The masking audiogram of a pure tone is complicated by phenomena that arise from the interaction of the test tone with the masking stimulus. The production of beats and of difference tones results in a masking audiogram that does not represent the pattern of activity in the cochlea or nerve due to a simple masking stimulus. In the present experiments a narrow band of noise was used to mask pure tones. The “beat” heard in the immediate vicinity of the masking noise is not prominent, and a test tone higher in frequency than the band of noise is detected in terms of the characteristic pitch of that tone rather than by means of a difference tone.
With a band of noise slightly wider than a critical band (Fletcher), the amount by which the test signal at the center of the band exceeds the level/cycle of the noise is less than that obtained with a considerably wider band of noise. This smaller signal‐to‐noise ratio obtained with the narrow band of noise is probably due to “beats,” since the test tone is heard as a “buzz” or “rattle.” For purposes of deriving excitation or loudness patterns, a better estimate of the maximum amount of masking is obtained by using a wide band of noise whose pressure spectrum level is the same as that of the narrow band.
