Best way to read in an analog trigger signal

raschemmel:
Input High Voltage Min:(0.7Vcc) - Max:(Vcc+0.5)

That's for data pins when VCC <= 2.4V or for XTAL pin at >= 2.4V
I think for the UNO @5V pin low is 1.5V and pin high is 3V any voltage between these is grey area.