The problem is that when I play back the wave files, there appear short klicks with the onset of every tone of the file. They are very inconspicuous, however, under experimental conditions they become audible. I used fade in and out for every tone, so the transition from one tone to the other is smooth.
Some sound cards and/or drivers have this problem. One solution, if feasible, is to play all the stimuli as a single stream. This can be done by concatenaning all the sound files (inserting silence between them), or by using software that can mix sound files in real time. Christophe Pallier www.pallier.org