Sound Masking Research Articles

The effects of aircraft noise

As typical and unique traffic noise, aircraft flyover noise is difficult to be effectively solved by traditional noise control treatments. For unsteady aircraft noise, music masking is considered to be a feasible method for subjective feeling improvement. This study aims to explore the effect of music likability and familiarity on the masking effect and analyze the relationships for young people. 15 music clips from six genres were firstly screened as masking sounds in terms of familiarity and likability difference. Two kinds of subjective scoring methods were adopted for total 60 participants to evaluate the annoyance reduction level. The correlation was analyzed and the masking effect prediction model was obtained from likability and familiarity. The results showed that the likability and familiarity had significant effects of masking effect. According to the annoyance reduction percentage, the masking effect had a significant positive correlation to likability. As for familiarity, there was a critical value for the best masking effect.

Recognition masking of auditory lateralization and pitch judgments.

Two experiments determined backward and forward recognition masking functions in a lateralization task. Observers were presented with a 20-msec pure tone that differed in intensity to the two ears. The task was to indicate whether the tone came from the right or left. A second backward-masking tone interfered with the lateralization of the first test tone if it was presented within 180–250 msec of the first tone presentation. In contrast, a forward-masking tone had to be presented within 80 msec of the test-tone presentation in order to interfere with lateralization of the test tone. The results also showed that observers tended to lateralize the test sound in the direction of the masking sound if the test and masking sounds occurred within a 100-msec period. In a third experiment, subjects were required to identify a test tone as high or low in pitch in a recognition masking task. Although pitch judgments showed as much or more backward masking than lateralization judgments, significantly less forward masking was found in the pitch judgment task. Relative to lateralization judgments, observers showed a smaller tendency to judge the pitch of the test tone in the direction of the pitch of the masking sound. Subject Classification: [43]65.75, [43]65.54, [43]65.62, [43]65.58.

Effects of reflex middle-ear muscle contractions on cochlear responses to bone-conducted sound.

The effects of contralaterally elicited middle-ear muscle (MEM) reflexes on cochlear microphonic responses to air- and bone-conducted tones were examined in decerobrate cats. Stapedius effects on bone condn air conduction were almost identical in configuration and amplitude to those on air conduction at all frequencies. However, tensor tympani effects were more complex, the configuration of the bone-conduction effects varying with the location of the transducer on the skull and with frequency. The relative contributions of the two muscles to the effects of joint contractions varied markedly between animals. It is suggested that non-reflex MEM contractions associated with activity of the facial musculature might provide protection against masking of environmental sounds by the low-frequency bone-conducted sound generated by such activity.

Middle ear muscle effects on cochlear responses to bone-conducted sound.

AbstractContractions of the stapedius and tensor tympani muscles were elicited by electrical stimulation of their motor nerves or of the muscles themselves in anesthetized cats. The effects of these contractions on cochlear microphonic responses to air‐ and bone‐conducted sound were examined. Stapedius contractions that produced changes in air conduction similar to those observed under physiological conditions had almost identical effects on bone conduction. Tensor tympani effects on bone conduction were of similar magnitude but greater complexity than those on air, and varied as a function of the location of the bone conductor on the skull. Control observations established that the effects were attributable to the middle ear muscles and not to other consequences of the experimental procedures, and that they did not reflect modification of an air‐conduction component of the bone‐conduction stimulus. The functional significance of these effects is discussed in terms of protection against masking of environmental sounds by self‐generated bone‐conducted sound.

Study of the Acoustical Performance of a Landscaped Office

The occupants of a newly opened landscaped office were subjected to two different masking spectra each day for an extended period. They were polled daily as to their preference and were allowed to comment on the sound masking. Levels of 51 dBA produced unanimously strong disapproval and rejection. Reactions at 48 dBA, while not so strong, were still negative towards the idea of added noise. Natural sound levels in the office were lowered to about 35–40 dBA, but even this relatively quiet condition was preferred to a low level of masking noise (45 dBA). The effectiveness of the noise for masking speech was measured using the rhyming test described by Griffiths [J. Acoust. Soc. Amer. 42, 236 (1967)] and a test crew. The results obtained showed a predictable relation to articulation index calculations based on S/N ratios. Physical measurements were also made to determine the effect of the acoustical ceiling, baffles, and acoustical screens on sound propagation in the landscaped office. The results suggest that there is currently perhaps undue stress on the need for the ultimate in absorption.

