The Masking of Binaural Beats of a Pure Sound with a Differential Sound

Abstract

This study concerns the masking of binaural beats between a pure tone, stimulating one ear, of f₀ + d frequency (d = 3 Hz) and the differential sound originated in the other ear by stimulation with the mixing of 2 pure tones of frequency f₁, f₂ (f₂ – f₁ = f₀). The masking sound is a third-octave filtered white noise, of nominal frequency f_n variable between 200 and 4000 Hz, and sound pressure also variable. For each f_n and for each constant value of f₀, f₁, f₂, the minimum sound pressure level of the narrow-band noises for masking the beat is measured as a function of the frequency f_n; the sound pressure level of the pure tones is maintained constant at 45 dB. The minimum sound pressure level of the narrow-band noises for masking the normal beats (a pure tone of 315 Hz at the left ear, of 318 Hz at the right ear) is also determined. The latter measurement gives, as expected, a very deep minimum at 315 Hz; from the other measurements it results some oscillations of experimental values, with a mean value generally decreasing as the nominal frequency of the masking noise is increased. This phenomenon is discussed.

Key Words:

• Monaural beats
• Binaural beats
• Auditory masking
• Periodicity pitch