Showing papers on "Noise published in 1973"

Stereo sound reproducing apparatus with noise reduction

Abstract: To reduce the effects of noise in stereo audio apparatus, cross talk is introduced between the output channels in a frequency sensitive manner, the amount of cross talk being controlled in accordance with an input or output signal level on the level of two or more combined signals.

Digital circuit for determining if signal source consists primarily of noise or contains information

Abstract: A digital squelch circuit responds to a band limited audio output signal of a radio receiver to count the number of cycles of the source per unit length of time. In response to the count being respectively above and below a predetermined value, the audio signal source is decoupled from and gated to an output terminal. The audio signal source is gated to the output terminal for a predetermined period subsequent to termination of the count with the predetermined time being less than a pre-established value in order to prevent squelching in the period between adjacent words of a voice source.

Community noise survey of Medford, Massachusetts

Abstract: An extensive noise measurement survey was made in Medford, Massachusetts, suburb of Boston, during March, April, and May 1971, to assess the importance of transportation noise in a typical urban community, and to obtain validation data for a mathematical model developed to simulate such noise levels. Noise measurements were made at 49 locations distributed uniformly across the community, with continuous 24‐h measurements at five of the locations. The median noise level over the entire community was 54 dBA during the morning rush hour, and 51 dBA during the midday period. Noise levels were influenced primarily by highway traffic, with a major highway arterial corridor producing the highest noise levels in the community.

Arousal from sleep by noises from aircraft with and without acoustically treated nacelles

Abstract: The electroencephalographic and behavioral responses during sleep of four subjects, aged 46 to 58 years, to three types of noises were tested over 14 consecutive nights. The stimuli were two DC-8 jet landing noises (each 30 seconds in duration and coming from DC-8 aircraft with and without acoustical treatment on the engine nacelles) and a 4-second burst of pink noise. Each of the noises was tested at nominal intensities of 61 and 79 dBA. Other physical descriptors of the noises were measured or computed. The results indicate that for an equivalent degree of sleep disruption, noise form the jet aircraft with untreated nacelles must be about 6 dBA less intense than the jet with acoustically treated nacelles. Predictions of the effects of noise on sleep appear, tentatively, to attain the highest accuracy when the physical descriptor of noise intensity includes information about the impulsive characteristics of that noise as well as its long-term spectral content.

Procedures for comparing hydrophone noise with minimum water noise

Abstract: In a recent paper by Henriquez, the noise level of a hydrophone is shown falling below the thermal water noise level at high frequencies. The writer believes this should not happen and presents a data‐processing procedure for noise evaluations which will ensure that it will not. The use of equivalent plane waves to represent electrical noise is deprecated, and the concept of the isotropic acoustic equivalent of electrical noise is introduced and used in their stead.

Gill‐net catches of cod (Gadus morhua L.) in relation to trawling noise

Abstract: More cod were caught in a gill‐net during periods with trawling noise than during periods without trawling noise. This indicates that trawling noise stimulates increased locomotor activity among cod.

Measurement of instrument noise spectra at frequencies below 1 hertz

Abstract: The use of peak-to-peak values in describing output noise of a magnetometer or low frequency amplifier is of questionable value for certain applications. A more precise statement of instrument noise is made with a plot of the noise power spectral density versus frequency. The spectral density plot provides a rich source of information which can be used in the selection and testing of such instrumentation.

Subjective Rating of Broad‐Band Noises Containing Pure Tones

Abstract: For rating the noise of broad‐band sources the custom is to utilize A‐weighted levels, but there is no consensus on the subjective importance of pure‐tone components that may be present. This study was to provide some direct evidence on this point. Nine subjects participated, individually, and the procedure was to have the subject match pairs of noises by adjusting the level of one of them. Two experiments used a modified random noise to which a pure tone in the range 250–2000 Hz could be added. The first experiment involved a simple comparison in a quiet environment. The second involved similar noises but with the addition of a local “wanted” sound in the form of music, and the subject matched noises from the viewpoint of “intrusiveness.” A third experiment was similar to the first but utilized actual machine noises as the basic spectra. All three experiments indicated that the A‐weighted level remains an adequate (slightly conservative) rating number even when pure tones are present.

The influence of intermittent sounds and white noise upon mental task and feeling

Abstract: This investigation was carried out to know whether the same kind of results as previously reported (Sato, 1972) could be obtained or not, even when the nature of the stimuli changes from flickering light to intermittent sound and white noise. Results: 1) The curve, in which variance indices of the correct responses of the task given Ss were plotted against the frequency of flutter, showed two peaks for all Ss. The one peak was at 2Hz, and the other at 12Hz. In the flickering light exp. previously reported, the Ss were divided into two groups, each group having only one peak on this curve. 2) All of the flutter and noise stimuli were estimated to be unpleasant on pleasant-unpleasant rating scales by the majority of Ss. But small number of Ss estimated them to be pleasant in every frequency. 3) The relationship between response variability of the task and the feeling caused by the flutter and the noise was only slight.

The Concept of “Effective Quiet.”

