Abstract:
A portable hand-held electrical testing device including a processor housed within an enclosure. The processor is configured to operate on commands by a user to process sub-microvolt electrical signals received through an input/output interface. The input/output interface includes a capacitive coupled amplifier with adjustable gain settings. Onboard memory linked to the processor stores processing data and instructions. A display device is mounted to said enclosure and is operatively connected to the processor to display processing results in real time.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates to the field of low voltage electrical signal measurement devices and in particular, to the design of a hand-held sub-microvolt electrical signal measurement device. While the invention is described with particular emphasis to its use with auditory screening applications, those skilled in the art will recognize the wider applicability of the inventive principles such as vibration monitoring, gas monitoring, blood analysis, and alcohol intoximeters, such as disclosed hereinafter. 
     Test equipment capable of accurately measuring low voltage electrical signals in the sub-microvolt range has a wide range of applications from the monitoring of bioelectric signals in a human body, such as those found in the auditory system, to vibration monitoring and the measurement of electrical signals from chemical reactions such as found in alcohol intoximeters, more commonly referred to as breathalyzers. Low voltage electrical signals in the sub-microvolt range can be extremely difficult to detect, as often the signal noise levels and interference present can mask the desired signals. Handheld test equipment, in which numerous electrical circuits are packaged in close proximity, is particularly susceptible to such signal noise and interference. However, many of the applications in which the measurement of low-voltage electrical signals in the sub-microvolt range is required would benefit greatly from the use of portable, self-contained, hand-held test instruments. 
     For example, universal neonatal auditory screening programs have expanded greatly because of improved auditory measurement capability, improved rehabilitation strategies, increased awareness of the dramatic benefits of early intervention for hearing impaired babies, and changes in governmental policies. Current neonatal auditory screening approaches, however, do not account adequately for the many different types and degrees of auditory abnormalities that are encountered with present screening approaches. Because of this, individual screening tests based on a single measurement can be influenced negatively by interaction among various independent auditory abnormalities. 
     Current screening approaches have not considered adequately the entire screening program including: (i) physical characteristics of the measurement device i.e., portability, physical size and ease of use, (ii) operational characteristics of the device i.e., battery life, amount of record storage, required operating training, etc. and/or (iii) program logistics i.e., retesting mechanisms, referral mechanisms, record processing, patient tracking, report writing, and other practical aspects. These factors can interact negatively to increase the total cost of an auditory screening program, including the primary economic cost of screening and testing, the secondary economic cost of additional testing, and non-economic costs such as parental anxiety incurred when provided with incorrect information. 
     These costs, both actual and human, can be reduced by reducing the cost per test, reducing the false positive rate, and resolving false positive screening results at the bedside prior to hospital discharge. The cost per screening can be reduced with a dedicated device optimized for screening in any location and enhanced to allow effective operation by minimally trained personnel. The performance characteristic of the device of our invention includes reduced measurement time, the ability to operate and configure without an external computer, the ability to integrate and interpret all test results, the ability to store a large number of test results, long battery life, and bi-directional wireless transfer of data to and from external devices. 
     False positive results can be reduced in two ways. First, the initial screening test performance can be improved with enhanced signal processing, more efficient test parameters, and by combining different types of tests. Second, false positive rates also can be reduced by providing a mechanism for resolving an initial screening test failure at the bedside at the time of the initial screening. This capability is provided through the availability of an automated screening auditory brainstem response (ABR) test capability provided by the same device. Secondly, operational processes of a screening program can be improved through the use of several onboard computer based expert systems. These computer based expert systems provide improved automatic interpretation of single test results, automatic interpretation of multiple test results, and improved referral processes through the matching of local referral sources with various test outcomes, such as a referral to a specific type of follow-up, whether it be a pediatrician, audiologist, otolaryngologist, or a nurse. The device disclosed hereinafter integrates in a single, hand-held device, a single stimulus transducer, a single processor and a single software application for otoacoustic emission (OAE) and ABR testing. 
