Sentences for testing speech intelligibility in noise

A list of ten spoken Swedish sentences was computer edited to obtain new lists with exactly the same content of sound, but with new sentences. A noise was synthesized from the speech material by the computer to produce exactly the same spectrum of speech and noise. The noise was also amplitude modulated by a low frequency noise to make it sound more natural. This material was tested monaurally on 20 normal-hearing subjects. The equality in intelligibility of some of the lists was investigated. Repeated threshold measurements in noise showed a standard deviation of 0.44 dB when the learning effect was outbalanced. Only a small part of the learning effect was due to learning of the word material. Intelligibility curves fitted to the data points in noise and without noise showed maximum steepnesses of 25 and 10%/dB respectively. At constant signal to noise ratio (S/N) the best performance was achieved at a speech level of 53 dB.