Inverse DFT

[Arnab IT]

I have working on a vb.net application . I have earlier use NI for polyval function in my application. I need to use a inverse DFT method. I have written a method in vb.net which calculates  inverse dft of 2d array. The method produces acceptable results but the problem is it is taking too much time. The input is an 1200 * 1200 array.Is there any method available for  inverse DFT ? 

Thanks,

Arnab

[Bum]

Why don't you use FFt instead of DFT?  From what i understand  Fast Fourier is a faster method of Discrete Fourier.   This is available in the digital signal processing ocx (cwanalysis.ocx i think).

Hope this Helps,

B

[Arnab IT]

 FFT can ONLY be used on a series that is a power of 2.Thats why i need to use DFT not fft

[Bum]

Please follow this link

http://zone.ni.com/reference/en-XX/help/371361E-01/lvanlsconcepts/fft_fundamentals/

i pulled the following paragraph from this page...

When the size of the input sequence is a power of two, N = 2^m, you can implement the computation of the DFT with approximately Nlog₂

(N) operations, which makes the calculation of the DFT much faster. DSP literature refers to the algorithms for faster DFT calculation as fast Fourier transforms (FFTs). Common input sequence sizes that are a power of two include 512, 1,024, and 2,048.

When the size of the input sequence is not a power of two but is factorable as the product of small prime numbers, the FFT-based VIs use a mixed radix Cooley-Tukey algorithm to efficiently compute the DFT of the input sequence.

hope this helps

B