by smoothing the absolute value signal  1026  using, for example, leakage integration to estimate the envelope of this signal. 
     The smoother  1032  receives the absolute value signal  1027 , and outputs a smoothed signal  1036  obtained by smoothing the absolute value signal  1027  using, for example, leakage integration to estimate the envelope of this signal. 
     The divider  1033  calculates the ratio between the smoothed signals  1035  and  1036 , and outputs a value  1037  of the ratio. That is, the value  1037  of the ratio is output to determine how many times of the absolute value of the sub speech signal  320  is almost equal to the absolute value of the main speech signal. 
     The correction coefficient updater  1034  receives the value  1037  of the value and the update enable/disable signal  1028 . When update becomes possible, the correction coefficient updater  1034  updates the correction value represented by the correction coefficient signal  1038  to the value  1037  of the ratio. 
     Thus, the signal  1029  output from the automatic equalizer  1011  is a signal having a volume almost equal to that of the main speech signal  310 . 
     According to this example embodiment, if no predetermined amount of wind blows against the main microphone  202 , that is, if no predetermined amount of wind noise is mixed in the main speech signal  310 , the signal processor  1010  outputs the main speech signal  310 . Alternatively, if the predetermined amount of wind noise is mixed in the main speech signal  310 , the signal processor  1010  outputs the output signal  1029  of the automatic equalizer  1011 . Therefore, the speech signal output from the signal processor  1010  is a signal with sufficiently reduced wind noise. 
     Eighth Example Embodiment 
     A signal processing apparatus according to the eighth example embodiment of the present invention will be described next with reference to  FIG. 12 .  FIG. 12  is a block diagram showing the arrangement of an automatic equalizer  1200  of the signal processing apparatus according to this example embodiment. The signal processing apparatus according to this example embodiment is different from that according to the above-described seventh example embodiment in that an automatic equalizer  1200  is provided instead of the automatic equalizer  1011 . The remaining components and operations are the same as those in the seventh example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The automatic equalizer  1200  includes absolute value calculators  1021  and  1022 , a multiplier  1023 , and an equalizer coefficient updater  1210 . 
     The multiplier  1023  receives a correction coefficient signal  1217  output from the equalizer coefficient updater  1210 , and outputs a signal  1029  obtained by multiplying a sub speech signal  320  by a correction coefficient represented by the correction coefficient signal  1217 . 
     The equalizer coefficient updater  1210  includes smoothers (Avs)  1031  and  1032 , a divider (Div)  1033 , a limiter  1211 , a smoother  1212 , and a multiplier  1213 . The arrangement of the smoother  1212  is the same as that shown in  FIG. 6C . In contrast to  FIG. 6C , however, α that is difficult to increase and easy to decrease is set to prevent a smoothed signal  1216 , based on which the correction coefficient is obtained, from becoming too large. 
     The limiter  1211  receives a value  1037  of a ratio. If the value  1037  of the ratio is smaller than a predetermined upper limit value, the value  1037  of the ratio is output as an output value  1215 ; otherwise, the limiter  1211  outputs the upper limit value as the output value  1215 . 
     The smoother  1212  receives the output value  1215  from the limiter  1211 , and outputs the smoothed signal  1216  obtained by smoothing the output value  1215  using, for example, leakage integration to estimate the envelope of the change of the value. The arrangement of the smoother  1212  is the same as that shown in  FIG. 6C . In contrast to  FIG. 6C , however, α that is difficult to increase and easy to decrease is set to prevent the smoothed signal  1216 , based on which the correction coefficient is obtained, from becoming too large. 
     The multiplier  1213  receives the smoothed signal  1216 , generates a correction coefficient signal  1217  by multiplying the smoothed signal  1216  by a predetermined constant  1214  that has been preset, and outputs the generated signal. 
     According to this example embodiment as well, it is possible to obtain the same effect as in the seventh example embodiment. A speech signal output from a signal processor  1010  is a signal with sufficiently reduced wind noise. 
     Ninth Example Embodiment 
     A signal processing apparatus according to the ninth example embodiment of the present invention will be described next with reference to  FIG. 13 .  FIG. 13  is a block diagram showing the overall arrangement of a signal processing apparatus  1300 . The signal processing apparatus  1300  according to this example embodiment is different from that according to the above-described seventh example embodiment in that a signal processor  1310  formed by arranging two noise suppressors  1311  and  1312  in the signal processor  1010  is provided. The remaining components and operations are the same as those in the seventh example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The noise suppressor  1311  receives a main speech signal  310 , generates a speech signal  1313  by suppressing the noise component of the main speech signal  310 , and outputs the generated signal. 
     The noise suppressor  1312  receives a signal  1029 , generates a speech signal  1314  by suppressing the noise component of the signal  1029 , and outputs the generated signal. 
     According to this example embodiment, noise in the main speech signal  310  and that in the output signal  1029  of an automatic equalizer  1011  are suppressed, thereby further reducing the noise components. Therefore, according to this example embodiment as well, it is possible to obtain the same effect as in the seventh example embodiment. A speech signal output from the signal processor  1310  is a speech signal with sufficiently reduced wind noise. 
     Note that even if the noise suppressor  1312  is arranged at the preceding stage of the automatic equalizer  1011 , it is possible to obtain the same effect. 
