Iso-spectrum level masking contours and frequency selectivity in humans.

AN iso-spectrum level masking contour is generated by having listeners bring to masked threshold a fixedfrequency tone in the presence of a range of one-third octave noise bands. For any given contour, the noise band spectrum level is held constant over noise bands. The resulting contour is a plot of tone sound pressure level (SPL) at masked threshold as a function of noise band center frequency. Since the masking effects of the noise bands depend largely on their spectral proximity to the tone, the contour, at low noise levels, assumes the shape of an inverted "V." As noise level increases, the contours broaden and assume different configurations, characteristic of the frequency of the masked (probe) tone: 2, 4 and 5 kHz in the present study.