Biomedical Engineering Reference
In-Depth Information
Figure 6-10.
Sign with the International Symbol for
Hearing Loss suitable for use to advertise available FM
receivers.
combined with hearing aids, a common
recommendation is to electroacousti-
cally verify that the FM output is 10 dB
greater or higher than the hearing aid
output. The way this +10 dB advantage is
achieved is with the understanding that
speech picked up by the hearing aid alone
would vary between 60 and 70 dB SPL
(typical of conversation speech), whereas
the speech picked up by an FM micro-
phone/transmitter would vary between
70 and 80 dB SPL. Such SNR advantage is
useful to counteract the effects of distance
and noise. However, using a fixed +10 dB
advantage in FM systems assumes that the
noise will never change and that the SNR
setting should never change. This “fixed”
+10 dB SNR approach is a limitation of
many traditional FM systems. Recently,
dynamic/adaptive FM systems have been
designed to overcome the fixed, tradi-
tional FM issue. Dynamic/adaptive FM
systems use sophisticated algorithms to
enhance speech in varying noise levels
and changing distance. In both hearing
aid and cochlear implant users, dynamic/
adaptive FM has been shown to be far
superior to traditional FM systems,
especially when noise levels increase
(Thibodeau, 2014; Wolfe et al., 2009).
Figure 6-11 illustrates how dynamic/
adaptive FM compares to the traditional
FM with both hearing aids and cochlear
implants as a function of increasing back-
