Abstract:
Methods and apparatus implementing a technique for producing an audio output customized to a listener&#39;s hearing impairment through a digital telephone. A user initially sets user parameters to represent the user&#39;s hearing spectrum. In receiving a call, the digital telephone receives an input signal. The digital telephone adjusts the input signal according to the user parameters and generates an output signal based upon the adjusted input signal.

Description:
TECHNICAL FIELD 
     The present disclosure relates to digital telephones, and more specifically to digital telephones with audio output that is customized to compensate for a user&#39;s individual hearing spectrum. 
     BACKGROUND 
     Conventional cellular phones provide an audio output which can be difficult to hear for a listener whose hearing is impaired. Increasing the output volume of the cellular phone is usually only partially effective when the listener&#39;s hearing is impaired. Typical hearing impairment occurs at select frequency bands. The hearing impairment may be complete or partial at any band. Uniform increasing of the output volume only addresses those bands which are partially impaired and so a uniform increase only partially aids the listener. In certain bands, which are completely impaired, the user still does not hear. The listener can also experience discomfort at the loudness of the output in bands which are not impaired in order to be able hear the other bands. 
     Conventional hearing aids typically provide selective amplification of sound to compensate for a user&#39;s specific hearing impairment. 
     Voice coder-decoders (“vocoders”) have been used in cellular phones to achieve compression in the amount of digital information necessary to represent human speech. A vocoder in a transmitting device derives a vocal tract model in the form of a digital filter and encodes a digital sound signal using one or more “codebooks”. Each codebook represents an excitation of the derived vocal tract filter in an area of speech. One typical codebook represents long-term excitations, such as pitch and voiced sounds. Another typical codebook represents short-term excitations, such as noise and unvoiced sounds. The vocoder generates a digital signal including vocal tract filter parameters and codebook excitations. The signal also includes information from which the codebooks can be reconstructed. In this way, the encoded signal is effectively compressed and hence uses less space than directly digitally representing every sound. 
     A receiving vocoder decodes a compressed digital signal using codebooks and the vocal tract filter. Based upon the parameters contained in the signal, the vocoder reconstructs the sound into an uncompressed digital sound. The digital signal is converted to an analog signal and output through a speaker. 
     SUMMARY 
     The present disclosure describes methods and apparatus implementing a technique for producing an audio output customized to a listener&#39;s hearing impairment through a digital telephone. A user initially sets user parameters to represent the user&#39;s hearing spectrum. In receiving a call, the digital telephone receives an input signal. The digital telephone adjusts the input signal according to the user parameters and generates an output signal based upon the adjusted input signal. 
     In a preferred implementation, a digital telephone includes a user parameter control element. The user parameter control element includes a memory for storing user parameters representing the user&#39;s hearing ability. The digital telephone receives a signal through a receiving element. A digital signal processor is connected to the user parameter control element and the receiving element. The digital signal processor includes a vocoder connected to the receiving element and a frequency transformation element. The digital signal processor shifts the signal from frequency bands in which the user parameters indicate the user&#39;s hearing is impaired to frequency bands in which the user parameters indicate the user&#39;s hearing is not impaired. The digital signal processor also amplifies the shifted signal in frequency bands in which the user parameters indicate the user&#39;s hearing is impaired. An output element connected to the digital signal processor outputs the amplified signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a digital telephone according to the present disclosure. 
     FIG. 2 is a block diagram of a digital signal processor. 
     FIG. 3 is a flowchart of adjusting a signal. 
     FIG. 4 is a flowchart of setting user parameters. 
    
    
     DETAILED DESCRIPTION 
     The present disclosure describes methods and apparatus for providing customized audio output from a digital telephone according to parameters set by a user. The preferred implementation is described below in the context of a cellular telephone. However, the technique is also applicable to audio output in other forms of digital telephony devices. 
     FIG. 1 shows a cellular phone  100 . Cellular phone  100  is preferably an IS-95 cellular system. A case  102  forms a body of cellular phone  100  and includes the components described below. An antenna/receiver  105  receives an input analog signal. Antenna/receiver  105  is preferably a conventional type. A demodulator  110  converts the input analog signal to a digital signal. The digital signal is preferably a compressed digital signal from another phone via a central office. The output of demodulator  110  is supplied as a digital signal to a digital signal processor (“DSP”)  115 . DSP  115  processes the digital signal as is conventional in the art. Additional processing is done according to user parameters supplied by a user parameter control circuit  120 . User parameter control circuit  120  includes a memory  122  to store the user parameters. In one implementation, memory  122  stores sets of user parameters for more than one user, possibly including pre-defined sets. The current user selects the appropriate set of user parameters, such as through a user control  125 . DSP  115  uses the selected set of user parameters for processing, as described below. 
