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Re: Infrasound and Infrapitch

I would like to point out that Guttman and Julesz ("Lower Limits of Auditory Periodicity Analysis", Letters to the Editor, JASA, Vol. 35(4), p. 610 (1963)) used periodic signals, consisting of repeated wide-band noise with  repetition periods corresponding to frequencies in the low/infrasonic region. There was no fundamental in their signal, thus no low-frequency/infrasonic exposure at all.

I agree that repetition frequency and frequency contents can easily be mistaken. In assessments of environmental noise, it is not unusual that a signal of higher frequency repeated with an infrasonic frequency is - erroneously - attributed to infrasound. Examples are broadband ventilation noise that is amplitude modulated by a low frequency, or sources of tonal noise with close frequency that cause beating at a low frequency. However, the sensation is completely different, whether the fundamental is there or not.

Best regards,

Henrik Møller

Section of Acoustics, Department of Electronic Systems
Aalborg University
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Richard M. Warren skrev:

The term infrasound can be misleading;  while the frequency threshold for hearing sinusoidal tones (at a reasonable amplitude) is roughly 20 Hz, holistic frequency perception of complex waveforms (e.g., iterated noise segments) continues for another five octaves of “infrapitch” below 20 Hz.  Guttman and Julesz (1963) found that a percept they called “whooshing” occurred from roughly 0.5 to 4 Hz, “motorboating” from 4 Hz to 20 Hz.  A noisy pitch is heard from 20 to 100 Hz, and a pure noiseless pitch with interesting timbres from 100 Hz up to 16 or 20 kHz.  Thus, infrapitch and pitch form a seamless continuum of perceptual “iterance” extending for 15 octaves for stochastic waveforms, subserved by partially overlapping neural mechanisms of periodicity detection and place detection.   

Studies of infrapitch, since the pioneering study of Guttman and Julesz, have been conducted by Irwin Pollack, Christian Kaernbach, and myself.  Infrapitch detection has also been studied in nonhuman vertebrates.

Richard M. Warren
Research Professor 
  and Distinguished Professor Emeritus
Department of Psychology
University of Wisconsin-Milwaukee
PO Box 413
Milwaukee, WI  53201