Abstract:
Method and apparatus for environment detection and adaptation in hearing assistance devices. Performance of feature extraction and environment detection to perform adaptation to hearing assistance device operation for a number of hearing assistance environments. The system detecting various noise sources independent of speech. The system determining adaptive actions to take place based on predicted sound class. The system providing individually customizable response to inputs from different sound classes. In various embodiments, the system employing a Bayesian classifier to perform sound classifications using a priori probability data and training data for predetermined sound classes. Additional method and apparatus can be found in the specification and as provided by the attached claims and their equivalents.

Description:
TECHNICAL FIELD 
     This disclosure relates to hearing assistance devices, and more particularly to method and apparatus for environment detection and adaptation in hearing assistance devices. 
     BACKGROUND 
     Many people use hearing assistance devices to improve their day-to-day listening experience. Persons who are hard of hearing have many options for hearing assistance devices. One such device is a hearing aid. Hearing aids may be worn on-the-ear, behind-the-ear, in-the-ear, and completely in-the-canal. Hearing aids can help restore hearing, but they can also amplify unwanted sound which is bothersome and sometimes ineffective for the wearer. 
     Many attempts have been made to provide different hearing modes for hearing assistance devices. For example, some devices can be switched between directional and omnidirectional receiving modes. However, different users typically have different exposures to sound environments, so that even if one hearing aid is intended to work substantially the same from person-to-person, the user&#39;s sound environment may dictate uniquely different settings. 
     However, even devices which are programmed for a person&#39;s individual use can leave the user without a reliable improvement of hearing. For example, conditions can change and the device will be programmed for a completely different environment than the one the user is exposed to. Or conditions can change without the user obtaining a change of settings which would improve hearing substantially. 
     What is needed in the art is an improved system for updating hearing assistance device settings to improve the quality of sound received by those devices. The system should be highly programmable to allow a user to have a device tailored to meet the user&#39;s needs and to accommodate the user&#39;s lifestyle. The system should provide intelligent and automatic switching based on detected environments and programmed settings and should provide reliable performance for changing conditions. 
     SUMMARY 
     The above-mentioned problems and others not expressly discussed herein are addressed by the present subject matter and will be understood by reading and studying this specification. The present subject matter provides method and apparatus for environment detection and adaptation in hearing assistance devices. Various examples are provided to demonstrate aspects of the present subject matter. One example of an apparatus employing the present subject matter includes: a microphone; an analog-to-digital (A/D) converter connected to convert analog sound signals received by the microphone into time domain digital data; a processor connected to process the time domain digital data and to produce time domain digital output, the processor including: a frequency analysis module to convert the time domain digital data into subband digital data; a feature extraction module to determine features of the subband data; an environment detection module to determine one or more sources of the subband data based on a plurality of possible sources identified by predetermined classification parameters; an environment adaptation module to provide adaptations to processing using the determination of the one or more sources of the subband data; a subband signal processing module to process the subband data using the adaptations from the environment adaptation module; and a time synthesis module to convert processed subband data into the time domain digital output. Variations include, but are not limited to, the previous example plus combinations including one or more of: a digital-to-analog (D/A) converter connected to receive the time domain digital output and convert it to analog signals; a receiver to convert the analog signals to sound; examples where the environment detection module is adapted to determine sources including wind, machine noise, and speech; where the speech source includes a first speech source associated with a user of the apparatus and a second speech source; where the environment adaptation module includes parameter storage for each of the plurality of possible sources, the parameter storage including a plurality of subband gain parameter storages; where the parameter storage further includes an attack parameter storage and a release parameter storage; where the parameter storage further includes a misclassification threshold parameter storage; where the environment detection module includes a Bayesian classifier; where the environment detection module includes storage for one or more a priori probability variables; where the environment detection module comprises storage for training data; a second microphone; further including a second A/D converter connected to convert analog sound signals received by the second microphone into additional time domain digital data, the additional time domain digital data combined with the time domain digital data provided to the processor for processing; and where the processor further includes a directivity module. 
