Frequency Transformation to find transfer function

Thread Starter


Joined Jul 12, 2015
Hello all,

I am working through a past year exam with a provided memo from the lecturer (The Lecturer does not reply to his emails).

I am trying to understand how the lecturer arrived at the final answer.
Why did he introduce the LPF as 0.5?
Is there a simple way to tackle this type of question?
Is there information on this site that I can read that will help me further?

The prescribed textbook that I am using is Digital signal processing: a practical approach / Emmanuel C. Ifeadhor, Barrie W. Jervis.

thank you.



Joined Apr 3, 2016
Perhaps from the equation for constructing a corresponding high pass filter from the low pass filter coefficients.

where T is the period of the sampling frequency.

flp = 1/(2T) - fhp

And where the cuttoff frequency, f, is expressed as a fraction of the sampling frequency: T=1

Flp = 1/2 - Fhp.

...must be in your book somewhere.
Last edited:

Thread Starter


Joined Jul 12, 2015
Hi Sir,
Thank you very much for your response. It makes a lot of sense on what you saying so that proves were the lecturer gets the 0.5 from but,
what about the final answer, where does he get that from ?

Below is the only information that I find in the text book on this type of question and there are no examples. (I took pics of the textbook)



Thank you.