amplitude frequency response using fft

[alonfz]

hi,
my question is this :
i have an impulse response saved in an array ( [0.25 0.5 0.25] ), which is a LPF coefficents. now i want to use fft command to compute the AFR of this filter , but my question is this how can i change the sampling period , meaning if the sampling period was T when h[n] was taken than how can i plot the same h[n] later but in 2T seconds as the sampling period ?

 

[GregLocock]

Since you are doubling the frequency resolution you are trying to add information. Therefore you will have to make some assumptions. Can you add trailing zeroes to the time history?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[jsolar]

The numeric values of the Fourier transform are identintical. It is just that the numbers on your frequency axis are now cut in half. Whereas originally you might have plotted them from zero to 0.5 Hz, you would now plot from zero to 0.25 Hz.