     Some other variations include: a microphone; an analog-to-digital (A/D) converter connected to convert analog sound signals received by the microphone into time domain digital data; a processor connected to process the time domain digital data and to produce time domain digital output, the processor including: a frequency analysis module to convert the time domain digital data into subband digital data; feature extraction means for extracting features of the subband data; environment detection means for determining one or more sources of the subband data based on a plurality of possible sources identified by predetermined classification parameters; environment adaptation means for providing adaptations to processing using the determination of the one or more sources of the subband data; and subband signal processing means for processing the subband data using the adaptations from the environment adaptation module. Some examples include a second microphone and second A/D converter and directivity means for adjusting receiving microphone configuration. 
     The present subject matter also includes variations of methods. For example a method, including: converting one or more time domain analog acoustic signals into frequency domain subband samples; extracting features from the subband samples using time domain analog signal information; detecting environmental parameters to categorize one or more sound sources based on a predetermined plurality of possible sound sources; and adapting processing of the subband samples using the one or more categorized sound sources. Further examples include the previous and combinations including one or more of: where the detecting includes using a Bayesian classifier to categorize the one or more sound sources; where the predetermined plurality of possible sound sources comprises: wind, machines, and speech; and including discriminating speech associated with a user of an apparatus performing the method from speech of other speakers; and including applying parameters associated with the one or more categorized sound sources, the parameters including a gain adjustment, an attack parameter, a release parameter, and a misclassification threshold parameter; where the gain adjustment is stored as individual gain settings per subband; including adjusting directionality using detected environmental parameters; and including processing the subband samples using hearing aid algorithms. 
     This Summary is an overview of some of the teachings of the present application and not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details about the present subject matter are found in the detailed description and appended claims. Other aspects will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which are not to be taken in a limiting sense. The scope of the present invention is defined by the appended claims and their legal equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of a hearing assistance device, according to one embodiment of the present subject matter. 
         FIG. 2  shows a process diagram of environment detection and adaptation, according to one embodiment of the present subject matter. 
         FIG. 3  shows a process diagram of directionality combined with environment detection and adaptation, according to one embodiment of the present subject matter. 
         FIG. 4  shows a process for classification of sound sources for reception in an omnidirectional hearing assistance device, according to one embodiment of the present subject matter. 
         FIG. 5  shows a process for classification of sound sources for reception in a directional hearing assistance device, according to one embodiment of the present subject matter. 
         FIG. 6  shows a flow diagram of a detection system, according to one embodiment of the present subject matter. 
         FIG. 7  shows a gain diagram of a gain reduction process, according to one embodiment of the present subject matter. 
         FIG. 8  shows one example of environment adaptation parameters to demonstrate various controls available according to one embodiment of the present subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the present subject matter refers to subject matter in the accompanying drawings which show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter. References to “an”, “one”, or “various” embodiments in this disclosure are not necessarily to the same embodiment, and such references contemplate more than one embodiment. The following detailed description is demonstrative and not to be taken in a limiting sense. The scope of the present subject matter is defined by the appended claims, along with the full scope of legal equivalents to which such claims are entitled. 
     The present subject matter relates to methods and apparatus for environment detection and adaptation in hearing assistance devices. 
     The method and apparatus set forth herein are demonstrative of the principles of the invention, and it is understood that other method and apparatus are possible using the principles described herein. 
     System Overview 
       FIG. 1  shows a block diagram of a hearing assistance device, according to one embodiment of the present subject matter. In one embodiment, hearing assistance device  100  is a hearing aid. In one embodiment, mic  1   102  is an omnidirectional microphone connected to amplifier  104  which provides signals to analog-to-digital converter  106  (“A/D converter”). The sampled signals are sent to processor  120  which processes the digital samples and provides them to the digital-to-analog converter  140  (“D/A converter”). Once the signals are analog, they can be amplified by amplifier  142  and audio sound can be played by receiver  150  (also known as a speaker). Although  FIG. 1  shows D/A converter  140  and amplifier  142  and receiver  150 , it is understood that other outputs of the digital information may be performed. For instance, in one embodiment, the digital data is sent to another device configured to receive it. For example, the data may be sent as streaming packets to another device which is compatible with packetized communications. In one embodiment, the digital output is transmitted via digital radio transmissions. In one embodiment, the digital radio transmissions are packetized and adapted to be compatible with a standard. Thus, the present subject matter is demonstrated, but not intended to be limited, by the arrangement of  FIG. 1 . 
