Text to speech in Storyline lessons

My experience with TTS: (not a scientific backing

Having tried various tools, including the aforementioned textaloud. My first conclusion would be that the best software (writer) to be used with voices is "Loquendo TTS Director", this software will give you complete control on the voices. Via speech tags, you can manipulate speed, pitch, duration, insert various pauses etc. You can make your own dictionary for words you would like to have pronounced in a customized way, it's also possible to have words spelled, or say number in time/date formats.

The voices available from Loquendo (version 7+) are the #1 I have seen/used. AT&T Natural Voice(s) would be  #2 and Acapela Telecom voices #3

My 2 cents:

The pros of using TTS vs Voice Narration:

• Though time consuming, Through the use of tags inside Loquendo TTS Director it's possible to read any text as natural as a human...and "accent less" (Received Pronunciation)
• Some text are instantaneously read very naturally without having to using the time consuming tags. Depending often on the voice used. e.g. Some text are read better by Simon than by Dave. (often related to the intonation and/or stress given to a specific word....but like I said in the point above...if you have time you can change all that by inserting tags)
• If you simply want to use TTS to include accessibility options...than Director or TextAloud will both be suffice and this would save you enormous amount of time compared to Voice Narration.
• Loquendo has an SDK and API for use with various devices...and this is what Maurizio should look into to realize his needs.

The cons:

• You can guess it already: To make sure that any text sounds 100% naturally, you will need to make use of tags....and this is 1. time consuming and 2. the learning curve is steep. The use of a macro program..(to remember multiple ctrl+c, or assign hotkeys for tags) could help you speeding up the process. However, since you don't want words to be pronounced similarly in ever text....you will have to constantly adjust tags....or use the Lexicon Manager inside Loquendo to create different dictionaries for different text :( + :)
• Actually the above is the only...problem.....but a huge one though! Once other issue that I have encountered is that Nuance has been very busy buying up companies that offered TTS....although nuance specializes in STT (Speech to text)...I believe that they are, or will be dominating the market when it comes to STT & TTS.....so, before buying anything, check on the main site whether Nuance has not recently acquired the company. 

I don't mind that a professional company like Nuance has been buying TTS scripts/programs/companies.....one problem though....They do not do anything with it as of yet. I looked through their offered software solutions, but no sign of TTS:(

Maurizio already mentioned about Loquendo and Nuance...I hope my contribution can help a bit more.

Cheers

Wim