     10th Example Embodiment 
     A signal processing apparatus according to the 10th example embodiment of the present invention will be described next with reference to  FIG. 14 .  FIG. 14  is a block diagram showing the overall arrangement of a signal processing apparatus  1400 . The signal processing apparatus  1400  according to this example embodiment is provided in a smartphone, as in the second example embodiment. The same components as in the second example embodiment are denoted by the same reference numerals, and a description thereof will be omitted. This example embodiment is different from the second example embodiment in that a signal processor  1401  is provided instead of the signal processor  301 . 
     As shown in  FIG. 14 , the signal processor  1401  includes Fourier transformers (FFTs: Fast Fourier Transform)  1410  and  1420 , a frequency domain amplitude processor  1430 , and an inverse Fourier transformer (inverse FFT)  1440 . 
     The Fourier transformer  1410  receives a main speech signal  310 , and outputs a signal  1411  obtained by Fourier-transforming the main speech signal  310 . 
     The Fourier transformer  1420  receives a sub speech signal  320 , and outputs a signal  1421  obtained by Fourier-transforming the sub speech signal  320 . 
     When a speech signal is Fourier-transformed by the Fourier transformer  1410  or  1420 , as described above, the speech signal is divided into a plurality of frequency components having predetermined amplitudes. 
     The inverse Fourier transformer (inverse FFT)  1440  receives a signal  1434  output from the frequency domain amplitude processor  1430 , generates a signal  1441  by inversely Fourier-transforming the signal  1434 , and outputs the generated signal. 
     The frequency domain amplitude processor  1430  includes a wind noise determiner  1431  and a speech signal selector  1432 . 
     The wind noise determiner  1431  receives the Fourier-transformed signal  1411 , and compares the amplitude value of the signal with a predetermined threshold for each of the predetermined number of divided frequency domains. Furthermore, the wind noise determiner  1431  determines, if the amplitude value is equal to or larger than the threshold, that wind noise is mixed in the signal in the frequency domain, and outputs a signal  1433  representing a determination result for each frequency domain. 
     The speech signal selector  1432  receives the Fourier-transformed signals  1411  and  1412  and the signal  1433 . Based on the determination result represented by the signal  1433 , the speech signal selector  1432  selects one of the Fourier-transformed signals  1411  and  1421  for each of the predetermined number of divided frequency domains. After that, the speech signal selector  1432  generates the signal  1434  combined with the selected signal, and outputs the generated signal. 
     According to this example embodiment, for each of the predetermined number of divided frequency domains, the presence/absence of a predetermined amount of wind noise is determined to select a signal in which no predetermined amount of wind noise is mixed. Thus, the speech signal  1441  output from the inverse Fourier transformer  1440  is a speech signal with sufficiently reduced wind noise. 
     11th Example Embodiment 
     A signal processing apparatus according to the 11th example embodiment of the present invention will be described next with reference to  FIG. 15 .  FIG. 15  is a block diagram showing the overall arrangement of a signal processing apparatus  1500 . The signal processing apparatus  1500  according to this example embodiment is different from that according to the above-described 10th example embodiment in that a frequency domain amplitude processor  1530  including a wind noise determiner  1531  instead of the wind noise determiner  1431  of the frequency domain amplitude processor  1430  is provided. The remaining components and operations are the same as those in the 10th example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The frequency domain amplitude processor  1530  includes the wind noise determiner  1531  and a speech signal selector  1432 . 
     The wind noise determiner  1531  receives Fourier-transformed signals  1411  and  1421 . Furthermore, the wind noise determiner  1531  multiplies, by a preset constant, the amplitude value of the signal  1421  obtained by Fourier-transforming a sub speech signal  320 , thereby generating a signal having an amplitude value slightly smaller than an amplitude value obtained when no predetermined amount of wind noise is mixed in a main speech signal  310 . In addition, the wind noise determiner  1531  compares, for each frequency domain, the amplitude of the signal generated from the signal  1421  with that of the signal  1411  to determine for each frequency domain whether wind noise is mixed in the signal  1411 , and outputs a signal  1433  representing a determination result for each frequency domain. The wind noise determiner  1531  may perform common or cooperative processing with another frequency instead of performing processing for each frequency. 
     The speech signal selector  1432  receives the Fourier-transformed signal  1411 , a Fourier-transformed signal  1421 , and the signal  1433 . Based on the determination result represented by the signal  1433 , the speech signal selector  1432  selects one of the Fourier-transformed signals  1411  and  1421  for each of the predetermined number of divided frequency domains. After that, the speech signal selector  1432  generates a signal  1434  combined with the selected signal, and outputs the generated signal. 
     According to this example embodiment, for each frequency domain, the presence/absence of wind noise is determined to select the signal in which no wind noise is mixed. Thus, a speech signal  1441  output from an inverse Fourier transformer  1440  is a speech signal with sufficiently reduced wind noise. 
     12th Example Embodiment 
     A signal processing apparatus according to the 12th example embodiment of the present invention will be described with reference to  FIG. 16 .  FIG. 16  is a block diagram showing the overall arrangement of a signal processing apparatus  1600 . The signal processing apparatus  1600  according to this example embodiment is different from that according to the above-described 11th example embodiment in that a signal processor  1601  including a frequency domain amplitude processor  1630  with an automatic equalizer (AEQ)  1631  is provided. The remaining components and operations are the same as those in the 11th example embodiment. 
     Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The automatic equalizer  1631  receives a signal  1411  obtained by Fourier-transforming a main speech signal  310  and a signal  1421  obtained by Fourier-transforming a sub speech signal  320 . Furthermore, for each frequency domain, the automatic equalizer  1631  outputs a signal  1632  obtained by correcting the frequency characteristic of the signal  1421  based on the signal  1411 . The automatic equalizer  1011  described with reference to  FIG. 13  corrects the volume. To the contrary, the automatic equalizer  1631  corrects a volume for each frequency, which means that the frequency characteristic is corrected. 
     A wind noise determiner  1531  receives the signal  1411  obtained by Fourier-transforming the main speech signal  310  and the signal  1632  obtained by Fourier-transforming the sub speech signal  320 . Furthermore, the wind noise determiner  1531  multiplies the amplitude value of the signal  1632  by a preset constant, thereby generating a signal having an amplitude value slightly smaller than an amplitude value obtained when no predetermined amount of wind noise is mixed in the main speech signal  310 . In addition, the wind noise determiner  1531  compares, for each frequency domain, the amplitude of the signal generated from the signal  1632  with that of the signal  1411 . Then, the wind noise determiner  1531  determines, for each frequency domain, whether the predetermined amount of wind noise is mixed in the signal  1411 , and outputs a signal  1433  representing a determination result for each frequency domain. 
     A speech signal selector  1432  receives the signals  1411  and  1632  and the signal  1433 , and selects, for each frequency domain, based on the determination result represented by the signal  1433 , one of the signals  1411  and  1632 , in which no predetermined amount of wind noise is mixed. The speech signal selector  1432  generates a signal  1434  combined with the selected signal, and outputs the generated signal. 
     According to this example embodiment, for each frequency domain, the presence/absence of wind noise is determined to select the signal in which no predetermined amount of wind noise is mixed. Thus, a speech signal  1441  output from an inverse Fourier transformer  1440  is a speech signal with sufficiently reduced wind noise. 
     13th Example Embodiment 
     A signal processing apparatus according to the 13th example embodiment of the present invention will be described next with reference to  FIG. 17 .  FIG. 17  is a block diagram showing the overall arrangement of a signal processing apparatus  1700 . The signal processing apparatus  1700  according to this example embodiment is different from that according to the 12th example embodiment in that a frequency domain amplitude processor  1730  including noise suppressors  1740  and  1750  is provided. The remaining components and operations are the same as those in the 12th example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The noise suppressor  1740  receives a signal  1411  obtained by Fourier-transforming a main speech signal  310 , generates a signal  1741  by suppressing the noise component of the signal  1411  for each frequency domain, and outputs the generated signal. 
     The noise suppressor  1750  receives an output signal  1632  from an automatic equalizer  1631 , generates a signal  1751  by suppressing the noise component of the signal  1632  for each frequency domain, and outputs the generated signal. 
     A wind noise determiner  1731  receives the output signal  1741  of the noise suppressor  1740  and the output signal  1751  of the noise suppressor  1750 . Furthermore, the wind noise determiner  1731  multiplies the amplitude value of the signal  1751  by a preset constant, thereby generating a signal having an amplitude value slightly smaller than an amplitude value obtained when no predetermined amount of wind noise is mixed in the main speech signal  310 . In addition, the wind noise determiner  1731  compares, for each frequency domain, the amplitude of the signal generated from the signal  1751  with that of the signal  1741  to determine for each frequency domain whether wind noise is mixed in the signal  1741 , and outputs a signal  1732  representing a determination result for each frequency domain. 
     A speech signal selector  1432  receives the signals  1741  and  1751  and the signal  1732 , and selects, for each frequency domain, based on the determination result represented by the signal  1732 , one of the signals  1741  and  1751 , in which no predetermined amount of wind noise is mixed. The speech signal selector  1432  generates the signal  1434  combined with the selected signal, and outputs the generated signal. 
     According to this example embodiment, for each frequency domain, the presence/absence of wind noise is determined to select the signal in which no wind noise is mixed. Thus, a speech signal  1441  output from an inverse Fourier transformer  1440  is a speech signal with sufficiently reduced wind noise. 
     14th Example Embodiment 
     A signal processing apparatus according to the 14th example embodiment of the present invention will be described next with reference to  FIG. 18 .  FIG. 18  is a block diagram showing the overall arrangement of a signal processing apparatus  1800 . The signal processing apparatus  1800  according to this example embodiment is different from that according to the above-described 13th example embodiment in that the locations of noise suppressors and an automatic equalizer (AEQ) are reversed. 
     That is, a frequency domain amplitude processor  1802  of the signal processing apparatus  1800  includes a wind noise determiner  1731 , a speech signal selector  1432 , noise suppressors  1740  and  1850 , and an automatic equalizer (AEQ)  1861 . The remaining components and operations are the same as those in the 13th example embodiment. Hence, the same reference numerals denote the same components and operations, and a detailed description thereof will be omitted. 
     The noise suppressor  1850  receives a signal  1421  obtained by Fourier-transforming a sub speech signal  320 , generates a signal  1851  by suppressing the noise component of the signal  1421  for each frequency domain, and outputs the generated signal. 
     The automatic equalizer  1861  receives a signal  1741  and the signal  1851 , and outputs, for each frequency domain, a signal  1862  obtained by correcting the frequency characteristic of the signal  1851  based on the signal  1741 . 
