Thank you very much for your quick response.
I'm currently working with Octave 3.6.2 which is the one offered in the Debian 7 repositories. I'll install 3.8 as soon as I have some time, meanwhile, I already did the processing I needed for this week.
I'll try to repeat the test and put some results tomorrow, but I was getting times of around 6 seconds per speech frame (640 samples) in Octave and 0.0007 seconds in MATLAB in the same conditions (got those timings with the tic and toc functions).
Nicanor.