Webster, J.C., Miller, P.H., Thompson, P.O., Davenport, E.W. (1952). The masking and pitch shifts of pure tones near abrupt changes in a thermal noise spectrum J. Acoust. Soc. Am. 24, 147-152

When a pure tone is mixed with a noise of uniform spectrum, its threshold is sraised. At levels above threshold, its loudness and pitch are changed by the presence of the noise. Introducing abrupt changes in the slope of the noise spectrum by filtering out (rejecting) one octave changes these effects in the vicinity of this gap. The masked threshold for a pure tone varies from the value for unfiltered noise at the edges of the gap to a value approximately 25 dB lower at the middle. This indicates that gappedi-noise may be used to mask out sounds outside of the gap without unduly raising the threshold of sounds in the gap. Presence of white noise generally raises the pitch of a pure tone whose frequency is between 500 and 4000 cps. Presence of noise with the gap does not raise the pitch of a pure tone located in the upper half of the gap. For a tone located in the lower half of the gap, the pitch is raised more than it would be in the presence of unfiltered noise. The changes in the judged loudnessof pure tones partially masked by a gapped-noise reaffirm the importance of the tails of the excitation pattern in their effect on loudness.