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Dynamic Acoustic Measurement Techniques Considering Human Perception

[+] Author Affiliations
Klaus Genuit

HEAD Acoustics GmbH

Wade Bray

HEAD Acoustics, Inc.

Paper No. IMECE2006-14717, pp. 61-67; 7 pages
doi:10.1115/IMECE2006-14717
From:
  • ASME 2006 International Mechanical Engineering Congress and Exposition
  • Noise Control and Acoustics
  • Chicago, Illinois, USA, November 5 – 10, 2006
  • Conference Sponsors: Noise Control and Acoustics Division
  • ISBN: 0-7918-4776-4 | eISBN: 0-7918-3790-4
  • Copyright © 2006 by HEAD acoustics GmbH

abstract

Dynamic measurement implies determining the content of signals having spectral structure and energy changing with time, sometimes on very short time scales. Dynamic measurements can present challenges to determine sufficient information in both the time and frequency domains. High resolution in frequency prevents finding short-term peak levels and recognizing true crest factors, and vice versa. If the dynamic measurement concerns sound, the much better simultaneous recognition of time and frequency information by the ear/brain than by conventional measurement methods can further complicate the challenge. People have at least three times better simultaneous time/frequency resolution than the familiar Fourier transform moved across the time axis, although quite often a compromise block size can be found that gives time/frequency measurement agreeing with human sound perception of both factors. Unlike technical measuring systems, human hearing is also very sensitive to patterns. The presence of tones, varying tones (amplitude and/or frequency), clicks, rattles, splashing sounds, etc., even at low levels in the presence of other less structured noise of considerably higher level, can dominate perception. Human consciousness effectively performs the opposite of averaging, ignoring the absolute value of slowly varying or stationary signals and focusing on things differing at short time bases from their surroundings in both time and frequency. In dynamic measurement it can be difficult to withdraw the important pattern from the absolute whole. Case studies will be given comparing conventional techniques with three high-resolution time/frequency methods useful in general engineering although developed to model the processes of human sound perception: a hearing model with very rapid time resolution at all frequencies [1], a relative (pattern) measurement technique subtracting a sliding average in both time and frequency from a running instantaneous spectrum [2], and a Fourier-based window deconvolution method giving pure spectral lines regardless of signal-to-block synchronization and permitting multiplication of frequency resolution for a given block length and time resolution [1], [3].

Copyright © 2006 by HEAD acoustics GmbH

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