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NOISE

المؤلف:  John Field

المصدر:  Psycholinguistics

الجزء والصفحة:  P190

2025-09-20

622

NOISE

Non-speech sounds which potentially reduce the intelligibility of speech. The term is also sometimes used for factors (e.g. ink blots) which reduce the legibility of written text and even for factors such as individual voice quality which are not essential to speech processing.

 The intelligibility of a speech signal depends upon the ratio between the level of speech and the level of noise; this is termed the S/N ratio. For normal understanding, there should be an S/N ratio of þ6 decibels (i.e. the average speech level should exceed the average noise level by 6 decibels). Where speech and noise are at equal levels, only about 50 per cent of words are recognised. However, even with negative S/N ratios, speech may remain partly intelligible– especially if the listener is familiar with the topic or if the sources of speech and noise are widely separated. An important factor is also whether the noise is continuous or intermittent: continuous noise has a far more powerful effect in masking speech.

 In order to test the capacity of the human ear or the ways in which we process a degraded speech signal, experimenters sometimes add white noise to speech. White noise is a constant hiss like an extended fricative or like radio static. It is aperiodic: its average loudness remains constant over the entire range of audible frequencies.

See also: Intelligibility