I ran some tests, including one that led You. Even tried the following conversion types: char * samples = (char *) frame-> data; and anyway, the result is a -1 for all x, from 0 to frame->datalen-1 My task was to remake the module mod_avmd, ie file mod_avmd.c. And this problem has put me into a dead end, to the point where I moved my job to another server. In other operating environments do not have this problem. I wrote about this in more detail in the Issues: http://jira.freeswitch.org/browse/FS-5944