## Forums Search for: FFT

## Large FFT vs Many FFTs

inHi DSP Gurus, I've been asked to research a DSP system to take an FFT to detect harmonic distortion. The base frequency will be 110kHz and I...

Hi DSP Gurus, I've been asked to research a DSP system to take an FFT to detect harmonic distortion. The base frequency will be 110kHz and I need to detect up to the 5th harmonic. Therfore I will need a samplerate of at least 1.2MHz. The requirements are to take 1 seconds worth of data and FFT it, giving a 1.2 million point FFT. The requirements state that the resulting very narrow bin wi...

## FFT via c6713 dsk

here is a code built "upon dsk_app" of calling FFT function. the problems are: 1- there is over flow when i call absx witch is abs of FFT out...

here is a code built "upon dsk_app" of calling FFT function. the problems are: 1- there is over flow when i call absx witch is abs of FFT out put. 2- i dont know if calling FFT is in the right place. 3- changing output frequency and input one. /* * Copyright 2003 by Spectrum Digital Incorporated. * All rights reserved. Property of Spectrum Digital Incorporated. */ /* * =======...

## producing spectrogram from audio file.. confusion with FFT

inHi there, Okay so I had already put up a post how in order to find the spectrogram of an audio file, I was going to perform a series of FFT's...

Hi there, Okay so I had already put up a post how in order to find the spectrogram of an audio file, I was going to perform a series of FFT's and from these compute the spectrogram.. I was confused about whether to use real fft or complex etc.. so I used the real fft function from kiss_fft, i.e. kiss_fftr( ) The spectrogram I get has the right shape overall, however it looks terribly nois...

## FFT VS DCT

inI see that all are asking why DCT is better than FFT or DFT. Where FFT is prepered than DCT? Why ? Is it only for phase...

I see that all are asking why DCT is better than FFT or DFT. Where FFT is prepered than DCT? Why ? Is it only for phase information? _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?

## large size FFT in DSP

inHi,all I need do a 65536 points FFT with TMS320C64x. Ti's dsplib does include some C callable fft programs (assemble, hand optimized),but...

Hi,all I need do a 65536 points FFT with TMS320C64x. Ti's dsplib does include some C callable fft programs (assemble, hand optimized),but it seems the maximal size they can cope with is 32768. If not necessary, I won't write this from beginning. Any comment?

## FFT overflow

inHi, This is my first post so please be patient. I am trying to implement an 8pt FFT. However i only have a 16bit adder. When i add 2 large...

Hi, This is my first post so please be patient. I am trying to implement an 8pt FFT. However i only have a 16bit adder. When i add 2 large numbers together the result is 17bits. I can remove the LSB but what is the best way to make the result 16bits again. Assume the FFT size will be 1024pts eventually. Thanks

## FFT alternating phase problem

inI am confused by the phase behavior of my FFT. I'm trying to get the phase of the fundamental harmonic with the usual arctan. The Phase alternates...

I am confused by the phase behavior of my FFT. I'm trying to get the phase of the fundamental harmonic with the usual arctan. The Phase alternates 180 degrees on odd/even samples. Am I doing something wrong or is this just an unadvertised feature of the FFT. Can I fix this? Background: FFT: 512 point 16 bit integer, 8051 8 bit cpu, 24mSec time Windows: Hamming, Blackman-Harris, Flattop Sig...

## Convolution using real-valued FFT

inI have implemented the basic overlap-add convolution using a standard complex FFT routine. This has lots of zeroes, first from padding data and...

I have implemented the basic overlap-add convolution using a standard complex FFT routine. This has lots of zeroes, first from padding data and IR (impulse response) to FFT size, then I have to copy data and IR to complex numbers (with zero imaginary part). Now I tried instead to replace the complex FFT routine with a real-valued FFT so I can skip copying all data and IR to complex numbers. ...

## fast convolution and normalization

inHi, i searched the web for quite some time now and just don't grok how to normalize when doing partitioned frequency domain...

Hi, i searched the web for quite some time now and just don't grok how to normalize when doing partitioned frequency domain convolution. Basically for an unnormalized FFT/IFFT pair (i use fftw, so all the FFT/IFFT i use is unnormalized), the necessary normalization factor would be 1/N applied once or 1/sqrt(N) applied twice. But now i have IFF(FFT(signal)*FFT(response)) and i wonder wh...

## FFT with sub-Hz resolution?

inNewbie question: I am learning FFT and wandering how to achieve sub-Hz resolution. If the sampling rate is Fs, and you take N points out of...

Newbie question: I am learning FFT and wandering how to achieve sub-Hz resolution. If the sampling rate is Fs, and you take N points out of the samples to do FFT, then the maximum resolution is 1Hz. Or can you take more points than sampled in a second to achieve sub-Hz resolution? Maybe the zoom FFT can achieve sub-Hz resolution? Can somebody enlighten me on this? Thanks!

## Sliding window FFT

inHi, I am trying to understand the difference between the sliding window FFT algorithm and the windowed FFT (i.e. the conventional...