     The wind noise determiner  1731  receives the output signal  1741  of the noise suppressor  1740  and an output signal  1862  of the automatic equalizer  1861 . Furthermore, the wind noise determiner  1731  multiplies the amplitude value of the signal  1862  by a preset constant, and generates a signal having an amplitude value slightly smaller than an amplitude value obtained when no predetermined amount of wind noise is mixed in a main speech signal  310 . In addition, for each frequency domain, the wind noise determiner  1731  compares the amplitude of the signal generated from the signal  1862  with that of the signal  1741 . Then, the wind noise determiner  1731  determines, for each frequency domain, whether the predetermined amount of wind noise is mixed in the signal  1741 , and outputs a signal  1732  representing a determination result for each frequency domain. 
     The speech signal selector  1432  receives the signals  1741  and  1862  and the signal  1732 , and selects, for each frequency domain, based on the determination result represented by the signal  1732 , one of the signals  1741  and  1862 , in which no predetermined amount of wind noise is mixed. The speech signal selector  1432  generates a signal  1434  combined with the selected signal, and outputs the generated signal. 
     According to this example embodiment, for each frequency domain, the presence/absence of wind noise is determined to select the signal in which no wind noise is mixed. Thus, a speech signal  1441  output from an inverse Fourier transformer  1440  is a speech signal with sufficiently reduced wind noise. 
     15th Example Embodiment 
     A signal processing apparatus according to the 15th example embodiment of the present invention will be described next with reference to  FIG. 19 .  FIG. 19  is a block diagram showing the overall arrangement of a signal processing apparatus  1900 . The signal processing apparatus  1900  according to this example embodiment is different from that according to the 14th example embodiment in that a frequency domain amplitude processor  1910  including an inverse Fourier transformer (inverse FFT) is provided at the preceding stage of a speech signal selector. That is, the frequency domain amplitude processor  1910  includes an automatic equalizer (AEQ)  1631 , inverse Fourier transformers  1911  and  1912 , a wind noise determiner  1913 , and a speech signal selector  1914 . Components and their operations denoted by the same reference numerals as in the 14th example embodiment are the same as those in the 14th example embodiment, and a detailed description thereof will be omitted. 
     The inverse Fourier transformer  1911  receives a signal  1411  Fourier-transformed by a Fourier transformer  1410 , and outputs a signal  1915  obtained by inversely Fourier-transforming the signal  1411 . 
     The inverse Fourier transformer  1912  receives an output signal  1632  from the automatic equalizer  1631 , and outputs a signal  1916  obtained by Fourier-transforming the signal  1632 . 
     The wind noise determiner  1913  receives the output signal  1915  of the inverse Fourier transformer  1911  and the output signal  1916  of the inverse Fourier transformer  1912 . Furthermore, the wind noise determiner  1913  multiplies the amplitude value of the signal  1916  by a preset constant, thereby generating a signal having an amplitude value slightly smaller than an amplitude value obtained when no predetermined amount of wind noise is mixed in a main speech signal  310 . In addition, for each frequency domain, the wind noise determiner  1913  compares the amplitude of the signal generated from the signal  1916  with that of the signal  1915 . Then, the wind noise determiner  1913  determines, for each frequency domain, whether the predetermined amount of wind noise is mixed in the signal  1915 , and outputs a signal  1917  representing a determination result for each frequency domain. 
     The speech signal selector  1914  receives the signals  1915  and  1916  and the signal  1917 , and selects, for each frequency domain, based on the determination result represented by the signal  1917 , one of the signals  1915  and  1916 , in which no predetermined amount of wind noise is mixed. The speech signal selector  1914  generates a signal  1918  combined with the selected signal, and outputs the generated signal. 
     According to this example embodiment, for each frequency domain, the presence/absence of wind noise is determined to select the signal in which no wind noise is mixed. Thus, the speech signal  1918  output from the speech signal selector  1914  is a speech signal with sufficiently reduced wind noise. 
     16th Example Embodiment 
     A signal processing apparatus according to the 16th example embodiment of the present invention will be described next with reference to  FIG. 20 .  FIG. 20  is a block diagram showing the overall arrangement of a signal processing apparatus  2000 . The signal processing apparatus  2000  according to this example embodiment is different from that according to the above-described 15th example embodiment in that noise suppressors are provided at the preceding stage of inverse Fourier transformers. 
     That is, a frequency domain amplitude processor  2010  includes an automatic equalizer  1631 , noise suppressors  2011  and  2012 , inverse Fourier transformers (inverse FFTs)  2013  and  2014 , a wind noise determiner  2015 , and a speech signal selector  2016 . Components and their operations denoted by the same reference numerals as in the 15th example embodiment are the same as those in the 15th example embodiment, and a detailed description thereof will be omitted. 
     The noise suppressor  2011  receives a signal  1441 , generates a signal  2021  by suppressing the noise component of the signal  1441  for each predetermined frequency domain, and outputs the generated signal. 
     The noise suppressor  2012  receives a signal  1632 , generates a signal  2022  by suppressing the noise components of the signal  1632  for each frequency domain, and outputs the generated signal. 
     The inverse Fourier transformer  2013  receives the signal  2021 , and outputs a signal  2023  obtained by inversely Fourier-transforming the signal  2021 . 
     The inverse Fourier transformer  2014  receives the signal  2022 , and outputs a signal  2024  obtained by inversely Fourier-transforming the signal  2022 . 
