An Acoustical Analysis of the Frequency-Attenuation Response of Musician Earplugs Page: 3
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Citation: Chesky K, Amlani AM (2015) An Acoustical Analysis of the Frequency-Attenuation Response of Musician Earplugs. Commun Disord
Deaf Stud Hearing Aids 3: 127. doi:10.4172/2375-4427.1000127
Page 3 of 5
Spectral analyses of each KEMAR-recorded condition were
determined by estimating the frequency content using a Fast-Fourier
Transformation (FFT) algorithm written in Matlab. Each way file was
analyzed using a 1024-sample FFT, yielding a spectral line resolution
of 43.07 Hz (i.e., sampling rate of 44100 Hz/1024-sample FFT). We
employed the use of a rectangular window, based on the findings of
Maddage and colleagues . Specifically, these authors revealed that
a rectangular (i.e., uniform) window best captured the pseudo-
random-dynamic properties of music, compared to a more traditional
smoothing window (i.e., hamming). To reduce the effect of spectral
leakage between windows, the FFT was overlapped by 75%. The use of
the additional overlap provided a high-resolution output in both the
frequency and time domains.
Leq/Dose: A limitation of the rectangular window is its inability to
capture the amplitude characteristics of a signal adequately. To
overcome this limitation, a second Matlab algorithm was written to
calculate the time average level, or equivalent continuous noise level
(Leq), for each condition. Specifically, the algorithm calculated the A-
weighted sound pressure level (dBA) in octave bands using a Kaiser-
window filter for anti-aliasing for a given input way file. The equation
used to calculate dBA was:
L=10 og _ 10L1+ Ki/10
where L represented the combined level in dB SPL, n the number of
bands being combined, i the ith band, Li the octave band level, and Ki
the A-weighted correction to simulate human auditory sensitivity for
the octave frequencies ranging between 31.5 and 8000 Hz, per ANSI
S1.4a-1985 (R2006) .
Influence of presentation level on spectrum of music
Figure 3 shows the spectral characteristics of the music stimuli
across the nine presentation levels measured in the unoccluded
condition. As expected, much of the acoustic energy in this music was
in the low frequencies. In addition to showcasing the influence of ear
canal resonance, the data show remarkable stability of the spectral
characteristics over the nine repeated measures and across intensity
ER 9 j
ER l5 re
C) 0 W 0 0J3 Q1 C
M (T O. ~(0 nC) M(0A) (DC>K(
SC) M ) D
Figure 3: Spectral characteristics of music at nine presentation
levels as measured unoccluded in KEMAR.
The spectral characteristics of the music stimuli for the nine
presentations levels and across the four MEP conditions are shown in
Figure 4. Similar to measurements of the unoccluded condition, the
spectral characteristics of the music stimuli were highly stable within
each of the four MEP conditions. Because the MEP was removed and
reinserted prior to each presentation level, this finding also
demonstrates that the spectral characteristics within each MEP
condition were not influenced by 1) repeated or varied insertions of
MEPs, 2) or anomalies due to disconnection and reconnection of
filters to MEP earplug. However, comparisons across MEP condition
show that each earplug type produced a unique spectral profile. These
data show that each MEP condition had a unique influence on the
spectral characteristics of the music.
J j J-j.-.. - J
Figure 4: Spectral characteristics of music as measured in KEMAR at 9 presentation levels.
Commun Disord Deaf Stud Hearing Aids
ISSN:2375-4427 JCDSHA, an open access journal
Volume 3 . Issue 1 . 1000127
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Chesky, Kris S. & Amlani, Amyn M. An Acoustical Analysis of the Frequency-Attenuation Response of Musician Earplugs, article, January 16, 2015; Los Angeles, California. (https://digital.library.unt.edu/ark:/67531/metadc1042574/m1/3/: accessed June 14, 2021), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Music.