Where Voices Crack

The crack you hear when a voice jumps too high lives in the passaggio, the bridge between chest and head voice. At that point your folds have to switch from thick, heavy vibration to thin, light vibration.

Slides and sirens are the fix. Pick a comfortable low note and slide your voice smoothly upward, like a slow ambulance siren. As you sense the crack coming, do the opposite of your instinct: do not push harder.