Voices and Languages
The Web user-interface allows access to all installed languages and voices. Click the row, marked with a small arrow, to open a list of all currently installed Languages and Voices. Changing the language will also influence the available voices. More importantly, when changing the language, remember to enter the text to be synthesized in that language.
Unfortunately, neither of the pre-installed voices are great, but Apple provides free access to much higher quality voices, if you care enough to install them. ‘Allison’ for instance is great and less robotic, but there is still room for improvement.
To install some of the better voices from Apple, open ‘System Preferences’ then ‘Dictation & Speech’ on OS X or Accessibility and Speech on macOS Sierra. Now click on the ‘Text to Speech’ and then on the selected ‘System Voice’ (e.g. Alex) and in the appearing drop-down, select Customize...
System Preferences / Accessibility and Speech dialog in macOS Sierra
Here you can discover (play) and install some amazingly good voices. Please do yourself a favor and install Allison and Tom, two very good American-English voices.
3rd party voices
The screen shot above also shows some 3rd party voices installed. For instance, there are Cepstral’s ‘Callie’ and CereProc’s ‘Katherine’ voices installed, (both provide some SSML capabilities) as well as Acapela’s ‘Heather’ voice. The Infovox iVox product, developed by the Acapela Group, allows to download and install additional voices into the macOS Voices repository. You can install those HQ voices and try them for a few weeks and then buy them for $20 to $30 each. The iVox Voice manager 4.4 works great on macOS Sierra (I need to re-start the Mac to gain full access to the voice) and we really love the English female voice named Heather
Selecting the right Voice for your speech synthesis needs
Unfortunately, not all voices sound natural, in fact most don’t. You want to carefully reflect on your options, after you have selected language and gender.
Play a couple of test sentences, to find out which of your voice options actually considers punctuation.
Inflection and tone are a big big part of our communication and ideally, “Hello.” and “Hello?” will sound differently.
For instance, with Allison or Heather you will hear a difference, but with Susan you won’t.