Ronald H. Nicholson Jr.
Guest
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 Posted:
Sun Dec 19, 2004 3:38 am Post subject:
concatenated FFT's? |
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I read about something like the following before, but don't know what
search terms to feed Google in order to find it.
If I have only the FFT results, length N, for 2 successive frames of
data, naively I can get an FFT of length 2N by first doing two IFFT's
and then an FFT on the concatenation of their output. Is there a more
efficient method?
IMHO. YMMV.
--
Ron Nicholson rhn AT nicholson DOT com http://www.nicholson.com/rhn/
#include <canonical.disclaimer> // only my own opinions, etc. |
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John Monro
Guest
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| Posted:
Sun Dec 19, 2004 7:57 am Post subject:
Re: concatenated FFT's? |
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Ronald H. Nicholson Jr. wrote:
| Quote: | I read about something like the following before, but don't know what
search terms to feed Google in order to find it.
If I have only the FFT results, length N, for 2 successive frames of
data, naively I can get an FFT of length 2N by first doing two IFFT's
and then an FFT on the concatenation of their output. Is there a more
efficient method?
IMHO. YMMV.
Ronald, |
Yes, there is! In fact, the FFT Butterfly is no more than an efficient
method of combining two length-N FTs to deliver a single length-2N FT.
All you need to do is put the two length-N FFTs end-to-end, and treat
that block of 2N samples as the input to the last stage of a length-2N
'decimation-in-time' FFT. Arrange the frames so that the more recent
frame is the one that receives the phase-rotation.
Regards,
John |
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