Abstract:
A selective noise canceling device is disclosed that evaluates an external audio signal and determines whether a given external audio signal should be suppressed or reproduced. A selective noise suppression circuit processes the external audio signal to classify the external audio signal as noise to be suppressed or as a desired audio signal to be reproduced. An external audio signal, or a desired portion thereof, is reproduced if a portion of the external audio signal is likely to be of interest to the user. The desired external signal may optionally be amplified over the primary selected audio signal for emphasis and the selected audio signal may optionally be suppressed entirely when the desired external signal is reproduced.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to active noise reduction techniques, and more particularly, to headsets and other devices employing such active noise reduction techniques.  
         BACKGROUND OF THE INVENTION  
         [0002]    Portable telephones and electronic devices are increasingly popular in today&#39;s mobile society. Cellular and wireless telephones, for example, receive a signal transmitted from a base station or base unit, respectively. The portable telephones allow users to make and receive telephone calls within a given radius of the base station (or base unit). Similarly, portable electronic devices, such as the Sony Walkman™, commercially available from Sony Corporation, including personal radios, cassette tape players, digital audio tape (DAT) players, MP3 players and compact disc players, allow a user to listen to desired audio content at virtually any location.  
           [0003]    Such portable devices provide users with great flexibility and convenience. The portable nature of such devices, however, encourages users to utilize such devices from virtually any location, or even while traveling. Thus, users may be distracted when adjusting settings of the portable devices, such as when making a telephone call, or by the content itself, thereby potentially exposing the user to undue risks. In response to an increased number of motor vehicle accidents due to drivers distracted while making a telephone call, for example, a number of jurisdictions have enacted legislation requiring users of cellular telephones to employ hands-free cellular devices.  
           [0004]    Portable telephones and electronic devices typically include headphones or integrated speakers to reproduce the audio signal. Headsets typically include a pair of earpieces coupled by a flexible headband that presses the earpieces against the head of the user. The application of the earpieces to the user&#39;s ears serves to reduce ambient noise in a passive manner. In many environments, however, such as on an airplane, passive noise reduction techniques are insufficient.  
           [0005]    Thus, a number of manufacturers provide headsets that incorporate an active noise reduction feature for canceling noise signals. Bose Corporation of Framingham, Mass., for example, sells a line of aviation headsets for use by airline passengers. The aviation headsets reduce engine and wind noise, and provide improved reproduction of a selected audio signal. Generally, the Bose aviation headset employs a microphone to monitor external sound at the user&#39;s ear. The measured sound is compared with the selected audio signal that the user desires to hear. The difference between the measured sound and the selected audio signal is unwanted external noise. An opposing correction signal (antinoise) is then generated by the headset. The antinoise is an equal and opposite vibration, 180 degrees out of phase with the noise to be blocked. When the unwanted noise and generated antinoise collide, destructive interference effects operate to cancel each other out.  
           [0006]    Such noise canceling headsets serve to cancel all noise, however, other than the selected audio signal. Generally, the noise cancellation feature emphasizes the selected audio signal, and suppresses all other audio signals. Thus, users of such headsets are in a relatively closed audio environment, essentially unaware of any outside audio stimulus other than associated with the selected audio signal. If another person speaks to a user of such headsets, for example, the noise cancellation feature would operate to suppress the speaker. Likewise, the noise cancellation feature would operate to suppress other audio signals, such as an emergency announcement or alarm, that would otherwise alert the user to a risk.  
           [0007]    A need therefore exists for a noise canceling device that evaluates the content of an external audio signal and determines whether a given audio signal should be suppressed or reproduced. A further need exists for a noise canceling headset that reproduces external audio signals that are of interest to a user. Yet another need exists for a noise canceling headset that classifies an external audio signal based on its content.  
         SUMMARY OF THE INVENTION  
         [0008]    Generally, a selective noise canceling device is disclosed that evaluates an external audio signal and determines whether a given external audio signal should be suppressed or reproduced. The disclosed selective noise canceling device includes a selective noise suppression circuit that processes the external audio signal to classify the external audio signal as either noise to be suppressed or a desired audio signal to be reproduced. The portion of the external audio signal that is to be reproduced in accordance with the present invention is referred to herein as the “desired external signal.” 
