Patent Publication Number: US-8995686-B2

Title: Sound volume control device, sound volume control method, and sound volume control program

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority under 35 U.S.C. §119 to Japanese Patent Applications No. 2011-046120 filed on Mar. 3, 2011, the entire contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sound volume control device and a sound volume control method for collecting and amplifying an acoustic signal such as a hearing aid and a sound collector. 
     2. Description of the Related Art 
     For a hearing-impaired person, not only it is difficult to hear small sound but also a comfortably-acceptable sound level is limited. Moreover, there is a case in which, after the sound has reached an audible level, the sound is felt to be annoying comparatively soon as the sound volume is further increased. It has been known that hearing impairment showing such a recruitment phenomenon exists. Accordingly, in an device which inputs sound simply collected by a microphone into an amplifier and increases sound volume to an audible level by increasing volume of the amplifier to provide the amplified sound for hearing using an earphone, there arises a problem depending on the kind of hearing impairment that the sound volume becomes excessive when the sound volume has changed in a sound source. 
     Therefore, an auditory supplement device for a hearing-impaired person such as a hearing aid needs to have amplification characteristics set to fit an individual&#39;s auditory property, and this is one of reasons why adjustment is difficult and requires fitting by a specialist or the like. 
     Accordingly, there have been proposed conventionally an acoustic characteristic checking device (refer to Patent document 1 “Japanese Patent Application Laid-Open Publication No. S62-125800”, for example) such as an order-made type hearing aid in which the acoustic characteristics of the order-made type hearing aid are fitted with the auditory property of a hearing-impaired person when the hearing-impaired person purchases the order-made type hearing aid, and a hearing aid adjustment device or a hearing aid (refer to Patent document 2 “Japanese Patent Application Laid-Open Publication No. 2001-204098, for example) which is configured to provide a sound quality suitable for an individual user thereof by asking the subject to hear audibility data in a range from a minimum audible value to an uncomfortable threshold value. 
     However, since each of the sound volume control devices of Patent documents 1 and 2 is configured to ask the user to actually hear test audibility data, there is a problem that burden on a user of the subject is heavy. 
     Further, the subject feels difference between component ratios of frequency components included in the audibility data used for the measurement and those included in sound felt to be annoying in actual life. Accordingly, there is also a problem that, only by the measurement using test equipment which provides limited test sound, it is difficult to specify acceptable maximum sound volume for each frequency band and it cannot be expected to obtain a good result. 
     Further, when the excessive sound volume is avoided by means of compressing a dynamic range across the whole frequency band, sometimes target sound is buried in noise and the sound becomes difficult to hear and poor in expression. 
     SUMMARY OF THE INVENTION 
     The present invention, for solving the above problem, aims at providing a sound volume control device and a sound volume control method which can adjust a maximum output sound level in a band in which a user feels in actual life that sound is excessive, without asking the user to hear test audibility data. 
     In order to resolve the above problem, a sound volume control device of the present invention comprises: a sound input section that converts input sound into a sound signal; a band dividing section that carries out band-division with respect to the sound signal; an excessive output notification section that outputs excessive output notification information according to user&#39; s operation; a correction band decision section that calculates audible signal distribution information of the user when the excessive output notification information is not output and excessive signal distribution information of the user when the excessive output notification information is output, for each band in the sound signal subject to the band-division in the band dividing section, and decides a correction band according to the calculated audible signal distribution information and excessive signal distribution information, and a sound output control section that controls sound volume of sound signal for the correction band decided by the correction band decision section to provide output sound, among bands in the sound signal subject to the band-division in the band dividing section. 
     The correction band decision section may include: an audible signal distribution information calculating section that calculates a signal level value for a frame when the excessive output notification information is not output and calculates the audible signal distribution information showing occurrence frequency distribution of frames having the same signal level value within a predetermined measurement time, for each band in the sound signal subject to the band-division in the band dividing section; an audible signal distribution information storing section that stores the audible signal distribution information calculated by the audible signal distribution information calculating section; an excessive signal distribution information calculating section that calculates a signal level value for a frame when the excessive output notification information is output and calculates the excessive signal distribution information showing occurrence frequency distribution of frames having the same signal level value within a predetermined measurement time, for each band in the sound signal subject to the band-division in the band dividing section; an excessive signal distribution information storing section that stores the excessive signal distribution information calculated by the excessive signal distribution information calculating section, and a frequency comparison correction band decision section that compares the occurrence frequency in the audible signal distribution information stored in the audible signal distribution information storing section and the occurrence frequency in the excessive signal distribution information stored in the excessive signal distribution information storing section, for each band in the sound signal subject to the band-division in the band dividing section, and decides, as a correction band, a band in which the occurrence frequency in the excessive signal distribution information is larger than the occurrence frequency in the audible signal distribution information. 
