Noise levels at the sites close to and far fromthemine were compared
by conducting two 20-minute measurements of the background sound
pressure levels at each SM2 recording point using a Z-weighted
B&K2270 sound level meter. All the animal sounds close to the microphone
were excluded from the recordings using BZ5503 software
(Bruel & Kjaer, Denmark). The standard sound-pollution measurement
equivalent sound levels (Leq) were then extracted from the recordings
(Rossing, 2007). The number of passings of the mining trucks per day
was determined by listening to the recordings made at the site close to
mine during 24 h over two days in each recording session using Raven
Pro 1.5 software. Recurrent sounds produced by themine were classified
and characterized. Different types of anthropogenic sounds were selected
from two days of recordings (48 h) from one SM2 at the site close to
the mine for each recording session. The two most frequent types of
noise were truck passing noise and the reverse warning sound of trucks.
Twenty noise events were randomly selected per day, totaling 240 truck
traffic events and 240 reversing truck sound events. For the less frequent
noises, such as explosions, horns, and sirens, all events heard during two
days were selected. These noise events were described using Raven Pro
1.5 by measuring their minimum, maximum and peak frequency, and
duration.