     The wind noise determiner  2015  receives the output signal  2023  of the inverse Fourier transformer  2013  and the output signal  2024  of the inverse Fourier transformer  2014 . Furthermore, the wind noise determiner  2015  multiplies the amplitude value of the signal  2022  by a preset constant, thereby generating a signal having an amplitude value slightly smaller than an amplitude value obtained when no predetermined amount of wind noise is mixed in a main speech signal  310 . In addition, for each frequency domain, the wind noise determiner  2015  compares the amplitude of the signal generated from the signal  2024  with that of the signal  2023 . Then, the wind noise determiner  2015  determines, for each frequency domain, whether the predetermined amount of wind noise is mixed in the signal  2023 , and outputs a signal  2025  representing a determination result for each frequency domain. 
     The speech signal selector  2016  receives the signals  2023  and  2024  and the signal  2025 , and selects, for each frequency domain, based on the determination result represented by the signal  2025 , one of the signals  2023  and  2024 , in which no predetermined amount of wind noise is mixed. The speech signal selector  2016  generates a signal  2026  combined with the selected signal, and outputs the generated signal. 
     According to this example embodiment, the speech signal  2026  output from the speech signal selector  2016  is a speech signal with sufficiently reduced wind noise. 
     17th Example Embodiment 
     A signal processing apparatus according to the 17th example embodiment of the present invention will be described next with reference to  FIG. 21 .  FIG. 21  is a block diagram showing the overall arrangement of a signal processing apparatus  2100 . The signal processing apparatus  2100  according to this example embodiment is different from that according to the above-described 16th example embodiment in that noise suppressors are provided at the preceding stage of an automatic equalizer. 
     That is, a frequency domain amplitude processor  2110  includes noise suppressors  2111  and  2112 , an automatic equalizer (AEQ)  2113 , inverse Fourier transformers (inverse FFTs)  2114  and  2115 , a wind noise determiner  2116 , and a speech signal selector  2117 . Components and their operations denoted by the same reference numerals as in the 16th example embodiment are the same as those in the 16th example embodiment, and a detailed description thereof will be omitted. 
     The noise suppressor  2111  receives a signal  1441 , generates a signal  2121  by suppressing the noise component of the signal  1441  for each predetermined frequency domain, and outputs the generated signal. 
     The noise suppressor  2112  receives a signal  1421 , generates a signal  2122  by suppressing the noise component of the signal  1421  for each frequency domain, and outputs the generated signal. 
     The automatic equalizer  2113  receives the signals  2121  and  2122 , and outputs, for each frequency domain, a signal  2123  obtained by correcting the frequency characteristic of the signal  2122  based on the signal  2121 . 
     The inverse Fourier transformer  2114  receives the signal  2121 , and outputs a signal  2124  obtained by inversely Fourier-transforming the signal  2121 . 
     The inverse Fourier transformer  2115  receives the signal  2123 , and outputs a signal  2125  obtained by inversely Fourier-transforming the signal  2123 . 
     The wind noise determiner  2116  receives the output signal  2124  of the inverse Fourier transformer  2114  and the output signal  2125  of the inverse Fourier transformer  2115 . Furthermore, the wind noise determiner  2116  multiplies the amplitude value of the signal  2125  by a preset constant, thereby generating a signal having an amplitude value slightly smaller than an amplitude value obtained when no predetermined amount of wind noise is mixed in a main speech signal  310 . In addition, the wind noise determiner  2116  compares the amplitude of the signal generated from the signal  2125  with that of the signal  2124 . Then, the wind noise determiner  2116  determines whether the predetermined amount of wind noise is mixed in the signal  2124 , and outputs a signal  2126  representing a determination result. 
     The speech signal selector  2117  receives the signals  2124  and  2125  and the signal  2126 , and selects, based on the determination result represented by the signal  2126 , one of the signals  2124  and  2125 , in which no predetermined amount of wind noise is mixed. The speech signal selector  2117  outputs the selected signal as a speech signal  2127 . 
     According to this example embodiment as well, the speech signal  2127  output from the speech signal selector  2117  is a speech signal with sufficiently reduced wind noise. 
     18th Example Embodiment 
     The 18th example embodiment of the present invention will be described next with reference to  FIGS. 22A and 22B .  FIG. 22A  is a view showing the outer appearance of a smartphone  2200  to which a signal processing apparatus according to this example embodiment is applied. In  FIGS. 22A and 22B , the same reference numerals as in the above-described example embodiments denote the same components and a description thereof will be omitted. 
     Referring to  FIG. 22A , the smartphone  2200  includes a case  2210 , and a main microphone  2221  is arranged close to an opening  2211  formed in the front surface of the case  2210 . In addition, two sub microphones  2222  and  2223  are arranged inside the two side surfaces of the case  2210  apart from the opening  2211 , respectively. 
     The signal processing apparatus according to this example embodiment will be described with reference to  FIG. 22B .  FIG. 22B  shows the overall arrangement of the smartphone  2200  as one of signal processing apparatuses. As shown in  FIG. 22B , the smartphone  2200  includes the main microphone  2221 , the sub microphones  2222  and  2223 , and a signal processor  2240 . 
     The main microphone  2221  is a high-quality microphone that is arranged close to the opening  2211  formed in the case of the smartphone  2200 , picks up a sound outside the apparatus via the opening  2211 , and outputs a speech signal  2224 . 
     The sub microphones  2222  and  2223  are arranged in the smartphone  2200 , pick up a pickup target sound outside the apparatus via the case, and output speech signals  2225  and  2226 , respectively. 