Dichotic Forward and Backward Masking of Speech and Nonspeech Sounds

When a CV syllable is played to one ear and noise of similar over-all spectrum and duration to the other with a delay of ±60 msec, recall of the syllable is more efficient when the syllable leads the noise. This contrasts with previous results in which two CV syllables are played one to each ear and the advantage is for the lagging syllable. A second experiment using brief pitch modulated signals carried on a steady vowel /ɛ/, under dichotic presentation with onset asynchronies of ±25 msec, showed an advantage in recall for the lagging signal. Superiority of backward over forward masking under dichotic presentation thus appears not to be confined to stimuli differentially categorized as speech sounds, but does depend on the relationship between the potential masker and maskee. [Research supported in part by grant from NICHD.]

Vehicle Warning Devices—Necessity versus Nuisance

Acoustical warning devices may be essential for public safety and a nuisance to nearby residents. The question arises, how much reduction in the level of the warning device can be tolerated before it loses its value as a warning signal? This paper presents the results of a short study related to possible reduction in acoustic level of a Diesel-engine horn. The important variables that were studied included (a) level and spectral content of the horn signal; (b) distance between Diesel engine and the driver of an automobile approaching a railroad crossing; (c) whether the automobile windows are open or closed; (d) the level of the masking sound the driver is experiencing. Use is made of the critical-bandwidth concept to obtain allowable Diesel-engine horn sound reductions for several automobile window configurations and three types of masking sounds.

Effects of Sound Masking on the Treatment in Dental Orthodontics

Effects of Sound Masking on the Treatment in Dental Orthodontics

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.

Miniaturized artificial larynx under development

Within the soundscapes of open-plan offices, irrelevant speech has consistently been reported as the most distracting, and causing performance decrements for workers. Notwithstanding this generalization, the ‘babble’ created by multiple simultaneously active talkers can sometimes provide beneficial sound masking, but due to spatial release from masking (SRM), speech may still be sufficiently intelligible up to a certain number of talkers (estimated to be about four). This was explored within a highly-realistic office simulation, where the cognitive performance, and subjective distraction of participants were tested. The experimental design was a 4 × 2 factorial (4 talker numbers, 2 levels of broadband sound masking, as the factors). The results indicated that within lower sound pressure level (SPL) of broadband sound masking, multi-talker sound environments degraded cognitive tasks performance more than those with a single talker, suggesting SRM effects. For higher SPL broadband sound masking, the cognitive test scores were similar within the different talker numbers. The subjective distraction increased monotonically with the number of talkers, with higher distraction within lower SPL broadband sound masking. Overall, the results call into question the single talker assumption (being the most distracting) within the international standard for measuring open-plan office acoustic environments (ISO 3382-3:2012). Soundscapes with 4 simultaneous talkers were still not adequately providing beneficial ‘babble’ masking, and were more distracting than 1 active talker. In conclusion, it is suggested that the acoustics environment of open-plan offices needs better characterization by incorporating some of the complexity and psychoacoustics of multi-talker scenarios.

Some Determinants of Interaural Phase Effects

It has recently been shown that the binaural threshold for a pure tone presented against a background of noise depends upon the interaural phase differences of the tone and the noise. For example, the threshold of a low frequency tone, in phase at the two ears, is low when it is heard against noise that is out of phase at the two ears, but is high when it is heard against noise that is in phase. The masked threshold of a 250-cycle tone presented against a background of intense noise is in fact about 15 db lower under antiphasic conditions than it is under homophasic conditions. (Homophasic refers to the condition in which the tone and the noise have the same interaural phase difference. Antiphasic refers to the condition in which either tone or noise, but not both, is out of phase at the two ears.) When the tone is masked by another tone, fairly close in frequency but not so close that beats are detected, the dependence of masking on interaural phase does not appear. The present experiment attempts to determine what characteristics masking sound (“masker”) must have if it is to produce interaural phase effects. A 250-cycle tone was presented against four different kinds of background. The masking sounds were (1) pure tones, (2) regular pulses (125 p.p.s.), (3) random pulses (average 125 p.p.s.) and (4) random noise. Combinations of filters permitted the presentation of these maskers in frequency bands that were varied in width and center frequency. The results indicate that the threshold for the tone in the presence of a regular, periodic masker does not depend to any significant degree upon interaural phase relations. A necessary characteristic of the masker that produces interaural phase effects is randomness or irregularity. Both masking and the interaural phase effects increase as the frequency band of a random masker approaches the frequency of the tone. Band width alone does not contribute to the interaural phase effects except as widening a band tends to bring one cut-off nearer the frequency of the tone. Wide and narrow band maskers, both of which contain the frequency of the tone, produce the same effects.

Sonic Altimeter for Aircraft

Abstract The author describes the development of an aircraft altimeter which works on the sound-echo principle now commonly employed for depth finding at sea. The problem was to devise means and equipment to send a powerful sound from the airplane and receive the echo back from the ground through the intense masking sounds produced by the engine and propeller. It is believed that the use of the sonic altimeter and sonic boundary markers will make fog flying reasonably safe.