Re: fft_zrip confusion
Re: fft_zrip confusion
- Subject: Re: fft_zrip confusion
- From: Mark Woollard <email@hidden>
- Date: Wed, 14 Apr 2004 20:32:31 +0100
Figured it out! My value for m_log2f was incorrect, being one larger
than it should, thus the fft was processing twice as much data as I'd
setup. First pass the extra portion of the buffers were zero but each
pass it accumulated as only the first half was reloaded with new data.
Mark
On 14 Apr 2004, at 18:58, Austin Shoemaker wrote:
ctoz takes your array of real floats and packs them into the complex
buffer. fft_zrip operates on the complex buffer to produce the FFT in
place. If you don't call ctoz every time before the fft_zrip, you
will be operating on the result of the last FFT, so you will get
different results each time. If you repeat the two lines you typed
below each time, you should get the same result every time. Are you
calling ctoz each time?
Regards,
Austin Shoemaker
On Apr 14, 2004, at 10:07 AM, Mark Woollard wrote:
I'm using this to do a forward fft on segments of a data stream.
Sample
values are in the range -1 to 1. First time I call fft_zrip it works
as
expected with a peak in the output data where I'd expect. But each
subsequent call the output values grow significantly, the input data
I've checked and is always within the described range. What am I
missing? Code segment:
// Apply fft
ctoz( (COMPLEX*) m_buffer, 2, &m_complex, 1, m_resultSize );
fft_zrip( m_weights, &m_complex, 1, m_log2f, FFT_FORWARD );
where m_buffer is an array of floats with the input data, m_complex a
COMPLEX_SPLIT with realp and imagp setup with buffers with enough
space
for the results. I've checked the m_buffer contents by adding printf
loop and the input isn't getting ramped up. m_log2f and m_resultsSize
are calculated at the start and are correct. I've not used ztoc as I'm
happy working with the split output and not scaled the output as this
doesn't matter to me either.
Thanks for any input, been scratching my head for a few hours on this
one!
Mark
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