RE: [Discuss-gnuradio] Resampling in the frequency domain

[Robert McGwier]

Ooops.

Too hasty!

2^ (roof(log_2(N)) + 1) long FFT.

Sorry.

Bob
N4HY


-----Original Message-----
From: address@hidden
[mailto:address@hidden Behalf
Of Robert McGwier
Sent: Saturday, February 19, 2005 3:54 PM
To: Alberto di Bene; address@hidden
Subject: RE: [Discuss-gnuradio] Resampling in the frequency domain


Alberto:

Glad to know you are here.

I would not revert to the time domain.  "Rename" the complex
bins of your fft by performing a simple circular shift until
the right bin is on zero.  Apply the low pass filter in the
frequency domain,  IFFT and then downsample.  Since these
frequencies or bins are discrete, you might need to retune
BUT this can now be done on the decimated signal.

REMEMBER,  fft is a circular convolution.  So if you use
a N tap filter, you will probably want to use an
roof(log_2(N))+1 long FFT and then do overlap save or
add to turn it into a linear convolution.

If this was not clear, please say so.

Cheers,
Bob
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