Sixteen brief sounds (music, vehicle sounds, and artificial sounds) were judged on each of 15 bipolar scales by 20 subjects. Without instructions, subjects use the descriptors “loud” and “noisy” as synonomous. On the other hand, subjects do not equate either loudness or noisiness with acceptability, although there appears to be a moderate relationship when only vehicle or aircraft sounds are rated by subjects. The implications of these findings for instructions in psychoacoustic research are discussed.
Tests were performed in an anechoic chamber using twenty college students to determine the Judged noisiness of stimuli varying both temporally and spectrally. The investigations were divided Into three test series.The first test series used thirty stimuli with six different time patterns and five different spectra.The second test used stimuli selected from the first test but modified to include signal durations ranging from 1 to 100 seconds. Duration in this case is the amount of time the stimuli were within 10 dB of the maximum level. The stimuli for the third test consisted of recordings of turboprop, turbofan, turbojet an4 helicopter flyovers.The results Indicated that the most accurate predictor of the Judged noisiness was perceived noise level using a tone correction suggested by the FAA and an integrated measure of duration.To illustrate the improvement in noisiness predicability of EPNL over PNL, the results of Test II (duration test) are used. For this test, 75% of the data was within 4 dB of the standard foi-EPNL with the FAA tone and integrated duration measure •s compared to 11 dB for PNL.iii
Two series of psychoacoustic tests were conducted to determine the applicability of the psychophysical theory of signal detectability (TSD) to prediction of the aural detectability of noise signatures in differing noise backgrounds. The first series of tests produced data supporting development of a simplifiedgraphical prediction method based on TSD. A second series validated the precision and accuracy of the prediction method under quasi-realistic conditions, Predicted levels of performance were typically within one or two dB of the data.
Subjective judgments of the effects of Doppler shifts on perceived noisiness were made by 20 college students in an anechoic chamber. The stimuli heard in the test included both recorded and simulated air-craft flyovers. Computer controlled generation of the simulated flyovers permitted independent variation of the source frequency, apparent altitude, amplitude, and Doppler patterns. Data collection was governed by a computer-based adaptive technique known as Parameter Estimation by Sequential Testing (PEST). The results of the tests will be discussed and a recording of one of the simulated flyover noises will be presented. The major finding was that effective perceived noise level (EPNL) is a fairly accurate predictor of flyovers containing Doppler shifts, except perhaps at altitudes of less than 500 ft, for which flyovers it underestimates apparent noisiness. Compensation for the risetime of the stimuli (an onset correction) did not improve the accuracy of prediction provided by EPNL.
Tests were performed in an anechoic chamber using 20 college students to determine the judged noisiness of stimuli varying both temporally and spectrally. The investigations were divided into three test series. The first test series used 30 stimuli with six different time patterns and five different spectra. The second test used stimuli selected from the first test but modified to include signal durations ranging from 1 to 100 sec. Duration in this case is the amount of time the stimuli were within 10 dB of the maximum level. The stimuli for the third test consisted of recordings of turboprop, turbofan, turbojet, and helicopter flyovers. The results indicated that the most accurate predictor of the judged noisiness was preceived noise level using a tone correction suggested by the FAA and an integrated measure of duration. To illustrate the improvement in noisiness predictability of EPNL over PNL, the results of Test II (duration test) are used. For this test, 75% of the data was within 4 dB of the standard for EPNL with the FAA tone and integrated duration measure as compared to 11 dB for PNL.
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