[rfolea]

Normally, you would get a single increment in your counter for every A/B Cycle (A goes high, then B goes high).

4X encoding means you get 4 increments for each cycle (one for the rising edge of A, another for the falling edge of A, another for the Rising edge of B, another for the falling edge of B).

So ... if you have a 128 count encoder, it will act like a 128x4 = 512 count encoder!

This increases the resolution of your encoder by 4x for free.

The 2X gives you two increments per cycle.