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Hearing aids system for impaired peoples

Article · January 2004

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International Journal of Computing & Information Sciences Vol.2, No. 1, April 2004 23

Hearing Aids System for Impaired Peoples

Othman O. Khalifa, M. H. Makhtar, and M. S. Baharom
Electrical & Computer Department, Kulliyyah of Engineering,
International Islamic University Malaysia
Jalan Gombak, 53100, Kuala Lumpur, Malaysia
Email: khalifa@iiu.edu.my

Abstract: Traditional analog hearing aids are similar to a simple radio. They can be tuned and adjusted
for volume, bass and treble. But hearing loss is not just a technical loss of volume. Rather, hearing
deficiency can increase sensitivity and reduce tolerance to certain sounds while diminishing sensitivity to
others. For instance, digital technology can tell the difference between speech and background noise,
allowing one in while filtering out the other. Approximately 10% of the world's population suffers from
some type of hearing loss, yet only a small percentage of this statistic use a hearing aid. The stigma
associated with wearing a hearing aid, customer dissatisfaction with hearing aid performance, and the
cost associated with a high performance solution are all causes of low market penetration. Through the
use of digital signal processing, digital hearing aid now offers what the analog hearing aid cannot offer.
It proposes the possibility of performing signal-to noise enhancement, flexible gain-processing, digital
feedback reduction, etc. In this paper, the simulation of simple digital hearing aid was developed using
MATLAB programming language. The implementation of this configurable digital hearing aid (DHA)
system includes the noise reduction filter, frequency shaper function, and amplitude compression function.
This digital hearing aid system is design to adapt for mild and moderate hearing loss patient since
different gain can be set to map different levels of hearing loss.

Keywords: Digital Aids system, filtering, noise reduction.

Received: July 14, 2004 | Revised: January 14, 2005 | Accepted: February 14, 2005

detection of a pure tone. This is why there are many

1. Introduction types of hearing aids with a wide range of functions
Hearing Aids systems are one of the most important and features to address individual needs. Table 1
issues for human being. They are a small shows the classification of degrees of Hearing Loss
[2].
electronic instrument which makes sound louder
and makes speech easier to hear and understand. A hearing aid is an electronic device that makes
The hearing aid is designed to pick up sound sounds louder and can help to offset hearing loss. The
waves with a tiny microphone, change weaker aim of the hearing aid is to amplify sound signals in
sounds into louder sounds and send them to the such a way that they become audible for the hearing
ear through a tiny speaker. With the microchips impaired person.
available today, hearing aids have gotten smaller
and smaller and have significantly improved Classification of Hearing level
quality. Roughly 10% of the world population bears Hearing Loss
from some hearing loss. However, only a portion Normal hearing -10 dB – 26 dB
uses hearing aid. This is due several factors which mild hearing loss 27 dB - 40 dB
include the stigma associated with wearing a hearing moderate hearing 40 dB - 70 dB
aid, customer dissatisfaction with the devices not loss
meeting their expectations, and the cost associated severe hearing loss 70 dB - 90 dB
with the new digital versions of hearing aids [1]. profound hearing greater than 90 dB
Hearing loss is typically measured as the shift in loss
auditory threshold relative to that of a normal ear for Table 1: Different degree of Hearing Loss
24 International Journal of Computing & Information Sciences Vol.2, No. 1 ,April 2004

Basically, all hearing aids were using the analogue Input Speech
technology for the treatment of sound. Improvements Signal
have been made by using the development of digital
sound treatment for the efficiency of hearing aids.
Nowadays, the digital hearing aids are small, which Noise
can be hidden inside the ear and have an almost Addition
perfect sound reproduction.
The research of Digital hearing aids have been
growth and now a small programmable computer that Noise
are capable in amplifying millions of different sound Reduction
Filter
signals had been constructed in the devices, thus
improving the hearing ability of hearing-impaired
people. The first digital hearing aids were launched
Frequency
in the mid 80’s, but these early models were slightly
unpractical. After ten years later, the digital hearing Shaper
aids really became successful, with small digital
devices placed either inside or discreetly behind the
Amplitude
ear [3]. Today, digital technology is very much a part
of daily life. Most households have a variety of Compression
digital products, such as telephones, video recorders
and personal computers. Hearing aids also was
Output Speech
benefited from the emergence of digital technology. Signal
Among the advantages of digital Signal Processing
that allows hands free operation. The aid
automatically adjusts the volume and pitch on it's Figure 1: System Block Diagram
own. It performs thousands of adjustments per
second which results in reduced background noise,
improved listening in noisy situations, sound
2.2 Noise Reduction Filter
A major anxiety for the people with hearing loss is
quality and Multiple program settings [4]. The user
the capability of hearing aid to differentiate intended
can switches between varieties of programs for
speech signal in a noisy environment. Hence, to
different listening situations.
eliminate the noise, a reduction filter function is used
in this design. To suppress the noise in the signal, the
2. Methodology wavelet filter function is used.
Below is a block diagram for the MATLAB
implementation of Digital Hearing Aid System.
The input speech signal takes the form of human 2.3 Frequency Shaper
voice. The input speech signal will pass through One major complaint of hearing aid users is that the
several functions i.e noise addition, noise reduction hearing aid amplifies all signals rather than the
filter, frequency shaper and amplitude compression significant signal that they desire to hear [5]. Most
before producing an adjusted output speech signal hearing impaired has difficulties to hear high
which is audible to the hearing impaired person. frequency signal. Therefore, the frequency shaper is
designed to correct for loss of hearing at certain
frequencies.
2.1Noise Addition It applies high gain for higher frequencies and vice
Since the input speech signal for this system is a versa. The typical frequency shaper transfer function
clean signal, some noise is added in order to simulate is shown in figure 2.
a real situation. In this system, the Adaptive White
Gaussian Noise (AWGN) and random noise are
added to the input speech signal by using MATLAB 2.4 Amplitude Compression
function. Noise (AWGN) has a continuous and Fundamentally, amplitude compression function is
uniform frequency spectrum over a specified the task of controlling the overall gain of a speech
frequency band and has equal power per Hertz of this amplification system. Amplitude compression will
band. It consists of all frequencies at equal intensity ensure that the amplified signal will not exceed
and has a normal (Gaussian) probability density saturation power. Saturation power is where the
function. sound signal begins to become uncomfortable.
Hearing Aids System for Impaired Peoples 25

