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Abstract

Most of the people who perform music do so in the capacity of choir singers. An understanding of the particular acoustic properties of the choral sound is of interest not only to performers, but also to educators, architectural acousticians, audio technicians, and composers. The goal of choir acoustics is to describe various aspects of choral sound in acoustic terms, thereby taking into account the acoustics of voice production, the acoustics of rooms, and psychoacoustic properties of the auditory system. This article is an overview of choir acoustics research done in Stockholm over the past 8 years. It is an abridged and adapted version of an overview given in the author's dissertation, Acoustical Aspects of Choir Singing. Three different kinds of experiments were made: (a) the control of phonation frequency and the vowel articulation of choir singers were investigated, by having individual choir singers perform vocal tasks on demand or in response to auditory stimuli; (b) typical values of sound levels, phonation frequency scatter, and long-time averaged spectra were obtained by measurements on choir singers rehearsing in ensemble under normal or near-normal conditions; and (c) models for certain aspects of choral sound were formulated and evaluated by synthesis. The choir singer's performance is based on two acoustic signals: her or his own voice (the feedback) and the rest of the choir (the reference). Intonation errors were found to be induced or increased by (a) large level differences between the feedback and the reference, (b) several perceptually unfavorable spectral properties of the reference, and (c) articulatory maneuvers, i.e., intrinsic pitch. The magnitude of the errors would be indirectly related to room acoustics (a and b) and to voice usage and musical/textual content (b and c). When singing alone, singers from one choir used a vowel articulation that was different from that in speech and also more unified; it was also in some respects different from solo singing. Long-time average spectrum effects of room acoustics and musical dynamics were large, as expected; those of choir type and musical material were smaller. To some extent, choirs adapted their sound level and voice usage to the room acoustics. Small random fluctuations in phonation frequency, called “flutter” and “wow,” are always present in human voices. With multiple voices, flutter and wow cause, through interference, a pseudorandom, independent amplitude modulation of partial tones, which is known to cue the perceptual “chorus effect.” The chorus effect is also influenced by the reverberation properties of the room. Choral sounds were explored by means of synthesis, and the importance of realistic flutter was established. Flutter in choir singers was analyzed and simulated in single synthesized voices. Expert listeners were unable to discriminate between simulated and authentic flutter.