           [0009]    The present invention reproduces an external audio signal, or a desired portion thereof, if a portion of the external audio signal is likely to be of interest to the user. For example, the selective noise canceling device of the present invention may reproduce audio signals alerting the user to harm, as well as other audio signals directed to the user that are acoustically distinct from the general background noise of the environment.  
           [0010]    The desired external signal may optionally be amplified over the primary selected audio signal for emphasis. In addition, the selected audio signal may optionally be suppressed entirely when the desired external signal is reproduced.  
           [0011]    A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 illustrates a selective noise canceling headset in accordance with the present invention;  
         [0013]    [0013]FIG. 2 is a schematic block diagram illustrating the selective noise canceling headset of FIG. 1 in further detail;  
         [0014]    [0014]FIG. 3 is a schematic block diagram illustrating a first embodiment of the selective noise suppression circuit of FIG. 2;  
         [0015]    [0015]FIG. 4 is a schematic block diagram illustrating a second embodiment of the selective noise suppression circuit of FIG. 2; and  
         [0016]    [0016]FIG. 5 is a schematic block diagram illustrating a third embodiment of the selective noise suppression circuit of FIG. 2. 
     
    
     DETAILED DESCRIPTION  
       [0017]    [0017]FIG. 1 illustrates a selective noise canceling headset  100  in accordance with the present invention. As shown in FIG. 1, the selective noise canceling headset  100  includes a pair of earpieces  110 - 1 ,  110 - 2  (collectively, earpieces  110 ) coupled by a flexible headband  120  that presses the earpieces  110  against the head of the user, in known manner. In addition, the selective noise canceling headset  100  includes one or more microphones  150  mounted on the earpieces  110  to monitor the external sound at the user&#39;s ear and generate a signal referred to herein as the “external audio signal.” 
         [0018]    According to one feature of the present invention, the selective noise canceling headset  100  also includes a selective noise suppression circuit  200 , discussed below in conjunction with FIG. 2, that processes the external audio signal obtained by the microphone  150  and selectively classifies the external audio signal as either noise to be suppressed or an audio signal to be reproduced. The portion of the external audio signal that is to be reproduced in accordance with the present invention is referred to herein as the “desired external signal.” 
         [0019]    Generally, an external audio signal will be reproduced by the selective noise canceling headset  100  in accordance with the present invention if the audio signal is likely to be of interest to the user, as discussed further below. For example, the selective noise canceling headset  100  may reproduce audio signals alerting the user to harm, such a dog barking, an alarm or an automobile horn, and other audio signals directed to the user that are acoustically distinct from the general background noise of the environment, such as spoken words. The user can optionally specify the kinds of external audio noise to be reproduced in a given environment.  
         [0020]    Thus, as shown in FIG. 2, the selective noise suppression circuit  200  receives the selected audio signal  210  from a media player  215 , such as a personal radio, cassette tape player, DAT player, MP3 player, compact disc player or portable telephone, and the external audio signal  220  generated by the microphone  150 . Various embodiments of the selective noise suppression circuit  200  are discussed below in conjunction with FIG. 3 through  5 . Generally, the selective noise suppression circuit  200  processes the selected audio signal  210  and external audio signal  220  to reproduce the selected audio signal  210 , as well as the desired external signal portion of the external audio signal  220 , and suppress the remaining portions of the external audio signal  220  (noise).  
         [0021]    Thus, the selective noise suppression circuit  200  applies the selected audio signal  210  and the desired external signal to the selective noise canceling headset  100 . In a further variation, the selective noise suppression circuit  200  can optionally cancel the selected audio signal  210  as well and reproduce only the desired external signal, for example, in presence of a known threat.  
