Patent Publication Number: US-2022230616-A1

Title: Method and device for acute sound detection and reproduction

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This is a continuation of and claims priority to U.S. patent application Ser. No. 17/321,892, filed 17 May 2021, which is a continuation of and claims priority to U.S. patent application Ser. No. 16/987,396, filed 7 Aug. 2020, which is a continuation of and claims priority to U.S. patent application Ser. No. 16/669,490, filed 30 Oct. 2019, which is a continuation of and claims priority to U.S. patent application Ser. No. 16/193,568, filed 16 Nov. 2018, now U.S. Pat. No. 10,535,334, which is a continuation of and claims priority to U.S. patent application Ser. No. 14/574,589, filed on Dec. 18, 2014, now U.S. Pat. No. 10,134,377, which claims priority to and is a continuation of U.S. patent application Ser. No. 12/017,878, filed on Jan. 22, 2008, now U.S. Pat. No. 8,917,894, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/885,917, filed on Jan. 22, 2007, all of which are herein incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device that monitors sound directed to an occluded ear, and more particularly, though not exclusively, to an earpiece and method of operating an earpiece that detects acute sounds and allows the acute sounds to be reproduced in an ear canal of the occluded ear. 
     BACKGROUND 
     Since the advent of industrialization over two centuries ago, the human auditory system has been increasingly stressed to tolerate high noise levels to which it had hitherto been unexposed. Recently, human knowledge of the causes of hearing damage have been researched intensively and models for predicting hearing loss have been developed and verified with empirical data from decades of scientific research. Yet it can be strongly argued that the danger of permanent hearing damage is more present in our daily lives than ever, and that sound levels from personal audio systems in particular (i.e. from portable audio devices), live sound events, and the urban environment are a ubiquitous threat to healthy auditory functioning across the global population. 
     Environmental noise is constantly presented in industrialized societies given the ubiquity of external sound intrusions. Examples include people talking on their cell phones, blaring music in health clubs, or the constant hum of air conditioning systems in schools and office buildings. Excess noise exposure can also induce auditory fatigue, possibly comprising a person&#39;s listening abilities. On a daily basis, people are exposed to various environmental sounds and noises within their environment, such as the sounds from traffic, construction, and industry. 
     To combat the undesired cacophony of annoying sounds, people are arming themselves with portable audio playback devices to drown out intrusive noise. The majority of devices providing the person with audio content do so using insert (or in-ear) earbuds. These earbuds deliver sound directly to the ear canal at high sound levels over the background noise even though the earbuds generally provide little to no ambient sound isolation. Moreover, when people wear earbuds (or headphones) to listen to music, or engage in a call using a telephone, they can effectively impair their auditory judgment and their ability to discriminate between sounds. With such devices, the person is immersed in the audio experience and generally less likely to hear warning sounds within their environment. In some cases, the user may even turn up the volume to hear their personal audio over environmental noises. It also puts them at high sound exposure risk which can potentially cause long term hearing damage. 
     With earbuds, personal audio reproduction levels can reach in excess of 100 dB. This is enough to exceed recommended daily sound exposure levels in less than a minute and to cause permanent acoustic trauma. Furthermore, rising population densities have continually increased sound levels in society. According to researchers, 40% of the European community is continuously exposed to transportation noise of 55 dBA and 20% are exposed to greater than 65 dBA. This level of 65 dBA is considered by the World Health Organization to be intrusive or annoying, and as mentioned, can lead to users of personal audio devices increasing reproduction levels to compensate for ambient noise. 
     A need therefore exists for enhancing the user&#39;s ability to listen in the environment without harming his or her hearing faculties. 
     SUMMARY 
     Embodiments in accordance with the present invention provide a method and device for acute sound detection and reproduction. 
     In a first embodiment, an earpiece can include an Ambient Sound Microphone (ASM) to capture ambient sound, at least one Ear Canal Receiver (ECR) to deliver audio to an ear canal; and a processor operatively coupled to the ASM and the at least one ECR. The processor can monitor a change in the ambient sound level to detect an acute sound from the change. The acute sound can be reproduced within the ear canal via the ECR responsive to detecting the acute sound. 
     The processor can pass (transmit) sound from the ASM directly to the ECR to produce sound within the ear canal at a same sound pressure level (SPL) as the acute sound measured at an entrance to the ear canal. In one arrangement, the processor can maintain an approximately constant ratio between an audio content level (ACL) and an internal ambient sound level (iASL) measured within the ear canal. In one arrangement, the processor can measure an external ambient sound level (xASL) of the ambient sound with the ASM and subtract an attenuation level of the earpiece from the xASL to estimate the internal ambient sound level (iASL) within the ear canal. 
