Chapter 6 136 Materials and methods Signal detection test The purpose of the signal detection test is to assess auditory fitness for job. The test was developed based on the acoustic characteristics of the real-working environment of Dutch locomotive engineers, where two auditory warning signals need to be reliably detected. Therefore, audio recordings were made in trains under different conditions (e.g., at different speeds), for details, see Van der Hoek-Snieders et al. (2021).These audio recordings weremade during normal operation of the trains and reproduced in a test situation. Prior, during, and after the acoustical measurements, the recording system was calibrated and checked. To determine the correct level of the recordings during off-line analysis, a calibration tone was recorded. When these audio recordings were made, six electric train types were in use for passenger conveyance. All were included for the acoustic measurements. The two auditory warning signals present in these train cabins were also both included. • The signals to be detected were the two warning signals for each specific train type: The Driver Safety Device (DSD) signal is a buzzer type signal that contains its most prominent signal peaks at 2000 and 4000 Hz. The Automatic Train Protection (ATP) signal sounds bell-like and contains its most prominent signal peaks at 4000 and 8000 Hz. • The interfering noise was a recording of the ambient noise of the respective train type driving at maximum speed. The noise inside a train cabin can be produced by the wheels, the track, the friction between both, and the train’s equipment, such as the motor, compressor, and air conditioning (Atmaja et al., 2018). The noise can be regarded as continuous. The level and spectrum of the noise, as well as the acoustic characteristics of the warning signals, differ between the six train types. In Figure 1, the acoustic environment of two train types is shown when driving at maximum speed, including the level and spectrum of the ambient noise and two acoustic warning signals.
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