Abstract: How quiet must be the intervals between high‐intensity noise bursts if recovery from the TTS produced by the latter is to be unaffected? Listeners were given 8‐h exposures to a 4000‐Hz OB noise (2800–5600 Hz) that was at 90 dB SPL for 22.5 sec and then at some lower intensity for 67.5 sec (90‐set duty cycle, ON fraction of 0.25). Under these conditions, the temporary threshold shift at the end of the 8 h was greater when the intervening periods were at 60 dB SPL than when they were 15–20 dB (ambient). Thus, for this particular octave band, “effective quiet” must be about 55 dB SPL. Implications of this result for damage‐risk criteria will be discussed. [Research supported by the National Institute for Occupational Safety and Health, Public Health Service.]

Audio circuit with noise muting feature

Abstract: An audio-visual slide projector having audio circuitry that is formed of a muting circuit and a record-reproduce circuit for the recording and playback of magnetic recording strips on a slide frame. The muting circuit is connected to the drive motor powering the slide changing apparatus of the projector and is energized during each slide change cycle to mute the record-reproduce circuit of the projector, thus, preventing noise from being applied to the output of the audio circuit.

Annoyance measurements related to urban traffic noise exposure

Abstract: JURY LISTENING TESTS WERE CONDUCTED TO DETERMINE QUANTITATIVELY THE ROLE OF NOISE FLUCTUATIONS IN ESTABLISHING THE TOTAL SUBJECTIVE ANNOYANCE OF URBAN TRAFFIC NOISE BOTH GAUSSIAN AND NON-GAUSSIAN NOISE LEVEL DISTRIBUTION HAVE BEEN STUDIED THE NOISE POLLUTION INDEX, IN THE FORM L SUB NP EQUALS L SUB EQ PLUS KO, APPEARS AS AN ACCEPTABLE PHYSICAL MEASURE FOR THE SUBJECTIVE ANNOYANCE OF TRAFFIC NOISE HEARD INDOORS THE COEFFICIENT K IS SENSITIVE TO A VARIETY OF FACTORS PECULIAR TO A GIVEN LISTENING SITUATION /AUTHOR/

Technology for low noise aircraft - The NASA Quiet Engines

Abstract: Review of the major goals, procedures, and results of the Quiet Engine Program that was initiated four years ago and is now nearing completion. This program has developed and demonstrated, in full-scale, experimental engine tests, technology advances which, if applied to the design of future aircraft, will help produce equipment with noise levels considerably lower than the older narrow-body aircraft and significantly lower than the new wide-body aircraft flying at present. However, the application of this noise reduction technology will result in increases in aircraft operating costs. Future aircraft noise reduction research should, therefore, consider improvements in the economics associated with noise reduction technology.

Effect of High‐Frequency Tail on the Loudness of a 250‐Hz Tone

Abstract: The effect of the peripheral spread of excitation to high frequencies on the loudness of a 250‐Hz tone was measured by loudness matching and by magnitude estimation and magnitude production. All listening was binaural through earphones. Most of the data were obtained with a 250‐Hz tone in the presence of a noise band 390–2400 Hz wide. The noise increased in intensity with the tone so that the signal‐to‐noise ratio remained constant throughout a given listening session. Loudness measurements were obtained using three signal‐to‐noise ratios: +10, 0, −10 dB. The data suggest that at low sound intensities the loudness functions for the 250‐Hz tone in quiet and in the presence of the noise band are parallel. At sound‐pressure levels above 60 dB the effect of the noise is to decrease somewhat the slope (exponent) of the loudness function. It appears that the contribution of high frequencies at high intensities does not appreciably affect the loudness of a 250‐Hz tone.

Relative Effects of White and Speech‐Correlated Noise on Speech Quality

Abstract: An experiment was designed to study the effects of speech and noise levels on speech quality using white and speech‐correlated noise (SCN). Two types of speech signals were used: (1) flat with respect to frequency (flat speech), and (2) flat below 1 kHz, and with frequency emphasis of 9 dB/oct above 1 kHz (shaped speech). Both speech and noise were bandlimited between 150 and 3600 Hz. The speech level ranged between 54 and 100 dBt SPL and the noise spectrum level between 2 and 33 dBt/Hz. A total of 45 noise and speech level combinations were used as test stimuli. Each test condition consisted of a pair of phonetically balanced sentences in the presence of one of the 45 test stimuli. The subjects were required to rate the speech quality on a 5‐point scale. Averaged over all conditions, the shaped speech was preferred over flat speech. For shaped speech, SCN was preferred over white noise. For flat speech the same was true for speech levels of about 80 dBt and higher, and the reverse was true for speech lev...

Reply to the critiques of A. Cohen, H. Davis, B.L. Lempert, and W.D. Ward of the paper "Impairment to hearing from exposure to noise".

Abstract: Critiques by A. Cohen, H. Davis, B. L. Lempert, and W. D. Ward of my paper “Impairment to Hearing from Exposure to Noise” are treated individually. Questions raised by the reviewers are discussed and areas for further discussion are noted.