     The audible signal distribution information storing section and the excessive signal distribution information storing section may delete the stored audible signal distribution information and the stored excessive signal distribution information sequentially from older information, respectively. 
     The frequency comparison correction band decision section may compare the occurrence frequency in the audible signal distribution information and the occurrence frequency in the excessive signal distribution information in the vicinity of a predetermined maximum audible sound volume level for each band in the sound signal subject to the band-division in the band dividing section, and decide, as the correction band, the band in which the occurrence frequency in the excessive signal distribution information is larger than the occurrence frequency in the audible signal distribution information. 
     The sound output control section may control sound volume by reducing apart exceeding the predetermined maximum audible sound volume level in the correction band decided by the correction band decision section down to an audible sound volume level according to a predetermined limiter curve and outputs the sound volume, and set the predetermined maximum audible sound volume level to be lower every time receiving the excessive output notification from the excessive output notification section. 
     The sound output control section may control sound volume by multiplying by a predetermined compression rate a part exceeding the predetermined maximum audible sound volume level in the correction band decided by the correction band decision section to compress a dynamic range and outputs the sound volume, and set a compression rate of the dynamic range to be larger every time receiving the excessive output notification from the excessive output notification section. 
     In order to resolve the above problem, a sound volume control device of the present invention comprises: a sound input section that converts input sound into a sound signal; a fast Fourier transform section that carries out fast-Fourier transform with respect to the sound signal and outputs Fourier coefficients; an excessive output notification section that outputs excessive output notification information according to user&#39;s operation; a correction band decision section that calculates audible signal distribution information of the user when the excessive output notification information is not output and excessive signal distribution information of the user when the excessive output notification information is output, using the Fourier coefficients from the fast Fourier transform section, and decides a correction band according to the calculated audible signal distribution information and excessive signal distribution information; and a sound output control section that controls sound volume of sound signal for a Fourier coefficient corresponding to the correction band decided by the correction band decision section to provide output sound, among the Fourier coefficients in the sound signal from the fast Fourier transform section. 
     In order to resolve the above problem, a sound volume control method of the present invention comprises the steps of: converting input sound into a sound signal; carrying out band-division with respect to the sound signal; determining whether or not excessive output notification information is output by user&#39;s operation; calculating a signal level value for a frame when the excessive output notification information is not output and calculating audible signal distribution information showing occurrence frequency distribution of frames having the same signal level value within a predetermined measurement time, for each band in the sound signal; calculating a signal level value for a frame when the excessive output notification information is output and calculating excessive signal distribution information showing occurrence frequency distribution of frames having the same signal level value within a predetermined measurement time, for each band in the sound signal; comparing the audible signal distribution information and the excessive signal distribution information for each band in the sound signal and deciding a correction band according to the comparison result; and controlling sound volume of sound signal for the correction band to provide output sound. 
     In order to resolve the above problem, a sound volume control program of the present invention causing a computer to execute the steps of: converting input sound into a sound signal; carrying out band-division with respect to the sound signal; determining whether or not excessive output notification information is output by user&#39;s operation; calculating a signal level value for a frame when the excessive output notification information is not output and calculating audible signal distribution information showing occurrence frequency distribution of frames having the same signal level value within a predetermined measurement time, for each band in the sound signal; calculating a signal level value for a frame when the excessive output notification information is output and calculating excessive signal distribution information showing occurrence frequency distribution of the frames having the same signal level value within a predetermined measurement time, for each band in the sound signal; comparing the audible signal distribution information and the excessive signal distribution information for each band in the sound signal and deciding a correction band according to the comparison result; and controlling sound volume of sound signal for the correction band to provide output sound. 