     In one embodiment, mic  2   103  is a directional microphone connected to amplifier  105  which provides signals to analog-to-digital converter  107  (“A/D converter”). The samples from A/D converter  107  are received by processor  120  for processing. In one embodiment, mic  2   103  is another omnidirectional microphone. In such embodiments, directionality is controllable via phasing mic  1  and mic  2 . In one embodiment, mic  1  is a directional microphone with an omnidirectional setting. In one embodiment, the gain on mic  2  is reduced so that the system  100  is effectively a single microphone system. In one embodiment, (not shown) system  100  only has one microphone. Other variations are possible which are within the principles set forth herein. 
     Processor  120  includes modules for execution that will detect environments and make adaptations accordingly as set forth herein. Such processing can be on one or more audio inputs, depending on the function. Thus, even though,  FIG. 1  shows two microphones, it is understood that many of the teachings herein can be performed with audio from a single microphone. It is also understood that audio transducers other than microphones can be used in some embodiments. 
       FIG. 2  shows a process diagram of environment detection and adaptation, according to one embodiment of the present subject matter.  FIG. 2  shows one example of processes performed by processor  120 . Signals from A/D converter  106  are received by processor  120  for conversion from time domain into frequency domain information via frequency analysis module  202 . It is noted that some of the details of conversion from time domain signals (such as from microphone  430 ) to frequency domain signals, and vice-versa, were omitted from the figures to simplify the figures. Several known approaches exist to digitize the data and convert it into frequency domain samples. For example, in various embodiments overlap-add structures (not shown) are available to assist in conversion to the frequency domain and, from frequency domain back into time domain. Some such structures are shown, for example, in  Adaptive Filter Theory  (4 th  Edition) by Simon Haykin, Prentice Hall, 2001, and, section 7.2.5 of  Multirate Digital Signal Processing , by Crochiere and Rabiner, Prentice Hall, 1983. Other time domain to frequency domain conversions are possible without departing from the scope of the present subject matter. The sampled frequency domain information is divided into frequency subbands for processing. 
     Feature extraction module  204  receives both frequency domain or subband samples  203  and time domain samples  205  to determine features of the incoming samples. The feature extraction module generates information based on its inputs, including, but not limited to: periodicity strength, high-to-low-frequency energy ratio, spectral slopes in various frequency regions, average spectral slope, overall spectral slope, spectral shape-related features, spectral centroid, omni signal power, directional signal power, and energy at a fundamental frequency. This information is used by the environment detection module  206  to determine what a probable source is from a predetermined number of possible sources. The environment adaptation module then adjusts signal processing based on the probable source of the sound, sending parameters for use in the subband signal processing module  210 . The subband signal processing module  210  is used to adaptively process the subband data using both the adaptations due to environment and any other applications-specific signal processing tasks. For example, when the present system is used in a hearing aid, the subband signal processing module  210  also performs hearing aid processing associated with enhancing hearing of a particular wearer of the device. 
     Time synthesis module  212  converts the processed subband samples into time domain digital output which is sent to D/A converter  140  for conversion into analog signals. The references cited above pertaining to frequency synthesis also provide information for the conversion of subband samples into time domain. Other frequency domain to time domain conversions are possible without departing from the scope of the present subject matter. It is understood that the system set forth is an example, and that variations of the system are possible without departing from the scope of the present subject matter. 
     Environment Detection 
       FIG. 3  shows a process diagram of directionality combined with environment detection and adaptation, according to one embodiment of the present subject matter. The directionality feature is described in detail in U.S. Provisional Patent Application Ser. No. 60/743,481, filed even date herewith, and commonly assigned, the entire disclosure of which is incorporated herein by reference. The system  300  has processor  120  is able to receive digital samples from a plurality of various sources. For demonstration, A/D converters  106  and  107  are shown to provide digital samples to processor  120 . The digital samples from mic  1  and mic  2  are processed by the directionality module, which can select favorable microphone configurations based on preprogrammed parameters for reception as set forth in the application incorporated by reference above. The directionality module  302  transmits time domain samples to the rest of the system which operates substantially as set forth above for  FIG. 2 . In some embodiments, information from the directionality module  302 , such as mode information and other information, is shared with other modules of the system  300 . Other variations exist which do not depart from the principles provided herein. 
