Pure-tone Masking Research Articles

Masking of Pulsed Tones by Bands of Noise

If a 2200-cps tone is pulsed 150 times/sec under appropriate conditions, a low pitch (periodicity pitch) will be heard corresponding to that of a 150-cps pure tone. This experiment investigates the effectiveness of different bands of filtered noise in the masking of such pulses and in the masking of two pure tone stimuli, 150 and 2200 cps. Although the pulses and 2200-cps pure tone yield quite different pitches, the present results indicate that the masking of each requires nearly identical frequency components and levels of noise. The 150-cps tone, although yielding a pitch approximating that of the pulses, requires greatly different characteristics of noise to mask. Considering differences in apparatus and technique, reasonable agreement with other studies of pure tone masking by bands of noise is found. If masking is viewed as a neural phenomenon, these data provide additional evidence of the neural nature of periodicity pitch.

Auditory Threshold Shifts Produced by Simultaneously Pulsed Contralateral Stimuli

Evidence from studies of tactual sensitivity indicates that transient suprathreshold stimuli presented simultaneously with and contralateral to test signals will mask such signals more effectively than do steady stimuli. The present report presents evidence that when pulsed masking sounds are presented simultaneously with pulsed auditory signals, two major effects are observed: First, a significantly greater amount of contralateral masking is obtained with the pulsed masker than with the steady masker, and, second, the pulsed masker is more effective in the monaural condition also. Furthermore, the masking effect of pulsed maskers increases with the increase of signal frequency, but not with increase of masker intensity. The frequency of the masker must be near that of the signal to be effective, and if pure-tone maskers are used with pure-tone signals, the masking effect shifts continuously to the localization effect as the signal frequency approaches the masker frequency. Some explanations of binaural and contralateral masking are discussed.

Normalized Representation of Noise-Band Masking and Its Application to the Prediction of Speech Intelligibility

Measurements are made of the masking of pure tones by various bands of noise. Curious masking spreads beyond upper frequency limits of noise are observed and these are expressed uniquely by means of the relative masking and the incremental bandwidth. Then the normalized representation of noise-band masking in some restricted ranges is achieved and applied for the prediction of speech intelligibility. Predicted articulation scores agree fairly well with measured ones.

Pitch Shifts with Pure Tone Masking

While gathering data on the masking of one pure tone by another, marked pitch shifts in the signal tone were noted. This paper presents preliminary results of a systematic investigation of this phenomenon. Signals of five frequencies and two levels were used together with eight masker frequencies for each signal frequency. For a given condition signal level was constant, but the signal was effectively raised above masked threshold by lowering masker level. For three masker levels listeners adjusted a matching tone, heard in the contralateral ear, to the pitch and loudness of the masked tone. Stimuli were presented alternately to each ear. The results indicate that with no masking a just noticeable difference (JND) in frequency is much larger when the stimuli to be discriminated are presented to opposite ears rather than to the same ear. Further, this JND increases rapidly for frequencies above about 3200 cps. Under conditions of masking, the results are similar to those obtained using a narrow band noise masker. In general, the pitch of the signal is shifted away from the frequency region of the masker. The maximum shift occurs when signal and masker frequencies are nearly equal. Also, as signal threshold is approached the amount of pitch shift increases. Possible relations between the slope of the masking function and the magnitude of the pitch shift are discussed.

Masking of Tones by Bands of Noise

Measurements were made of the masking of pure tones by bands of noise, the width of each band corresponding to a pitch interval of 250 mels, with band level varied from 40 to 120 db SPL. The masked audiograms were compared to the frequency characteristics of the bands of noise. It was found that published values for the critical bands predict the masking for tone within the band. More masking than would be predicted is found for the frequencies above a band. Below the band, the masked threshold is again predicted precisely by the critical-band hypothesis, but only to a point beyond which, for high noise levels, a “remote” masking, which is constant as a function of frequency for any particular level, is observed and is much more than can be predicted from the effective levels (from either system noise or imperfect filtering) obtaining at those low frequencies where this masking is observed. Whereas for tone within the band masking increases linearly with level, this “remote” masking rises in an accelerated manner with level and then decelerates at the highest levels. Some speculative interpretation is attempted. [This work was supported under Contract No. AF 18(600)-131 with the U. S. Air Force.]

Masking of Tones by Bands of Noise

Measurements were made of the masking of pure tones by bands of noise, each band width corresponding to a pitch interval of 250 mels, with band level varied from 40 to 120 db (above 0.0002 microbar). A modified Békésy audiometer permitted recording as a function of frequency, so that masked audiograms could be compared with the noise spectra to ascertain how well the ear followed the frequency characteristics of the noise bands at different levels. It was found that values for the critical band according to Fletcher and to Hawkins and Stevens predict quite precisely the masking for tones whose frequencies lie within the band. More masking than would be predicted is found for frequencies above the band, the discrepancy increasing as the noise level increases. Below the band, the masked threshold is again predicted precisely by the critical-band hypothesis, but only to a point, beyond which, for high noise levels, a “remote” masking is observed that is constant with frequency for any particular level and is much more than can be predicted from the effective levels (from either system noise or imperfect band rejection) obtaining at those low frequencies where this masking is observed. Whereas masking for tones within the band increases linearly with level, this “remote” masking rises in an accelerated manner, as a function of level, and then shows deceleration at the highest levels. Some speculative interpretation is attempted.

The Masking of Pure Tones and of Speech by White Noise

This report presents the results of a study of the monaural masking of pure tones by white noise at eight sensation levels (SL) from 20 to 90 db. The observed values of masking were employed to determine two basic functions: (a) The critical band width of a masking noise, i.e., the ratio, in decibels, between the level of a pure tone and the level per cycle of the noise that is just able to mask the tone. (b) The function relating the amount of masking to the effective level of the masking noise. With the aid of these two functions, a set of contours was constructed to represent the masked threshold for pure tones heard monaurally against background of white noise having an ideal flat spectrum at the ear of the listener. A study was also made of the masking by white noise of speech in the form of continuous discourse. Measurements of the threshold of detectability and of the threshold of intelligibility were made at the same eight noise levels used to mask pure tones.

The Role of Interaural Phase in Loudness

Recent experiments have shown that the interaural phase angle is a critical factor in the masking of pure tones and speech by white noise. The present study extends these findings to the role of interaural phase in loudness. It is found that the reduction in loudness which is effected by noise under several conditions of interaural phase parallels the masking that is produced under similar conditions. These effects are marked, however, only at signal-to-noise ratios in the region of the masked threshold. At higher signal-to-noise ratios, approximating listening in the quiet, the effect of interaural phase on loudness is nil. A convenient basis for discussion is provided by considering the masked and masking signals in terms of the figure-ground relation between them.