     The earpiece can further include an Ear Canal Microphone (ECM) to measure an ear canal sound level (ECL) within the ear canal. In this configuration, the processor can estimate the internal ambient sound level (iASL) within the ear canal by subtracting an estimated audio content sound level (ACL) from the ECL. For instance, the processor can measure a voltage level of the audio content sent to the ECR, and apply a transfer function of the ECR to convert the voltage level to the ACL. The processor can be located external to the earpiece on a portable computing device. 
     In a second embodiment, an earpiece can comprise an Ambient Sound Microphone (ASM) to capture ambient sound, at least one Ear Canal Receiver (ECR) to deliver audio to an ear canal, an audio interface operatively coupled to the processor to receive audio content, and a processor operatively coupled to the ASM and the at least one ECR. The processor can monitor a change in the ambient sound level to detect an acute sound from the change, adjust an audio content level (ACL) of the audio content delivered to the ear canal, and reproduce the acute sound within the ear canal via the ECR responsive to detecting the acute sound and based on the ACL. 
     The audio interface can receive the audio content from at least one among a portable music player, a cell phone, and a portable communication device. During operation, the processor can maintain an approximately constant ratio between an audio content level (ACL) and an internal ambient sound level (iASL) measured within the ear canal. In one arrangement, the processor can mute the audio content and pass the acute sound to the ECR for reproducing the acute sound within the ear canal. In another arrangement, the processor can amplify the acute sound with respect to the audio content level (ACL). 
     In a third embodiment, a method for acute sound detection and reproduction can include the steps of measuring an ambient sound level (xASL) of ambient sound external to an ear canal at least partially occluded by the earpiece, monitoring a change in the xASL for detecting an acute sound, and reproducing the acute sound within the ear canal responsive to detecting the acute sound. The reproducing can include enhancing the acute sound over the ambient sound. The step of reproducing can produce sound within the ear canal at a same sound pressure level (SPL) as the acute sound measured at an entrance to the ear canal. 
     The method can further include receiving audio content from an audio interface that is directed to the ear canal, and maintaining an approximately constant ratio between a level of the audio content (ACL) and a level of an internal ambient sound level (iASL) measured within the ear canal. The ACL can be determined by measuring a voltage level of the audio content sent to the ECR, and applying a transfer function of the ECR to convert the voltage level to the ACL. The method can further include measuring an Ear Canal Level (ECL) within the ear canal, and subtracting the ACL from the ECL to estimate the iASL. The iASL can be estimated by subtracting an attenuation level of the earpiece from the xASL. 
     In a fourth embodiment, a method for acute sound detection and reproduction suitable for use with an earpiece can include the steps of measuring an external ambient sound level (xASL) in an ear canal at least partially occluded by the earpiece, monitoring a change in the xASL for detecting an acute sound, estimating a proximity of the acute sound, and reproducing the acute sound within the ear canal responsive to detecting the acute sound based on the proximity. The step of estimating a proximity can include performing a cross correlation analysis between at least two microphones, identifying a peak in the cross correlation and an associated time lag, and determining the direction from the associated time lag. The method can further include identifying whether the acute sound is a vocal signal produced by a user operating the earpiece or a sound source external from the user. 
     In a fifth embodiment, a method for acute sound detection and reproduction suitable for use with an earpiece can include measuring an external ambient sound level (xASL) due to ambient sound outside of an ear canal at least partially occluded by the earpiece, measuring an internal ambient sound level (iASL) due to residual ambient sound within the ear canal at least partially occluded by the earpiece, monitoring a high frequency change between the xASL and the iASL with respect to a low frequency change between the xASL and the iASL for detecting an acute sound, and reproducing the xASL within the ear canal responsive to detecting the high frequency change. The method can further include determining a proximity of a sound source producing the acute sound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial diagram of an earpiece in accordance with an exemplary embodiment; 
         FIG. 2  is a block diagram of the earpiece in accordance with an exemplary embodiment; 
         FIG. 3  is a flowchart of a method for acute sound detection in accordance with an exemplary embodiment; 
         FIG. 4  is a more detailed approach to the method of  FIG. 3  in accordance with an exemplary embodiment; 
         FIG. 5  is a flowchart of a method for acute sound source proximity in accordance with an exemplary embodiment; 
         FIG. 6  is a flowchart of a method for binaural analysis in accordance with an exemplary embodiment; 
         FIG. 7  is a flowchart of a method for logic control in accordance with an exemplary embodiment; 
         FIG. 8  is a flowchart of a method for estimating background noise level in accordance with an exemplary embodiment; 
         FIG. 9  is a flowchart of a method for maintaining constant audio content level (ACL) to internal ambient sound level (iASL) in accordance with an exemplary embodiment; and 
         FIG. 10  is a flowchart of a method for adjusting audio content gain in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. 
