In-Vehicle Speech and Noise Corpora - Digital Signal Processing for In-Vehicle Systems and Safety - page 145

Fig. 9.5 Model of acoustic environment in the car

noise, then the resulting car noise is less car specific/dominant (i.e., n e > n ce ).

This scenario is less favorable for car verification than the previous case.
• Environment Dominant Noise : Finally, noise sources external to the car such as
horn from a nearby car or engine sounds from a passing truck are considered
outside the scope of this study. This is because these sounds are least car specific
(if n e << ). This would cause increased confusability in

acoustic vehicle platform identification. This case would require the most
generic noise models for speech systems.

n ce then n c ðÞ n c ðÞ

^

In practice, it is very difficult to obtain these noise types in isolation since all
noise sources cannot be controlled simultaneously in naturalistic driving. However,
in the process of car noise data collection, we have minimized external noise by
carefully choosing the recording conditions.
For analysis, three noise conditions in the same vehicle are analyzed for their
spectral content and variability. These conditions consist of NAWC, ACWC, and
NAWO, as shown in Fig. 9.6 . These environments were chosen because of their
high probability of occurrence. Furthermore, these noise scenarios represent unique
environments because the dominant sounds in each case are different (e.g., in
ACWC, AC noise is dominant).
The spectral content of the vehicle acoustic environments under ACWC,
NAWC, and NAWO conditions are shown in Fig. 9.6 . As seen in Fig. 9.6 b when
the AC is on and the windows are closed, the car noise is least time varying. The
main noise sources in this environment are AC, car engine, and road noise, but the
AC is the dominant source of noise. The spectral slopes indicate that the ACWC
scenario has the most high-frequency content compared to the other two noise
types. Also, this condition is the most conducive for car verification since the AC
and the fan/air blower are the most dominant noise sources. In the other two cases,
wind noise and road noise are the main noise sources. When AC is turned off, as
seen in Fig. 9.6a , the car noise is a mixture of road and engine noises. The only car-
dependent noise type when the AC is off and windows closed is the car engine noise
which is masked by the road noise. Finally, the last plot shows NAWO condition,
where the main noise sources are wind noise, road noise, and engine noise. NAWO