actual freq to normalized freq

hi all,

does anyone knows how to convert actual freq to normalized freq from [0,Π]?

Eg: Actual freq=500hz.
Sampling freq=5khz.

thanks

regards
scdoro

Hi scdoro,

you know that for discrete-time signal or system, the normalized frequency is defined between -pi until +pi (in matlab -1 until +1). For real signal/system, then it is sufficient to be defined between 0 until +pi (in matlab 0 until +1), as you wrote.

From textbooks +pi corresponds to fs/2. So with given information you have, the normalized freq. fn is

500/5000 = fn/pi -> fn = (500/5000)*pi

best

thanks mimomod for your help.

btw, i have another question which i am stuck in how to begin..It is in the attachement.

Qn) what should be the reasonable value which i should choose for 'fp in "step 2"?

I have devise steps below for the approach.Can you help me see if its correct

steps:
1) Required to find the prototype lowpass cutoff frequency for 'fp and 'fs.
*2) Choose a reasonable value for 'fp
3) Obtain alpha1 and alpha2 by substituting 'fp,Wup,wlp values into the four equations
4) Now, we can obtain 'fs since alpha1,alpha2,Wus,wls values are found and given
5) Compute the analog butterworth lowpass prototype specification
6) Design Analog butterworth lowpass filter
7) Perform billinear transformation to obtain digital lowpass butterworth filter
7) Transform digital lowpass to bandstop using the frequency band transformation


thanks

regards
scdoro