     According to the sound volume control device and the sound volume control method of the present invention, it is possible to adjust a maximum output level of sound in a band in which a user feels in actual life that sound is excessive, without asking the user to hear test audibility data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration example of a sound volume control device according to a first embodiment of the present invention. 
         FIG. 2  is a flowchart showing an operation example of each constituent included in the sound volume control device according to the first embodiment of the present invention. 
         FIG. 3  is a diagram showing a comparison example between audible signal distribution information and excessive signal distribution information in a frequency comparison correction band decision section according to the first embodiment of the present invention. 
         FIG. 4  is a diagram showing a change example of a gain characteristic (amplification characteristic) which changes when a maximum audible level is reduced by a dynamic range compressing section in a sound output control section according to the first embodiment of the present invention. 
         FIG. 5  is a diagram showing another change example of a gain characteristic (amplification characteristic) which changes when a maximum audible level is reduced by the dynamic range compressing section in the sound output control section according to the first embodiment of the present invention. 
         FIG. 6  is a block diagram showing a configuration example of a sound volume control device according to a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Sound volume control devices according to first and second embodiments of the present invention will be described below. Note that a hearing aid, a sound collector or the like to be used by a hearing-impaired person will be described as an example of the sound volume control devices according to the first and second embodiments of the present invention. 
     (First Embodiment) 
     First, a sound volume control device according to the first embodiment of the present invention will be described. 
     In  FIG. 1 , the sound volume control device  1  includes a sound input section  11 , a band dividing section  12 , an excessive output notification section  13 , a correction band decision section  14  and a sound output control section  15 . 
     The sound input section  11  converts input sound into a sound signal S 1  and outputs the sound signal S 1  to the band dividing section  12 . The band dividing section  12  divides the sound signal S 1  for each predetermined frequency band (carries out band-division with respect to the sound signal S 1 ) and outputs it as a band-divided sound signal S 2 . 
     The excessive output notification section  13  outputs excessive output notification information S 3  to the correction band decision section  14  in response to button operation or the like by a user when the user who uses the sound volume control device  1  determines that output sound actually input to a user&#39;s ear via the sound volume control device  1  is excessive. The correction band decision section  14  calculates audible signal distribution information S 4  of the user to be described below when the excessive output notification information S 3  is not output from the excessive output notification section  13 , and excessive signal distribution information S 5  of the user to be described below when the excessive output notification information S 3  is output from the excessive output notification section  13 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 , and decides a correction band according to the calculated audible signal distribution information S 4  and excessive signal distribution information S 5 . 
     Here, the correction band decision section  14  includes an audible signal distribution information calculating section  141 , an audible signal distribution information storing section  142 , an excessive signal distribution information calculating section  143 , an excessive signal distribution information storing section  144  and a frequency comparison correction band decision section  145 . 
     The audible signal distribution information calculating section  141  calculates a signal level value which is power in a predetermined unit time (that is, power for a frame which includes successive sound data subject to the band-division) when the excessive output notification information S 3  is not output from the excessive output notification section  13 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 . For example, the power is calculated by integrating spectrum power for each band in the band-divided sound signal S 2  in the predetermined unit time. Then, the audible signal distribution information calculating section  141  calculates the audible signal distribution information S 4  showing occurrence frequency distribution of frames having the same signal level value within a predetermined measurement time and stores the calculation result into the audible signal distribution information storing section  142 . Here, the audible signal distribution information calculating section  141  counts the number of frames having the same signal level value within the predetermined measurement time in calculating the audible signal distribution information S 4  when the excessive output notification information S 3  is not output, and normalizes the count value by a predetermined parameter to provide an occurrence frequency. The predetermined parameter corresponds, when the audible signal distribution information storing section  142  deletes the audible signal distribution information S 4  sequentially from older information after a predetermined time has elapsed, to a value obtained by dividing a time width of this predetermined time by a frame time width, for example. 
     The audible signal distribution information storing section  142  stores the audible signal distribution information S 4  calculated by the audible signal distribution information calculating section  141 . Here, the audible signal distribution information storing section  142  is configured to avoid too much influence of the old audible signal distribution information S 4  when use environment has changed, by deleting audible signal distribution information S 4  sequentially from older information after the predetermined time has elapsed. Note that the audible signal distribution information storing section  142  may not delete the audible signal distribution information S 4  sequentially from older information after the predetermined time has elapsed, but instead be configured to reduce the influence of the old audible signal distribution information S 4  by utilizing a weighted average or the like. 
