Open/Free Synthesized Voices
Most operating systems now have built-in speech synthesis engines, which is great! Some of the most common languages are supported by default, and large comapnies like Apple, Google and Microsoft often compete over speech synthesis quality, so some of the highest-quality speech engines are available for free already.
There are also proprietary companies who license custom voices, including child-aged or gender-neutral voices, for many languages.
However, there are some languages that haven’t been implemented, and sometimes users want to sound different than just the standard system voice, so it makes sense to provide additional voice output options. Additionally, some AAC users want to utilize an AAC system that hasn’t licensed these extended libraries of voices.
There are a few cross-platform, open source speech synthesis libraries, but those that can run across platforms are often very old and very computer-y. One promising library is Coqui TTS, which currently requires the python runtime library and doesn’t run in mobile environments. We hope to find developers who would be willing to address this shortcoming and open up a broader range of voices to AAC users. If you can help with that effort, please join or Slack channel and let us know!