I'm looking for recommendations for speech synthesis software that can be used to generate audio stimuli. The audio stimuli that I'm trying to generate will be long sequences of isolated syllables. Thus, the best case would be something that can easily read a text file like: pa/da/ba/ki/tu. I realize that programs like TextEdit on OSX can do this, but they don't offer much control over the output. I would like to be able to control the duration of each syllable, the spacing between syllables, and so on.
Ideally, the software would be free and have a history of use for generating research-quality stimuli.
I'd also prefer software that can run on an Intel-based Mac, but suggestions for other operating systems are welcome.