     The excessive signal distribution information calculating section  143  calculates a signal level value which is power in a predetermined unit time (that is, power for a frame which includes successive sound data subject to the band-division) when the excessive output notification information S 3  is output from the excessive output notification section  13 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 . For example, the power is calculated by integrating spectrum power for each band in the band-divided sound signal S 2  in the predetermined unit time. Then, the excessive signal distribution information calculating section  142  calculates the excessive signal distribution information S 5  showing occurrence frequency distribution of frames having the same signal level value in a predetermined measurement time, and stores the calculation result into the excessive signal distribution information storing section  144 . Here, the excessive signal distribution information calculating section  143  counts the number of frames having the same signal level value in a predetermined measurement time in calculating the excessive signal distribution information S 5  when the excessive output notification information S 3  is output, and normalizes the count value by a predetermined parameter to provide an occurrence frequency. The predetermined parameter corresponds, when the excessive signal distribution information storing section  144  deletes the excessive signal distribution information S 5  sequentially from older information after a predetermined time has elapsed, to a value obtained by dividing a time width of this predetermined time by a frame time width, for example. 
     The excessive signal distribution information storing section  144  stores the excessive signal distribution information S 5  calculated by the excessive signal distribution information calculating section  143 . Here, the excessive signal distribution information storing section  144 , as with the audible signal distribution information storing section  142 , is configured to avoid too much influence of the old excessive signal distribution information S 5  when use environment has changed, by deleting excessive signal distribution information S 5  sequentially from older information after the predetermined time has elapsed. Note that the excessive signal distribution information storing section  144 , as with the audible signal distribution information storing section  142 , may not delete the excessive signal distribution information  5  sequentially from older information after the predetermined time has elapsed, but instead be configured to reduce the influence of the old excessive signal distribution information S 5  by utilizing a weighted average or the like. 
     The frequency comparison correction band decision section  145  compares the occurrence frequency in the audible signal distribution information S 4  stored in the audible signal distribution information storing section  142  and the occurrence frequency in the excessive signal distribution information S 5  stored in the excessive signal distribution information storing section  144 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 . Then, the frequency comparison correction band decision section  145  decides as the correction band a band in the band-divided sound signal S 2  in which the occurrence frequency in the excessive signal distribution information S 5  is larger than the occurrence frequency in the audible signal distribution information S 4 , and outputs it to the sound output control section  15  as correction band information S 6 . This will be specifically described below with reference to  FIG. 3 . 
     Further, the sound output control section  15  controls sound volume only for the correction band to provide output sound, among bands in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 , according to the correction band information S 6  from the correction band decision section  14 . Here, the sound output control section  15  includes a dynamic range compressing section  151 , a signal synthesizing section  152  and a sound output section  153 . 
     Next, the operation of the sound volume control device  1  configured as above will be described with reference to the flowchart of  FIG. 2 . 
     First, at a moment such as the turn-on of a power source which is not shown in the drawing, the sound volume control device  1  starts to operate and then, when sound is input from the outside into the sound volume control device  1  such as a hearing aid or a sound collector, the sound input section  11  converts the input sound into the sound signal S 1  and outputs the sound signal S 1  to the band dividing section  12  (Step  200 ). 
     The band dividing section  12  divides the sound signal S 1  for each predetermined frequency band, and outputs it to the correction band decision section  14  and the sound output control section  15  as the band-divided sound signal S 2  (Step  210 ). Here, the correction band decision section  14  is connected with the excessive output notification section  13  as shown in  FIG. 1 . The excessive output notification section  13  outputs the excessive output notification information S 3  to the correction band decision section  14  when a user who uses the sound volume control device  1  such as a hearing aid or a sound collector feels that excessive output is output from the sound volume control device  1  and operates a button or the like. 