       FIG. 4  shows a process for classification of sound sources for reception in an omnidirectional hearing assistance device, according to one embodiment of the present subject matter. The process  400  first determines if speech is detected  402 . (Examples of speech detection are provided in conjunction with the discussion of  FIG. 6 .) If so, the system then detects whether a wearer of the device is speaking  404 ,  408  and if so then manages that sound according to parameters set for “own speech”  410 . Such parameters may include attenuation of own speech or other signal processing tasks. If the speech is not detected from the wearer, then it is deemed “other speech”  406  and that sound is managed as if it were regular noise  420 . 
     If speech is not detected  402 , the process then determines whether the sound is wind, machine or other sound  414 . If wind noise  442 , then special parameters for wind noise management are used  440 . If machine noise  432 , then special parameters for machine noise management are used  430 . If other sound  422 , then the sound is managed as if it were regular noise  420 . 
     The process set forth here are intended to demonstrate principles of the present subject matter and are not intended to be an exhaustive or exclusive treatment of the possible embodiments. Other embodiments featuring variations of these features are possible without departing from the scope of the present subject matter. 
       FIG. 5  shows a process for classification of sound sources for directional reception in a hearing assistance device, according to one embodiment of the present subject matter. The process  500  first determines if speech is detected  502 . If so, the system then detects whether a wearer of the device is speaking  504 ,  508  and if so then manages that sound according to parameters set for “own speech”  510 . Such parameters may include attenuation of own speech or other signal processing tasks. If the speech is not detected from the wearer, then it is deemed “other speech”  506  and that sound is managed as if it were regular noise  520 . 
     If speech is not detected  502 , the process then determines whether the sound is wind noise  515 . If wind noise  542 , then special parameters for wind noise management are used  540 . If not wind noise, then the process detects for machine noise  517 . If machine noise  532 , then special parameters for machine noise management are used  530 . If other sound  522 , then the sound is managed as if it were regular noise  520 . 
     The process set forth here are intended to demonstrate principles of the present subject matter and are not intended to be an exhaustive or exclusive treatment of the possible embodiments. Other embodiments featuring variations of these features are possible without departing from the scope of the present subject matter. 
       FIG. 6  shows a flow diagram of a detection system, according to one embodiment of the present subject matter. In one embodiment, frequency domain samples from the source input are converted into the frequency domain by frequency analysis module  602 . The resulting subband samples are processed by filter  604  to determine the time-varying nature of the samples. In one embodiment, the metric is related to a ratio of a time dependent mean (M) of the input over the time-dependent deviation of the input from the mean (D) or MID as provided by U.S. Pat. No. 6,718,301 to William S. Woods, the entire disclosure of which is incorporated herein by reference. Filter  606  also processes the samples to determine, among other things, spectral shape related features such as spectral centroid, spectral slopes, and high v. low frequency ratio. Block  608  measures the periodicity strength of the time domain input samples. The resulting data is sent to buffer  610  and then processed by a Bayesian classifier  614 . The Bayesian classifier is used because it is computationally efficient. The Bayesian classifier  614  incorporates inputs from stored and preprogrammed a priori probability parameters  616  that the detected sounds are likely to be one of the predetermined sources (e.g., wind, machinery, own speech, other speech, other noise). The goal of the Bayesian classification scheme is to choose the sound class that is most likely to occur given the feature values  610 , training data  612  and the a priori probabilities  616 , or probability that a sound class (e.g., wind, machinery, own speech, other speech, other noise) occurs in the real world. By changing the a priori probabilities, it is possible to increase/decrease the accuracy of the selection of sound class arising from the same sound class (“hit rate”) and increase/decrease the misclassifications of a sound class into a different sound class (“false alarm rate”). The resulting classification result and strength data is produced and stored  618  to be used to adapt processing for the particular environment detected. Classification result is the resulting classification. Classification strength is the relative likelihood that a sound class is statistically detected. Thus, system  600  could be used to perform the feature extraction module  204  and environment detection module  206  of  FIGS. 2 and 3 . Other systems may be employed without departing from the scope of the present subject matter. 
