Patent Publication Number: US-2012039495-A1

Title: Audio processing apparatus, audio processing method, and program

Description:
BACKGROUND 
     The present disclosure relates to an audio processing apparatus, an audio processing method, and a program. 
     The recent years have witnessed widespread use of audio reproduction apparatuses capable of reproducing audio data. Also, there has been proposed an audio reproduction apparatus furnished with a noise canceling function of reducing noise components by outputting through earphones or headphones an audio signal with its phase opposite to that of the ambient noise, as described in Japanese Patent Laid-Open No. Hei 9-187093 (called Patent Document 1 hereunder) for example. 
     There are other audio reproduction apparatuses capable of acquiring a user&#39;s hearing characteristics and reproducing audio data by automatically equalizing the data in keeping with the acquired hearing characteristics of the user. For example, the audio reproduction apparatus may successively output test tones at different frequencies with their sound volumes varied over time, and acquire as the user&#39;s hearing characteristics the sound volume in effect upon user operation performed on each test tone. The audio reproduction apparatus may then adjust the frequency characteristics of a reproduced signal in accordance with the user&#39;s hearing characteristics acquired, whereby the user can perceive the original sound image based on the audio data. One such audio reproduction apparatus is disclosed in Japanese Patent Laid-Open No. Hei 6-217389 (called Patent Document 2 hereunder). 
     SUMMARY 
     Typically, the acquisition of hearing characteristics is but one of the steps in carrying out automatic equalization and thus can pose a problem in terms of usability if the step is too time-consuming. Moreover, the hearing characteristic tests using test tones with only their sound volumes varied over time can be too stale to sustain the user&#39;s willingness to perform the tests. 
     The present disclosure has been made in view of the above circumstances and provides an audio processing apparatus, an audio processing method, and a program innovated and improved to provide the user with freshly inspired hearing characteristic tests. 
     According to one embodiment of the present disclosure, there is provided an audio processing apparatus including: a first signal generation portion configured to generate an audio signal of which the frequency is varied over time; an operation portion; a storage portion configured to store characteristic information in accordance with the frequency and an amplitude of the audio signal in effect when the operation portion is operated; a reproduction portion configured to reproduce audio data; and a correction portion configured to correct a reproduced signal from the reproduction portion based on the characteristic information stored in the storage portion. 
     Preferably, the audio processing apparatus of the present disclosure may further include: a sound pickup portion; a second signal generation portion configured to generate an ambient sound reduction signal for reducing an ambient sound based on the pickup of the ambient sound by the sound pickup portion; and a control portion configured to control the second signal generation portion in operation; wherein the control portion may operate the second signal generation portion while the first signal generation portion is being caused to generate the audio signal. 
     Preferably, the second signal generation portion may generate the ambient sound reduction signal different in frequency characteristic from the ambient sound in accordance with the frequency of the audio signal generated by the first signal generation portion. 
     Preferably, the second signal generation portion may generate the ambient sound reduction signal in a manner rendering the ambient sound lower on the same frequency band as the audio signal generated by the first signal generation portion than on other frequency bands. 
     Preferably, the first signal generation portion may generate the audio signal of which not only the frequency but also the amplitude is varied over time. 
     Preferably, the control portion may control whether or not to operate the second signal generation portion upon reproduction of the audio data by the reproduction portion. 
     Preferably, if the second signal generation portion does not generate the ambient sound reduction signal, the correction portion may correct the reproduced signal from the reproduction portion in accordance with the characteristic information stored in the storage portion and in keeping with the ambient sound picked up by the sound pickup portion. 
     Preferably, the correction portion may emphasize the reproduced signal on the same frequency band as the ambient sound. 
     Preferably, when operating upon reproduction of the audio data by the reproduction portion, the second signal generation portion may generate the ambient sound reduction signal based on the characteristic information stored in the storage portion. 
     Preferably, the audio processing apparatus according to the embodiment of the present disclosure may further include a left-ear audio output portion and a right-ear audio output portion; wherein the storage portion may store left-ear characteristic information and right-ear characteristic information; and the correction portion may correct the reproduced signal output to the left-ear audio output portion in accordance with the left-ear characteristic information and the reproduced signal output to the right-ear audio output portion in keeping with the right-ear characteristic information. 
     Preferably, the audio processing apparatus according to the embodiment of the present disclosure may further include a display portion configured to display a screen in accordance with the characteristic information having been acquired. 
     Preferably, the storage portion may store the audio data based on the reproduced signal having undergone the correction by the correction portion. 
     According to another embodiment of the present disclosure, there is provided a program for causing a computer to function as an apparatus including: a first signal generation portion configured to generate an audio signal of which the frequency is varied over time; an operation portion; a storage portion configured to store characteristic information in accordance with the frequency and an amplitude of the audio signal in effect when the operation portion is operated; a reproduction portion configured to reproduce audio data; and a correction portion configured to correct a reproduced signal from the reproduction portion based on the characteristic information stored in the storage portion. 
