Very Very stupid question ( Magnitude response of Z transform) URGENT!

[sgharagoz]

So you all know how to get the magnitude response of a Z-transform!
1- replace Z=exp(iƟ) then |X(Ɵ)| = √ a^2+ b^2

Also there is another way

2-|X(Ɵ)|^2 = X(Ɵ) x x(Ɵ*)
So you multiply frequency response its conjugate!

The answer is almost identical BUT one of them is squared!

So if they ask me to find a magnitude response or find the 3dB Ɵ Which one should I choose?

Cheers!

 

[emresel]

As you said, method 2 gives you square of the magnitude (not magnitude). So at the end of method 2, you should take square root of the resulting term.
Then you are free to use both method to find 3db cuttoff point.

Hope helps