     A user control  125 , such as a control on the exterior of cellular phone  100 , provides user input to user parameter control circuit  120 . A digital to analog converter (“DAC”)  130  converts the adjusted digital signal to an output analog signal. A speaker  135  plays the analog signal such that the user hears the analog signal according to the user parameters. Cellular phone  100  also preferably includes an audio input or microphone (not shown) for receiving audio input, such as speech, from the user. 
     FIG. 2 shows details of DSP  115 . DSP  115  includes a vocoder  205  and a frequency transformation circuit  210 . Vocoder  205  receives the digital signal from demodulator  110  and uncompresses the signal using a vocal tract filter  215 . Vocoder  205  preferably includes a vocal tract filter  215  and, as conventional vocoders do, two codebooks, a long-term codebook  220  and a short-term codebook  225 . Vocoder  205  uses long-term codebook  220  to decode long-term excitations, such as pitch and voiced sounds, encoded in the digital signal. Vocoder  205  uses short-term codebook  225  to decode short-term excitations, such as noise and unvoiced sounds, encoded in the digital signal. The codebook excitations are filtered by the vocal tract filter  215 , which is defined by decoded parameters, to reproduce the decoded sound. In one implementation, the digital signal also includes information from which the codebooks of the source of the digital signal can be reconstructed. Vocoder  205  uses the reconstructed codebooks to facilitate the decoding process. Vocoder  205  also includes one or more filters  230  for transforming the encoded digital signal to a decoded and decompressed digital signal. 
     Vocoder  205  preferably includes an internal parameter modifier  230 . Vocoder  205  configures internal parameter modifier  230  according to user parameters received from user parameter control circuit  120 . Internal parameter modifier  230  has the effect of frequency shifting portions of the signal from frequency bands in which the user&#39;s hearing is impaired, into bands in which the user can hear or can hear better. Vocoder  205  configures parameter modifier  230  preferably by modifying the pitch lag parameter and/or by adjusting the poles and zeroes of the filter according to the user parameters. Details of the shifting technique are described below. 
     Frequency transformation circuit  210  adjusts the digital signal produced by vocoder  205  according to different frequency bands. A fast Fourier transform (“FFT”) circuit  235  applies an FFT to the digital signal to convert the signal from the time domain to the frequency domain and divide the converted signal into a number of frequency bands. The number of bands affects the refinement of the adjustment to the signal and so a balance is established among refinement, performance, and cost according to the application. A band amplification circuit  240  selectively amplifies bands of the frequency divided signal. 
     Band amplification circuit  240  preferably amplifies the signal in those frequency bands in which the user&#39;s perception of sound is attenuated. Band amplification circuit  240  amplifies each band by an amount which brings the sound within the user&#39;s hearing range for that frequency band. A band table  245  receives user parameters from user parameter circuit  120  and supplies band parameters to band amplification circuit  240 . The band parameters indicate which bands are to be amplified as well as the amount of appropriate amplification. The user parameters are set through an audio test, as described below. An inverse FFT (“IFFT”) circuit  250  transforms the amplified signal from the frequency domain to the time domain, compiling the divided signal back into a unified digital signal. DAC  130  converts the digital signal to an analog signal to be output by cellular phone  100  through speaker  135 . 
     Flowchart  300  shows the software or hardware of a preferred implementation, as shown in FIG.  3 . Antenna/receiver  105  receives an analog signal and demodulator  110  converts the analog signal to a digital signal, step  305 . DSP  115  adjusts the digital according to user parameters using vocoder  205  and frequency transformation circuit  210 . The user parameters are set previously through an audio test, as described below. Vocoder  205  modifies parameters of the signal in order to shift portions of the decoded signal such that more of the signal is in frequency bands in which the user can hear, step  310 , and decodes the digital signal. Frequency transformation circuit  210  transforms the signal into the frequency domain by applying an FFT, step  320 . Frequency transformation circuit  210  amplifies portions of the transformed signal corresponding to frequency bands in which the user&#39;s hearing is attenuated, step  325 . Frequency transformation circuit  210  returns the signal to the time domain by applying an inverse FFT, step  330 . DAC  130  converts the adjusted digital signal to an analog signal, step  335 , and the resulting analog signal is played through speaker  135 , step  340 . 