     According to a further embodiment of the present disclosure, there is provided an audio processing method including: generating an audio signal of which the frequency is varied over time; storing onto a storage medium characteristic information in accordance with the frequency and an amplitude of the audio signal in effect when a user performs an operation; reproducing audio data; and correcting a reproduced signal of the audio data based on the characteristic information stored on the storage medium. 
     According to the embodiments of the present disclosure outlined above, it is possible to provide the user with freshly inspired hearing characteristic tests. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory view showing an external appearance of an audio processing apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is an explanatory view showing results of a comparative example of hearing characteristic tests; 
         FIG. 3  is a functional block diagram showing a typical structure of an audio processing apparatus as a first embodiment of the present disclosure; 
         FIG. 4  is an explanatory view showing a typical structure of a test tone generation circuit; 
         FIG. 5  is an explanatory view showing a specific example of test tones generated by a sine wave generation circuit; 
         FIG. 6  is an explanatory view showing a specific example of hearing characteristic information; 
         FIG. 7  is a flowchart showing how the audio processing apparatus as the first embodiment typically operates; 
         FIG. 8  is an explanatory view showing a variation of the test tone; 
         FIG. 9  is an explanatory view showing how the test tone variation is typically generated; 
         FIG. 10  is another explanatory view showing how the test tone variation is typically generated; 
         FIG. 11  is another explanatory view showing how the test tone variation is typically generated; 
         FIG. 12  is another explanatory view showing how the test tone variation is typically generated; 
         FIG. 13  is another explanatory view showing how the test tone variation is typically generated; 
         FIG. 14  is another explanatory view showing how the test tone variation is typically generated; 
         FIG. 15  is a functional block diagram showing a typical structure of an audio processing apparatus as a second embodiment of the present disclosure; 
         FIG. 16  is an explanatory view showing a typical structure of a noise canceling sound generation circuit; 
         FIG. 17  is an explanatory view showing how the frequency characteristic of a noise canceling sound is typically varied; 
         FIG. 18  is a functional block diagram showing a typical structure of an audio processing apparatus as a third embodiment of the present disclosure; and 
         FIG. 19  is an explanatory view showing a specific example of hearing characteristic test results displayed on a screen by a display portion. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Some preferred embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. Throughout this specification and the accompanying drawings, like reference characters designate like or corresponding components, and their explanations may be omitted where redundant. 
     Also in this specification and the accompanying drawings, a plurality of components that are substantially the same functionally and structurally may be distinguished from one another by having their common reference character supplemented with different alphabetical characters. If there is no specific need to distinguish such multiple components having substantially the same function and structure, they will be accompanied solely by their common reference character. 
     The ensuing description of the preferred embodiments will be given under the following headings: 
     1. Basic structure of the audio processing apparatus;
 
2. First embodiment;
 
     2-1. Structure of the audio processing apparatus as the first embodiment; 
     2-2. Operations of the audio processing apparatus as the first embodiment; 
     2-3. Test tone variation; 
     3. Second embodiment;
 
4. Third embodiment;
 
     5. Variations; and 
     6. Conclusion. 
     1. BASIC STRUCTURE OF THE AUDIO PROCESSING APPARATUS 
     The present disclosure may be implemented in diverse embodiments as will be explained below under the headings of “2. First embodiment” through “4. Third embodiment” for example. An audio processing apparatus  20  on which the embodiments are based includes: 
     (1) a first signal generation portion (test tone generation circuit  220 ) for generating an audio signal (test tones) of which the frequency is varied over time;
 
(2) an operation portion  24 ; and
 
(3) a storage portion  230  for storing characteristic information corresponding to the frequencies and amplitudes of the audio signal in effect when the operation portion is operated.
 
     Described below in reference to  FIG. 1  is the basic structure such as one outlined above and common to the diverse embodiments of the present disclosure. 
       FIG. 1  is an explanatory view showing an external appearance of the audio processing apparatus  20  according to an embodiment of the present disclosure. As shown in  FIG. 1 , the audio processing apparatus  20  includes an operation portion  24 , earphones  26 , and a display portion  28 . 
     The display portion  28  displays diverse screens such as a menu screen and a reproduction selection screen for guiding user operations; screens for displaying attribute information including title names, artist names and/or genres of audio data; and screens for indicating audio data reproduction status. The display portion  28  may be a liquid crystal display (LCD) device, an organic light-emitting diode (OLED) device, or some other suitable display device. 
     The operation portion  24  is structured to accept the operation instructions and information input by the user. For example, by operating the operation portion  24 , the user can input instructions such as those for selecting audio data, for starting reproduction, for pausing, and for fast-forwarding to the audio processing apparatus  20 . Also, the embodiment allows the user to perform hearing characteristic tests by operating the operation portion  24 . The operation portion  24  is not limited to any specific form. For example, the operation portion  24  may be composed of a mouse, a keyboard, a touch panel, buttons, and/or switches. 
