Speech and Language Therapy
The UK's longest running speech and language therapy website
Authentic Voice Model

Pert, S. (2016). Authentic voice for trans and non-binary people model. Indigo Gender Service and Manchester University. https://www.speechtherapy.co.uk/page-19/page-70/
Note that the model depicts possible areas to consider and that not all service users will want to change/develop/work on all areas.
The model is designed to map discussions with service users and highlight areas some people may not have previously considered.
The model is intended to be used by a Speech and Language Therapist skilled in Voice & Communication Therapy and their service user(s).