I'm using a microcontroller (dsPIC30F3013) to do an FFT on some "real" data

(from a microphone) and I don't have enough internal RAM to get the

frequency resolution I need.

I found a forum entry by Rick Lyons as follows:

-quote-

Does the dsPIC33 allow you to perform

512-point FFT on complex-valued input

samples? If so, there's a way to perform

a 1024-point *real-input* FFT using

a 512-point complex FFT routine.

[-Rick-]

-end quote-

The FFT routine I have available does take a complex input (two six *** bit

words), and the existing code merely stuffs zeroes into the imaginary part

of each complex input.

So, can anyone tell me what the trick is for allowing this complex-input FFT

to be more efficient with real input data such that I can effectively cut in

half the input record length I need to use.

Thanks in advance.

Bob

--

== All google group posts are automatically deleted due to spam ==

On Jun 28, 5:18m, "BobW" < XXXX@XXXXX.COM >

Google is your friend. Try searching on 'real FFT' - the 3rd entry for

me is this which seems useful:

http://www.yqcomputer.com/

Eric

Google is your friend. Try searching on 'real FFT' - the 3rd entry for

me is this which seems useful:

http://www.yqcomputer.com/

Eric

If anybody is interested, I found the answer. It was in the last place I

looked.

Rick Lyon's book "Understanding Digital Signal Processing" has an excellent

and (relatively) simple description of the technique. It involves a decent

amount of processing beyond the complex FFT, but it's doable.

So, with Rick's help, I think that I can do what I need to do with the

limited RAM that I have available.

Bob

--

== All google group posts are automatically deleted due to spam ==

1. 64-point complex FFT with 32 bit floating-point representation

2. 1024 POINTS FFT V2.0 Xilinx Core

3. Implementation of 1024 point FFT in Actel FPGA

4. [Newbie] 64-point complex FFT with 32 bit floating-point representation

5. cepstrum = fft(log(fft(x))) or cepstrum = inverse-fft(log(fft(x)))?

6. To all FFT guru's (2048 point FFT on Virtex 2 pro)

7. How many points for an FFT and Complex vector multiplication

8. fixed-point real FFT for embedded

9. Number of Points used in FFT calcuations using Spectral Measurements

10. STUPIDENT:: should FFT{x-mean(x)} = FFT{x}-FFT{mean(x)} ?

11. Execution times of FFT in MATLAB vs complex FFT in C

12. What is the difference between fft(x) and fftshift(fft(fft(x)))?

13. Why FFT(x-mean(x)) and FFT(x)-FFT(mean(x)) different

14. should FFT{x-mean(x)} = FFT{x}-FFT{mean(x)} ?

15. Where do I get FFT, is ok if it uses real inputs only

3 post • Page:**1** of **1**