     The earphones  26  function as an audio output portion for outputting the reproduced signal of audio data. Also, the earphones  26  output test tones for acquiring the user&#39;s hearing characteristics. Although  FIG. 1  indicates the audio output portion in the form of the earphones  26  for example, the audio output portion may be structured alternatively in the form of speakers or headphones. 
     Whereas  FIG. 1  shows a portable audio reproduction apparatus as an example of the audio processing apparatus  20 , the audio processing apparatus  20  is not limited to that example. Alternatively, the audio processing apparatus  20  may be any one of information processing apparatuses including PC&#39;s (personal computers), home-use video processing apparatuses (DVD recorder, video cassette recorder, etc.), PDA&#39;s (personal digital assistants), home-use videogame consoles, household electrical appliances, mobile phones, and portable videogame machines. 
     What is particularly innovative of the audio processing apparatus  20  embodying the present disclosure is the manner in which hearing characteristic tests are carried out thereby. In the ensuing description, a comparative example of hearing characteristic tests will be explained first, followed by detailed explanations of the preferred embodiments of the present disclosure under the headings of “2. First embodiment” through “4. Third embodiment.” 
     (Comparative Example of Hearing Characteristic Tests) 
     In the comparative example of hearing characteristic tests, test tones are output successively at different frequencies with their sound volumes varied over time. The sound volume in effect when the user has performed an operation on each of the test tones involved is acquired as the user&#39;s hearing characteristics. The example is explained below in more detail with reference to  FIG. 2 . 
       FIG. 2  is an explanatory view showing results of the comparative example of hearing characteristic tests. In  FIG. 2 , broken lines denote test tones, and a solid line represents the user&#39;s hearing characteristics. As indicated in  FIG. 2 , the comparative example of hearing characteristic tests involves successively outputting test tones at frequencies f 1  through f 9  with their sound volumes increased over time. The sound volume in effect when the user has performed an operation on each test tone is acquired as the user&#39;s hearing characteristics. 
     One disadvantage of the comparative example above of hearing characteristic tests is that it takes a long time to acquire detailed hearing characteristics because of the numerous test tones to be output. The hearing characteristic tests are but one of the steps in carrying out automatic equalization and thus can pose a problem in terms of usability if this step is too time-consuming. Moreover, the hearing characteristic tests using test tones with only their sound volumes varied over time can be too stale to sustain the user&#39;s willingness to perform the tests. 
     Another disadvantage of the above-described comparative example of hearing characteristic tests is that the user&#39;s hearing characteristics acquired thereby can be affected by external noise. In particular, low frequencies constitute a frequency range that is inherently difficult for humans to hear. In an environment where there exists external noise containing numerous low-frequency components, low-frequency test tones can be buried in the noise. In that case, exact hearing characteristics are difficult to acquire. Ideally, hearing characteristic tests should be performed in an anacoustic chamber where there is no external noise. However, using the anacoustic chamber solely for the purpose of hearing characteristic tests is not a realistic option. 
     The embodiments of the present disclosure have been created in part with a view to overcoming the above disadvantages of the comparable techniques. In carrying out the present disclosure, a first embodiment thereof envisages providing the user with freshly inspired hearing characteristic tests while reducing the time required to perform the tests. A second embodiment of the present disclosure is implemented to perform the hearing characteristic tests while minimizing the effects of external noise. A third embodiment of the present disclosure is implemented to let the user recognize his or her own hearing characteristics. What follows is a detailed description of the audio processing apparatus  20  practiced as each of these embodiments. 
     2. FIRST EMBODIMENT 
     (2-1. Structure of the Audio Processing Apparatus as the First Embodiment) 
       FIG. 3  is a functional block diagram showing a typical structure of an audio processing apparatus  20 - 1  as the first embodiment of the present disclosure. As shown in  FIG. 3 , the audio processing apparatus  20 - 1  as the first embodiment is made up of an operation portion  24 , earphones  26 , a display portion  28 , a control portion  210 , a test tone generation circuit  220 , a storage portion  230 , an audio reproduction circuit  240 , and an equalizer  250 . 
     The control portion  210  controls the overall performance of the audio processing apparatus  20 - 1 . For example, the control portion  210  controls the operation of the equalizer  250 , display of the display portion  28 , and test tone generation of the test tone generation circuit  220 . 
     Under control of the control portion  210 , the test tone generation circuit  220  generates test tones with their frequencies varied over time. The test tone generation circuit  220  is explained below in detail with reference to  FIG. 4 . 
       FIG. 4  is an explanatory view showing a typical structure of the test tone generation circuit  220 . As shown in  FIG. 4 , the test tone generation circuit  220  is composed of a sine wave generation circuit  222 , a frequency modulation circuit  224 , and an amplitude adjustment circuit  226 . 
