Repetition pitch
From Wikipedia, the free encyclopedia
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 differential between the two arrivals.
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[edit] Echo
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). 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 and does not produce pitch itself (like white noise, which contains all audible frequencies in equal strength).
[edit] Varied Sources
Probably the first written report of the phenomenon dates from Christian Huygens, who observed 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 (1693). In free field, one might be able to observe a gliding RP when a plane flies over. In music, the phenomenon is sometimes deliberately created by electronic means (delay and add) to superimpose a pitch or coloration effect to the original music (see Flanging). In room acoustics and sound recording, however, the phenomenon often causes an unwanted coloration of the original sound.
[edit] Uses
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. In psychological and physiological acoustics, RP has been subject of various studies.
[edit] External links
- Repetition pitch, from Frans A. Bilsen
