Wideband Hands-Free in Cars – New Challenges for System Design and Testing - Digital Signal Processing for In-Vehicle Systems and Safety - page 104

quality would immediately be noticeable to the driver since she/he will always have a
perceptual comparison of the high-quality audio playback in the car for other media.
Speech intelligibility in the car will be significantly increased, which is highly benefi-
cial, especially in background noise situations while driving. As a consequence, the
listening effort for the driver is reduced, the distraction from the primary task (driving)
will be reduced as well. Thus, the driver's distraction may be reduced substantially if
wideband technology is implemented properly. However, in order to achieve a
superior wideband speech quality, a variety of requirements different from narrow-
band telephony have to be taken into account. This includes careful system design of
all components involved in the transmission. The impact of delay and the components
contributing to delay are described in Sect. 6.2 . The listening speech quality analyses
for wideband car hands-free systems are described in Sect. 6.3 ,andthespecial
requirements on echo performance are given in Sect. 6.4 .
6.2 Transmission Delay
Since wideband transmission is most likely IP-based when connecting to a fixed line
network, a higher delay can be expected as compared to narrowband calls. The higher
delay not only contributes to a degraded communicational quality but also requires a
more thorough investigation of the echo loss required for wideband systems. This
concerns spectral as well as temporal characteristics and is discussed in Sect. 6.4 .
An overview of the components of a typical hands-free system and their effect
on delay is given in Fig. 6.1 .
Fig. 6.1 Typical components of a car hands-free system and their contribution to transmission
delay