Speech Assistant uses iOS voices. Some voices will need to be downloaded before use:

To download a voice:

1. Go to iPad Settings → Accessibility → Spoken Content → Voices.
2. Select the cloud icon next to the desired voice to download it.

To change the voice in the app:

1. Select the Settings icon (wheel icon) in the action button area (top right corner of the screen).
2. Select “Speech, Recordings, and Sound” → “Select Voice.”

Select a voice — a blue checkmark will appear next to the selected voice.