     Processes, techniques, apparatus, and materials as known by one of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the enabling description where appropriate, for example the fabrication and use of transducers. Additionally in at least one exemplary embodiment the sampling rate of the transducers can be varied to pick up pulses of sound, for example less than 50 milliseconds. 
     In all of the examples illustrated and discussed herein, any specific values, for example the sound pressure level change, should be interpreted to be illustrative only and non-limiting. Thus, other examples of the exemplary embodiments could have different values. 
     Note that similar reference numerals and letters refer to similar items in the following figures, and thus once an item is defined in one figure, it may not be discussed for following figures. 
     Note that herein when referring to correcting or preventing an error or damage (e.g., hearing damage), a reduction of the damage or error and/or a correction of the damage or error are intended. 
     At least one exemplary embodiment of the invention is directed to an earpiece for ambient sound monitoring and warning detection. Reference is made to  FIG. 1  in which an earpiece device, generally indicated as earpiece  100 , is constructed in accordance with at least one exemplary embodiment of the invention. As illustrated, earpiece  100  depicts an electro-acoustical assembly  113  for an in-the-ear acoustic assembly, as it would typically be placed in the ear canal  131  of a user  135 . The earpiece  100  can be an in the ear earpiece, behind the ear earpiece, receiver in the ear, open-fit device, or any other suitable earpiece type. The earpiece  100  can be partially or fully occluded in the ear canal, and is suitable for use with users having healthy or abnormal auditory functioning. 
     Earpiece  100  includes an Ambient Sound Microphone (ASM) Ill to capture ambient sound, an Ear Canal Receiver (ECR)  125  to deliver audio to an ear canal  131 , and an Ear Canal Microphone (ECM)  123  to assess a sound exposure level within the ear canal. The earpiece  100  can partially or fully occlude the ear canal  131  to provide various degrees of acoustic isolation. The assembly is designed to be inserted into the user&#39;s ear canal  131 , and to form an acoustic seal with the walls  129  of the ear canal at a location  127  between the entrance  117  to the ear canal and the tympanic membrane (or ear drum)  133 . Such a seal is typically achieved by means of a soft and compliant housing of assembly  113 . Such a seal is pertinent to the performance of the system in that it creates a closed cavity  131  of approximately 5 cc between the in-ear assembly  113  and the tympanic membrane  133 . As a result of this seal, the ECR (speaker)  125  is able to generate a full range bass response when reproducing sounds for the user. This seal also serves to significantly reduce the sound pressure level at the user&#39;s eardrum  133  resulting from the sound field at the entrance to the ear canal. This seal is also the basis for the sound isolating performance of the electro-acoustic assembly  113 . 
     Located adjacent to the ECR  125 , is the ECM  123 , which is acoustically coupled to the (closed) ear canal cavity  131 . One of its functions is that of measuring the sound pressure level in the ear canal cavity  131  as a part of testing the hearing acuity of the user as well as confirming the integrity of the acoustic seal and the working condition of itself and the ECR. The ASM  111  is housed in an assembly  113  and monitors sound pressure at the entrance to the occluded or partially occluded ear canal. All transducers shown can receive or transmit audio signals to a processor  121  that undertakes audio signal processing and provides a transceiver for audio via the wired or wireless communication path  119 . 
     Referring to  FIG. 2 , a block diagram of the earpiece  100  in accordance with an exemplary embodiment is shown. As illustrated, the earpiece  100  can include a processor  206  operatively coupled to the ASM  111 , ECR  125 , and ECM  123  via one or more Analog to Digital Converters (ADC)  202  and Digital to Analog Converters (DAC)  203 . The processor  206  can monitor the ambient sound captured by the ASM  111  for acute sounds in the environment, such as an abrupt high energy sound corresponding to the on-set of a warning sound (e.g., bell, emergency vehicle, security system, etc.), siren (e.g., police car, ambulance, etc.), voice (e.g., “help”, “stop”, “police”, etc.), or specific noise type (e.g., breaking glass, gunshot, etc.). The processor  206  can utilize computing technologies such as a microprocessor, Application Specific Integrated Chip (ASIC), and/or digital signal processor (DSP) with associated storage memory  208  such as Flash, ROM, RAM, SRAM, DRAM or other like technologies for controlling operations of the earpiece device  100 . The memory  208  can store program instructions for execution on the processor  206  as well as captured audio processing data. 
     The earpiece  100  can include an audio interface  212  operatively coupled to the processor  206  to receive audio content, for example from a media player or cell phone, and deliver the audio content to the processor  206 . The processor  206  responsive to detecting acute sounds can adjust the audio content and pass the acute sounds directly to the ear canal. For instance, the processor can lower a volume of the audio content responsive to detecting an acute sound for transmitting the acute sound to the ear canal. The processor  206  can also actively monitor the sound exposure level inside the ear canal and adjust the audio to within a safe and subjectively optimized listening level range. 