     A wind noise determiner  2241  compares the strength of the speech signal  2224  output from the main microphone  2221  with a predetermined threshold, and outputs a binary signal  2243  to a speech signal selector  2242 . The threshold is set to a signal strength slightly higher than that obtained when no predetermined amount of wind noise is mixed in the speech signal  2224  output from the main microphone  2221 . Thus, it can be determined based on the binary signal  2243  whether the speech signal  2224  includes the predetermined amount of wind noise. 
     The speech signal selector  2242  receives the output signals  2224  to  2226  from the microphones  2221  to  2223 , respectively. Furthermore, if it is determined based on the binary signal  2243  that the speech signal  2224  includes no predetermined amount of wind noise, the speech signal selector  2242  outputs the speech signal  2224  to a speech processor  302  as an output signal  2245 . 
     If it is determined based on the binary signal  2243  that the speech signal  2224  includes the predetermined amount of wind noise, the speech signal selector  2242  selects the signal having an intermediate signal amplitude from the signals  2224  to  2226 , and sets the selected signal as the output signal  2245 . 
     According to this example embodiment, even if the three microphones  2221  to  2223  are used, it is possible to obtain a speech signal with sufficiently reduced wind noise. 
     19th Example Embodiment 
     A signal processing apparatus according to the 19th example embodiment of the present invention will be described next with reference to  FIG. 23 . In  FIG. 23 , the same reference numerals as in the above-described 18th example embodiment denote the same components and a description thereof will be omitted. This example embodiment is different from the above-described 18th example embodiment in that Fourier transformers  2311  to  2313 , a frequency domain amplitude processor  2314 , and an inverse Fourier transformer  2315  are provided. 
     The Fourier transformers  2311  to  2313  receive speech signals  2224  to  2226 , and output signals  2316  to  2318  obtained by Fourier-transforming the speech signals  2224  to  2226 , respectively. 
     As described above, when the Fourier transformers  2311  to  2313  Fourier-transform the speech signals, each of the speech signals is divided into a plurality of frequency components having predetermined amplitudes. 
     Noise suppressors  2321  to  2323  receive the signals  2316  to  2318 , generate signals  2326  to  2328  by suppressing the noise components of these signals for each frequency domain, and output the generated signals, respectively. 
     For each predetermined frequency domain, a wind noise determiner  2324  compares the strength of the signal  2326  with a predetermined threshold, and outputs a binary signal  2329  to a speech signal selector  2325 . In this case, the threshold is set to a signal strength slightly higher than that obtained when no predetermined amount of wind noise is mixed in the speech signal  2224  output from the main microphone  2221 . Thus, based on the binary signal  2329 , it can be determined whether the speech signal  2224  includes the predetermined amount of wind noise. 
     The speech signal selector  2325  receives the output signals  2326  to  2328  from the noise suppressors  2321  to  2323 , respectively. Furthermore, if it is determined based on the binary signal  2329  that the speech signal  2224  includes no predetermined amount of wind noise, the speech signal selector  2325  outputs the speech signal  2224  to a speech processor  302  as an output signal  2330 . 
     If it is determined based on the binary signal  2329  that the speech signal  2224  includes the predetermined amount of wind noise, the speech signal selector  2325  selects a signal having an intermediate signal amplitude from the signals  2326  to  2328 , and sets the selected signal as the output signal  2330 . 
     The inverse Fourier transformer  2315  receives the signal  2330  output from the speech signal selector  2325 , generates a signal  2319  by inversely Fourier-transforming the signal, and outputs the generated signal to the speech processor  302 . 
     According to this example embodiment as well, the speech signal  2319  output from the inverse Fourier transformer  2315  is a speech signal with sufficiently reduced wind noise. 
     20th Example Embodiment 
     A signal processing apparatus according to the 20th example embodiment of the present invention will be described next with reference to  FIG. 24 .  FIG. 24  shows the overall arrangement of a signal processing apparatus  2400 . The signal processing apparatus  2400  according to this example embodiment is different from that according the above-described 19th example embodiment in that two automatic equalizers are provided. 
     That is, a frequency domain amplitude processor  2420  includes automatic equalizers (AEQs)  2421  and  2422 , noise suppressors  2321  to  2323 , a wind noise determiner  2324 , and a speech signal selector  2325 . Components and their operations denoted by the same reference numerals as in the 19th example embodiment are the same as those in the 19th example embodiment, and a detailed description thereof will be omitted. 
     The automatic equalizer  2421  receives signals  2316  and  2317 , and outputs, for each of a predetermined number of divided frequency domains, a signal  2423  obtained by correcting the frequency characteristic of the signal  2317  based on the signal  2316 . 
     The automatic equalizer  2422  receives the signal  2316  and a signal  2318 , and outputs, for each frequency domain, a signal  2424  obtained by correcting the frequency characteristic of the signal  2318  based on the signal  2316 . 
     The noise suppressors  2321  to  2323  receive the signals  2316 ,  2423 , and  2424 , generate signals  2326  to  2328  by suppressing the noise components of these signals for each frequency domain, and outputs the generated signals, respectively. 
     The wind noise determiner  2324  compares the strength of the signal  2326  with a predetermined threshold for each predetermined frequency domain, and outputs a binary signal  2329  to the speech signal selector  2325 . In this example, the threshold is set to a signal strength slightly higher than that obtained when no predetermined amount of wind noise is mixed in a speech signal  2224  output from a main microphone  2221 . Thus, it can be determined based on the binary signal  2329  whether the speech signal  2224  includes the predetermined amount of wind noise. 
