# Frequency Transformation to find transfer function

Discussion in 'Homework Help' started by naickej4, Aug 31, 2016.

1. ### naickej4 Thread Starter Member

Jul 12, 2015
190
10
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.

2. ### DGElder Member

Apr 3, 2016
347
87
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: Aug 31, 2016
naickej4 likes this.
3. ### naickej4 Thread Starter Member

Jul 12, 2015
190
10
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.