Biomedical Engineering Reference
In-Depth Information
background noise is one of the chief com-
plaints of hearing aid wearers (Kochkin
et al., 2010).
different SNRs (i.e., speech performance
measures in noise). It is also valuable to
determine at what SNR a listener will sur-
render the attempt to understand speech
in noise, or speech preference measures.
Speech preference can be assessed by
using the acceptable noise level (ANL)
test.
Signal-to-Noise Ratio
Anyone who has tried to hold a conver-
sation in a noisy place knows that the
presence of noise can make it difficult
to hear. The level of the speech signal
compared to the level of the background
noise, including the reflected speech sig-
nal, is referred to as the signal-to-noise
ratio (SNR). When the level of the signal
is greater than that of the noise, the SNR
is indicated by a positive sign before the
amount of the difference. Conversely, a
negative sign denotes that the level of the
noise is greater than that of the signal.
With a large positive SNR, it is quite easy
to understand the signal. However, if the
level of the noise increases or the level of
the signal decreases, we have greater dif-
ficulty understanding speech (Nabelek &
Pickett, 1974). For satisfactory communi-
cation, the level of the signal needs to be
at least 6 dB (+6 dB SNR) above the level
of the noise (Moore, 1989). These diffi-
culties understanding speech associated
with challenging SNRs are exacerbated
by those with hearing loss (Nabelek &
Mason, 1981) and for children and the
elderly (Helfer & Wilber, 1990; Nabelek
& Robinson, 1982).
The ANL measures the maximum
level of background noise a listener is
willing to accept before abandoning
the effort to follow the speech. The lis-
tener is asked to adjust the maximum
level of background noise they judge to
be acceptable while listening to speech
(Nabelek, Tucker, & Letowski, 1991). The
average ANL falls between +10 and +12
dB for adults and between +8 and +10 dB
for children (Bryan, Franklin, Ware, &
Horne, 2013; Franklin, Thelin, Nabelek, &
Burchfield, 2006; Freyaldenhoven & Smi-
ley, 2006). This can be interpreted as adult
listeners prefer to listen to speech in noise
with a SNR of about +10 to +12 dB, while
children prefer a SNR of about +8 to +10
dB. There is a slight difference in the SNR
(≈6 dB) that listeners need for satisfactory
communication and agreement between
the SNR listeners prefer (≈12 dB). Thus,
there may be listening situations in which
a listener can understand speech, even if
it is at a challenging SNR but will give up
the attempt at listening because the SNR
is below their ANL.
Visual Cues and Barriers
Acceptance of Noise
To this point, this chapter has discussed
primarily acoustics. It is also worth our
time and effort to think about some
It is important to understand how well
a listener can understand speech under
