Gender-Affirming Voice Training for Trans Women: Acoustic Outcomes and Their Associations With Listener Perceptions...

To investigate acoustic outcomes of gender-affirming voice training for trans women wanting to develop a female sounding voice and to describe what happens acoustically when male sounding voices become more female sounding.

Prospective treatment study with repeated measures.

N = 74 trans women completed a voice training program of 8-12 sessions and had their voices audio recorded twice before and twice after training. Reference data were obtained from N = 40 cisgender speakers. Fundamental frequency (f_o), formant frequencies (F₁-F₄), sound pressure level (L_eq), and level difference between first and second harmonic (L₁-L₂) were extracted from a reading passage and spontaneous speech. N = 79 naive listeners provided gender-related ratings of participants' audio recordings. A linear mixed-effects model was used to estimate average training effects. Individual level analyses determined how changes in acoustic data were related to listeners' ratings.

Group data showed substantial training effects on f_o (average, minimum, and maximum) and formant frequencies. Individual data demonstrated that many participants also increased L_eq and some increased L₁-L₂. Measures that most strongly predicted listener ratings of a female sounding voice were: f_o, average formant frequency, and L_eq.

This is the largest prospective study reporting on acoustic outcomes of gender-affirming voice training for trans women. We confirm findings from previous smaller scale studies by demonstrating that listener perceptions of male and female sounding voices are related to acoustic voice features, and that voice training for trans women wanting to sound female is associated with desirable acoustic changes, indicating training effectiveness. Although acoustic measures can be a valuable indicator of training effectiveness, particularly from the perspective of clinicians and researchers, we contend that a combination of outcome measures, including client perspectives, are needed to provide comprehensive evaluation of gender-affirming voice training that is relevant for all stakeholders.