     The earpiece  100  can further include a transceiver  204  that can support singly or in combination any number of wireless access technologies including without limitation Bluetooth™, Wireless Fidelity (WiFi), Worldwide Interoperability for Microwave Access (WiMAX), and/or other short or long range communication protocols. The transceiver  204  can also provide support for dynamic downloading over-the-air to the earpiece  100 . It should be noted also that next generation access technologies can also be applied to the present disclosure. 
     The power supply  210  can utilize common power management technologies such as replaceable batteries, supply regulation technologies, and charging system technologies for supplying energy to the components of the earpiece  100  and to facilitate portable applications. A motor (not shown) can be a single supply motor driver coupled to the power supply  210  to improve sensory input via haptic vibration. As an example, the processor  206  can direct the motor to vibrate responsive to an action, such as a detection of a warning sound or an incoming voice call. 
     The earpiece  100  can further represent a single operational device or a family of devices configured in a master-slave arrangement, for example, a mobile device and an earpiece. In the latter embodiment, the components of the earpiece  100  can be reused in different form factors for the master and slave devices. 
       FIG. 3  is a flowchart of a method  300  for acute sound detection and reproduction in accordance with an exemplary embodiment. The method  300  can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method  300 , reference will be made to components of  FIG. 2 , although it is understood that the method  300  can be implemented in any other manner using other suitable components. The method  300  can be implemented in a single earpiece, a pair of earpieces, headphones, or other suitable headset audio delivery devices. 
     The method  300  can start in a state wherein the earpiece  100  has been inserted and powered on. As shown in step  302 , the earpiece  100  can monitor the environment for ambient sounds received at the ASM  111 . Ambient sounds correspond to sounds within the environment such as the sound of traffic noise, street noise, conversation babble, or any other acoustic sound. Ambient sounds can also correspond to industrial sounds present in an industrial setting, such as factory noise, lifting vehicles, automobiles, and robots to name a few. 
     Although the earpiece  100  when inserted in the ear can partially occlude the ear canal, the earpiece  100  may not completely attenuate the ambient sound. During the monitoring of ambient sounds in the environment, the earpiece  100  also monitors ear canal levels via the ECM  123  as shown in step  304 . The passive aspect of the physical earpiece  100 , due to the mechanical and sealing properties, can provide upwards of a 22-26 dB noise reduction. However, portions of ambient sounds higher than 26 dB can still pass through the earpiece  100  into the ear canal. For instance, high energy low frequency sounds are not completely attenuated. Accordingly, residual sound may be resident in the ear canal and heard by the user. 
     Sound within the ear canal  131  can also be provided via the audio interface  212 . The audio interface  212  can receive the audio content from at least one among a portable music player, a cell phone, and a portable communication device. The audio interface  212  responsive to user input can direct sound to the ECR  125 . For instance, a user can elect to play music through the earpiece  100  which can be audibly presented to the ear canal  131  for listening. The user can also elect to receive voice communications (e.g., cell phone, voice mail, messaging) via the earpiece  100 . For instance, the user can receive audio content for voice mail or a phone call directed to the ear canal via the ECR  125 . As shown in step  304 , the earpiece  100  can monitor ear canal levels due to ambient sound and user selected sound via the ECM  123 . 
     If at step  306 , audio is playing (e.g., music, cell phone, etc.), the earpiece  100  adjusts a sound level of the audio based on the ambient sound to maintain a constant signal to noise ratio with respect to the ear canal level at step  308 . For instance, the processor  206  can selectively amplify or attenuate audio content received from the audio interface  212  before it is delivered to the ECR  125 . The processor  206  estimates a background noise level from the ambient sound received at the ASM  111 , and adjusts the audio level of delivered audio content (e.g., music, cell phone audio) to maintain a constant signal (e.g., audio content) to noise level (e.g., ambient sound). By way of example, if the background noise level increases due to traffic sounds, the earpiece  100  automatically increases the volume of the audio content. Similarly, if the background noise level decreases, the earpiece  100  automatically decreases the volume of the audio content. The processor  206  can track variations on the ambient sound level to adjust the audio content level. 
