The Importance of Low Frequency Masking on Auditory Perception. Literature Review.

Abstract

In this review, previous studies on the effect of the low frequency masking on speech comprehension are presented. First the theoretical background of masking focusing on low frequency masking of speech is presented. Previous studies and experiments that analysed low frequency masking patterns are reviewed and used as baseline knowledge for further investigation on speech intelligibility for normal hearing and hearing impaired people. Furthermore the combined effect of the reverberation and noise on speech intelligibility, before and after acoustical treatments of different rooms, was reviewed and presented in this report. The review showed that low frequency noise is an efficient masker of speech and lead to reduce speech intelligibility because of the increase of masking of higher frequencies (upward spread of masking) which is strongly dependent on the level and frequency of the masker. Especially maskers up to 350 Hz at sound pressure levels that normally occur at public spaces (offices, schools etc.) were indicated as efficient maskers of speech with the masking effect to increase with the increase of low frequency components in the masking noise. Hearing impaired people are strongly affected by the combined effect of reverberation and noise which makes it difficult to communicate in noisy environments. Spaces with poor acoustic properties increase the masking of higher frequencies (especially in speech) by lower frequency speech components. Finally, the importance of a good acoustic environment for speech intelligibility especially for vulnerable groups such as young and old, non native listeners and people with hearing impairments, was documented and presented.