     The correction band decision section  14  determines whether or not the excessive output notification information S 3  output from the excessive output notification section  13  is input into the correction band decision section  14  (Step  220 ). Here, when the excessive output notification information S 3  is not output from the excessive output notification section  13  and the excessive output notification information S 3  is not input into the correction band decision section  14  (“No” in Step  220 ), the audible signal distribution information calculating section  141  in the correction band decision section  14  calculates the audible signal distribution information S 4  when the excessive output notification information S 3  is not output from the excessive output notification section  13 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12  (Step  230 ), and stores the calculated audible signal distribution information S 4  into the audible signal distribution information storing section  142 . Specifically, the audible signal distribution information calculating section  141  calculates a signal level value for a frame in the predetermined unit time (e.g., 1 milli-second) when the excessive output notification information S 3  is not output from the excessive output notification section  13 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 . The audible signal distribution information calculating section  141  then counts the number of frames having the same signal level value in the predetermined measurement time (e.g., within several seconds to several tens of seconds). The audible signal distribution information calculating section  141  normalizes the count value by the predetermined parameter and calculates the audible signal distribution information S 4  as the occurrence frequency of the audible signal. The audible signal distribution information S 4  shows occurrence frequency distribution of the audible signal with respect to a horizontal axis of a signal level value and a vertical axis of an occurrence frequency as shown in  FIG. 3  to be described below. 
     On the other side, when the excessive output notification information S 3  is output from the excessive output notification section  13  according to the user&#39;s operation and input into the correction band decision section (“YES” in Step  220 ), the excessive signal distribution information calculating section  143  in the correction band decision section  14  calculates the excessive signal distribution information S 5  of the user when the excessive output notification information S 3  is output from the excessive output notification section  13 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12  (Step  240 ), and stores the excessive signal distribution information S 5  into the excessive signal distribution information storing section  144 . Specifically, the excessive signal distribution information calculating section  143 , as with the audible signal distribution information calculating section  141 , calculates a signal level value for a frame in the predetermined unit time (e.g., 1 milli-second) when the excessive output notification information S 3  is output from the excessive output notification section  13 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 . The excessive signal distribution information calculating section  143  then counts the number of frames having the same signal level value in the predetermined measurement time (e.g., within several seconds to several tens of seconds). The excessive signal distribution information calculating section  143  normalizes the count value by the predetermined parameter and calculates the excessive signal distribution information S 5  as the occurrence frequency of the excessive signal. The excessive signal distribution information S 5  shows occurrence frequency distribution of the excessive signal with respect to a horizontal axis of a signal level value and a vertical axis of an occurrence frequency as shown in  FIG. 3  to be described below. 
     Next, in the correction band decision section  14 , the frequency comparison correction band decision section  145  compares the occurrence frequency in the the audible signal distribution information S 4  stored in the the audible signal distribution information storing section  142  and the occurrence frequency in the excessive signal distribution information S 5  stored in the excessive signal distribution information storing section  144 , for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 , and decides the correction band according to the comparison result (Step  250 ). Here, the frequency comparison correction band decision section  145  outputs the correction band decided in this manner to the sound output control section  15  as the correction band information S 6 . 
     In  FIG. 3 , the audible signal distribution information S 4  and the excessive signal distribution information S 5  are shown with respect to a horizontal axis of a signal level and a horizontal axis of an occurrence frequency. 
     As described above, for the audible signal distribution information S 4  and the excessive signal distribution information S 5 , each of the audible signal distribution information calculating section  141  and the excessive signal distribution information calculating section  143  calculates a signal level value for a frame in the band-divided sound signal S 2  for each band in the band-divided sound signal S 2  in the predetermined unit time (e.g., 1 milli-second). Then, each of the audible signal distribution information calculating section  141  and the excessive signal distribution information calculating section  143  counts the number of frames having the same signal level value in the predetermined measurement time (e.g., within several seconds to several tens of seconds) and normalizes the count value by the predetermined parameter. The audible signal distribution information S 4  and the excessive signal distribution information S 5  show occurrence frequency distribution information sets of an audible signal and an excessive signal, respectively, with respect to a horizontal axis of a normalized signal level value and a vertical axis of a normalized occurrence frequency. 
