Academic journal article Journal of Singing

Pitch Accuracy with and without Vibrato

Academic journal article Journal of Singing

Pitch Accuracy with and without Vibrato

Article excerpt

IS THE PITCH OF A STRAIGHT TONE more accurate than the pitch of tone sung with vibrato? The intuitive answer would probably be in favor of the straight tone, given that there is less variation in the fundamental frequency and all its harmonics. An answer based on some research on the perception of pitch is not straightforward, however. It requires parsing out two factors, (1) the psychophysics of pitch perception with and without frequency modulation, and (2) the motor control for producing a constant fundamental frequency (F^sub 0^).

Factor 1 has been studied with string instrument playing.1 A virtuoso violist played tones with and without vibrato (D^sub 4^, C#^sub 5^, A^sub 5^, and G^sub 6^). If the intent of the performer playing with vibrato was to be in tune with a specific pitch (i.e., not intending to be sharp or flat), listeners judged his average pitch with the same degree of accuracy as if he played a straight tone. His average vibrato extent was a little less than a quarter tone up and down from the center frequency, similar to vocal vibrato. The authors drew the conclusion that pitch perception with vibrato is based on the average pitch in a vibrato cycle and that the frequency modulation does not mask the ability to perceive this average pitch.

This bring us to factor 2, the motor control for producing a constant fundamental frequency. Figure 1 shows an example of a jazz-like straight tone changing to a tone with vibrato. The singer was a well trained amateur who sings multiple styles. The mean (average) F^sub 0^ per individual vibrato cycle is shown superimposed with dots on the vibrato portion. Several observations are noteworthy. First, the straight tone is a little sharper relative to the vibrato portion. Second, the straight tone is not straight. Variations on the order of 1-2 Hz are present. For a mean frequency of 191 Hz, this is an approximate 0.5% jitter, which is quite normal in voice production and can be attributed to irregularity in muscle contraction. The variation of the vibrato-cycle average F^sub 0^ is slightly greater, attributable to the fact that the singer had not settled into a steady vibrato, perhaps by choice. In lieder or operatic productions, the same singer generally has less variability in the vibrato extent. …

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