Masking of Speech by Bands of Noise

Abstract

The threshold of intelligibility for two-syllable (spondee) words was measured in the presence of different levels of masking noise. Twelve different bands were used, one (20 to 6600 cps) approximating a white noise and each of the other eleven containing a band of frequencies corresponding to a pitch interval of 250 mels. The absolute thresholds for these bands were also measured to permit transformation of the noise level from an absolute scale to a scale of sensation level. The results show linear relations between the masked threshold and noise level for white noise and for bands of noise between 394 and 1420 cps. For noise bands above 1420 cps this masking function is accelerated, while the two bands below 394 cps yield sigmoid masking functions. Of the bands used, the most effective contained frequencies between 670 and 1000 cps. The signal-to-noise ratio at threshold for this band was about −25 db while for bands above or below it became gradually smaller than −25 db, reaching a minimum of −60 db for the highest and lowest bands. White noise was more effective than any band, giving a threshold S/N ratio of −15 db.