     If at step  310 , an acute sound is detected within the ambient sound, the earpiece  100  activates “sound pass-through” to reproduce the ambient sound in the ear canal by way of the ECR  125 . The processor  206  permits the ambient sound to pass through the ECR  125  to the ear canal  131  directly for example by replicating the ambient sound external to the ear canal within the ear canal. This is important if the acute sound corresponds to an on-set for a warning sound such as a bell, a car, or an object. In such regard, the ambient sound containing the acute sound is presented directly to the ear canal in an original form. Although, the earpiece  100  inherently provides attenuation due to the physical and mechanical aspects of the earpiece and its sealing properties, the processor  206  can reproduce the ambient sound within the ear canal  131  at an original amplitude level and frequency content to provide “transparency”. For instance, the processor  206  measures and applies a transfer function of the ear canal to the passed ambient sound signal to provide an accurate reproduction of the ambient sound within the ear canal. 
     In one embodiment, the earpiece  100  looks for temporal and spectral characteristics in the ambient sound for detecting acute sounds. For instance, as will be explained ahead, the processor  206  looks for an abrupt change in the Sound Pressure Level (SPL) of an ambient sound across a small time period. The processor  206  can also detect abrupt magnitude changes across frequency sub-bands (e.g. filter-bank, FFT, etc.). Notably, the processor  206  can search for on-sets (e.g., fast rising amplitude wave-front) of an acute sound or other abrupt feature characteristics without initially attempting to initially identify or recognize the sound source. That is, the processor  206  is actively listening for a presence of acute sounds before identifying the type of sound source. 
     Even though the earplug inherently provides a certain attenuation level (e.g., noise reduction rating), the processor  206  in view of the ear canal level (ECL) and ambient sound level (ASL) can reproduce the ambient sound within the ear canal to allow the user to make an informed decision with regard to the acute sound. The ECL corresponds to all sounds within the ear canal and includes the internal ambient sound level (iASL) resulting from residual ambient sounds through the earpiece and the audio content level (ACL) resulting from the audio delivered via the audio interface  212 . Briefly, xASL is the external ambient sound external to the ear canal and the earpiece (e.g., ambient sound outside the ear canal). iASL is the residual ambient sound that remains internal in the ear canal. The following equations describe the relationship among terms: 
       iASL=xASL−NRR  (EQ 1)
 
       iASL=ECL−ACL  (EQ 2)
 
     As EQ 1 shows, the iASL is the difference between the external ambient sound (xASL) and the attenuation of the earpiece (Noise Reduction Rating) due to the physical and sealing properties of the earpiece. The processor  206  can measure an external ambient sound level (xASL) of the ambient sound with the ASM  111  and subtracts an attenuation level of the earpiece (NRR) from the xASL to estimate the internal ambient sound level (iASL) within the ear canal. 
     EQ 2 is an alternate, or supplemental, method for calculating the iASL as the difference between the ECL and the Audio Content Level (ACL). By way of the ECM  123 , the processor  206  can estimate an internal ambient sound level (iASL) within the ear canal by subtracting the estimated audio content sound level (ACL) from the ECL. The processor  206  measures a voltage level of the audio content sent to the ECR  125 , and applies a transfer function of the ECR  125  to convert the voltage level to the ACL. 
     The processor  206  evaluates the equations above to pass sound from the ASM  111  directly to the ECR  125  to produce sound within the ear canal at a same sound pressure level (SPL) and frequency representation as the acute sound measured at an entrance to the ear canal. Further, the processor  206  can maintain an approximately constant ratio between an audio content level (ACL) and an internal ambient sound level (iASL) measured within the ear canal. 
     At step  314 , the earpiece  100  can estimate a proximity of the acute sound. For instance, as will be shown ahead, the processor  206  can perform a correlation analysis on at least two microphones to determine whether the sound source is internal (e.g., the user) or external (e.g., an object other than the user). At step  316 , the earpiece  100  determines whether it is the user&#39;s voice that generates the acute sound when the user speaks, or whether it is an external sound such as a vehicle approaching the user. If at step  316 , the processor  206  determines that the acute sound is a result of the user speaking, the processor  206  does not activate a pass-through mode, since this is not considered an external warning sound. The pass-through mode permits ambient sound detected at the ASM  111  to be transmitted directly to the ear canal. If however, the acute sound corresponds to an external sound source, such as an on-set of a warning sound, the earpiece at step  318  activates “sound pass-through” to reproduce the ambient sound in the ear canal by way of the ECR  125 . The earpiece  100  can also present an audible notification to the user indicating that an external sound source generating the acute sound has been detected. The method  300  can proceed back to step  302  to continually monitor for acute sounds in the environment. 
       FIG. 4  is a detailed approach to the method  400  of  FIG. 3  for an Acute-Sound Pass-Through System (ACPTS) in accordance with an exemplary embodiment. The method  400  can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method  400 , reference will be made to components of  FIG. 2 , although it is understood that the method  400  can be implemented in any other manner using other suitable components. The method  400  can be implemented in a single earpiece, a pair of earpieces, headphones, or other suitable headset audio delivery devices. 