     The speech signal selector  2325  receives the output signals  2326  to  2328  from the noise suppressors  2321  to  2323 , respectively. Furthermore, if it is determined based on the binary signal  2329  that the speech signal  2224  includes no predetermined amount of wind noise, the speech signal selector  2325  outputs the speech signal  2224  to an inverse Fourier transformer  2315  as an output signal  2330 . 
     If it is determined based on the binary signal  2329  that the main speech signal  2224  includes the predetermined amount of wind noise, the speech signal selector  2325  selects the signal having an intermediate signal amplitude from the signals  2326  to  2328 , and sets the selected signal as the output signal  2330 . 
     According to this example embodiment, a speech signal  2319  supplied to a speech processor  302  is a speech signal with sufficiently reduced wind noise. 
     21st Example Embodiment 
     A multicopter incorporating a signal processing apparatus according to the 21st example embodiment of the present invention will be described next with reference to  FIGS. 25 and 26 .  FIG. 25  is a view for explaining the signal processing apparatus and the outer appearance of the multicopter incorporating a communication apparatus to which the signal processing apparatus according to this example embodiment is applied.  FIG. 26  is a block diagram showing the signal processing apparatus according to this example embodiment. 
     Referring to  FIG. 25 , a multicopter  2500  includes a known multicopter main body  2510  and a communication apparatus  2520  attached to the lower portion of the multicopter main body. 
     The communication apparatus  2520  includes a case  2521  having a cubic shape, an opening  2522  is formed in the bottom surface of the case  2521 , and a main microphone  2531  is arranged close to the opening  2522 . Furthermore, sub microphones  2532  to  2535  are respectively arranged inside the four side surfaces of the case  2521 . With this arrangement, the main microphone  2531  picks up a sound outside the case via the opening  2522 , and each of the sub microphones  2532  to  2535  picks up a sound outside the case via the case. 
     In addition, the communication apparatus  2520  generates speech by sufficiently reducing a predetermined amount of wind noise of the sound picked up by each of the microphones  2531  to  2535 , and transmits the generated speech as a radio wave signal to the outside of the apparatus. 
     As shown in  FIG. 26 , the signal processing apparatus  2520  according to this example embodiment includes the microphones  2531  to  2535 , Fourier transformers  2541  to  2545 , a frequency domain amplitude processor  2560 , and an inverse Fourier transformer  2591 . 
     The Fourier transformers (FFTs)  2541  to  2545  receive speech signals  2536  to  2540 , and output signals  2546  to  2550  obtained by Fourier-transforming the speech signals, respectively. 
     When the Fourier transformers  2541  to  2545  Fourier-transform the speech signals, each of the speech signals is divided into a plurality of frequency components having predetermined amplitudes. 
     An automatic equalizer  2561  receives the signals  2546  and  2547 , and outputs, for each of a predetermined number of divided frequency domains, a signal  2566  obtained by correcting the frequency characteristic of the signal  2546  based on the signal  2547 . Note that if it can be determined that correction is unnecessary, no correction needs to be performed or the automatic equalizer  2561  may be omitted. 
     An automatic equalizer  2562  receives the signals  2547  and  2548 , and outputs, for each frequency domain, a signal  2567  obtained by correcting the frequency characteristic of the signal  2547  based on the signal  2548 . 
     An automatic equalizer  2563  receives the signals  2548  and  2549 , and outputs, for each frequency domain, a signal  2568  obtained by correcting the frequency characteristic of the signal  2548  based on the signal  2549 . 
     An automatic equalizer  2564  receives the signals  2549  and  2550 , and outputs, for each frequency domain, a signal  2569  obtained by correcting the frequency characteristic of the signal  2549  based on the signal  2550 . 
     An automatic equalizer  2565  receives the signals  2546  and  2550 , and outputs, for each frequency domain, a signal  2570  obtained by correcting the frequency characteristic of the signal  2550  based on the signal  2546 . 
     Noise suppressors  2571  to  2575  receive the signals  2566  to  2570 , generate signals  2576  to  2580  by suppressing the noise components of the signals for each frequency domain, and output the generated signals, respectively. 
     For each predetermined frequency domain, a wind noise determiner  2581  compares the strength of the signal  2576  with a predetermined threshold, and outputs a binary signal  2583  to a speech signal selector  2582 . In this case, the threshold is set to a signal strength slightly higher than that obtained when no predetermined amount of wind noise is mixed in the speech signal  2536  output from the main microphone  2531 . Thus, based on the binary signal  2583 , it can be determined whether the speech signal  2536  includes the predetermined amount of wind noise. 
     The speech signal selector  2582  receives the binary signal  2583  and the output signals  2576  to  2580  respectively from the noise suppressors  2571  to  2575 . Furthermore, if it is determined based on the binary signal  2583  that the speech signal  2536  includes no predetermined amount of wind noise, the speech signal selector  2582  outputs the signal  2576  to an inverse Fourier transformer  2591  as an output signal  2584 . 
     If it is determined based on the binary signal  2583  that the speech signal  2536  includes the predetermined amount of wind noise, the speech signal selector  2582  selects a signal having an intermediate signal amplitude from the signals  2577  to  2580 , and sets the selected signal as the output signal  2584 . 
