Sound Classification in Hearing Aids by the Harmony Search Algorithm - Music-Inspired Harmony Search Algorithm: Theory and Applications - page 171

Fig. 1. The variety of sounds in everyday life
An automatic sound classifier would potentially be a very useful application. How-
ever, at present, many of the medium-cost hearing aids in the market cannot automati-
cally adapt to the changing acoustical environment. In spite of the impressive
advances in microelectronics, digital hearing aids suffer yet from severe design trade-
offs, which, in the effort of making this chapter stand by itself, are briefly described in
Section 0. These limitations mainly arise from the need of reducing the power con-
sumption in order to maximize the battery life. As a consequence, implementing
sound classification algorithms embedded in hearing aids becomes a very challenging
task [4-14]. The underlying reason is that it requires optimizing each parameter for the
sound classifier in order to reduce its computational complexity while maintaining a low
error probability, and thus, a good dynamic adaptation to the sound surroundings.
In particular, the feature extraction process, essential to properly characterize the
sound to be classified, is one of the most time-consuming tasks. Therefore, reducing
the number of features is probably one of the most successful ways of diminishing the
complexity of the classification system. The problem here is that, as will be com-
mented in Section 3, an excessively small number of features may increase error
probability. Thus, selecting those more appropriate features [15] is a crucial point for
the application at hand. Here, 'appropriate' means within this framework that they
should have low computational cost (i.e. a reduced number of mathematical opera-
tions per second to be computed) without degrading the hearing aid operation. Just in
this effort, this chapter explores the feasibility of using the harmony search (HS) algo-
rithm [16-21] to select the more satisfactory features constrained to the severe limita-
tions previously mentioned.
As it was commented above, hearing loss is currently an important health problem.
Approximately 13% of the population in highly developed countries suffers from con-
siderable hearing loss whose negative consequences could be mitigated by using some
kind of hearing aid [1-14]. These hearing losses strongly affect the speech communi-
cation and disqualify many hearing-impaired people from normal life activities. Hear-
ing impairment is more prevalent with increasing age. For instance, almost 50% of
those elder over the age of 75 are 'hard of hearing'. Taking into account that the