Masking of White Noise by Pure Tone, Frequency-Modulated Tone, and Narrow-Band Noise.

Threshold measurements were made by Békésy audiometry for white noise in the presence of pure tones, frequency modulated tones, and narrow-band noises in normal ears. Pure tones in the frequency range of 700-1000 cps caused maximal masking. When the masking tone had a high distortion factor (13 dB below the fundamental), the masking effect was greater than that for undistorted tones, and was centered between 300 and 400 cps at 120 dB SPL and 500 cps at lower intensities. Tones with a distortion factor of 30 dB or more below the fundamental produced masking effects indistinguishable from pure tones with the distortion factor greater than 70 dB below the fundamental. The masking peak at 800 cps may be explained on the basis of mechanical resonant frequency. While there was some intersubject variation in the masking of white noise by frequency-modulated tones, the maximum effect obtained by frequency-modulated tones was centered at 800 cps, as is the case with pure-tone masking. The masking effect was independent of modulation rate and frequency deviation. Narrow-band noise centered near 2000 cps produced the greatest masking effect on white noise. Greater masking-both in shift and spread-was obtained from a narrow-band noise produced by a commercial noise generator than by Zwicker's narrow-band noise with a cutoff slope of 60 dB/oct. [ABSTRACT FROM AUTHOR]