     The sine wave generation circuit  222  generates a sine wave serving as the basis for the test tones to be used in hearing characteristic tests. The frequency modulation circuit  224  modulates the frequency of the sine wave generated by the sine wave generation circuit  222  in accordance with a control signal from the control portion  210 . The amplitude adjustment circuit  226  adjusts the amplitude of the sine wave output from the frequency modulation circuit  224  in keeping with a control signal from the control portion  210 . 
     Test tones are then generated by the test tone generation circuit  220  and fed to the earphones  26  for output as a sound. Although  FIG. 4  shows the amplitude adjustment circuit  226  disposed downstream of the frequency modulation circuit  224 , this is merely an example. Alternatively, the amplitude adjustment circuit  226  may be located upstream of the frequency modulation circuit  224 . 
     The above-described sine wave generation circuit  222  regulates the frequency and amplitude of the sine wave dynamically so as to generate test tones, i.e., sweep tones with at least their frequencies varied over time. Explained below in reference to  FIG. 5  is a specific example of the test tones generated by the sine wave generation circuit  222 . 
       FIG. 5  is an explanatory view showing a specific example of test tones generated by the test tone generation circuit  222 . In  FIG. 5 , broken lines denote test tones, and a solid line represents the user&#39;s hearing characteristics detected (previous characteristics are unknown). As illustrated in  FIG. 5 , the sine wave generation circuit  222  generates a plurality of test tones of which the frequencies are increased while their sound volumes (i.e., amplitudes) are kept constant. For example, the sine wave generation circuit  222  generates successively the test tones ranging from a tone with a sound volume V 1  to a tone with a sound volume V 6 . 
     Upon hearing each of these test tones, the user operates the operation portion  24 . For example, the user may press the operation portion  24  the moment a test tone is heard. Alternatively, the user may keep pressing the operation portion  24  while a test tone is being heard. As another alternative, the user may press the operation portion  24  the moment a test tone stops being heard. As a further alternative, the user may keep pressing the operation portion  24  while a test tone is not being heard. 
     It is assumed here that the user keeps pressing the operation portion  24  while a test tone is being heard. On that assumption, given the test tone with the sound volume V 1  shown in  FIG. 5 , the user keeps pressing the operation portion  24  while the frequency of the test tone being heard ranges from F 1  to F 12 . In this case, it may be determined that a sound volume V 1 /frequency F 1  combination in effect when the user performs an operation (i.e., pressing the operation portion) and a sound volume V 1 /frequency F 12  combination in effect when the user performs another operation (i.e., releasing the operation portion) constitute the boundaries delimiting the user&#39;s audible and inaudible ranges. Thus the sound volume V 1 /frequency F 1  combination and sound volume V 1 /frequency F 12  combination are recorded to the storage portion  230  as the user&#39;s hearing characteristic information. 
     As discussed above, the first embodiment of the present disclosure is efficient in that it can acquire a plurality of items of hearing characteristic information using a single test tone. The user&#39;s hearing characteristic information is acquired likewise regarding the other test tones and is recorded to the storage portion  230 . 
     For example, the test tone with the sound volume V 1  has its frequencies F 1  and F 12  widely apart from each other as shown in  FIG. 5 . Consequently, if the test tone frequency is varied at a constant speed, then it may take a long time for the frequency to change from F 1  to F 12 . In such a case, the control portion  210  may arrange to raise the rate at which the frequency is varied within a frequency range where the user is highly likely to hear the test tone based on the average hearing characteristic model. This arrangement can reduce the time it takes to carry out the hearing characteristic tests. 
     The storage portion  230  stores diverse content data such as audio data as well as the user&#39;s hearing characteristic information acquired through hearing characteristic tests. A specific example of hearing characteristic information is explained below in reference to  FIG. 6 . 
       FIG. 6  is an explanatory view showing a particular example of hearing characteristic information. As shown in  FIG. 6 , the storage portion  230  stores the relations between frequencies and sound volumes as hearing characteristic information. Although  FIG. 6  shows an example in which the frequencies and sound volumes in effect when the user performed operations during hearing characteristic tests are stored unchanged in the storage portion  230 , this is not limitative of the first embodiment. Alternatively, the control portion  210  may mathematize the relations between the frequencies and volumes in effect when the user performed operations on each of the test tones involved and store the mathematized hearing characteristic information into the storage portion  230 . 
     The storage portion  230  may be any one of such storage media as nonvolatile memories, magnetic disks, optical disks, and MO (Magneto-Optical) disks. The nonvolatile memories include EEPROM (Electrically Erasable Programmable Read-Only Memory), EPROM (Erasable Programmable ROM) for example. The magnetic disks include hard disks and other disk-shaped magnetic bodies. The optical disks include CD (Compact Disc), DVD-R (Digital Versatile Disc Recordable), and BD (Blu-Ray Disc (registered trademark)). 
