Repetition pitch
Repetition pitch is an unexpected sensation of tonality or pitch that often occurs in nature when a sound is reflected against a sound-reflecting surface (for example: a brick wall), and both the original and the reflected sound arrive at the ear of an observer, but with a short time delay between the two arrivals.{{cite journal|last=Bilsen|first=F.A|year=1966|title=Repetition Pitch: Monaural interaction of a sound with the repetition of the same, but phase shifted, sound|journal=Acustica |volume=17|pages=295–300}}
Pitch and delay time
When the delay of the repeated sound is too large, the observer perceives an echo; when the delay of the repeated sound is generally smaller than 30 ms, he perceives the original sound only, but with a tonality (coloration, pitch) superimposed. Therefore, this perceptual phenomenon has been named Repetition Pitch (RP). In general, the perceived RP (expressed in Hz-equivalent) is equal to the reciprocal value of the delay time (T) between the original and the repeated sound, or in formula: RP = 1/T (with T expressed in seconds). RP is most salient when the original sound is wide-band in frequency content and does not produce pitch itself (like white noise, which contains all audible frequencies in equal strength).Bilsen, F. A., and Ritsma, R. J. (1969/70). “Repetition pitch and its implication for hearing theory,” Acustica 22, 63-73.
Varied sources
Probably the first written report of the phenomenon dates from 1693 when Christiaan Huygens noted such a pitch in the (wide-band) sound from a fountain repeatedly reflected against the steps of a large stone staircase in the garden of the castle of Chantilly in France.{{Cite web |last=DBNL |title=No 2840. Christiaan Huygens à [Ph. de la Hire]. [novembre 1693]., Oeuvres complètes. Tome X. Correspondance 1691-1695, Christiaan Huygens |url=https://www.dbnl.org/tekst/huyg003oeuv10_01/huyg003oeuv10_01_0186.php |access-date=2025-02-19 |website=DBNL |language=nl}} In an open field, one might be able to hear a gliding RP when a plane flies over.{{Cite web |title=Chapter 23 |url=http://whyyouhearwhatyouhear.com/subpages/chapter23.html |archive-url=http://web.archive.org/web/20230323072145/http://whyyouhearwhatyouhear.com/subpages/chapter23.html |archive-date=2023-03-23 |access-date=2025-02-19 |website=whyyouhearwhatyouhear.com}} In music, the phenomenon is sometimes deliberately created by electronic means (delay and add) to superimpose a pitch or coloration effect on the original music (see Flanging). In room acoustics and sound recording, however, the phenomenon often causes an unwanted coloration of the original sound. See [http://fabilsen.home.xs4all.nl/#Repetition_Pitch Repetition Pitch] for various sound demos.
Uses and studies
Blind people might use RP to locate obstacles by clicking the street surface with their cane, thus producing a wide-band impulsive sound that is reflected against the obstacle.Bassett, J.G., and Eastmond, E.J. (1964). “Echolocation: measurement of pitch versus distance for sounds reflected from a flat surface,” J. Acoust. Soc. Am. 36, 911-916.Cotzin, M., and Dallenbach, K.M. (1950). “Facial vision: the role of pitch and loudness in the perception of obstacles by the blind,” Am. J. Psychol. 63, 485Wilson, J.P. (1967). “Psychoacoustics of obstacle detection using ambient or self-generated noise,” in Animal Sonar Systems, edited by R. G. Busnel (Louis-Jean, France), pp. 89-114. RP has been subject of various studies, both psychophysical, electrophysiological and behavioural.Fourcin, A.J. (1965). “The pitch of noise with periodic spectral peaks,” Proc. 5th Int. Congr. Acoust., Liège, B42, pp. 1-4.Bilsen, F. A. (1977). “Pitch of noise signals: evidence for a ‘central spectrum’,” J. Acoust. Soc. Am. 61, 150-161.Fay, R.R., Yost, W.A., and Coombs, S. (1983). “Psychophysics and neurophysiology of repetition noise processing in a vertebrate auditory system,” Hearing Res. 12, 31-55.Yost, W.A. (1996). “Pitch of iterated rippled noise,” J. Acoust. Soc. Am. 100, 511-518.Hartmann, W.M. (1997). Signals, Sound, and Sensation (AIP Press, Woodbury, NY), pp. 361-376.{{cite web|url=http://www.fabilsen.home.xs4all.nl/RP-literature.html|publisher=fabilsen.home.xs4all.nl|title=RP-literature|accessdate=2016-12-03}}