     An auditory abnormality is not a single, clearly defined entity with a single cause, a single referral source and a single intervention strategy. The peripheral auditory system has three separate divisions, the external ear, the middle ear, and the sensorineural portion consisting of the inner ear or cochlea, and the eight cranial nerves. Abnormalities can and do exist independently in all three divisions and these individual abnormalities require different intervention and treatment. Prior art physical and operational characteristics of devices and their influences on program logistics can interact negatively to increase the total cost of an auditory screening program. The primary economic cost is the cost of each screening test though this is not the only economic cost. A screening test failure is called a “refer” and usually is resolved with an expensive full diagnostic test scheduled several weeks after hospital discharge, resulting in significant economic cost. A substantial portion of these costs is unnecessary if the screening false positive rate is high. Non economic costs include parental anxiety for false positive screening results, unfavorable professional perception of program effectiveness for programs with high false positive rates and even inappropriate professional intervention because of misleading screening results. 
     The invention of multiple measurements into a single hand-held instrument allows for very important new functionality not available with existing neonatal auditory screening devices. This functionality includes (1) detection of common external and middle ear abnormalities; (2) the detection of less common sensorineural hearing loss associated with outer hair cell abnormalities, and (3) the detection of even less common sensorineural hearing loss associated with inner hair cell or auditory nerve abnormality. Moreover, the device disclosed hereinafter has the potential to improve the accuracy and reliability of OAE measurements, to allow for optimal interpretation of both the OAE and ABR results, and to improve the referral process. 
     Attempts have been made in the past to provide the capabilities provided by the present invention. In particular, U.S. Pat. Nos. 5,601,091 (&#39;091) and 5,916,174 (&#39;174) disclose audio screening apparatus which purport to provide a hand-held portable screening device. However, the screening device disclosed in those patents is used in conjunction with a conventional computer, and requires a docking station for full application use. In no way does the disclosure of either patent provide a hand-held device that can be used independently of any other computer. That is to say, the invention disclosed hereinafter provides a device of significantly reduced size i.e., hand-held, which is capable of providing OAE and ABR testing. It can be operated in a stand-alone mode, independently of any other computer connection, if desired. The device includes a patient database, with names, and full graphic display capability. The device also preferably is provided with a wireless infrared and an RS 232 connection port to provide output directly to printers or to a larger database where such is required. The &#39;174 and &#39;091 patents also operate on a linear averaging method to remove background noise. While such a method works well for its intended purposes, use of a linear averaging method is time consuming. 
     Accordingly, there is a need for portable, hand-held test equipment capable of accurately measuring low voltage electrical signals in the sub-microvolt range, and which is capable of providing improved signal reliability in a reduced time frame using an on-board processor to access and store information in an associated memory storage device. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly stated, an effective sub-microvolt electric testing device is provided. In the preferred embodiment, the device includes a portable hand-held enclosure containing a digital signal processor. The processor has a memory and a computer program associated with it for control of CODEC components capable of generating sub-microvolt electrical output signals on four discrete output channels and for receiving sub-microvolt electrical input signals on four discrete input channels. A display device is mounted to the enclosure, and displays test information, test setup procedures, and test results including the graphing of test results. The enclosure includes a connection point for one or more probes, the connection point being operatively connected to the digital signal processor. The device also includes an onboard power supply, making the device completely self contained. 
     In one embodiment of the present invention, an effective auditory screening device is provided. The integration of an OAE screening device and ABR screening device into a single, hand-held instrument enables a user to detect less common sensorineural hearing loss associated with outer hair cell abnormalities and the detection of less common sensor hearing loss associated with inner hair cell abnormalities. In the preferred embodiment, the device includes a portable hand-held enclosure containing a digital signal processor. The processor has a computer program associated with it, capable of conducting both otoacoustic emission test procedures and auditory brainstem response test procedures for a test subject. A display device is mounted to the enclosure, and displays patient information, auditory screening setup procedures, and auditory screening test results, including graphical analysis. The enclosure includes a connection point for a probe, the connection point being operatively connected to the signal processor. The device also includes an onboard power supply, making the device completely self contained. 