         [0022]    [0022]FIG. 3 illustrates a first exemplary embodiment of the selective noise suppression circuit  200  of FIG. 2. As shown in FIG. 3, the selective noise suppression circuit  200  includes an audio classifier  310  and a noise canceling circuit  340 . As shown in FIG. 3, the audio classifier  310  processes the external audio signal and returns a binary zero (0) if the external audio signal is noise and should be cancelled by the noise canceling circuit  340 , or a binary one (1) if the external audio signal is useful and should be reproduced as the desired external signal with the selected audio signal. In this manner, the audio classifier  310  indicates whether the entire external audio signal should be suppressed or reproduced by the noise canceling circuit  340 . The audio classifier  310  may be embodied in accordance with the audio content analysis techniques described in, for example, Silvia Pfeiffer et al., “Automatic Audio Content Analysis,” Proc. ACM Multimedia 96, 21-30, Boston, Mass. (November 1996), incorporated by reference herein.  
         [0023]    [0023]FIG. 4 illustrates a second exemplary embodiment of the selective noise suppression circuit  200 ′ of FIG. 2. As shown in FIG. 4, the selective noise suppression circuit  200 ′ includes an audio classifier  410 , an amplifier  420 , an adder  430  and a noise canceling circuit  440 . The audio classifier  410  and noise canceling circuit  440  can be embodied in the same manner as the corresponding elements in FIG. 3. Thus, the audio classifier  410  processes the external audio signal and returns a binary zero (0) or one (1) if the external audio signal is noise and should be cancelled or if the external audio signal is useful and should be reproduced, respectively.  
         [0024]    In addition, if the external audio signal is useful, the signal is amplified by an amplifier  420  also controlled by the on/off signal generated by the audio classifier  410 . Thus, the output of the amplifier  420  is zero (0) if the external audio signal is not useful, or an amplified version of the external audio signal if the external audio signal is useful. The output of the amplifier  420  is added to the selected audio signal by an adder  430 , and the combined output is applied to the noise canceling circuit  440 . In this manner, the output of the noise canceling circuit  440  can emphasize the amplified external audio signal over the selected audio signal, if desired.  
         [0025]    [0025]FIG. 5 illustrates a third exemplary embodiment of the selective noise suppression circuit  200 ″ of FIG. 2. As shown in FIG. 4, the selective noise suppression circuit  200 ″ includes an audio classifier/segmenter  510 , an amplifier  520 , an adder  530  and a noise canceling circuit  540 . The audio classifier  510 , adder  530  and noise canceling circuit  540  can be embodied in the same manner as the corresponding elements in FIGS. 3 and 4. In the embodiment of FIG. 5, the amplifier  520  is no longer controlled by the output of the audio classifier  510 , but rather amplifies any signal present at its input.  
         [0026]    The audio classifier/segmenter  510  segments the external audio signal into various signals, classifies each individual signal as useful or noise, and suppresses the noise using a filter  515 . The output of the filter  515  is the desired external signal (DES) . The audio classifier/segmenter  510  may be embodied in accordance with the techniques described in T. Zhang and C-C. Jay Kuo, “Heuristic Approach for Generic Audio Data Segmentation and Annotation,” Proc. ACM Multimedia 99 (ACM Special Interest Groups), Nov. 5, 1999, incorporated by reference herein. Generally, the audio classifier/segmenter  510  will reproduce the external audio signal if the audio signal is likely to be of interest to the user. For example, the selective noise canceling headset  100  may reproduce audio signals alerting the user to harm, such an alarm or an automobile horn, and other audio signals directed to the user that are acoustically distinct from the general background noise of the environment, such as spoken words. The desired external signal is amplified by the amplifier  520  and the output of the amplifier  520  is added to the selected audio signal by an adder  530 . The combined output is applied to the noise canceling circuit  540 . In this manner, the output of the noise canceling circuit  540  can emphasize the amplified desired external signal, if desired, over the selected audio signal.  
         [0027]    In a further variation, the audio classifier/segmenter  510  can initiate the replay of a recorded message associated with a given predefined audio segment. For example, the audio classifier/segmenter  510  can initiate a message such as “dog barking on left side” if such a signal is identified in accordance with the present invention. In an embodiment where the external audio signal is amplified, the final audio signal can be defined as follows:  
         Final Audio Signal=α*(external audio signal)+(1-α)*(selected audio signal),  
         [0028]    where a determines the intensity of the signal.  
         [0029]    It is to be understood that the embodiments and variations shown and described herein are merely illustrative of the principles of this invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention.