Showing papers on "Noise published in 1972"

Noise eliminating device

Abstract: In a noise reducing device for reducing noises contained in audio signals, a frequency band wherein noises contained in audio signals are highly sensible to an auditor, but the frequency of appearance therein of the audio signals is substantially low is blocked by a required number of band-elimination filters provided in series in a transmission line for transmitting the audio signals, each of the band-elimination filters being bypassed by a corresponding variable impedance circuit, while the same frequency band is passed through a corresponding number of band-pass filters, the outputs of said band-pass filters being supplied respectively to corresponding control signal producing circuits to produce control signals, whereby said variable impedance circuits bypassing the band-elimination filters are controlled respectively by said control signals, and the band-elimination filters are thereby brought into a state effectively blocking the frequency band when the input audio signal level in said frequency band is lower than a predetermined value and vice versa.

Description of the Lincoln Laboratory Wideband ELF Noise Recording Systems

Abstract: : The report describes the systems used to record wideband (12 Hz - 300 Hz) extremely low frequency (ELF) electromagnetic noise in a number of geographic locations. The first section centers on the analog recording system employed in Florida. Simply stated, analog tapes were recorded and later converted to digital tapes for further processing. Section II describes the 'NAVCOM' system which employed on site digital recording. The final section describes the calibration procedures used to relate the digitalized data to absolute electromagnetic field levels. A distinctive feature of both systems is the care taken to preserve the wide dynamic range of the ELF noise while reducing the amount of man-made interference recorded. Results of analyzing the recorded noise data to optimize communications system performance in this frequency band are described in companion reports.

The NASA Quiet Engines.

Abstract: The present status of the Quiet Engine Program is reviewed, and the future prospects suggested by recent quiet engine test results are discussed. Following a brief survey of noise sources, quiet engine design features, and the major elements of the Quiet Engine Program, a review is presented of specific quiet engine test that includes the two baseline quiet engines tested and flyover noise comparison results. It is shown that the application to future aircraft of the developed and demonstrated engine noise reduction technology can bring about a substantial reduction in aircraft noise levels. The minimization of the economic penalty associated with this noise reduction technology is being studied.

The Effect of Noise on Lip-Reading Performance

Abstract: Normal hearing young adults received a lip-reading test in quiet (55dB SPL), and in continuous and in intermittent white noise backgrounds of 90dB SPL. Scores decreased from the quiet to the continuous noise to the intermittent noise background, but differences were not statistically significant. It is hypothesised that the predictable nature of the noises allowed the subjects to adapt to them.

Noise generated by quiet engine fans. 1: FanB

Abstract: Acoustical tests of full scale fans for jet engines are presented. The fans are described and some aerodynamic operating data are given. Far field noise around the fan was measured for a variety of configurations over a range of operating conditions. Complete results of one third octave band analysis are presented in tabular form. Power spectra and sideline perceived noise levels are included.

Studies on the Function of the Concentration Maintenance (TAF) (Part 17)

Abstract: Changes of TAF, EEG and Average Auditory Evoked Response (AER) caused by the exposure to two qualitatively different kinds of noise (white noise and variable noise) with the same sound pressure of 90 phon for 1 hour were analyzed. The results obtained are as follows:1) TAF-L and TAF-D of the white noise group after the exposure significantly lowered in comparison with the values before exposure, whereas in the variable noise group they tended to lower after the exposure.2) The difference in EEG before and after exposure was greater in the white noise group than in the variable noise group.3) Comparing each frequency band of EEG during the exposure by group a significant difference was observed between the two groups and it was noted that the exposure to white noise greatly affected the EEG.4) The difference in N1 latency of AER before and after the exposure was greater in the white noise group than in the variable noise group.5) In the white noise group, a significant correlation was observed between the lowering of TAF-L and the delay of N1 latency of AER.The present study on AER is further evidence of the accuracy of TAF in measuring stress.