     The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the accompanying drawings which form part of the specification: 
         FIG. 1  is a top plan view of one illustrative embodiment of an electrical testing device of the present invention; 
         FIG. 2  is a view in end elevation of the electrical testing device; 
         FIG. 3  is a view in end elevation of the electrical testing device end opposite to that shown in  FIG. 2 ; 
         FIG. 4  is a block diagrammatic view of an electrical testing device shown in  FIG. 1 ; 
         FIG. 5  is a block diagrammatic view of a second set of generic electrical input and output channels shown in  FIG. 4 ; 
         FIG. 6  is a block diagrammatic view of an auditory screening embodiment of the electrical testing device shown in  FIG. 1 ; 
         FIG. 7  is a block diagrammatic view of the DPOAE interface in  FIG. 6 ; 
         FIG. 8  is a block diagrammatic view of the ABR interface in  FIG. 6 ; 
         FIG. 9  is a block diagrammatic view of the signal output phase of the OAE testing employed with the device of  FIG. 6 ; 
         FIG. 10  is a block diagrammatic view of the signal input phase of the OAE testing employed with the device of FIG.  6 ; 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description illustrates the invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. 
     Referring now to FIG.  1  through  FIG. 3 , reference numeral  10  illustrates one embodiment of the hand-held sub-microvolt electrical signal measurement device of the present invention. The measurement device  10  includes an enclosure  12 , which in the preferred embodiment, and for purposes of illustration and not for limitation, measures 7¼″ long by 3¾″ wide by 1½″ deep. It is important to note that the device  10  can be carried by the user without compromise, and truly represents a portable hand-held device having full functionality as described below. The device  10  includes a keyboard  14  and an LCD display  16 . One or more LED indicators are optionally included, such as an LED pass/refer indicator  18 , and an LED AC charging indicator  20 . Again, by way of illustration and not by limitation, it should be noted that the LCD display  16  measures, in the preferred embodiment, approximately, 2″ by 3⅜″. The measurement is not necessarily important, except to show that the LCD display  16  is fully functional for a user, and the device  10  can operate independently of any other computer system. 
     In the embodiment illustrated, the enclosure  12  also houses an infrared port  22 , and a compatible RS-232 port  24 , a probe connection  26  suitable for use with an input probe  28 , such as an ear probe, and an interface  30  for a plurality of output electrodes  31 . Probe  28  is convention and is not described in detail. Suitable probes, such as ear probes, are commercially available from Etymotic Research, Pat. Nos. ER-10C, ER-10D, and GSI 2002-3250, for example. 
     Referring now to  FIG. 4 , a block diagram view of the hand-held sub-microvolt electrical signal measurement device  10  is shown and described. Preferably, the system shown in  FIG. 4  is manufactured on a single printed circuit board, with mixed signal design for both analog and digital operation. The device  10  preferably is low powered, and generally operates at 3.3 volts, except for the LCD display  16  and some low power portions of the analog circuitry employed with the device  10 . To reduce undesired signal interference, it has been found that it is preferable that all analog and digital circuit components share a common electrical ground point within the device  10 . 
     A suitable micro-processor  40  is the control for the device  10 . In the preferred embodiment illustrated, the processor  40  is a Motorola model No. 56303 digital signal processor, however, those of ordinary skill in the art will recognize that any suitable micro-processor or micro-controller having sufficient computational power and speed may be utilized. All signal processing functions described hereinafter are performed by the processor  40 , as well as the control of all input and output functions of the device  10 . In addition, graphic functions, user interface functions, data storage functions, and other device functionality are controlled by the processor  40 . 
     In conventional design logic, the digital signal processor  40  is used for signal processing, and a separate micro-controller is used for device control. In device  10 , the digital signal processor  40  performs the functions of the separate micro-controller in addition to signal processing, eliminating the requirement of a separate micro-controller, resulting in substantial savings in circuit board space, manufacturing cost and operational power consumption. 
     To reduce undesired signal interference during the data-acquisition phase of operations, the processor  40  in device  10  is either shut-down or switched to a “sleep” mode during data collection operations, which can be carried out independently of the processor  40 . Further reduction in external signal noise is achieved by the execution of software in data and program memory  40 M internal to processor  40 , thereby eliminating external bus access signal noise. 
     A memory subsystem  42  is operatively connected to the processor  40 . The memory subsystem  42  includes a random access memory (RAM)  42 A for storing intermediate results and holding temporary variables, and a flash memory  42 B for storing non-volatile, electrically programmable variables, test result data and system configuration information. In the embodiment illustrated, the flash memory  42 B is substantially oversized, enabling the device  10  to accommodate several hundred data records, as well as multiple configurations files. 
