21,243 research outputs found
A method for determining internal noise criteria based on practical speech communication applied to helicopters
The relationship between the internal noise environment of helicopters and the ability of personnel to understand commands and instructions was studied. A test program was conducted to relate speech intelligibility to a standard measurement called Articulation Index. An acoustical simulator was used to provide noise environments typical of Army helicopters. Speech material (command sentences and phonetically balanced word lists) were presented at several voice levels in each helicopter environment. Recommended helicopter internal noise criteria, based on speech communication, were derived and the effectiveness of hearing protection devices were evaluated
Evaluation of the annoyance due to helicopter rotor noise
A program was conducted in which 25 test subjects adjusted the levels of various helicopter rotor spectra until the combination of the harmonic noise and a broadband background noise was judged equally annoying as a higher level of the same broadband noise spectrum. The subjective measure of added harmonic noise was equated to the difference in the two levels of broadband noise. The test participants also made subjective evaluations of the rotor noise signatures which they created. The test stimuli consisted of three degrees of rotor impulsiveness, each presented at four blade passage rates. Each of these 12 harmonic sounds was combined with three broadband spectra and was adjusted to match the annoyance of three different sound pressure levels of broadband noise. Analysis of variance indicated that the important variables were level and impulsiveness. Regression analyses indicated that inclusion of crest factor improved correlation between the subjective measures and various objective or physical measures
Improvements to Existing Transit Detection Algorithms and Their Comparison
In Tingley (2003), all available transit detection algorithms were compared
in a simple, rigorous test. However, the implementation of the Box-fitting
Least Squares (BLS) approach of Kovacs et al. (2002) used in that paper was not
ideal for those purposes. This letter revisits the comparison, using a version
of the BLS better suited to the task at hand and made more efficient via the
knowledge gained from the previous work. Multiple variations of the BLS and the
matched filter are tested. Some of the modifications improve performance to
such an extent that the conclusions of the original paper must be revised.Comment: 4 paper, 0 figures, accepted for publication in Astronomy &
Astrophysics Letter
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