On response measurements using deterministic types of periodic signal and FFT

Authors

  • W.T. Chu Acoustics Lab., Inst. for Res. in Construction, Nat. Res. Council Canada, Ont., Canada

Keywords:

acoustic signal processing, acoustic variables measurement, fast Fourier transforms, FFT analyzers, aliasing, leakage, picket fence effects, random errors, periodic signals, system response measurements, dual channel A/D converter

Abstract

System response measurements appear in many areas of scientific and technical investigations. The speed of these measurements has been greatly improved with the advent of FFT analyzers. Conventional FFT analyzers require two channels to measure the system response using white noise as a stimulus. Bias errors such as aliasing, leakage, and picket fence effects have to be properly addressed and random errors have to be minimized by averaging. Uses of deterministic types of periodic signal as stimulus are not common although most of these errors would disappear. The inflexibility of the commercial FFT analyzers may be an important reason. To analyze periodic signals, it is necessary to use an `exact' multiple of the period of the signal to avoid leakage effect. It is also necessary to ensure that the signal frequencies coincide `exactly' with the analysis frequencies to avoid picket fence effect. This will require some tailoring of the sampling frequency and the number of data points. We explore the application of deterministic types of periodic signal for system response measurements using a dual channel A/D converter and a special FFT routine. Two types of periodic signal are discussed: (1) pure tones for single frequency measurements and (2) m-sequence or maximum-length sequence (MLS) for broadband measurements

Additional Files

Published

1994-09-01

How to Cite

1.
Chu W. On response measurements using deterministic types of periodic signal and FFT. Canadian Acoustics [Internet]. 1994 Sep. 1 [cited 2026 Apr. 29];22(3):45-6. Available from: https://jcaa.caa-aca.ca/index.php/jcaa/article/view/842

Issue

Vol. 22 No. 3 (1994)

Section

Proceedings of the Acoustics Week in Canada

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