     A memory mapped input/output device  44  is operatively connected to the memory subsystem  42  and to the digital signal processor  40 . The memory mapped input/output  44  in turn is operatively connected to the LCD display  16 , the keyboard  14 , an output LED indicator  18  and a real time clock  46 . 
     The LCD display  16  provides the user with a display array preferably having a minimum size of 128×256 pixels. A display array of this size is sufficient to present full waveforms of signal tests conducted by the device  10 . The device  10  enables the LCD  16  to present signal information to a user graphically in real time on the device  10  itself, complemented with textual and numeric information about the quality of the data, signal amplitudes, signal frequency, noise floors and other related signal information. 
     The keyboard  14  preferably is a membrane switch keyboard, which incorporates only the minimum keys necessary for operation of the device  10 . All keys are programmable, except for an On/Off key  15 . 
     The real-time clock  46  is operatively connected to the processor  40  through the memory mapped input/output device  44 . The real-time clock  46  enables the processor  40  to provide a time stamp for each data collection or test performed. 
     The output LED  18  is used to convey test results to non-trained users to avoid confusion or misinterpretation of the LCD graphics display  16 . For example, the processor  40  may be programmed to illuminate the output LED  18  in response to a predetermined input criteria, such as an input signal strength exceeding a predetermined minimum value. The output LED  18  further allows the use of the device  10  in low light areas, where the LCD display  16  may be difficult to read or interpret. 
     The plurality of analog to digital/digital to analog coder/decoders  48  (codecs  48 ) are operatively connected to the signal processor  40  along a dedicated serial link. As will be appreciated by those skilled in the art, the codecs  48  are special integrated circuit chips that perform analog to digital and digital to analog conversion. The codecs  48  in turn are operatively associated with a one or more input/output devices interfaces  52 , which provide the functionality of the device  10  under control of the processor  40 . Preferably, the digital signals generated and received by codecs  48  have 20-bit resolution for both analog to digital and digital to analog conversions. 
     In one embodiment of the present invention  10 , input/output interface  52  includes four input channels and four output channels adapted for sub-microvolt electrical signals. As shown in  FIG. 5 , the input/output interface  52  consists of a plurality of analog signal processing chips, not shown individually, which filter and amplify the signals received from a number of discrete input channels  32 . Specifically, signals received from each input channel  32  are routed through an electrical insulator circuit  52 A, consisting of a plurality of metal oxide varistors, resistors, and capacitors, which function as surge arrestors to isolate the input channels  32  from any dangerous electrical currents or voltages. The insulator circuit  52 A functions to replace conventional insulator circuits which utilize optical signal pathways, thereby eliminating the associated signal noise resulting from the conversion between electrical signals and optical signals. 
     Signals from the input channels  32  are then routed through a switching network  52 B, wherein an individual signal is automatically selected and passed to a capacitive coupled differential operational amplifier  52 C having high gain. A common mode cancellation amplifier  52 D is included in the input/output interface  52  to further reduce signal noise levels. The resulting amplified signal is then routed to the codecs  48 . In addition to selecting an individual signal from the input channels  32 , the switching network  52 B permits a variety of signal measurements on the input channels  32  to be carried out using the same differential operational amplifier  52 C, by altering the amplifier gain setting. 
     Returning to  FIG. 4 , a mode configuration system  54 , a reset watchdog system  56 , a clock crystal  58 , a power supply  60 , preferably a nickel-metal hydride battery, and a battery charger  62  all are also positioned within the enclosure  12  and operatively connected to the processor  40 . While each of these blocks is required for operation of the device  10 , they are standard in nature and are not described in detail. 
     The processor  40  has an input-output channel  64 , which preferably includes an infrared connection  22 , a fiber-optic connection  23  and an isolated RS-232 interface  24 . The device  10  can communicate with any infrared compatible or RS-232 compatible personal computer, printer, or other digital device (not shown) for data transmission. Data transmission may include test subject information, configuration data for the signal processor  40 , or software program updates for storage in the memory subsystem  42 . 
     A audio output  66  in the form of a buzzer also is provided. The audio output  66  provides an audio feedback to the user for keyboard actions and an audio indication for error conditions. 