     At step  402 , the earpiece  100  captures ambient sound signals from the ASM  111 . At step  404 , the processor  206  applies analog and discrete time signal processing to condition and compensate the ambient sound signal for the ASM  111  transducer. At step  406 , the processor  206  estimates a background noise level (BNL) as will be discussed ahead. At step  408 , the processor  206  identifies at least one peak in a data buffer storing a portion of the ambient sound signal. The processor  206  at step  410  gets a level of the peak (e.g., dBV). Block  412  presents a method for warning signal detection (e.g. car horns, klaxons). When a warning signal is detected at step  416 , the processor  206  invokes at step  418  a pass-through mode whereby the ASM signal is reproduced with the ECR  125 . Upon activating pass-through mode, the processor  206  can perform a safe level check at step  452 . If a warning signal is not detected, the method  400  proceeds to step  420 . 
     At step  420 , the processor  206  subtracts the estimated BNL from an SPL of the ambient sound signal to produce signal “A”. A high energy level transient signal is indicative of an acute sound. At step  422 , a frequency dependent threshold is retrieved at step  424 , and subtracted from signal “A”, as shown in step  422  to produce signal “B”. At step  426 , the processor  206  determines if signal “B” is positive. If not, the processor  206  performs a hysterisis to determine if the acute sound has already been detected. If not, the processor at step  428  determines if an SPL of the ambient sound is greater than a signal “C” (e.g. threshold). If the SPL is greater than signal “C”, the earpiece generates a user generated sound at step  434 . The signal “C” is used to ensure that the SPL between the signal and background noise is positive and greater than a predetermined amount. For instance, a low SPL threshold (e.g., “C” 40 dB) can be used as shown in step  430 , although it can adapt to different environmental conditions. The low SPL threshold provides an absolute measure to the SPL difference. At step  436 , a proximity of a sound source generating the acute sound can be estimated as will be discussed ahead. The method  400  can continue to step  432 . 
     Briefly, if a transient, high-level sound (or acute sound) is detected in the ambient sound signal (ASM input signal), then it is converted to a level, and its magnitude compared with the BNL is calculated. The magnitude of this resulting difference (signal “A”) is compared with the threshold (see step  422 ). If the value is positive, and the level of the transient is greater than a predefined threshold (see step  428 ), the processor  206  invokes the optional Source Proximity Detector at step  436 , which determines if the acute sound was created by the User&#39;s voice (i.e., a user generated sound). If a user-generated sound is NOT detected, then Pass-through operation at step  438  is invoked, whereby the ambient sound signal is reproduced with the ECR  125 . If the difference signal at step  428  is not positive, or the level of the identified transient is too low, then the hysteresis is invoked at step  432 . The processor  206  decides if the pass-through was recently used at step  440  (e.g. in the last 10 ms). If pass-through mode was recently activated, then processor  206  invokes the pass-through system at step  438 ; otherwise there is no pass-through of the ASM signal to the ECR as shown at step  442 . Upon activating pass-through mode, the processor  206  can perform a safe level check at step  452 . 
       FIG. 5  is a flowchart of a method  500  for acute sound source proximity. The method  500  can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method  500 , reference will be made to components of  FIG. 2 , although it is understood that the method  500  can be implemented in any other manner using other suitable components. The method  500  can be implemented in a single earpiece, a pair of earpieces, headphones, or other suitable headset audio delivery device. 
     Briefly,  FIG. 5  describes a method  500  for Source Proximity Detection (SPD) to determine if the Acute sound detected was created by the User&#39;s voice operating the earpiece  100 . The SPD method  500  uses as its inputs the external ambient sound signals from left and right electro-acoustic earpiece  100  assemblies (e.g., a headphone). In some embodiments the SPD method  500  employs Ear Canal Microphone (ECM) signals from left and right earpiece  100  assemblies placed on left and right ears respectively. The processor  206  performs an electronic cross-correlation between the external ambient sound signals to determine a Pass-through or Non Pass-through operating mode. In the described embodiment whereby the cross-correlation of both the ASM and ECM signals is involved, a pass-through mode is invoked when the cross-correlation analysis for both the left and right earpiece  100  assemblies return a “Pass-through” operating mode, as determined by a logical AND unit. 
     For instance, at step  502  a left ASM signal from a left headset incorporating the earpiece  100  assembles is received. Simultaneously, at step  504  a right ASM signal from a right headset is received. At step  510 , the processor  206  performs a binaural cross correlation on the left ASM signal and the right ASM signal to evaluate a pass through mode  516 . At step  506  a left ECM signal from the left headset is received. At step  508 , a right ECM signal from the right headset is received. At step  514 , the processor  206  performs a binaural cross correlation on the left ECM signal and the right ECM signal to evaluate a pass through mode  518 . A pass through mode  524  is invoked if both the ASM and ECM cross correlation analysis are the same as determined in step  520 . A safe level check can be performed by processor  206  at step  522 . 
