Cepstral voices in festival - very grainy sounding

[Cubber]

I followed the instructions from this thread: http://www.cepstral.com/forum/viewtopic ... t=festival and was able to install and use a few cepstral voices in festival. However I notice a significant quality reduction when using the voice in swift vs festival. The voice sounds very grainy vs when played using swift. Is there any way to fix this other than completly switching to swift. I would much rather use the cepstral voices on my system than the festival ones but I have quite a few scripts that already use festival and would like to just switch the voice, not the system.