Volume 119 No. 12 2018, 13939-13944 ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu ijpam.eu PC BASED AUDIOMETER GENERATING AUDIOGRAM TO ASSESS ACOUSTIC THRESHOLD Mahalakshmi.A, Mohanavalli.M, Raja Sankari.V.M, Shobha Christila.S Department of Biomedical Engineering Sri Ramakrishna Engineering College Coimbatore, India Abstract This article presents an implementation of a software application in the LabVIEW programming environment which recreates the functions and features of a standard audiometer. The implemented audiometer is a virtual instrument with all the features and functions of an audiometer currently available on the market as a standalone device. The sound signal is delivered to patient via head phones and the patient feeds back the response to the system using the switch. Based on the response of patient automatic audiogram is plotted between frequency and intensity which is the volume of sound pressure. The resulting audiogram indicates whether the patient has hearing loss or not and to quantify the amount of hearing loss. Keywords acoustic function, audiometer, audiogram. I. INTRODUCTION Hearing loss is the common problem a human faces due to natural birth or during the aging process. Some people contract hearing loss by being exposed to continuous noise. This is further aggravated by the day today increase in noise pollution.the testing of hearing ability shows parameters of symmetry versus asymmetry, air conduction versus bone conduction, speech recognition in every ear and the dynamic of hearing level over time. Audiometric tests are commonly used to diagnosis the patient s hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or distinguished speech from background noise. An audiometer is a machine used for evaluating hearing acuity. They usually consist of an embedded hardware unit connected to a pair of headphones and a test subject feedback button, sometimes controlled by a standard PC. An audiometer typically transmits recorded sounds such as pure tones or speech to the headphones of the test subject at varying frequencies and intensities, and records the subject's responses to produce an audiogram of threshold sensitivity, or speech understanding profile Pure-tone audiometry is a behavioral test used to measure hearing sensitivity. Pure-tone thresholds (PTTs) indicate the softest sound audible to an individual at least 50% of the time. Hearing sensitivity is plotted on an audiogram, which is a graph displaying intensity as a function of frequency. Speech audiometry has become a fundamental tool in hearing-loss assessment. In conjunction with pure-tone audiometry, it can aid in determining the degree and type of hearing loss. Speech audiometry also provides information regarding discomfort or tolerance to speech stimuli and information on word recognition abilities.. Hearing range describes the range of frequencies that can be heard by humans or other animals, though it can also refer to the range of levels. The human range is commonly given as 20 to 20,000 Hz, though there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal. In a clinical audiogram test, pure tones between 250 and 8000 Hz are presented at varying levels, to determine a patient's pure tone detection thresholds (the quietest audible sounds) in the left and right ear. Thresholds between -10 and +20 db HL are considered in the normal range, while thresholds above 20 db HL are considered diagnostic for mild, moderate, severe or profound hearing loss 13939
PURE TONE (FUNCTION GENERATOR) DECISION MAKING RESPONSE SWITCH SIGNAL PROCESSING ARDUINO INPUT AUDIOGRAM GENERATED LabVIEW ENVIRONMENT HEAD PHONES USER Fig:1 Hearing level based upon intensity A. Bone Conduction Bone conduction is the conduction of sound to the inner ear through the bones of the skull. Bone conduction transmission can be used with individuals with normal or impaired hearing. Some hearing aids employ bone conduction, achieving an effect equivalent to hearing directly by means of the ears. A headset is ergonomically positioned on the temple and cheek and the electromechanical transducer, which converts electric signals into mechanical vibrations, sends sound to the internal ear through the cranial bones. Likewise, a microphone can be used to record spoken sounds via bone conduction. B. Air Conduction Air conduction is the transmission of sound vibrations to the eardrum through the external auditory meatus (opposed to bone conduction ). Air conduction in Medicine. air conduction. The atmospheric transmission of sound to the inner ear through the external auditory canal and via structures of the middle ear. II. METHODOLOGY In this project a person can be diagnosed if he/she had any hearing loss and to detect the range of audibility. The block diagram consists of three parts they are Input LabVIEW Environment User Fig:2 Block Diagram A. Input The function generator is used for generation of pure tone which will be the input signal for the circuit. The input range given to the circuit is about 5V and 3 KHz of sinusoidal signal. The input from the function generator is given to the audio amplifier circuit. The audio amplifiers can able to filter the output response of the function generator by varying the different attributes by Nominal Gain Bandwidth (22 Hz, 20 khz, 300 khz, ), Gain (0 db, 20 db, 26 db, 30 db, 36 db, 48 db, ) and Output Power (27 mw to 200 W). LM386 Audio amplifier is not a minimal component audio amplifier. It consists of extra capacitors to reduce the noise in the audio signal. The LM386 is quite a versatile chip. Only a couple resistors and capacitors are needed to make a working of audio amplifier. The actual output power will depend on supply voltage and speaker impedance. In an amplifier circuit, the LM386 takes an audio input signal and increases its potential anywhere from 20 to 200 times. This is known as the voltage gain. B. LabVIEW Environment The process of decision making is done in the LabVIEW environment. The input is taken from the patient response switch. According to the response from the values of db will be incremented or decremented using the arduino which is programmed. An audiogram is a graph that shows the audible threshold for standardized frequencies and intensities. The Y axis represents intensity measured in decibels (db) and the X axis represents frequency measured in hertz (Hz). Each ear will be tested individually. When you hear a tone, the patient will press a button. Then the test results illustrated as a graph shows the hearing threshold of the patient, i.e. the softest sounds are able to hear at different frequencies (Hz).With the help of patient response the audiogram is plotted automatically by the decision making. 13940
