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hi,

i am currently working in DSP and i was trying to plot different windows using scilab (rectangular,hamming,hanning,barlett,kaiser,blackman) i realised that only hamming and hanning windows are possible. why so? is that like scilab doesnot support the other windows? also if i give my cutoff frequency (3rd parameter) in the range of 0-0.5 for high pass,low pass,band pass and bandstop filters in the wfir function (inbuilt in scilab) only then i get the outputs. why above this range the function does not work?
hoping for a reply soon.
regards,
lipika


Scilab 30-12-16, 12:16 p.m. lipikasarkar

Answers:

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Please change the beta values in this function to get all the windows except Bartlett- https://help.scilab.org/docs/5.5.1/en_US/window.html As the documentation indicates, the function has been designed such that cfreq accepts values only within 0-0.5 range- https://help.scilab.org/docs/5.5.1/en_US/wfir.html

30-12-16, 12:33 p.m. shamika

There are essentially three well-known methods for FIR filter design namely :
1. The window method.
2. The frequency sampling technique.
3. Optimal filter design methods
Every method has its own advantages and disadvantages and is selected depending on the type of filter to be designed.The window method is basically used for the design of prototype filters like the low-pass, high-pass, band-pass etc. They are not very suitable for designing of filters with any given frequency response. On the other hand, the frequency sampling technique is suitable for designing of filters with a given magnitude response. The ideal frequency response of the filter is approximated by placing appropriate frequency samples in the z - plane and then calculating the filter co-efficients using the ifft algorithm.

Secondly, The use of windows offers very little design flexibility e.g. in low pass filter design, the passband edge frequency generally cannot be specified exactly since the window smears the discontinuity in frequency. Thus the ideal LPF with cut-off frequency, is smeared by the window to give a frequency response with passband response with passband cutoff frequency and stopband cut-off frequency.

So, in order to design a FIR filter with any cut-off frequency range frequency sampling based techniques like Weighted Chebyshev approximation should be used instead.
Hope your doubt is cleared.


04-01-17, 1:43 p.m. mani_raj0691

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