Longitudinal voice changes: Facts and interpretation

To study intraindividual vocal changes over time, a longitudinal research design is preferred. However, this procedure reveals many restrictions concerning methodology and interpretation, especially in cases of (semi)retrospective studies. This is illustrated by an investigation of the voices of 20 male Dutch-speaking reporters of the Belgian Radio Broadcasting service. These men read the same text they did 30 years previously for a digital registration. After having copied the high-quality archival recordings digitally, the results of the acoustical analysis of both recordings (recent and archival) were compared. This was done to search for the contribution of aging. In this article we report on the results of the speaking fundamental frequency (SFF) and the standard deviation of the SFF (SFFsd) as a measure of intraindividual variability, and the voice onset time (VOT). Results indicate that, in connected speech, SFF decreased, SFFsd became more restricted, and the VOT increased strongly. The interpretation of the results compels us to conclude that it is extremely difficult to define the specific effect of aging alone, since it is only one element among many others, including methodological concerns.