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.