       FIG. 6  is a flowchart of a method  600  for binaural analysis. The method  600  can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method  600 , reference will be made to components of  FIG. 2 , although it is understood that the method  600  can be implemented in any other manner using other suitable components. The method  600  can be implemented in a single earpiece, a pair of earpieces, headphones, or other suitable headset audio delivery devices. 
     Briefly,  FIG. 6  describes a component of the SPD method  500  wherein a cross-correlation of two input audio signals  602  and  604  (e.g., left and right ASM signals) is calculated. The input signals may first be weighted using a frequency-dependent filter (e.g. an FIR-type filter) using filter coefficients  606  and filtering networks  608  and  610 . Alternatively, an interchannel cross-correlation calculated with function  612  can return a frequency-dependent correlation such as a coherence function. The absolute maximum peak of a calculated cross-correlation 614 can be subtracted from a mean (or RMS)  616  correlation, with subtractor  622 , and compared  628  with a predefined threshold  626 , to determine if the peak is significantly greater than the average correlation (i.e. a test for peakedness). Alternatively, the maxima of the peak may simply be compared with the threshold  628  without the subtraction process  622 . If the lag-time of the peak  618  is at approximately lag-sample 0, then the sound source is determined, at step  624 , as being on the interaural axis-indicative of User-generated speech, and a no-pass through mode is returned  630  (a further function described in  FIG. 7  may be used to confirm that the sound source originates in the User-head, rather than external to the user- and further confirming that the acute sound is a User-generated voice sound). The logical AND unit  632  activates the pass-through mode  636  if both criteria in the decision units  628  and  624  confirm that the absolute maxima of the peak is above a predefined threshold  626 , AND the lag of the peak is NOT at approximately lag sample zero. A safe level check may be performed by processor  206  at step  634 . 
       FIG. 7  is a flowchart of a method  700  for logic control. The method  700  can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method  700 , reference will be made to components of  FIG. 2 , although it is understood that the method  700  can be implemented in any other manner using other suitable components. The method  700  can be implemented in a single earpiece, a pair of earpieces, headphones, or other suitable headset audio delivery devices. 
     Briefly,  FIG. 7  describes a further component of the SPD method  500 , which is optional to confirm that the acute sound source is from a location indicative of user-generated speech; i.e. inside the head. Method steps  702 - 712  are similar to Method steps  502 - 514  of  FIG. 5 . The cross-correlations of step  710  and  712  provide a time-lag of the maximum absolute peak for a pair of input signals; the ASM and ECM signals for the same headset (e.g. the ASM and ECM for the left headset). At step  714  a left lag of a peak of the left cross correlation is determined, and simultaneously, a right lag of a peak of the right cross correlation is determined at step  718 . If a lag of a respective peak is greater than zero—this indicates that the sound arrived at the ECM signal before the ASM signal. Decision step  716  determines if the lag is greater than zero for both the left and right headsets- and activates the pass-through mode  722  if so. A safe level check may be performed by processor  206  at step  720 . 
       FIG. 8  is a flowchart of a method  800  for estimating background sound level. The method  800  can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method  800 , reference will be made to components of  FIG. 2 , although it is understood that the method  800  can be implemented in any other manner using other suitable components. The method  800  can be implemented in a single earpiece, a pair of earpieces, headphones, or other suitable headset audio delivery devices. 
     Briefly, method  800  receives as its input  802  either or both the ASM signal from ASM  111  and a signal from the ECM  123 . An audio buffer  804  of the input audio signal is accumulated (e.g. 10 ms of data), which is then processed by squaring step  806  to obtain the temporal envelope. The envelope is smoothed (e.g. an FIR-type low-pass digital filter) at step  808  using a smoothing window  810  stored in data memory (e.g. a Hanning or Hamming shaped window). At step  812 , transient peaks in the input buffer can be identified and removed to determine a “steady-state” Background Noise Level (BNL). At step  814  an average BNL  816  can be obtained (similar to, or the same as, the RMS) that is frequency dependent or a single value averaged over all frequencies. If the ECM  123  is used to determine the BNL, then decision step  818  adjusts the ambient BNL estimation to provide an equivalent ear-canal BNL SPL, by deducting an Earpiece Noise Reduction Rating  828  from the BNL estimate  826 . Alternatively, if the ECM  123  is used, then the Audio Content SPL level (ACL)  822  of any reproduced Audio Content  820  is deducted from the ECM level at step  824 . The updated BNL estimate is then converted to a Sound Pressure Level (SPL) equivalent  832  (i.e. substantially equal to the SPL at the ear-drum in which the earphone device is inserted) by taking into account the sensitivity (e.g. measured in V per dB) of either the ASM  111  or ECM  123  at steps  830  and  834  respectively. The resulting BNL SPL is then combined at step  842  with the previous BNL estimate  840 , by averaging  838  a weighted previous BNL (weighted with coefficient  836 ), to give a new ear-canal BNL  844 . 
