The Masking and Pitch Shifts of Pure Tones near Abrupt Changes in a Thermal Noise Spectrum

Abstract

When a pure tone is mixed with a noise of uniform spectrum, its threshold is raised. At levels above threshold, its loudness and pitch are changed by the presence of the noise. Introducing abrupt changes in the noise spectrum by filtering out 1 octave changes these effects in the vicinity of this gap. The masked threshold for a pure tone is approx. 25 db lower at the middle of the gap than at the edges of the gap. This indicates that gapped-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, but raises the pitch of a tone located in the lower half of the gap more than it would be in the presence of unfiltered noise.