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Even better, use a RFFT, i.e. a FFT that takes a real-valued input vector, of length N,
and computes only N+1 of the (complex) output values: X(0), X(1), ..., X(N/2). The real values
will be stored in X(0), X)(1), ...,X(N/2) and the imaginary values in X(N-1), X(N-2),...,
X(N/2+1).  

Regards
Sigmund. 

-------- Message d'origine--------
De: a...@yahoogroups.com de la part de Balaji Duddukuri
Date: mar. 3/21/2006 5:19
À: d...@126.com
Cc: a...@yahoogroups.com
Objet : RE: [audiodsp] how to comput 2N point array by using N point fft?
 
Hi,
 Method is available in proakis text book,
In fact there are 2 methods and these two methods can me applied to a real
sequence only.
Method 
1. Here you will put 2N real samples into two N samples arrays and then pass
this to FFT input. with one N array as imaginary and one more N as real
sequence. Now the result will have FFT result.

2.Other method is pass one sample to imaginary and one to real then compute
FFT then there is an equation in proakis if you apply it on this you will get
the result FFT.
Alternatively You can go through TI site whre there is an application note
which has Complete implementation.
First try to do it in Matlab then you can implement in c.

Regards
Balaji

-----Original Message-----
From: a...@yahoogroups.com [mailto:a...@yahoogroups.com] On Behalf Of
d...@126.com
Sent: Monday, March 20, 2006 5:20 PM
To: a...@yahoogroups.com
Subject: [audiodsp] how to comput 2N point array by using N point fft?

everyone:
   hi.
   I want to save time in the process of fft,I know there is one method of
using a complex N point fft to comput a real 2N point array.But I dont know
how to do it .can anyone help me?

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