Tognola G, Grandori F, Ravazzani P
Department of Biomedical Engineering, Polytechnic of Milan, Italy.
Audiology. 1999 May-Jun;38(3):127-34. doi: 10.3109/00206099909073014.
The objective of this study was to investigate the effects of time-windowing on click evoked otoacoustic emissions (CEOAEs); 466 CEOAEs from full-term babies were considered. Data were acquired according to the default ILO88 response window (2.5-20 ms). Because CEOAEs are time-varying signals, each emission was analysed by means of the wavelet transform (WT), a technique which allows a simultaneous representation of the time and frequency features of a signal. By means of the WT it was possible to extract the temporal pattern of the elementary frequency components of the compound emissions. The effects of time-windowing were evaluated on each single emission component: rms and correlation values were computed from six 2.5-ms long time windows in the 2.5-17.5 ms range. Results indicated that both rms and correlation were not constant with time but reached a maximum in specific time-windows, depending on the frequency of the component. For low-frequency components, the correlation typically had a maximum in the interval 10-12.5 ms, whereas high-frequency components had a maximum around 5 ms. Above 12.5 ms, the correlation was greatly decreased for all frequency components. As a result, the comparison between the performance of the default ILO88 window (2.5-20 ms) and the window 2.5-12.5 ms showed that for all frequencies in the 1.5-6 kHz range there was a statistically significant improvement in the correlation. No improvement was observed for frequencies below 1.5 kHz because of their contamination by the residual background noise.
本研究的目的是调查时间窗对瞬态诱发耳声发射（CEOAEs）的影响；研究纳入了466例足月儿的CEOAEs。数据是根据默认的ILO88响应窗（2.5 - 20毫秒）采集的。由于CEOAEs是随时间变化的信号，因此对每个发射信号采用小波变换（WT）进行分析，该技术能够同时呈现信号的时间和频率特征。借助小波变换，可以提取复合发射信号基本频率成分的时间模式。对每个单独的发射成分评估时间窗的影响：均方根（rms）和相关值是从2.5 - 17.5毫秒范围内6个2.5毫秒长的时间窗中计算得出的。结果表明，均方根和相关性并非随时间恒定不变，而是在特定的时间窗内达到最大值，这取决于成分的频率。对于低频成分，相关性通常在10 - 12.5毫秒的区间内达到最大值，而高频成分则在5毫秒左右达到最大值。在12.5毫秒以上，所有频率成分的相关性都大幅下降。因此，将默认的ILO88窗（2.5 - 20毫秒）与2.5 - 12.5毫秒的窗的性能进行比较后发现，在1.5 - 6千赫兹范围内的所有频率，相关性都有统计学上的显著改善。对于低于1.5千赫兹的频率，由于受到残余背景噪声的干扰，未观察到改善。