     The inverse Fourier transformer  2591  receives the output signal  2584  output from the speech signal selector  2582 , generates a signal  2592  by inversely Fourier-transforming the signal, and outputs the generated signal to a speech processor  302 . 
     According to this example embodiment, the wind noise components in the speech signals  2536  to  2540  corresponding to the respective microphones  2531  to  2535  are reduced by selecting signals whose frequency characteristics fall within a predetermined range. Furthermore, noise is suppressed while correcting the amplitude for each of the predetermined number of divided frequency domains. If the main speech signal includes the predetermined amount of wind noise, signals having intermediate signal amplitudes are selected and combined. With this processing, the speech signal  2592  output from the inverse Fourier transformer  2591  is a speech signal with sufficiently reduced wind noise. 
     22nd Example Embodiment 
     The 22nd example embodiment of the present invention will be described next with reference to  FIG. 27 .  FIG. 27  is a view showing the outer appearance of a smartphone  2700  to which the signal processing apparatus according to each of the above-described example embodiments is applied. In  FIG. 27 , the same reference numerals as those in the above-described example embodiments denote the same components and a description thereof will be omitted. 
     Referring to  FIG. 27 , the smartphone  2700  includes a case  2710 , and a main microphone  202  and a sub microphone  203  for speech communication are provided in the case  2710 . Furthermore, two openings  2711  and  2712  are formed at a predetermined interval in the case  2710 . The main microphone  202  is arranged close to the opening  2711 , and the sub microphone  203  is arranged close to the opening  2712 . 
     The opening  2712  is closed by a windshield  2713  such as rubber. Note that the direction of the opening  2712  closed by the windshield  2713  may be different from that of the opening  2711 . 
     When picking up speech by the main microphone  202  at the time of speech communication or speech recording, the smartphone  2700  to which the signal processing apparatus according to each of the above-described example embodiments is applied, as described above, can obtain a speech signal in which no predetermined amount of wind noise is mixed. That is, if a wind blows against the opening  2711  and the predetermined amount of wind noise is mixed in a main speech signal, a sub speech signal of the sub microphone  203  in which no predetermined amount of wind noise is mixed is used. Thus, even if there is a wind, it is possible to always obtain a speech signal with sufficiently reduced wind noise. 
     23rd Example Embodiment 
     The 23rd example embodiment of the present invention will be described next with reference to  FIG. 28 .  FIG. 28  is a view showing the outer appearance of a smartphone  2800  to which the signal processing apparatus according to each of the above-described example embodiments is applied. In  FIG. 28 , the same reference numerals as those in the above-described example embodiments denote the same components and a description thereof will be omitted. 
     Referring to  FIG. 28 , the smartphone  2800  includes a case  2810 , and a main microphone  202  and a sub microphone  203  for speech communication are provided in the case  2810 . Furthermore, an opening  2811  is formed in the front surface of the case  2810 . The main microphone  202  is arranged close to the opening  2811 , and the sub microphone  203  is arranged inside a side surface of the case  2810  apart from the opening  2811 . 
     If the sub microphone  203  is arranged inside the side surface of the case  2810  in this way, even if a wind blows against the front surface of the case  2810 , no wind blows against the side surface of the case  2810 . Therefore, if a wind blows against the opening  2811  and a predetermined amount of wind noise is mixed in a main speech signal, a sub speech signal of the sub microphone  203  in which no predetermined amount of wind noise is mixed is used. Thus, even if there is a wind, it is possible to always obtain a speech signal with sufficiently reduced wind noise. 
     24th Example Embodiment 
     The 24th example embodiment of the present invention will be described next with reference to  FIG. 29 .  FIG. 29  is a view showing the outer appearance of a smartphone  2900  to which the signal processing apparatus according to each of the above-described example embodiments is applied. In  FIG. 29 , the same reference numerals as those in the above-described example embodiments denote the same components and a description thereof will be omitted. 
     Referring to  FIG. 29 , the smartphone  2900  includes a case  2910 , and a main microphone  202  for speech communication is arranged close to an opening  2911  formed in the front surface of the case  2910 . Furthermore, the main microphone  202  picks up a sound outside the case  2910  via the opening  2911 . 
     In addition, a sub microphone  203  formed from a bone conduction microphone is provided in the case  2910 . 
     When picking up speech by the main microphone  202  at the time of speech communication or speech recording, the smartphone  2900  to which the signal processing apparatus according to each of the above-described example embodiments is applied, as described above, can obtain a speech signal in which no predetermined amount of wind noise is mixed. 
     Other Example Embodiments 
     While the invention has been particularly shown and described with reference to example embodiments thereof, the invention is not limited to these example embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims. For example, an opening facing a microphone may be closed by a film of a predetermined thickness, thereby implementing sealing so as to pick up a sound. Those skilled in this art can readily understand that the components related to the speech signal processing according to the present invention can be implemented using only hardware, only software, or both hardware and software. 
     The present invention is applicable to a system including a plurality of devices or a single apparatus. The present invention is also applicable even when an information processing program for implementing the functions of example embodiments is supplied to the system or apparatus directly or from a remote site. Hence, the present invention also incorporates the program installed in a computer to implement the functions of the present invention by the computer, a medium storing the program, and a WWW (World Wide Web) server that causes a user to download the program. Especially, the present invention incorporates at least a non-transitory computer readable medium storing a program that causes a computer to execute processing steps included in the above-described example embodiments.