C. User The headphone used in our project is SONY MDR XD 450. The headphone has unique specifications with deep clear audio with an extended frequency range. The earpads provide wrap-around comfort with an improved acoustic seal. With the balanced rigidity and high response extra diaphragm, which maintains powerful performance through hours of listening and it also delivers powerful sound directly. When the patient hears the beep sound they will respond through this switch. The switch turns on which is binary in nature. This sends logic 1 value that is made as a variable in LabVIEW based on which the intensities and frequencies are varied automatically in LabVIEW which is the function of decision making block. Pure tone is transmitted to the ear through an earphone and measuring the lowest intensity in decibels (db) at which this tone is perceived 50% of the time. This measurement is called threshold. The testing procedure is repeated at specific frequencies from 250 to 8000 hertz (Hz, or cycles per second) for each ear, and the thresholds are recorded on a graph called an audiogram. If the subject hears the sound during the testing sequence, a button on the user interface is pressed. The test is run three times for each of the predefined frequencies and intensity and the final value is their mean value, which represents the points on the final audiogram. After completing the test, the STOP button is pressed and the audiogram for the tested ear is generated. Frequency and intensity varying circuit Gain is the amplification of the input potential and is a characteristic of the amplifier. Volume can adjust the sound level within the range of amplification set by the gain. Gain sets the range of possible volume levels. For example, if gain is set to 20, the range of volume is 0 to 20. Gain control can be achieved by connecting a 10 μf capacitor between pins 1 and 8.Without a capacitor between pins 1 and 8, the gain will be set to 20. With the 10 μf capacitor, the gain will be set to 200. The gain can be changed to any value between 20 and 200 by placing a resistor (or potentiometer) in series with the capacitor. Fig:3 Circuit Diagram of LM386 Audio Amplifier A 470 pf capacitor between the positive input signal and ground, which filters radio interference picked up by the audio input wires. 100 μf and 0.1 μf capacitors between the positive and negative power rails to decouple the power supply. The 100 μf capacitor will filter low frequency noise while the 0.1 μf capacitor will filter high frequency noise. A 10K Ohm resistor and a 10 μf capacitor in series between pin 7 and ground to decouple the audio input signal. In this circuit, the volume 10K potentiometer can vary from 0 to 10k but it is kept as stable of about 10k for producing the gain from 0 Hz to 8000 Hz. From this different frequency range can be obtained which is used for giving the different input to the headphones of the patient. Based on the response of the patient the audiogram is plotted for different frequency range. 13941
Flowchart of the overall system START GENERATION OF TONE WITH 20db AND 250Hz SEND THE GENERATED TONE TO HEADPHONE AND LabVIEW yyyyy CAN PATIENT HEAR THE SOUND Results Thus the implementation of the audiogram for evaluating the amount of hearing loss was successfully implemented in the LabVIEW environment with the help of remote and headphones. The pure tone of different frequencies and intensities are generated by the frequency and intensity varying circuit. The generated sound is transmitted to the headphones of the subject. Based on response of the subject, the intensity and the frequency ranges may be increase or decrease. The response of the subject can be done by the remote controller and it is interfaced with the LabVIEW via DAQ. The audiogram is plotted in the LabVIEW based on the response of the subject.test results can be acquired in a short time. This test can be performed almost anywhere with the availability of a PC. YES DECREASES THE INTENSITY BY 5dB NO INCREASES THE INTENSITY BY 10 db AGAIN SEND THE GENERATED TONE TO HEADPHONE AND LabVIEW Fig:4 Block Diagram in LabVIEW YES CAN PATIENT HEAR THE SOUND NO PLOT AUDIOGRAM FOR PARTICULAR INTENSITY AND FREQUENCY NO YES DOUBLE THE FREQUENCY IS FREQUENCY = 8KHz? STOP Fig:5 Plotting of an audiogram Conclusion Thus the audiogram was plotted using the software application which can be implemented on any PC equipped with the LabVIEW environment with a remote and 13942
headphones. An audiometer typically transmits recorded sound such as pure tones to the headphones of the test subject at varying frequencies and intensities and records the subject's responses to produce an audiogram of threshold sensitivity. Based on the response of patient automatic audiogram is plotted between different frequency and intensity.the patient can run the test individually and can send the results to the specialized medical personnel for qualified interpretation. Future scope This project can be further enhanced by generating the speech tones for different frequency and intensity which is transmitted to the headphones of the subject and the procedure is same as that of the pure tone. Audiometer calibration process can be implemented automatically. This can give an idea about environment noise level and audiometer can be minimized the effect of interference on the measurement signals. Then the audiogram is plotted for both air and bone conduction which is further useful for evaluating the accurate amount of hearing loss. In the bone conduction test, the test signals which are the vibrations at different specific frequencies and amplitudes are presented to a bone by a vibrator placed on the mastoid of forehead of the subject. References [1] Digital Medical Audiometer by Dan IUDEAN, Technical University of Cluj-Napoca, Mediamira Science Publisher, Acta Electro Technica China Academic Journal, Romania-2014 [2] Using LabVIEW to Design and Develop A Hearing Loss Calibration system by Er Poi Voon,National University of Singapore -2015 [3] A Computer Based Digital Audiometer for Evaluating Hearing Loss by S Leeudomwong 2016 [4] Design of Smart Hearing aid by V. Alan Immanuel Benjamin, International Journal of Electronics and Communication Engineering and Technology (IJECET) Volume 7, Issue 6, November-December 2016, pp. 32 38, Article ID: IJECET_07_06_005 [5] A New Computer Controlled Graphic Audio Equalizer IC by Mitchell Lee, IEEE Wireless Communications, 30(4), 1984, pp. [6] Design and Implementation of an Audiometry System Capable of Monitoring Neuronal Activity Related to the Patient's Hearing by A. Soto Otálora, ARPN Journal of Engineering and Applied Sciences, VOL. 10, NO. 4, March 2015 13943
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