     The audio reproduction circuit  240  (reproduction portion) shown in  FIG. 3  reads audio data from the storage portion  230  or obtains audio data from the outside and reproduces the audio data thus retrieved or acquired. During its reproducing process, the audio reproduction circuit  240  may expand compressed audio data and convert the audio data from digital to analog form, for example. 
     In accordance with a control signal from the control portion  210 , the equalizer  250  (correction portion) corrects the frequency characteristic of a reproduced signal from the audio reproduction circuit  240  and forwards the corrected reproduced signal to the earphones  26 . More specifically, based on the user&#39;s hearing characteristic information stored in the storage portion  230 , the control portion  210  supplies the equalizer  250  with the control signal for emphasizing or deemphasizing particular frequency bands. In keeping with the control signal from the control portion  210 , the equalizer  250  may emphasize the frequency band where the user&#39;s hearing is low and deemphasize the frequency components of which the user&#39;s hearing is high enough. Also, the equalizer  250  performs overall sound quality correction (averaging) and enhancement (clarification of the sound image). 
     The first embodiment of the present disclosure, as explained above, permits execution of hearing characteristic tests using the test tones of which the frequencies are varied over time. By correcting the reproduced signal of audio data in accordance with the user&#39;s hearing characteristic information acquired through the hearing characteristic tests, the first embodiment allows the user to perceive the original sound image based on the corrected audio data. 
     (2-2. Operations of the Audio Processing Apparatus as the First Embodiment) 
     The foregoing paragraphs discussed the typical structure of the audio processing apparatus  20 - 1  practiced as the first embodiment of the present disclosure. What follows is an explanation of how the audio processing apparatus  20 - 1  as the first embodiment typically operates. 
       FIG. 7  is a flowchart showing typical operations of the audio processing apparatus  20 - 1  as the first embodiment. As shown in  FIG. 7 , the test tone generation circuit  220  first generates a test tone of which the frequency is varied over time (in step S 304 ). 
     If the user operates the operation portion  24  (in step S 308 ), the storage portion  230  stores the frequency and sound volume in effect when the user performed the operation (in step S 312 ). The audio processing apparatus  20 - 1  repeats steps S 304  through S 312  until all test tones have been processed and finished (in step S 316 ). 
     Then if the user gives an instruction to reproduce audio data by means of the operation portion  24  (in step S 320 ), the audio reproduction circuit  2490  starts reproducing the audio data (in step S 324 ). The equalizer  250  corrects the reproduced signal from the audio reproduction circuit  240  based on the user&#39;s hearing characteristic information stored in the storage portion  230  (in step S 328 ). The reproduced signal corrected by the equalizer  250  is output from the earphones  26  (in step S 332 ). 
     (2-3. Test Tone Variation) 
     The foregoing paragraphs discussed the audio processing apparatus  20 - 1  as the first embodiment of the present disclosure, the apparatus being shown to use the test tones of which the frequencies are varied over time. However, the test tones used by the audio processing apparatus  20 - 1  for hearing characteristic tests are not limited to those of which the frequencies alone are varied over time as illustrated in  FIG. 5 . Alternatively, the audio processing apparatus  20 - 1  may generate a test tone of which, as well as the frequency, the sound volume is varied over time. Described below is a specific example of such a test tone as well as a typical method for generating that test tone. 
       FIG. 8  is an explanatory view showing a variation of the test tone. In  FIG. 8 , a broken line denotes the test tone and a solid line represents the user&#39;s hearing characteristics detected (previous characteristics are unknown). The test tone generation circuit  220  can generate a test tone that changes vibrationally on the frequency-sound volume plane in keeping with the predicted hearing characteristics of the user. Using this test tone permits efficient acquisition of the user&#39;s detailed hearing characteristic information. A typical method for generating such a test tone is explained below in reference to  FIGS. 9 through 14 . 
       FIGS. 9 through 14  are explanatory views showing how the above-described test tone variation is typically generated. First, in accordance with a control signal from the control portion  210 , the test tone generation circuit  220  varies the frequency and sound volume of a generated test tone in such a manner that the test tone plots a straight line with a gradient on the x-y plane (i.e., frequency-volume plane) as shown in  FIG. 9 . 
     When the user performs an operation at point P 1 , the test tone generation circuit  220  varies the frequency and sound volume of the test tone in such a manner that the test tone plots a sine wave with its baseline (L 1 ) taken along a line parallel to the y-axis and with its origin taken at point P 1 , as shown in  FIG. 10 . When the user performs another operation at point P 2 , the test tone generation circuit  220  varies the frequency and sound volume of the test tone in such a manner that the test tone plots a sine wave with its baseline (L 2 ) taken along a line connecting points P 1  (first point) and P 2  (second point) and with its origin taken at point P 2 , as shown in  FIG. 11 . 
