The Impacts of Testosterone Therapy Beyond Fundamental Frequency in Transmasculine Voice: Vocal Quality and Fricative Articulation.

Prior investigation of the effects of testosterone therapy on transmasculine voices has demonstrated that most trans men who undergo testosterone therapy will have a resulting voice in the normative fundamental frequency range of cisgender men, yet there is little information about the effects of testosterone therapy on other features of voice and speech. The purpose of this study was to expand upon the current body of literature about the effects of testosterone therapy on transmasculine voices by including measures of vowel duration, jitter, shimmer, and spectral changes in fricative skew and fricative kurtosis. This study analyzed multiple progressive voice change recordings posted by 21 trans men on public platforms. Voice samples included at least 10 data points (ie, a collection of unique recordings from different dates) not exceeding the first year of testosterone therapy. Six linear mixed-effects regression models separately measured the effects of time point on mean fundamental frequency, vowel duration, jitter, shimmer, and spectral analysis (fricative kurtosis and fricative skew). The results confirmed that given testosterone therapy over a year, there was a significant decrease in fundamental frequency, a decrease in shimmer, and an increase in fricative kurtosis. There were no significant changes in vowel duration, jitter, and fricative skew. This study identifies voice features that could be the focus of future research that involves in-person testing. Additionally, the results motivate research focused on novel approaches to specialized voice therapy treatments that consider the impact of the voice features that did or did not change following testosterone therapy.