schmitt trigger and noise
why does noise need to be reduced


Noise needs to be tackled because it creates  problems.  

One example below:
Assume the output signal is a pulse from a circuit which counts number of people entering a door. If the noise is not addressed, it will count wrong number of people. Connecting the orange pulse directly to a pulse counter will lead to wrong counts. Connecting the green pulse(Schmidt trigger output) will give more accurate results. 



There is one good note on schmitt trigger.