     In one implementation of modifying the long term codebook, the pitch lag parameter that determines the reconstructed form of the long term codebook, is adjusted so that portions of the underlying audio signal are mapped from frequency bands or regions where the user cannot hear to regions where the user can hear. Alternatively, regions where the user&#39;s hearing requires intolerably high levels of amplification are also mapped onto regions where the necessary amplification levels are more acceptable. In this case, the threshold level of intolerable amplification is based on the maximum amplitude signal of the cellular phone. The mapping preferably retains variation in pitch in order to allow for inflection in the voice while avoiding frequencies where the listener has very large or uncorrectable hearing loss as well as avoiding unnecessary jumps over frequency ranges. The technique involves comparing the measurement of the minimum energy γ(i) required in a frequency band i that extends from f(i−1) to f(i) to the maximum allowable energy threshold E max (i) If γ(i) exceeds E max (i), then the region is unacceptable and the frequencies from f(i−1) to f(i) are mapped into the nearest acceptable frequency range where the threshold is not exceeded. 
     The range of pitch lags supported by the vocoder determines the range of frequencies that are of interest. Typical values of pitch lags are d min =16 samples and d max =150 samples, which correspond to frequencies of 500 Hz and 53.3 Hz, respectively, for a signal sampled at 8 kHz. The overall frequency range is divided into m regions (not necessarily of equal size), referred to as region  1  through region m. No adjacent areas have the same characteristic with respect to acceptability, as described above, because the frequency defining the edge of the range can be increased or decreased to include the adjacent area. 
     Mapping an unacceptable region can be divided into five cases. In the first case, there is only one region covering the overall vocoder pitch range. In this case, there is no mapping to perform. 
     In the second case, there are only two regions (m=2). One region is unacceptable, e.g., the user cannot hear in the frequency band, and the other is acceptable, e.g., the user can hear in the frequency band. In this case, the entire frequency range from f(0) to f(2) is compressed into the region from f(0) to f(1) or from f(1) to f(2), depending on which region is acceptable. The mapping is preferably performed by linear compression. The compressed frequency f new  is solved for in terms of the original frequency f old  as follows          f   new     =         [       f   old     -     f        (   0   )         ]                         f        (   2   )       -     f        (   1   )             f        (   2   )       -     f        (   0   )             +     f        (   1   )                                
     where region 1 is the unacceptable region, or          f   new     =         [       f   old     -     f        (   0   )         ]                         f        (   1   )       -     f        (   0   )             f        (   2   )       -     f        (   0   )             +     f        (   0   )                                
     where region 2 is the unacceptable region. 
     In the third case, an unacceptable region is either region 1 or region m, and the adjacent acceptable region has another unacceptable region on the other side. The entire unacceptable region and half of the acceptable region are compressed into the half of the acceptable region adjacent to the unacceptable region. As above, fnew can be expressed as:          f   new     =         [       f   old     -     f        (   0   )         ]                           f   mid          (   1   )       -     f        (   1   )               f   mid          (   1   )       -     f        (   0   )             +     f        (   1   )                                
     where region 1 is the unacceptable region, or          f   new     =         [       f   old     -       f   mid          (     m   -   1     )         ]                         f        (     m   -   1     )       -       f   mid          (     m   -   1     )             f        (   m   )       -       f   mid          (     m   -   1     )             +       f   mid          (     m   -   1     )                                
     where region m is the unacceptable region. The f mid  frequency is a midpoint in the acceptable region. For example, for region i, f mid (i)=[f(i−1)+f(i)]/2. Half the acceptable region is used because the other unacceptable region on the other side of the acceptable region is mapped onto the unused half of the acceptable region, as described below. 