     A serial port  68  also is operatively connected to the processor  40 . The serial port  68  is utilized to provide direct programming of the processor  40  from a personal computer, for example, and is intended for use only for initial software download and major software program upgrades of the processor  40 . 
     Referring now to  FIG. 6 , a block diagram view of one embodiment of the device  10 , configured for use as an auditory screening device  200 , is shown and described. The device  200  contains OAE and ABR simulator capabilities in a single, hand-held package. Preferably, the system shown in  FIG. 6  is manufactured on a single printed circuit board, with mixed signal design for both analog and digital operation. The device  200  preferably is low powered, and generally operates at 3.3 volts, except for the LCD display  216  and some low power portions of the analog circuitry employed with the device  200 . To reduce undesired signal interference, it has been found that it is preferable that all analog and digital circuit components share a common electrical ground point within the device  200 . 
     A digital signal processor  240  is the control for the device  200 . In the preferred embodiment illustrated, the processor  240  is a Motorola model No. 56303 DSP. All signal processing functions described hereinafter are performed by the processor  240 , as well as the control of all input and output functions of the device  200 . In addition, the graphic functions, user interface, patient data storage functions and other device functionality are controlled by the processor  240 . In conventional design logic, the digital signal processor  240  is used for signal processing, and a separate micro controller is used for device control. In device  200 , the digital signal processor  240  performs the functions of the separate micro controller in addition to signal processing, eliminating the requirement of a separate microprocessor, resulting in substantial savings in circuit board space, manufacturing cost and operational power consumption. To reduce undesired signal interference during the data-acquisition phase of operations, the processor  240  in device  200  is either shut-down or switched to a “sleep” mode during data collection operations, which can be carried out independently of the processor  240 . Further reduction in external signal noise is achieved by the execution of software in data and program memory  240 M internal to processor  240 , thereby eliminating external bus access signal noise. 
     A memory subsystem  242  is operatively connected to the processor  240 . The memory subsystem  242  includes a random access memory (RAM)  242 A for storing intermediate results and holding temporary variables, and a flash memory  242 B for storing non-volatile, electrically programmable variables, patient data, and configuration information. In the embodiment illustrated, the flash memory  242 B is substantially oversized, enabling the device  200  to accommodate several hundred full patient records, as well as multiple configurations files. 
     A memory mapped input/output device  244  is operatively connected to the memory subsystem  242  and to the digital signal processor  240 . The memory mapped input/output  244  in turn is operatively connected to the LCD display  216 , the keyboard  214 , the pass/referral LED indicator  218  and a real time clock  246 . 
     The LCD display  216  provides the user with a display array preferably having a minimum size of 128×256 pixels. A display array of this size is sufficient to present full waveforms of audiometric tests conducted by the device  200 . The device  200  enables the LCD  216  to present signal information to a user graphically in real time on the device  200  itself, complemented with textual and numeric information about the quality of the data, signal amplitudes, signal frequency, noise floors and other related signal information. 
     The keyboard  214  preferably is a membrane switch keyboard, which incorporates only the minimum keys necessary for operation of the device  200 . All keys are programmable, except for an On/Off key (not shown). 
     The real-time clock  246  is operatively connected to the processor  240  through the memory mapped input/output device  244 . The real-time clock  246  enables the processor  240  to provide a time stamp for each patient and test performed, as well as providing time signals for internal operation of the device  200 . 
     An LED AC charging indicator  217  provides a visual indication of battery charging status, while the LED pass/refer diode  218  is used to convey test results to non-trained users, namely a nurse as opposed to an audiologist or otolaryngologist. Use of the LED  218  avoids confusion or misinterpretation of the LCD graphics display  216 , and allows use of the device  200  in low light areas, where the LCD display  216  may be difficult to interpret. 
     The plurality of analog to digital/digital to analog coder/decoders  248  (codecs  248 ) are operatively connected to the signal processor  240  along a dedicated serial link. As will be appreciated by those skilled in the art, the codecs  248  are special integrated circuit chips that perform analog to digital and digital to analog conversion. The codecs  248  in turn are operatively associated with a plurality of input/output devices, which provide the functionality of the device  200  under control of the processor  240 . 