     When the user performs yet another operation at point P 3 , the test tone generation circuit  220  varies the frequency and sound volume of the test tone in such a manner that the test tone plots a sine wave with its baseline (L 3 ) taken along a line whose gradient is obtained by adding up the gradient of the line connecting points P 2  and P 3  and the difference between the gradient of the line connecting points P 1  and P 2  and the gradient of the line connecting points P 2  and P 3 , and with its origin taken at point P 3 , as shown in  FIG. 12 . 
     In like manner, when the user performs an operation at point Pn, the test tone generation circuit  220  varies the frequency and sound volume of the test tone in such a manner that the test tone plots a sine wave with its baseline (Ln) taken along a line whose gradient is obtained by adding up the gradient of the line connecting points Pn and Pn−1 and the difference between the gradient of the line connecting points Pn and Pn−1 and the gradient of the line connecting points Pn−1 and Pn−2, and with its origin taken at point Pn. 
     Below is a supplementary explanation of the relations between the baselines and the sine wave, with reference to  FIGS. 13 and 14 . As shown in  FIG. 13 , the audio processing apparatus  20 - 1  is arranged to store beforehand the coordinates of the plotted positions constituting the sine wave. If the gradient of the baseline is θ, the control portion  210  rotates by the gradient θ each of the plotted positions making up the sine wave as illustrated in  FIG. 14 . If the coordinates of each plotted position before the rotation are (x, y), then the coordinates of each plotted position after the rotation (x′, y′) are expressed by the following mathematical expressions: 
         x′=x  cos θ− y  sin θ
 
         y′=y  sin θ+ y  cos θ
 
     Thereafter, the control portion  210  moves the origin of the rotated sine wave to the point where the user performed an operation, and provides the test tone generation circuit  220  with a control signal designating the frequency and sound volume corresponding to each of the plotted positions constituting the moved sine wave. This allows the test tone generation circuit  220  to generate a test tone that changes vibrationally on the frequency-volume plane as shown in  FIG. 8 . The control portion  210  performs the above-described process based on the sine wave whose phase is inverted every time the user performs the operation anew. 
     3. SECOND EMBODIMENT 
     The foregoing paragraphs discussed the audio processing apparatus  20 - 1  as the first embodiment of the present disclosure. What follows is an explanation of an audio processing apparatus  20 - 2  practiced as the second embodiment of the present disclosure. As will be discussed below in detail, the audio processing apparatus  20 - 2  as the second embodiment is capable of performing hearing characteristic tests while suppressing the influence of external noise. 
       FIG. 15  is a functional block diagram showing a typical structure of the audio processing apparatus  20 - 2  as the second embodiment of the present disclosure. As shown in  FIG. 15 , the audio processing apparatus  20 - 2  as the second embodiment is made up of an operation portion  24 , a microphone  25 , earphones  26 , a display portion  28 , a control portion  210 , a test tone generation circuit  220 , a storage portion  230 , an audio reproduction circuit  240 , an equalizer  250 , and a noise canceling sound generation circuit  260 . 
     Many parts of the audio processing apparatus  20 - 2  as the second embodiment are substantially the same as those of the audio processing apparatus  20 - 1  as the first embodiment. For that reason, the ensuing explanation will stress the structural differences between the second embodiment and the first embodiment. 
     The microphone  25  (sound pickup portion) picks up the ambient sound of the audio processing apparatus  20 - 2 . The microphone  25  is positioned close to the earphones  26  in order to implement noise cancellation. For example, the microphone  25  may be contained inside the enclosures constituting the earphones. 
     Based on the ambient sound picked up by the microphone  25 , the noise canceling sound generation circuit  260  (second signal generation portion) generates a noise canceling sound (ambient sound reduction signal) for reducing the ambient sound at the locations where the user perceives sounds. A typical structure of the noise canceling sound generation circuit  260  is explained below in reference  FIG. 16 . 
       FIG. 16  is an explanatory view showing a typical structure of the noise canceling sound generation circuit  260 . As shown in  FIG. 16 , the noise canceling sound generation circuit  260  includes an analog-digital converter (ADC)  261 , a digital filter  262 , a noise canceling sound generation portion  264 , a digital filter  266 , and a digital-analog converter (DAC)  267 . 
     The ADC  261  is supplied with a sound pickup signal representative of the ambient sound from the microphone  25  and converts the supplied pickup signal from analog to digital form. 
     The digital filter  262  adjusts the frequency characteristic of the sound pickup signal converted to digital form by the ADC  261  in accordance with a control signal from the control portion  210 . The noise canceling sound generation portion  264  generates a noise canceling sound whose phase is opposite to that of the sound pickup signal fed from the digital filter  262 . The noise canceling sound generation portion  264  may adopt any suitable method for generating the noise canceling sound. 
     The digital filter  266  adjusts the frequency characteristic of the noise canceling sound generated by the noise canceling sound generation portion  264  in accordance with a control signal from the control portion  210 . The controls exercised by the control portion  210  will be discussed later. 