     In one embodiment a linear Bayesian classifier was chosen as Bayesian classifier  614 . Given a set of feature values for the input sound, the a priori probability of each sound class, and training data, the Bayesian classifier chooses the sound class with the highest probability (“posteriori probability”) as the classification result. The Bayesian classifier also produces a classification strength result. 
     In various embodiments, different features may be used to determine sound classifications. Some features that demonstrate the principles herein are found in one embodiment as follows: 
     Speech Detection Features 
     a. Periodicity strength 
     b. High-to-low-frequency energy ratio 
     c. Low frequency spectral slope 
     d. M/D at 0-750 Hz 
     e. M/D at 4000-7750 Hz 
     Wind and Machine Noise Detection Features For Omni Hearing Assistance Devices 
     a. Periodicity strength 
     b. High-to-low-frequency energy ratio 
     c. Low frequency spectral slope 
     d. M/D at 750-1750 Hz 
     e. M/D at 4000-7750 Hz 
     Machine Noise Detection Features for Directional Hearing Assistance Devices 
     a. Periodicity strength in logarithmic scale 
     b. High-to-low-frequency energy ratio 
     c. Low frequency spectral slope 
     d. M/D at 0-750 Hz 
     e. M/D at 4000-7750 Hz 
     Own Speech Detection 
     a. High-to-low frequency energy ratio 
     b. Energy at the fundamental frequency 
     c. Average spectral slope 
     d. Overall spectral slope 
     Wind Noise Detection for Directional Hearing Assistance Devices 
     a. Omni signal power (unfiltered) 
     b. Directional signal power (unfiltered) 
     c. Detection Rules (Hysteresis Example)
         i. Wind noise is not detected if omni signal power is greater than an upper threshold (T u ) plus directional signal power   ii. Wind noise is detected if omni signal power is less than a lower threshold (T l ) plus directional signal power   iii. Otherwise, wind noise detection status is unchanged       

     The Wind Noise Detection for Directional Hearing Assistance Devices in various embodiments can provide hysteresis to avoid undue switching between detections. In various embodiments, the upper threshold (T u ) and lower threshold (T l ) are determined empirically. In various embodiments each microphone can be fed into a signal conditioning circuit which acts as a long term averager of the incoming signal. For example, a one-pole filter can be implemented digitally to perform measurement of power from a microphone by averaging a block of 8 samples from the microphone for wind noise detection. 
     It is understood that departures from the foregoing embodiments are contemplated and that other features and variables and variable ranges may be employed using the principles set forth herein. 
     Environment Adaptation 
     In various embodiments, the system employs gain adjustments that raise gain if the incoming sound level is too low and lower gain if the incoming sound level is too high.  FIG. 7  shows a gain diagram of a gain reduction process, according to one embodiment of the present subject matter. Other gain control techniques are possible without departing from the scope of the present subject matter. 
       FIG. 8  shows one example of environment adaptation parameters to demonstrate various controls available according to one embodiment of the present subject matter. As can be seen from the figure, the system provides in various embodiments, individual sound adaptation control. The adaptation parameters shown are only one type of example of the flexibility and programmability of the present subject matter. One advantage of frequency domain processing is that individual subband gain control is straightforward. If larger frequency ranges are desired, subbands can be grouped to form a “channel.” Thus, frequency domain processing lends some benefits for algorithms focusing on particular frequency ranges. Thus, in the example of  FIG. 8 , eight gain control parameters control the gain in eight independent channels (groupings of subbands) for the wind noise, machine noise, other sound and other speech sound classes. The number of parameters can be varied as desired, as demonstrated by the use of fewer gain control parameters for “own speech.” There are also parameters for attack and release and for misclassification threshold (φ) that may be individually and programmably controlled per sound class. Thus, the processing options are vast and highly programmable with the present architecture. 
     It is further understood that the principles set forth herein can be applied to a variety of hearing assistance devices, including, but not limited to occluding and non-occluding applications. Some types of hearing assistance devices which may benefit from the principles set forth herein include, but are not limited to, behind-the-ear devices, on-the-ear devices, and in-the-ear devices, such as in-the-canal and/or completely-in-the-canal hearing assistance devices. Other applications beyond those listed herein are contemplated as well. 
     Conclusion 
     This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative, and not restrictive. Thus, the scope of the present subject matter is determined by the appended claims and their legal equivalents.