     An otoacoustic emission interface  250  (DPOAE I/F) is operatively connected to the signal processor  240  through the associated codecs  248 . The otoacoustic emission interface  250  preferably is a low noise, differential analog circuit with high common mode noise rejection. As shown in  FIG. 7 , the otoacoustic emission interface  250  is intended to drive two sound transducers  251 R,  251 L through a pair of differential operational amplifiers  250 A,  250 B to produce a variety of signals, from pure tones at various frequencies to chirps, clicks, sine waveforms, etc. The otoacoustic emission interface  250  can present tones at standard sound pressure levels. The device employed with the otoacoustic emission interface  250  includes a microphone  251 M, also inserted in the ear canal, which collects signals coming back from the ear, and provides sufficient linear amplification through a dual-stage amplifier  250 C to present the signals to the codecs  248 . The transducers and microphone interface circuits include a plurality of electrostatic discharge diodes and induction coils to provide electrical shock protection  250 D. In various embodiments of this invention, the otoacoustic emission interface  250  also can be used for otoreflectance measurements for assessing some middle ear conditions. 
     The ABR interface  252 , shown in  FIG. 8 , consists of a plurality of analog signal processing chips, not shown individually, which filter and amplify the signals received from the scalp of a subject via electrode wires  232 . Specifically, signals received from each of the individual electrodes  234  are routed through an electrical insulator circuit  252 A, consisting of a plurality of metal oxide varistors, resistors, and capacitors, which functions to isolate the electrodes  234  from any dangerous electrical currents or voltages. The insulator circuit  252 A functions to replace conventional insulator circuits which utilize optical signal pathways, thereby eliminating the associated signal noise resulting from the conversion between electrical signals and optical signals. Signals from the electrodes  234  are then routed through a switching network  252 B, wherein an individual signal is automatically selected and passed to a differential operational amplifier  252 C. A common mode cancellation amplifier  252 D is included in the ABR interface  252  to further reduce signal noise levels. The resulting amplified signal is then routed to the codecs  248 . 
     In this mode of operation, the ear is presented with a repeated acoustic stimuli that cause neurons to fire beginning with the eighth cranial nerve and sequentially through neurons in the auditory pathways in the central nervous system from the brainstem to the cortex. Through the mechanism of volume conduction, the electrical potentials generated from these neuronal firings can be detected by the electrodes  234  on the surface of the skin. 
     An additional function of the ABR interface  252  is to provide automated impedance check of the placement of electrodes  234 . Once the electrodes  234  are in place, a small current is injected through the electrodes  234  into the scalp of the subject, and the impedance between electrodes  234  is measured. In addition to selecting an individual signal from the electrodes  234 , the switching network  252 B permits impedance measurements of the electrodes  234  to be carried out using the same differential operational amplifier  252 C, by altering the amplifier gain setting. Impedance can be varied by placement of the electrodes. Once the impedance is within the predetermined range for operation, ABR signal connection can begin. It is important to note that impedance checking can be accomplished without unplugging the electrodes. That is to say, checking is automatic. 
     Returning to  FIG. 6 , a mode configuration system  254 , a reset watchdog system  256 , a clock crystal  258 , a power supply  260 , preferably a nickel-metal hydride battery, and a battery charger  262  all are operatively connected to the processor  240 . While each of these blocks is required for operation of the device  200 , they are standard in nature and are not described in detail. 
     The processor  240  has an input-output channel  264 , which preferably includes infrared connection  22 , fiber-optic connection  23  and isolated RS-232 interface  24 . The device  200  can communicate with any infrared compatible or RS-232 compatible personal computer, printer, or other digital device (not shown) for data transmission. Data transmission may include patient information, configuration data for the signal processor  240 , or software program updates for storage in the memory subsystem  242 . 
     A audio output  266  in the form of a buzzer may be provided. The audio output  266  provides an audio feedback to the user for keyboard actions and an audio indication for error conditions. 
     A serial port  268  also is operatively connected to the processor  240 . The serial port  268  is utilized to provide direct programming of the processor  240  from a personal computer, for example, and is intended for use only for initial software download and major software program upgrades of the processor  240 . 
