I have had this discussion with others and have been told some people can and some can't... I'm not too sure. Others more experienced on the board can add to that.

I can do it with a lowerpitch and more aggressive tone. You have toexhale/blow outward with a "tremble" or "purring sound"near the top of your mouth, where the air will flow. If you can make this sound you can then practice with the call. I place mine in and press my tongue gently against the roof of my mouth and teeth.Exhale quickly, as you go you can speed up and slow down, also changing the pressure on the call.

I use the Primos double reed calls, they make great noise for me.