In this simulation, one sample of hearing loss patient

is obtained from “Jabatan Audiologi dan Sains
Pertuturan, Fakulti sains Kesihatan Bersekutu,
Universiti Kebangsaan Malaysia”. This patient
suffers moderate hearing loss which characterized by:
- Threshold of hearing at 40 dB.
- Threshold of pain at 90 dB.
- Have difficulties to hear high frequency.

4. Results
Figure 4 below is the original speech signal which is
plot on time versus amplitude axis.

Figure 2: Typical Frequency transfer function

3. Implementation & Simulation

The code, written in MATLAB, loads the input wave
signal, takes the sampling frequency and the number
of bits of that signal. Then, Adaptive White Gaussian
Noise (AWGN) and random noise are added to the
signal before they are processed by various
MATLAB function to get an output which is audible Figure 4: Original Speech Signal
to the hearing impaired person.
For the analysis purposes, a sample of speech signal Next, Adaptive White Gaussian Noise is added to the
is selected. The sample is a male speaker voicing, "I original wave signal. The purpose of this addition
am Mohd Syahril Nizar, a final year student at UIA" just to simulate noises in the real life situation.
This signal is added by Adaptive White Gaussian Figure 5 shows the signal after noise addition.
Noise (AWGN) and random noise.

For simplicity, a Graphic User Interface (GUI) was

built to run this Digital Hearing Aid System
simulation demo. To run the demo successfully, it is
needed to input all the parameters which are
maximum gain to be applied, saturation power and
four frequency values where the gain changes. Figure
3 below shows GUI of this system.

Figure 5: Corrupted Speech Signal

Afterward, the denoising process takes place which

removes most of the noise in the signal as shown in
figure 6.

Comparing the spectrograms of the original signal

and the filtered signal, we can see that the amplitude
of the noise in the signal was noticeably reduced as
shown in figure 7.
Figure 3: GUI of Digital Hearing Aids
26 International Journal of Computing & Information Sciences Vol.2, No. 1 ,April 2004
form. The benefits of using digital aids could
Improve quality of life by improving sound quality,
Higher listening comfort, better communication in
noisy environment, better speech intelligibility in
group conversations and more flexibility in case of
progressive hearing less.

6. References
[1] Frost and Sullivan, World Audiology Products
Markets, 1997.

Figure 6: Signal after denoising [2] G. J. Proakis and G. D. Manolakis, Gigital Signal
Processing ; principles, algorithm, and application,
3rd edition, Prentice Hall, New Jersey, 1996.

[3] http://www.hearingresearch.org/ross.html

[4] http://www.helpinguhear.com/ hearing_aids.html

[5] Trudy Stetzler, Neeraj Magotra, Pedro Gelabert,

Prethi Kasthuri, Sridevi Banglore, Low Power Real
Time Programmable DSP Development Platform for
Digital Hearing Aids System, Texas Instrument.

Othman O. Khalifa is an assistant professor in

Electrical and Computer department, faculty of
engineering, International Islamic University
Malaysia. He holds PhD degree in image processing
Figure 7: Spectrogram of Original and from the University of Newcastle, UK in 2000. He
Adjusted Signal also leads and teaches modules at both BSc and MSc
levels in Communications and computer information
However the strength of the adjusted signal is not engineering. His interest research areas are: wavelets,
increase as our expectation. Possibly the cause of this fractals, signal/image processing, voice/Face
error is due to the gain function improperly implied. recognition.

5. Conclusion
The newer digital aids offer more ability to fine-
tune the sound without distorting the quality and
help the listener. In this digital hearing aids
system implementation using MATLAB, sound
processing is digitalized. Thus, it is possible to
refine the sound signal, for instance by reducing
noise and improving speech signals. In addition,
by using digital technology, the amplification
can be done only at the frequencies that the user
needs to amplify. This will eliminate the
problem with conventional amplifier which
amplified the whole signal including noise. In
general, digital hearing aids, when the incoming
signals are converted to digital signals. This
digitalization makes its possible to precisely
analyze & filter the signals. The signals can be
processed in one or more frequency channels. At the
end, the digital signal is again converted to its analog

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