TTS - Diphone database I am working on text to speech conversion. I have done speech synthesis by 

concatenation of phonemes.The transition between phonemes is not 

smooth.I want to shift to diphone synthesis.  Where can I find diphone 

database for the English language. Any other alternative might help.
Have you had a look at the diphone synthesizer resources in the Festival Speech Synthesis framework?

The state of the art for Text2Speech (though still not practical for production due to GPU compute requirements) is Deepmind's WaveNet. 

Their results are definitely smoother than concatenative or parametric methods.  Good luck!