Variations of the yelp are the most frequently used calls. Rhythm is important. It really does not matter whether you are raspy or smooth, or using friction or diaphragm calls. Rhythm in your calls will make the difference. Pre-recorded tapes of turkey calls can help you to learn the various calls and associated rhythm.
Turkeys hear much better than humans.
Before the hen comes off the roost, she calls softly. After you get in position, try giving a tree yelp while the gobbler is still on the roost. Another handy call to use is the cluck. Turkeys frequently cluck while feeding and moving around undisturbed. You can make the clucking sound on any of the calls.