Acoustical factors related to pitch precision in choir singing

Choirs seem to exhibit varying proficiency of intonation (meaning the overall degree of precision in pitch) under differing acoustic conditions. If so, which conditions are the most conducive to correct intonation? Amateur male choir singers were asked to sing (one at a time) just intervals from a synthetic vowel tone whose spectrum arrd vibrato content were varied. The standard deviation in fundamental frequency over the ensemble of singers was adopted as a measure of the difficulty of intonation for a given stimulus. Spectrum variations such as change of vowel did in some cases cause significant changes in the ease of intonation. Absence of vibrato, presence of common partials and presence of high partials were found to facilitate intonation. Standard deviations of 10-15 cent were found to be typical of a musically acceptable performance under normal rehearsal conditions, whereas values up to 2-3 times greater resulted from stimulustone manipulation. Skilled choir singers were less influenced by stimulus variations than unskilled ones.