     The DAC  267  converts the noise canceling sound fed from the digital filter  266  from digital to analog form. The noise canceling sound converted to analog form by the DAC  267  is sent to the earphones  26  for output. 
     (Noise Canceling During Hearing Characteristic Tests) 
     With the second embodiment, the noise canceling sound generation portion  264  under control of the control portion  210  can boost the accuracy of hearing characteristic tests. Specifically, the control portion  210  operates the noise canceling sound generation portion  264  during a hearing characteristic test, i.e., while a test tone is being output. This structure permits more accurate acquisition of the user&#39;s hearing characteristics because the hearing characteristic tests are carried out while the influence of the external noise is being suppressed. 
     Furthermore, the control portion  210  may vary the filter characteristic of the digital filter  266  in keeping with the frequency changes of the test tone generated by the test tone generation circuit  220 . For example, the control portion  210  may allow the digital filter  266  selectively to pass or emphasize that frequency component in the noise canceling sound which is the same as the frequency of the test tone. More specifically, if the test tone frequency is Fx, the control portion  210  may let pass the frequency band component containing the frequency Fx of the noise canceling sound and cut off the other frequency band components. Explained below in reference to  FIG. 17  is a specific example of the noise canceling sound frequency characteristic acquired under such control of the control portion  210 . 
       FIG. 17  is an explanatory view showing how the frequency characteristic of a noise canceling sound is typically varied. If the frequency of the test tone generated by the test tone generation circuit  220  is monotonically increasing as shown in  FIG. 5 , the noise canceling sound generation circuit  260  shifts the frequency band of the noise canceling sound gradually toward the high frequency side. This structure helps prevent the test tone from being buried in the noise component because the noise component in the frequency of the test tone being output is reduced. 
     The foregoing paragraphs discussed the example in which the control portion  210  varies the filter characteristic of the digital filter  266  in order to adjust the frequency characteristic of the noise canceling sound. Alternatively, the control portion  210  may vary the filter characteristic of the digital filter  262  so as to adjust the frequency characteristic of the noise canceling sound. Also, the noise canceling sound generation portion  264  may generate the noise canceling sound while adjusting its frequency characteristic in accordance with the frequency changes in the test tone. 
     (Noise Canceling During Audio Data Reproduction) 
     The control portion  210  may also operate the noise canceling sound generation circuit  260  during audio data reproduction. In this case, the earphones  26  output the reproduced signal corrected by the equalizer  250  in keeping with the user&#39;s hearing characteristic information, as well as the noise canceling sound generated by the noise canceling sound generation circuit  260 . 
     Furthermore, the control portion  210  may control the operation of the noise canceling sound generation circuit  260  in accordance with the user&#39;s hearing characteristic information. For example, if the external noise picked up by the microphone  25  has a frequency that is difficult for the user to hear, the control portion  210  may cause the noise canceling sound generation circuit  260  to reduce its noise canceling amount or may turn off the noise canceling sound generation circuit  260  altogether. This structure helps reduce the power dissipation involved in noise canceling. 
     On the other hand, if the control portion  210  does not operate the noise canceling sound generation circuit  260  during audio data reproduction, the control portion  210  may cause the equalizer  250  to correct the reproduced signal in keeping with the external noise picked up by the microphone  25  in addition to the user&#39;s hearing characteristic information. For example, the control portion  210  may cause the equalizer  250  to emphasize the reproduced signal on the frequency band of the external noise. This structure allows the user to perceive the sound image of audio data more clearly even if the noise canceling sound generation circuit  260  is not in operation. 
     4. THIRD EMBODIMENT 
     The foregoing paragraphs discussed the audio processing apparatus  20 - 2  as the second embodiment of the present disclosure. What follows is an explanation of an audio processing apparatus  20 - 3  practiced as the third embodiment of the present disclosure. As will be discussed below in detail, the audio processing apparatus  20 - 3  as the third embodiment is capable of enhancing the user&#39;s awareness of his or her hearing characteristics. 
       FIG. 18  is a functional block diagram showing a typical structure of the audio processing apparatus  20 - 3  practiced as the third embodiment of the present disclosure. As shown in  FIG. 18 , the audio processing apparatus  20 - 3  as the third embodiment is made up of an operation portion  24 , a microphone  25 , earphones  26 , a display portion  28 , a control portion  212 , a test tone generation circuit  220 , a storage portion  230 , an audio reproduction circuit  240 , an equalizer  250 , and a noise canceling sound generation circuit  260 . 
     Many parts of the audio processing apparatus  20 - 3  as the third embodiment are substantially the same as those of the audio processing apparatus  20 - 2  as the second embodiment. For that reason, the ensuing explanation will stress the structural differences between the third embodiment and the second embodiment. 
