It would be interesting to learn the approach taken when developing this.<p>I sounds clear enough, but there are a few issues which would need to be resolved before I would use it. For example, when I entered "o:", which should be a long pure vowel, I got a diphthong. The first example [ˈnɑɹkoʊˌklɛpˈtɑkɹəsi] has the IPA for a General American accent but sounds more like Received Pronunciation to me. Some IPA characters aren't voiced at all. These might be fixable, but how easy this is depends on the implementation approach.<p>Decades ago, I developed a formant speech synthesizer (the details are here: <a href="http://web.onetel.com/~hibou/Formant%20Speech%20Synthesizer.txt" rel="nofollow">http://web.onetel.com/~hibou/Formant%20Speech%20Synthesizer....</a>). Formant speech synthesizers work by passing a pulsed or random input through a series of filters to generate speech sounds, and can be easily adapted to different accents and speakers. However, it is difficult to get them to sound natural, so they usually sound more like Daleks than people.<p>I've also done some rule-based text to speech. This works quite well for Standard English pronunciations in a Glasgow accent, the closest accent to English spelling and therefore the one which can be most reliably generated with the smallest number of exceptions.<p>More recent approaches to speech synthesis sound more natural but are limited to a particular accent and speaker. It's never a Glasgow accent, and developing one for a new speaker and accent is a major undertaking. Were I to switch accents to Received Pronunciation or General American, there would be many more exceptions to the pronunciation rules. Storing pronunciations in a dictionary only works for words stored in the dictionary.