How singing experience affects the “brightness” of humming?

During singing practice, people are often told to sing in bright voice to improve singing performance. The purpose of this study is to determine how singing practice affects the acoustical characteristics and expressiveness of “brightness.” In this study, eight singers (having experience in chorus for 0 to 13 years) sang three types of humming with G4 (392 Hz). Singers were told to sing either “bright,” “dark,” or “normal” humming. Subjects (n = 16) listened to different types of humming in pairs, and judged which was brighter. The results showed that the subjects perceived “bright” humming as bright. As singers practiced longer, their “brightness” was more expressive. Acoustical analysis revealed that fundamental frequencies of “bright” humming were higher than dark humming by 3 Hz, and that bright humming had higher amplitude in spectrum from 4900 to 6400 Hz by 4.5 to 6.5 dB. In the following experiment, subjects listened to and judged the brightness of humming, whose amplitude in the range was systematically amplified. As a result, the more amplified the humming had in the range, the more likely subjects evaluated it as bright. Our results suggest that singers can obtain the ability to express “brightness” by producing these acoustical characteristics through practicing singing.