The spoken phrases and names of the ATC system come from a cloud-base Text-To-Speech (TTS) engine. Several spreadsheets of vocabulary are fed to the cloud engine to be spoken and saved as individual sound files. These are then processed and saved as part of the X-Plane resources which are distributed as part of the application. While the TTS engine is very good at getting reasonable pronunciations for most things, it is by no means perfect. Regionalization and other types of specialization are often necessary to improve the accuracy of the speech.
We have made our spreadsheets public so that the community can edit them to correct mistakes that they may find. We will periodically grab the latest spreadsheets with community corrections and rebuild our internal speech resources to include the new corrected pronunciations, then make them available as part of standard X-Plane updates.
The spreadsheet currently contains 5 tabs along the bottom for the categories: Airlines, Airports, Aircraft Makers, Aircraft Models and VORs, as well as an instructions tab. Each category tab has two common editable fields. One is what the ATC engine will display as text on screen. The other is what will be spoken as audio output.
It’s important to note that some users will disable ATC speech and just want to see textual ATC commands. Others may disable the text and only want to hear spoken commands. Because of this, the ATC engine needs data for text and speech. For example, you may want to display “B737-800” as an aircraft type in text, but you may want to say “737 800” in speech; without the ‘B’ and without pronouncing the ‘dash’. That’s why the two columns exist independently.
Speech and pronunciation can also be adjusted by using the SSML standard. Note that you do NOT need to add <speak></speak> tags. It’s implied. There are many resources available on the web to help learn SSML syntax as well as pronunciation characters. They all should work fine, independent of the TTS engine used. It is suggested that you create a free Amazon Web Services account and use the Amazon Polly Text-To-Speech synthesizer online to listen to your syntax before editing the spreadsheet. However, you can also use Google’s online synthesizer or various others.
Please do not attempt to use pronunciation to create regional accents in the spoken words as this will make things more difficult. For example, the word Boston should be “Baw-stun” even if regionally they’d say “Bah-stin”. This type of feature IS actually possible someday but it is NOT done on the pronunciation level in the spreadsheet.