Opening area and circularity of the lips during whistling

In recent years, instruction books on human whistling have been published. According to these books, when whistling pitch increases, lip opening is squeezed. Therefore, in this study, the opening area and circularity of the lips during the whistling process were measured. We conducted an experiment in which the lips of two professional whistlers were photographed. The subjects whistled twice at specified five pitches. The lip openings were extracted from the photographs, and the area and circularity were measured using an in-house software. The results show that during whistling, the lip opening area tended to decrease with the increase in frequency.