     Here, in the present embodiment, the frequency comparison correction band decision section  145  compares, as shown in  FIG. 3 , the audible signal distribution information S 4  and the excessive signal distribution information S 5  in the vicinity of a predetermined maximum audible level 1 according to the user, for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 . The frequency comparison correction band decision section  145  decides as the correction band a band in the band-divided sound signal S 2  in which the occurrence frequency of excessive signal distribution information S 5  is larger than the occurrence frequency of audible signal distribution information S 4  in the vicinity of the predetermined maximum audible level 1. 
     Next, when the correction band information S 6  is output from the frequency comparison correction band decision section  145  in the correction band decision section  14  to the sound output control section  15 , the dynamic range compressing section  151  in the sound output control section  15  first performs change processing with respect to the dynamic range gain characteristic (amplification characteristic) as shown in  FIGS. 4 and 5  to be described below (Step  260 ). Specifically, the dynamic range compressing section  151  changes the dynamic range of the band-divided sound signal S 2  only for the correction band designated by the correction band information S 6  according to the correction band information S 6  to reduce the maximum audible level 1 for the correction band down to a maximum audible level 2 (Step  270 ). Namely, the dynamic range compressing section  151  performs the change processing with respect to the dynamic range gain characteristic in Step  260  every time the excessive output notification information S 3  is output from the excessive output notification section  13  and input to the correction band decision section  14  according to the user&#39;s operation. The dynamic range compressing section  151  then compresses the dynamic range of the band-divided sound signal S 2  only for the correction band according to the gain characteristic after the change processing (Step  270 ). 
     Each of  FIGS. 4 and 5  is a diagram showing an example of the change in the gain characteristic (amplification characteristic) which changes according to the maximum audible level-down performed by the dynamic range compressing section  151  in the sound output control section  15 . Note that, in each of  FIGS. 4 and 5 , the horizontal axis shows an input level of the band-divided sound signal S 2  in the correction band designated by the correction band information S 6  and the vertical axis shows an output level thereof. 
     In the example of  FIG. 4 , the dynamic range compressing section  151  in the sound output control section  15  activates a limiter having the upper limit of predetermined maximum audible level 1 according to the user and reduces the dynamic range from the maximum audible level 1 to the maximum audible level 2 according to the gain characteristic, for the band-divided sound signal S 2  only in the correction band designated by the correction band information S 6 . Here, in the case shown in  FIG. 4 , the dynamic range compressing section  151  changes the gain characteristic in a larger extent by the processing of Step  260  to increase a reduction step from the maximum audible level 1 to the maximum audible level 2 and gradually reduces the value of maximum audible level 2, every time the excessive output notification information S 3  is output from the excessive output notification section  13  according to the user&#39; s operation. Here, the maximum audible level 1 in  FIG. 4  is the same as the maximum audible level 1 in  FIG. 3 . 
     In the example of  FIG. 5 , the dynamic range compressing section  151  in the sound output control section  15  activates the limiter having the upper limit of a predetermined maximum audible level 1 according to the user and reduces the dynamic range from the maximum audible level 1 to the maximum audible level 2 as shown in  FIG. 5 , for the band-divided sound signal S 2  only in the correction band designated by the correction band information S 6 , and also the dynamic range compressing section  151  further changes the slope in the gain characteristic of the band-divided sound signal S 2  by multiplication of a predetermined compression rate. Here, in the case shown in  FIG. 5 , the dynamic range compressing section  151  changes the gain characteristic such as the predetermined compression rate and the like in a larger extent by the processing in Step  260  to gradually reduce the value of maximum audible level 2 and also change the slope in the gain characteristic of the band-divided sound signal S 2 , every time the excessive output notification information S 3  is output from the excessive output notification section  13  according to the user&#39;s operation. Here, the maximum audible level 1 in  FIG. 5 , as with the maximum audible level 1 in  FIG. 4 , is the same as the maximum audible level 1 in  FIG. 3 . 
     Thereby, in both cases shown in  FIGS. 4 and 5 , the dynamic range compressing section  151  in the sound output control section  15  can reduce the maximum audible level 2 gradually every time the excessive output notification information S 3  is output from the excessive output notification section  13 . Accordingly, sound volume is not reduced abruptly and usability and use feeling of the present device is improved in this point. Note that the dynamic range compressing section  151  in the sound output control section  15  may only reduce the dynamic range down to sound volume which is not felt to be excessive by the user, for the band-divided sound signal S 2  only in the correction band designated by the correction band information S 6 , and the method thereof is not limited to the methods shown in  FIGS. 4 and 5 . Further, so as to enable the dynamic range compressing section  151  in the sound output control section  15  to update the dynamic range compression gain characteristic, the present device may be configured such that the excessive output notification information S 3  is output directly to the dynamic range compressing section  151  from the excessive output notification section  13 . 