Hi, I am trying to understand the difference between the sliding window FFT algorithm and the windowed FFT (i.e. the conventional method). Say we have a 6000 sample time domain data that we wish analyze in frequency. We can take two approaches: 1- Pad the data stream with 2192 zeros and apply a 8192 point FFT. 2- Choose a short window size (e.g 256 points) and slide this window acros...

## How to do a FFT ? Comment faire une FFT ?

inHello , I am a new user of the TMS320C6711 DSP and i would like to know how i must do to make an fft with this device. Actually I...

Hello , I am a new user of the TMS320C6711 DSP and i would like to know how i must do to make an fft with this device. Actually I acquire six tensions with an analog to digital converter and i would like to analyse the frequencies of these tension. Thank you per advance for your help regards Vincent.W The devices that i employed : - OSR 116 acquissition board : http:/...

## Filtering of complete sample - FIR versus IIR versus FFT

inHi. I have some quite long samples. I would like to produce filtered versions of these. Originally I used a FFT to do this. I would fft...

Hi. I have some quite long samples. I would like to produce filtered versions of these. Originally I used a FFT to do this. I would fft the entire sample (e.g. 20 seconds of 44.1khz mono 16-bit sound). I would then (for lowpass filtering) zero the magnitudes in the stop band and leave the phases alone. I would then inverse FFT to get the filtered sample back again. Using the fftw3 library on ...

## FFT not showing high frequency oscillation

inHi all, I am new to DSP and FFT, but have managed to implement Smith's FFT algorithm. I use it to analyze audio amplifier signals. I have...

Hi all, I am new to DSP and FFT, but have managed to implement Smith's FFT algorithm. I use it to analyze audio amplifier signals. I have this one particular signal, a 1kHz sine with approx an 80kHz parasitic oscillation injected only on part of the wave (approx lasting a 1/4 phase). It is sampled at 5MSa/s. When I run this through my FFT program, the 1kHz sin wave shows up fine, but ...

## Wimax FFT size support question

I have been looking into the 802.16 Wimax system ( OFDMA ) to get a basic understanding. The system seems to be able to support multiple FFT...

I have been looking into the 802.16 Wimax system ( OFDMA ) to get a basic understanding. The system seems to be able to support multiple FFT sizes, such as 128, 256, 512, 1024 etc. I am not able to understand couple of issues: 1. Is the FFT size fixed for a basestation(BS)? If not when can it change? How would a system designer go about selecting the FFT size? 2. Does a "compliant" subsc...

## Execution times of FFT in MATLAB vs complex FFT in C

inHello, I measured the execution time of a 2^20 point FFT in MATLAB. It takes 703ms do do one 2^20 point complex FFT in MATLAB. If I do a 2^20...

Hello, I measured the execution time of a 2^20 point FFT in MATLAB. It takes 703ms do do one 2^20 point complex FFT in MATLAB. If I do a 2^20 complex FFT in C it takes 3.3 seconds. How come it takes 4 times longer in C compared to in MATLAB? Has anyone compared the Intel Math Kernel Library (MKL) FFT with MATLAB in terms of execution time? Thanks for any replies.

## Can anyone point me to some basic (not so mathematical) pseudocode for a reasonably efficient FFT?

inYes, I know, that's not the way to learn about FFT. But there's only a small probability that the resampler + FFT solution I have in mind will...

Yes, I know, that's not the way to learn about FFT. But there's only a small probability that the resampler + FFT solution I have in mind will actually do what I need anyway, so I was hoping to get a ballpark feeling before getting in too deep (time constraint). TIA, Tony Tony (remove the "_" to reply by email)

## FFT and normalization

Hi Group, I know my question may sound stupid. But I can not come up with a solution. So I post it here with the hope that someone could shed...

Hi Group, I know my question may sound stupid. But I can not come up with a solution. So I post it here with the hope that someone could shed me some light. Thanks in advance! I am working on some image processing with FFT. It requires that the function to be FFTed into spatial frequency space. However, I found out that the result of FFT depends on the number of segments I choose. For e...

## FFT usage

inHi all, I'm using an FFT routine as given at http://www.yov408.com/html/codespot.php?gg=36 - in fact, its been used by my group a lot, so it...

Hi all, I'm using an FFT routine as given at http://www.yov408.com/html/codespot.php?gg=36 - in fact, its been used by my group a lot, so it has a good reputation ;) I have a few questions to ask about it though. I've modified the code to allow the user to specifiy whether they want the complex conjugate of an FFT. The logic seems fairly simply - just a simple flag and a reversal of the...

## convolution with FFT: same resut with or without zero-padding?

inHi. Given n = 6 xa = rand(n,1) xb = rand(n,1) If I do ya = fft(xa) yb = fft(xb) z = ya.*yb w = ifft(z) I get...

Hi. Given n = 6 xa = rand(n,1) xb = rand(n,1) If I do ya = fft(xa) yb = fft(xb) z = ya.*yb w = ifft(z) I get the result that I want (w); I'm interested in obtaining exactly the same result zero-padding input vectors to the next power of two, for faster FFT (my n is actually ~ 1e6 and I have several such input vectors); I tried doing n2 = 2^nextpow2(n) ...