     As an auditory screening device  200 , the present invention utilizes a auditory phenomena known as a distortion product otoacoustic emission (DPOAE). A DPOAE is a tone generated by a normal ear in response to the application of two external tones. When two tones, f 1  and f 2  are applied to an ear, the normal non-linear outer hair cells generate a third tone f dp , which is called a distortion product. The distortion product f dp  then propagates from the outer hair cells back to the ear canal where it is emitted. The level of the DPOAE can be used as a measure of outer hair cell function. If the outer hair cell system is absent or otherwise not functioning properly, the non-linearity will be absent or reduced and the f dp  will either not be generated or generated at a lower than expected level. 
     The measured DPOAE is highly dependent upon the specific tones that invoke it. The frequencies of f 1  and f 2 , and their respective levels in the ear canal, L 1  and L 2  must be controlled precisely. Under known signal conditions, the largest distortion product f dp  is generated at a very specific frequency (f dp =2f 1 −f 2 ), and level L dp . Comparison of the level of L dp  with known values from individuals with normal outer hair cell systems forms the basis of the decision of whether the patient either passed the screening, illuminating the pass/refer LED  218 , or requires a referral for a more complete diagnostic testing. 
     Signals other than pure tones can be presented to the ear, which will also evoke an auditory response from the ear, such as clicks, chirps, etc. The DPOAE response is used with the auditory screening device  200  as an example of one such input. Other auditory stimuli generating an auditory response would be processed by the auditory screening device  200  the same way as the DPOAE. 
     As shown in  FIG. 9 , during operation, the processor  240  sends a filtered output signal from a filter  269  through the digital to analog converter portions  270  of the codecs  248 . The output signals are then routed through amplifier components  250 A and  250 B in the DPOAE interface  250  and transmitted to the output components  251 R and  251 L of the ear probe  228  utilized in conjunction with the device  200 . 
     As shown in  FIG. 10 , the ear probe  228  includes a microphone  251 M which returns signals through a third amplifier  250 C in the DPOAE interface  250 . The amplified analog signal is routed through an analog-to-digital converter  280  in the codecs  248 , and conveyed to the processor  240 . 
     In the processor  240 , the incoming analog signal is sampled using a frame buffer  282 . The size of each new frame in the frame buffer  282  is calculated to be an integer number of samples of the two primary tones at frequencies f 1  and f 2 , and also, an integer number of samples of the otoacoustic tone produced by the ear at f dp . This is a critical step to assure quality of subsequent signaling processing, by avoiding windowing techniques, which can introduce substantial artifacts. Tables of numbers for each standard frequency employed in the device  200  and for other frequencies in use or intended use in the device  200  are available, and are programmed into the algorithm once the user selects the test frequencies. Should a combination of frequencies be required for which no common integer number can be found to fit in a practical size frame, the frame size is adjusted to f dp  and the frame is windowed prior to Fourier Transformation, but this method is used only in extreme cases since in normal operation, the required frequencies are available. 
     The data from a single frame is passed to a point Discrete Fourier Transform (DFT) block  284  which calculates the signal&#39;s magnitude and phase content, but only at frequencies of interest, including f 1 , f 2 , and f dp  to determine a noise floor. Windowing is induced prior to processing the DFT to reduce edge effects, although windowing induces energy at other bands. The block  284  is used only for temporary calculations, and the windowed data is not reused again. The output of block  284  is the magnitude and phase of primary signals at f 1  and f 2  and the noise floor figure of time at f dp . The output of block  284  forms an input to frame rejection block  286  and to an on-line calibration calculation block  288 . 
     With the information on the magnitudes at various frequencies, a noise calculation algorithm is employed at and/or around f dp  to determine the noise floor. The magnitude of the noise floor and frequency content are used against a set of predetermined conditions, i.e. a comparison against an empirically derived table contained in the processor  240 , to determine the outcome of the frame. That outcome has three distinct possibilities. First, if the noise magnitude and frame content exceed a multi-threshold condition at measured frequency bands, the new frame is rejected. Second, if the noise magnitudes fall between a set of reject thresholds and a set of accept thresholds, the data in the frame is disregarded, but the noise information is kept to update the noise level average. Third, if the noise magnitudes are below the accept thresholds, the frame is kept and passed on for further processing and the noise magnitudes are averaged together with the noise average of the previous frame. This information is used to update thresholds, such that the system adapts to environmental conditions. 