     Next, the signal synthesizing section  152  combines the band-divided sound signal S 7  in the correction band in which the dynamic range is compressed by the dynamic range compressing section  151  and the band-divided sound signal S 2  in bands except the correction band each in which the dynamic range is not compressed and left without change (Step  280 ), and outputs the result as a synthetic sound signal S 8  to the sound output section  153 . The sound output section  153  then receives the synthetic sound signal S 8  from the signal synthesizing section  152  and converts the synthetic sound signal S 8  into output sound which is output to a user&#39;s ear or the like via an earphone or the like (Step  290 ). 
     Consequently, according to the sound volume control device  1  of the present embodiment, the correction band decision section  14  calculates the audible signal distribution information S 4  of the user when the excessive output notification information S 3  is not output from the excessive output notification section  13  and the excessive signal distribution information S 5  of the user when the excessive output notification information S 3  is output, for each band in the band-divided sound signal S 2  subject to the band-division in the band dividing section  12 , and decides a correction band according to the audible signal distribution information S 4  and the excessive signal distribution information S 5 , and the sound output control section  15  provides output by compressing the dynamic range in the correction band so as to cause the sound signal in the correction band not to have excessive volume. Thereby, it is possible to adjust the maximum output level of the sound in the band where the user feels in actual life that sound is excessive, without asking the user to hear the test audibility data. 
     In particular, in the sound volume control device  1  of the present embodiment, the dynamic range compressing section  151  in the sound output control section  15  is configured to perform the change processing with respect to the dynamic range gain characteristic to compress the dynamic range of the band-divided sound signal S 2  only in the correction band according to the gain characteristic after the change processing, every time the excessive output notification information S 3  is output from the excessive output notification section  13  according to the user&#39;s operation, and thereby the maximum audible level 2 or the slope of the gain characteristic is reduced gradually according to the number of outputs of the excessive output notification information S 3  from the user. As a result, according to the sound volume control device  1  of the present embodiment, it becomes possible to perform the compression of the dynamic range by gradually learning the sound which is felt sometimes to be annoying by the user who uses the present device in an actual utilization environment, and it is possible to perform the dynamic range compression processing more suitable for the utilization environment by gradually performing the threshold value decision based on a subjective view of the user which is difficult to perform in a conventional adjustment method. 
     (Second Embodiment) 
     Next, the sound volume control device according to the second embodiment of the present invention will be described with reference to  FIG. 6 . Note that, in  FIG. 6 , the same constituent as that of the sound volume control device  1  in the first embodiment shown in  FIG. 1  is provided with the same reference numeral for the explanation. 
     A sound volume control device  2  includes a sound input section  11 , a fast Fourier transform (FFT) section  12 ′, an excessive output notification section  13 , a correction band decision section  14  and a sound output control section  15 ′. The sound output control section  15 ′ includes a dynamic range compressing section  151 , an inverse fast Fourier transform (IFFT) section  152 ′ and a sound output section  153 . 
     Thus, the sound volume control device  2  includes the fast Fourier transform section  12 ′ and the inverse fast Fourier transform section  152 ′ instead of the band dividing section  12  and the signal synthesizing section  152  in the sound volume control device  1  of the first embodiment shown in  FIG. 1 , respectively, and the other constituents are the same as those of the sound volume control device  1  in the first embodiment. While the sound volume control device  1  of the first embodiment shown in  FIG. 1  is configured to divide the sound signal S 1  for each predetermined frequency band thereof in the band dividing section  12  and decide a correction band where the dynamic range is to be compressed, the sound volume control device  2  is configured to carries out Fourier transform with respect to the sound signal S 1  in the fast Fourier transform section  12 ′ to divide the sound signal S 1  into Fourier coefficients S 2 ′ which are waveform components of plural frequency components and decide a correction band where the dynamic range is to be compressed. 
