Cepstral Community

I am using the swift program with Windows XP to generate speech with Cepstral David. I would like the volume to be higher than the default. However if I set the volume to 2.0 or 2.2 there are occasional loud clicks in the sound. Other than the clicks, the increase in volume is good.

If I output from swift to a wav file then use sox to increase the volume by a factor of 2.2 there is minimal clipping and the sound is perfect.

My application is jampal (You can see it on http://jampal.sf.net), an mp3 player and library system and I use David to announce the songs. I would like his volume to be similar to the volume of the songs being played, but the default volume is lower. I have an option in the program to increase the volume but then the clicking sounds are produced.

I'd like to find out more about this too. Our users are disabled/hard of hearing and always want it louder.

What I find curious is that an amplified recording, with the same (i.e., a little) amount of clipping is perceived to be much louder. I'm guessing this has to do with spectral differences, but I don't really know.

For my tests I was using David, on the Macintosh.