[LAU] Jack "Force 16 bit"

Hi all, I've managed to install Ubuntustudio 10.10 on my Macbook pro. When I tried to work on Ardour I got terrible distortion. So I tried to see where it comes from. Checked the master, OK. Checked the Sound card (gnome alsa mixer), also good. I thought I'll try some different settings within Jack, so I set the "Force 16 bit" parameter in Jack, while Ardour is still set to "Sample Format"=32 bit floating point. Now the distortion is gone but I don't know if it was the right thing to do. Anyone knows why this helped me? And more than this, did I do the right thing or have I done something really stupid... Appreciate your opinions, Moshe