     The control portion  212  of the third embodiment possesses not only the function of the control portion  210  in the above-described first and second embodiments but also the function of generating a screen for enhancing the user&#39;s awareness of his or her hearing characteristics and of causing the display portion  28  to display the generated screen. For example, as shown in  FIG. 19 , the display portion  212  may cause the display portion  28  to display a screen reflecting the results of the hearing characteristic tests taken by the user. 
       FIG. 19  is an explanatory view showing a specific example of hearing characteristic test results displayed on the screen of the display portion  28 . As shown in  FIG. 19 , the screen showing hearing characteristic test results includes a graphic representation illustrating the difference between the user&#39;s hearing characteristics (in solid line) and the average hearing characteristic (in broken line), along with a message explaining specifics of the user&#39;s hearing characteristics. By checking such a screen showing the hearing characteristic test results, the user can accurately grasp his or her own hearing characteristics. 
     It has been found that users who hear sounds with relatively high sound volumes tend to have their hearing characteristics worsened. Given such findings, the control portion  212  may provide the user when hearing sounds with a relatively large sound volume with a screen displayed on the display portion  28  prompting the user to take hearing characteristic tests. For example, based on the user&#39;s past history of sound volumes in effect during audio reproduction, the control portion  212  may calculate indexes regarding the reproduced sound volumes such as the average of the actual sound volumes reproduced and the frequency with which sounds were reproduced with volumes exceeding a predetermined threshold. If these indexes are found to exceed predetermined settings, the control portion  212  may cause the display portion  28  to display the screen prompting the user to take hearing characteristic tests. As another alternative, when the user is hearing sounds with a relatively high sound volume, the control portion  212  may act to reduce the sound volume of the reproduced audio data. 
     5. VARIATIONS 
     It is to be understood that while the disclosure has been described in conjunction with specific embodiments with reference to the accompanying drawings, it is evident that many alternatives, modifications and variations will become apparent to those skilled in the art in light of the foregoing description. It is thus intended that the present disclosure embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims. 
     For example, where the earphones  26  are composed of a right-ear phone (right-ear audio output portion) and a left-ear phone (left-ear audio output portion), hearing characteristic tests may be carried out separately on the user&#39;s right ear and left ear. This structure permits acquisition of hearing characteristic information separately on the right ear and left ear and allows the acquired information to be stored separately into the storage portion  230 . The equalizer  250  can then correct the reproduced signal for the right ear based on the right-ear hearing characteristic information and the reproduced signal for the left ear on the basis of the left-ear hearing characteristic information. 
     Also, the storage portion  230  may be arranged to store the audio data based on the reproduced signal corrected by the equalizer  250 . This structure eliminates the need for correcting the audio data as it is reproduced based on the user&#39;s hearing characteristic information. If such audio data is moved from this audio processing apparatus to another audio processing apparatus, the latter apparatus can output the reproduced signal having been corrected on the basis of the user&#39;s hearing characteristic information. 
     The audio processing apparatus  20  may be further provided with a communication portion for transmitting to another audio processing apparatus the user&#39;s hearing characteristic information acquired through hearing characteristic tests. Upon receipt of the user&#39;s hearing characteristic information thus transmitted, the other audio processing apparatus can also correct the reproduced signal based on the user&#39;s information. If the storage portion  230  is a piece of removable storage media, then the movement of hearing characteristic information to another audio processing apparatus may be accomplished by attaching the removed storage portion  230  carrying the information in question to the other apparatus. 
     6. CONCLUSION 
     The first embodiment of the present disclosure uses test tones of which the frequencies are varied over time during hearing characteristic tests. This embodiment provides the user with freshly inspired hearing characteristic tests and can shorten the time it takes to carry out the tests. The second embodiment of the present disclosure suppresses the influence of external noise when hearing characteristic tests are performed. This embodiment permits more accurate acquisition of the user&#39;s hearing characteristic information than before. The third embodiment of the present disclosure allows the display portion  28  to display the screen showing hearing characteristic test results as well as the screen for urging the execution of the hearing characteristic tests. This helps enhance the user&#39;s awareness of his or her own hearing characteristics. 
     In this description, the steps constituting the processes executed by the audio processing apparatus  20  of the present disclosure need not necessarily be performed chronologically, i.e., in the order in which they are depicted in the accompanying flowcharts. Alternatively, these steps may be carried out by the audio processing apparatus  20  parallelly or in sequences different from those given by the flowcharts. 
     According to the embodiment of the present disclosure, it is also possible to create a computer program for causing the hardware such as the CPU (Central Processing Unit), ROM and RAM (Random Access Memory) inside the audio processing apparatus  20  to exert functions equivalent to those of the above-described components making up the audio processing apparatus  20 . It is further possible to offer storage media carrying that computer program. 
     The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2010-181269 filed in the Japan Patent Office on Aug. 13, 2010, the entire content of which is hereby incorporated by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factor in so far as they are within the scope of the appended claims or the equivalents thereof.