Effect of spectral envelope smearing on speech reception. II.
This paper describes two experiments on the effect of reduced spectral contrast on the speech-reception threshold (SRT) for sentences in a background of interfering sound. Signal processing is performed by smoothing the envelope of the squared short-time fast Fourier transform by a convolution with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. In the first experiment the effect of reduced spectral contrast on the SRT for male speech is investigated and compared with previously obtained results for female speech [ter Keurs et al., J. Acoust. Soc. Am. 91, 2872-2880 (1992)]. Spectral energy is smeared over bandwidths of 1/8, 1/4, 1/3, 1/2, 1, 2, and 4 oct. The results show that, despite the differences in spectral pattern between male and female voices, the SRT in noise increases similarly for both voices for smearing bandwidths over 1/3 oct. In terms of the ripple density of the spectral envelope the results indicate that the range of lower spectral modulations, up to a limit of about 1.5 periods/oct, is sufficient for the intelligibility of speech in interfering sounds. In the second experiment the extent of the threshold difference between a speech masker and a noise masker is investigated for spectral smearing bandwidths of 1/2, 1, and 2 oct. The release from masking found for the speech masker relative to the (steady-state) noise masker decreases with spectral envelope smearing.
ter Keurs
M
M
Department of Oto-rhino-laryngology, Free University Hospital, Amsterdam, The Netherlands.
Festen
J M
JM
Plomp
R
R
D000161:Acoustic Stimulation; D000328:Adult; D001309:Auditory Threshold; D005260:Female; D006801:Humans; D008297:Male; D009622:Noise; D010700:Phonetics; D012737:Sex Factors; D013061:Speech Acoustics; D013067:Speech Perception / Q000502:physiology*