       FIG. 9  is a flowchart of a method  900  for maintaining constant audio content level (ACL) to internal ambient sound level (iASL). The method  900  can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method  900 , reference will be made to components of  FIG. 2 , although it is understood that the method  900  can be implemented in any other manner using other suitable components. The method  900  can be implemented in a single earpiece, a pair of earpieces, headphones, or other suitable headset audio delivery devices. 
     Briefly,  FIG. 9  describes a method  900  for Constant Signal-to-Noise Ratio (CSNRS). At step  904  an input signal is captured from the ASM  111  and processed at step  910  (e.g. ADC, EQ, gain). Similarly, at step  906  an input signal from the ECM  123  is captured and processed at step  912 . The method  900  also receives as input an Audio Content signal  902 , e.g. a music audio signal from a portable Media Player or mobile-phone, which is processed with an analog and digital signal processing system as shown in step  908 . An Audio Content Level (ACL) is determined at step  914  based on an earpiece sensitivity from step  916 , and returns a dBV value. 
     In one exemplary embodiment, method  900  calculates a RMS value over a window (e.g. the last 100 ms). The RMS value can then be first weighted with a first weighting coefficient and then averaged with a weighted previous level estimate. The ACL is converted to an equivalent SPL value (ACL), which may use either a look-up-table or algorithm to calculate the ear-canal SPL of the signal if it was reproduced with the ECR  125 . To calculate the equivalent ear canal SPL, the sensitivity of the ear canal receiver can be factored in during processing. 
     At step  922  the BNL is estimated using inputs from either or both the ASM signal at step  902 , and/or the ECM signal at step  906 . The BNL may be adjusted by the earpiece noise reduction rating  924 . These signals are selected using the BNL input switch at step  918 , which may be controlled automatically or with a specific user-generated manual operation at step  926 . The Ear-Canal SNR is calculated at step  920  by differencing the ACL from step  914  and the BNL from step  922  and the resulting SNR  930  is passed to the method step  932  for AGC coefficient calculation. The AGC coefficient calculation  932  calculates gains for the Audio Content signal and ASM signal from the Automatic Gain Control steps  928  and  936  (for the Audio Content and ASM signals, respectively). AGC coefficient calculation  932  may use a default preferred SNR  938  or a user-preferred SNR  934  in its calculation. After the ASM signal and Audio content signal have been processed by the AGCs  928  and  936 , the two signals are mixed at step  940 . 
     At step  942 , a safe-level check determines if the resulting mixed signal is too high, if it were reproduced with the ECR  125  as shown in block  944 . The safe-level check can use information regarding the user&#39;s listening history to determine if the user&#39;s sound exposure is such that it may cause a temporary or a permanent hearing threshold shift. If such high levels are measured, then the safe-level check reduces the signal level of the mixed signals via a feedback path to step  940 . The resulting audio signal generated after step  942  is then reproduced with the ECR  125 . 
       FIG. 10  is a flowchart of a method  950  for maintaining a constant signal to noise ratio based on automatic gain control (AGC). The method  950  can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe the method  950 , reference will be made to components of  FIG. 2 , although it is understood that the method  950  can be implemented in any other manner using other suitable components. The method  950  can be implemented in a single earpiece, a pair of earpieces, headphones, or other suitable headset audio delivery devices. 
     Method  950  describes calculation of AGC coefficients. The method  950  receives as its inputs an Ear Canal SNR  952  and a target SNR  960  to provide a SNR mismatch  958 . The target SNR  964  is chosen from a pre-defined SNR  954 , sorted in computer memory or a manually defined SNR  956 . At step  958 , a difference is calculated between the actual ear-canal SNR and the target SNR to produce the mismatch  962 . The mismatch level  962  is smoothed over time at step  968 , which uses a previous mismatch  970  that is weighted using single or multiple weighting coefficients  966 , to give a new time-smoothed SNR mismatch  974 . Depending on the magnitude of this mismatch, various operating modes  972 ,  978  can be invoked, for example, as described by the AGC decision module  976  (step  932  in  FIG. 9 ). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions of the relevant exemplary embodiments. Thus, the description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the exemplary embodiments of the present invention. Such variations are not to be regarded as a departure from the spirit and scope of the present invention.