Acoustical barriers in classrooms: the impact of noise on performance in the classroom

There is general concern about the levels of noise that children are exposed to in classroom situations. We report the results of a study that explores the effects of typical classroom noise on the performance of primary school children on a series of literacy and speed tasks. One hundred and fifty eight children in six Year 3 classes participated in the study. Classes were randomly assigned to one of three noise conditions. Two noise conditions were chosen to reflect levels of exposure experienced in urban classrooms (Shield & Dockrell, 2004): noise by children alone, that is classroom–babble, and babble plus environmental noise, babble and environmental. Performance in these conditions was compared with performance under typical quiet classroom conditions or base. All analyses controlled for ability. A differential negative effect of noise source on type of task was observed. Children in the babble and environmental noise performed significantly worse than those in the base and babble conditions on speed of processing tasks. In contrast, performance on the verbal tasks was significantly worse only in the babble condition. Children with special educational needs were differentially negatively affected in the babble condition. The processes underlying these effects are considered and the implications of the results for children’s attainments and classroom noise levels are explored

EMD-based filtering (EMDF) of low-frequency noise for speech enhancement

An Empirical Mode Decomposition based filtering (EMDF) approach is presented as a post-processing stage for speech enhancement. This method is particularly effective in low frequency noise environments. Unlike previous EMD based denoising methods, this approach does not make the assumption that the contaminating noise signal is fractional Gaussian Noise. An adaptive method is developed to select the IMF index for separating the noise components from the speech based on the second-order IMF statistics. The low frequency noise components are then separated by a partial reconstruction from the IMFs. It is shown that the proposed EMDF technique is able to suppress residual noise from speech signals that were enhanced by the conventional optimallymodified log-spectral amplitude approach which uses a minimum statistics based noise estimate. A comparative performance study is included that demonstrates the effectiveness of the EMDF system in various noise environments, such as car interior noise, military vehicle noise and babble noise. In particular, improvements up to 10 dB are obtained in car noise environments. Listening tests were performed that confirm the results