     Accordingly, in the sound volume control device  2 , when an input sound signal S 1  is input from the sound input section  11  to the fast Fourier transform section  12 ′, the fast Fourier transform section  12 ′ obtains the Fourier coefficients S 2 ′ from the input sound signal S 1  and outputs the Fourier coefficients S 2 ′ to the correction band decision section  14  and the sound output control section  15 ′. 
     When excessive output notification information S 3  is not received from the excessive output notification section  13 , an audible signal distribution information calculating section  141  calculates a signal level value which is power for a predetermined unit time (that is, power for a frame which includes successive sound data subject to the Fourier transform) for each input Fourier coefficient S 2 ′ as in the first embodiment, and counts the number of frames having the same signal level value in a predetermined measurement time (e.g., within several seconds to several tens of seconds). For example, the power is calculated by squaring the input Fourier coefficient S 2 ′ in the predetermined unit time. Then, the audible signal distribution information calculating section  141  calculates audible signal distribution information S 4  as an occurrence frequency of audible signals by normalizing the count value by a predetermined parameter, and updates the audible signal distribution information S 4  stored in an audible signal distribution information storing section  142 . 
     On the other side, the correction band decision section  14 , when receiving the excessive output notification information S 3  which is output from the excessive output notification section  13  by user&#39;s operation, calculates a signal level value which is power for a predetermined unit time (that is, power for a frame which includes successive sound data subject to the Fourier transform) for each input Fourier coefficient S 2 ′. For example, the power is calculated by squaring the input Fourier coefficient S 2 ′ in the predetermined unit time. Then, the correction band decision section  14  similarly calculates excessive signal distribution information S 5  and updates the excessive signal distribution information S 5  stored in an excessive signal distribution information storing section  144 . 
     Then, in the correction band decision section  14 , a frequency comparison correction band decision section  145 , as in the first embodiment, compares the excessive signal distribution information S 5  and the audible signal distribution information S 4 , decides a band where the excessive signal distribution information S 5  shows a higher frequency than the audible signal distribution information S 4  in the vicinity of a predetermined maximum audible level 1, as a correction band of a correction target, and outputs the decided correction band information S 6  to the sound output control section  15 ′. 
     Next, in the sound output control section  15 ′, the dynamic range compressing section  151  first performs dynamic range compression such as reduction from the maximum audible level 1 to the maximum audible level 2, as in the case of the first embodiment, with respect to a Fourier coefficient S 2 ′ corresponding to a frequency band which is determined to be the correction band among the Fourier coefficients S 2 ′ from the fast Fourier transform section  12 ′ according to the correction band information S 6  from the correction band decision section  14 , and outputs the result and the other Fourier coefficients S 2 ′ to the IFFT section  152  as Fourier coefficient S 7 ′. 
     The inverse fast Fourier transform (IFFT) section  152 ′ performs the inverse fast Fourier transform with respect to the Fourier coefficient S 7 ′ including the Fourier coefficient S 2 ′ corresponding to the correction band in which the dynamic range compression is performed by the dynamic range compressing section  151 , to return the Fourier coefficient S 7 ′ to a sound signal S 8  on the time axis, and outputs the sound signal S 8  to the sound output section  153 . Then, the sound output section  153  outputs output sound S 9  according to the sound signal S 8 , as in the first embodiment. 
     In the sound volume control device  2 , the fast Fourier transform section  12 ′ and the inverse fast Fourier transform section  152 ′ are provided instead of the band dividing section  12  and the signal synthesizing section  152 , respectively, in the sound volume control device  1  of the first embodiment shown in  FIG. 1 . Accordingly, as in the sound volume control device  1  of the first embodiment, it is possible to adjust the maximum output level of the sound in a band where the user feels in actual life that sound is excessive, without asking the user to hear the test audibility data. Further, it is possible to perform the dynamic range compression processing more suitable for the utilization environment by performing the change processing with respect to the dynamic range gain characteristic every time the excessive output notification information S 3  is output. 
     Lastly, each of the above embodiments is an example of the present invention. Therefore, it is to be added that the present invention is not limited to the above embodiments and various modifications are possible according to design and the like in a range without departing from the technical idea according to the present invention.