     In the fourth case, the unacceptable region is region 2 or region “m−1”. Half of the unacceptable region is mapped onto the adjacent acceptable region 1 or region m. Thus, half of the unacceptable region closest to the acceptable region 1 or m and the entire acceptable region 1 or m is mapped into the entire acceptable region 1 or m. The other half of the unacceptable region is mapped onto the acceptable region on the other side of the unacceptable region, as described below. As above, f new  can be expressed as:          f   new     =         [       f   old     -     f        (   0   )         ]                         f        (   1   )       -     f        (   0   )               f   mid          (   1   )       -     f        (   0   )             +     f        (   0   )                                
     where region 2 is the unacceptable region, or          f   new     =         [       f   old     -       f   mid          (     m   -   1     )         ]                         f        (   m   )       -     f        (     m   -   1     )             f        (   m   )       -       f   mid          (     m   -   1     )             +     f        (     m   -   1     )                                
     where region m−1 is the unacceptable region. 
     In the fifth case, the unacceptable region i is mapped onto an acceptable region that is not region 1 or region m. Half of the unacceptable region is mapped onto the half of the adjacent acceptable region which is adjacent to the unacceptable region. For example, the upper half of region i is mapped onto the lower half of region i+1 along with the lower half of region i+1. As above, f new  can be expressed as:          f   new     =         [       f   old     -       f   mid          (     i   -   1     )         ]                         f        (     i   -   1     )       -       f   mid          (     i   -   1     )             f        (   i   )       -       f   mid          (     i   -   1     )             +       f   mid          (     i   -   1     )                                
     where unacceptable region i is mapped onto acceptable region i−1, or          f   new     =         [       f   old     -       f   mid          (   i   )         ]                         f        (     i   +   1     )       -     f        (   i   )             f        (     i   +   1     )       -       f   mid          (   i   )             +     f        (   i   )                                
     where unacceptable region i is mapped onto acceptable region i+1. 
     The user sets the user parameters in an audio test by responding to a series of tones produced by the cellular phone. As shown in FIG. 4, in a process  400  of setting the user parameters, cellular phone  100  generates an initial test tone played through speaker  135 , step  405 . This initial test tone is at a first amplitude and frequency, preferably at an amplitude which can be heard by a person with average hearing and at a frequency corresponding to the lowest of the frequency bands used in DSP  115 . The user indicates if the user can hear the initial test tone, such as by pressing a button in user control  125 , step  410 . If the user can hear the initial test tone, cellular phone  100  generates another test tone at the same frequency but at a lower amplitude, step  415 . Cellular phone  100  continues to generate test tones at successively lower amplitudes until the user does not indicate the user can hear the test tone or some minimum threshold has been reached, step  420 . This final test tone marks the hearing threshold of the user for the current frequency. 
     If the user does not indicate the user can hear the initial test tone, such as by taking no action, step  410 , cellular phone  100  generates a test tone at the same frequency but at a higher amplitude, step  415 . Cellular phone  100  continues to generate test tones at successively higher amplitudes until the user indicates the user can hear the test tone or some maximum threshold has been reached, step  420 . This final test tone marks the hearing threshold of the user for the current frequency. 
     User parameter control circuit  120  records the amplitude and frequency of the user&#39;s hearing threshold for the current frequency in memory  122 , step  425 . Cellular phone  100  repeats steps  405  through  425  for each frequency band, step  430 . After user parameter control circuit  120  has recorded a hearing threshold for each frequency, user parameter control circuit has a table of user parameters modeling the user&#39;s hearing ability. As noted above, the number of frequency bands used corresponds to the number of frequency bands or regions discussed above in the operation of vocoder  205  and frequency transformation circuit  210 . 
     In an alternative implementation, the digital signal processor described above is included in a digital telephone in a conventional telephone network. An analog signal received at the digital telephone is converted to a digital signal and adjusted as described above. Alternatively, the digital telephone can be a combined software and hardware implementation in a computer system. 
     In another alternative implementation, the components of the cellular phone described above interact with a hearing aid device. In this case, the cellular phone transmits the adjusted signal to the hearing aid device which in turn plays the audio signal through its own speaker. 
     The components of the digital signal processor described above can be implemented in hardware or programmable hardware. Alternatively, the DSP can include a processing unit using software which can be accessed through a port or card connection. 
     Numerous implementations have been described. Additional variations are possible. For example, the signal received by the telephone can be a digital signal supplied over a digital network. The user parameters can be obtained by downloading values to the telephone rather than through manual entry by a user. Accordingly, the technique of the present disclosure is not limited by the exemplary implementations described above, but only by the scope of the following claims.