The songs were downloaded from iTunes (Apple Inc., 2012) in
m4a format, with an average bit-rate of 256 kbps to achieve high
quality sound. The audio samples were then modified using Adobe
Audition CS6 (Adobe Systems Inc., U.S.) batch processes. The root
mean square amplitudes of the audio samples were standardized to
an internal reference to achieve equivalent sound pressure levels
across the songs, and then scaled to 70 dB SPL using a Brüel and
Kjær measuring amplifier. This is considered a reasonable volume
to present songs while avoiding amplitudes that could cause
discomfort or hearing loss. The audio samples were then played
using a standard PC soundcard through a Sennheiser headset (Series
HD 518: Sennheiser Electronics GmbH and Co. KG).