     When the information about magnitudes of primary tones at f 1  and f 2 , and the noise floor information at and/or around f dp , an online calibration of the level of magnitudes takes place. Several actions occur in the calibration block  288 . First, if the noise floor is large when no primary tones are present, the frequency of the primaries is adjusted within predetermined limits. A new f dp  is calculated, and the noise content of frequency bins at and around f dp  is checked again. This process is repeated until a stable, low noise floor is established. No primary tones are played through the speaker through this process. Once the primaries are presented, they are stepped up to the full output amplitude, as programmed by the user and calibrated in the ear by increasing the output of the codecs  248 . No data collection from the ear has taken place yet. At this time, if the level is not reached in a user predetermined time, and at the rate of increase of the primaries, the test is aborted due to lack of fit or the low quality of fit of the probe in the ear canal. 
     Once a proper fit of the probe in the ear canal is achieved, and testing begins, data collection takes place. During the entire process of data collection, the levels of tones at f 1  and f 2  are checked to ensure that they remain within predetermined limits throughout the test. If they exceed those limits, the output is adjusted up or down to compensate until a maximum compensation limit is reached, at which time, the test is aborted and the user is notified. Also, the magnitude at and/or around f dp  is continuously monitored to assure low noise floor, and if necessary, the frequency of the primary tones are adjusted on-line within predetermined limits to avoid the high external noise region. The change in frequencies of the primaries is minimal, and within the specified tolerances of the device  200 , and have been shown not to affect the magnitude of the tone within the ear at f dp . 
     The block  290  is a store/copy buffer. As a frame of signal data is collected in new frame buffer  282 , a copy of it is saved by the store/copy buffer  290  for processing of the subsequent frames. The store/copy buffer  290  receives frame data from new frame buffer  282  and has a variable depth, depending the number of frames averaged together. Buffer  290  provides an output to a slide buffer block  292  and an average buffer  294 . The slide buffer  292  operates with the stored previous frames, which are slid by a predetermined amount and the empty spaces padded with zeros for subsequent processing in the average buffer  294 . 
     In the average buffer  294 , the frames are averaged together to reduce the uncorrelated noise present. Theoretically, the noise is reduced by a factor of one over the square root of the number of averaged frames, i.e.: 
         1       No   .   Avg   .   Frames         .       
 
The frames are averaged in a linear fashion, sample by sample and a new frame is created at the end of the averaging operation. The advantage of this method is that the data is essentially correlated against a slid copy of itself, slid far enough away to avoid averaging the same information content. This provides either a substantial reduction in uncorrelated noise energy for the same amount of sampling time or a substantial reduction in sampling time to obtain the equivalent noise reduction when compared to standard linear averaging.
 
     The minimum limit to the sliding of the data, and to the reuse of old data frame is the autocorrelation function of the data in the frame, which can be predetermined or calculated on-line. This method is equivalent to taking much smaller frames and averaging them together. However, for the purposes of the subsequent Fourier Transformations and filtering taking place, the frame size is required to be large (i.e., 960 samples at 48 kilohertz sampling rate), to obtain several full cycles of each of the tones at f 1 , f 2 , and f dp . The problem with taking a large number of very small frames is that the Fourier Transforms or other signal processing methods require several cycles of data for proper operation. The method of the present invention outperforms standard linear averaging of large frames because of the reduction in time as well as providing proper operation of the Fourier Transforms. 
     The final average buffer  296  obtains the averaged data from the average buffer  294 , and collects it in a buffer that is used for subsequent processing and signal statistics. The output of the final average buffer  296  is digitally filtered in filter  298  which removes any remaining high or low frequency components not required for final data presentation. 
     The averaged and filtered data is converted to frequency domain, in the embodiment illustrated, by using a discrete Fourier Transform at block  300 , and the resulting data then is ready for presentation to an operator as indicated at block  302 . As will be appreciated by those skilled in the art, other signal processing methods are available to convert data, and those other methods are compatible with the device  200 . 
     In further alternate embodiments of the present invention  10 , utilized as vibration detectors or alcohol intoximeters, the input/output interface  52  is replaced with, or coupled to, one or more suitable electrical signal sensors configured to measure signals representative of the desired test material, for example, a vibration waveform or an electrical signal representative of breath alcohol content. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results are obtained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.