The application of frequency and time domain kurtosis to the assessment of hazardous noise exposures

Abstract

Five computer synthesized broadband noises, each having the same average spectrum and the same unweighted Leq of 100 dB SPL but very different temporal structures were used to produce hearing loss in chinchillas. Despite the same exposure energies and spectra, each noise exposure produced a different magnitude and frequency distribution of hearing loss and sensory cell loss. The results indicate that the statistical properties of a signal are important in the determination of hearing loss. When the audiometric and histological results are compared to a metric based upon kurtosis measured in the time and the frequency domain for each exposure, there is a strong indication that these matrices are good predictors of the magnitude and frequency distribution of the acoustic trauma. [Research sponsored by NIOSH Grant 2R010H02317.]

Occupational Hearing Loss from Non-Gaussian Noise

“…Impulse peak levels generally exceed 140 dB whereas impact peak levels are usually lower than 140 dB, 7 but the durations of impacts are often longer because of differences in the sound sources themselves and also due to the reverberation and reflection characteristics of indoor environments. Both impulses and impacts may be superimposed on a background of continuous or varying noise, which increases the hazard to hearing, [8][9][10][11] as will be discussed in subsequent paragraphs.…”

“…Complex Noise-Animal Experiments For many years, investigators have found that noise exposures that include impulse or impact noise produce greater than expected damage to the auditory system, in both animals and humans. 8,10,[94][95][96] This observation led some to recommend a penalty to the permissible limits for complex noise exposures with a substantial component of impulse/impact noise. Evidence of this appears in Note #3 of ISO 1999 and Note #2 of an earlier version, 13,20 where caution is advised for impulsive or tonal conditions, which could be considered 5 dB more harmful than broadband, steady, nontonal noise.…”

“…The aspect of peakedness appeared to be fundamental to the outcome, and the kurtosis statistic proved to be a very good descriptor of the resulting hearing damage. 10,11,97 In these studies of non-Gaussian noise, certain parameters of complex noise were varied, and the effects were compared with predictions on the basis of equal energy. In most cases, the effect of noise exposures involving impulse/impact noise at low to moderate levels have proven to be adequately predicted by L eq , and at higher levels certain complex noise exposures exhibited more damage than would have been predicted.…”

“…Several investigations have shown greater hearing damage when impulses or impacts were superimposed on background noise than would have been predicted for either type of noise separately. [8][9][10][11] In an extensive series of experiments to investigate the effects of complex noise, Ahroon et al exposed 23 groups of chinchillas (n ¼ 135) for 5 days to octave bands of noise, impact noise alone, or various combinations of impact and octave-band noise, all of equal energy. 9 Their results showed that hearing damage was greater than would have been predicted by equal energy depending on several factors: peak SPL, impact repetition rate, presence or absence of background noise, and the frequency component of the background noise.…”

Understanding a New Method as Powerful Prevention of Noise-Induced Hearing Loss: Kurtosis Metric

“…Damage percentage of outer and inner hair cell loss based on different beta values, i.e., β = 3 (A), β = 21 (B), β = 84 (C), and its potential pure-tone audiometric results. It is a graphical display inferred from data ofLei et al (1994). OHC: outer hair cell, IHC: inner hair cell.…”