## Forums Search for: FFT

## FFT Based Filtering?

inHello, I'm writing a simple C++ application, which performs the following tasks; 1) generates high/low pass daub 4-tap filters 2)...

Hello, I'm writing a simple C++ application, which performs the following tasks; 1) generates high/low pass daub 4-tap filters 2) performs a fft of those filters 3) performs a fft of the input, test signal 4) multiples the fft of the filters, with the fft of the test signal 5) performs a ifft of the result of the previous step, to output the filtered result of the test signal. ...

## FFT harmonics question

inGuys, I am making an FFT of a sin() wave from a signal generator (a few tens of Hz) with a sampling rate of 2500/sec. my FFT size is 8192...

Guys, I am making an FFT of a sin() wave from a signal generator (a few tens of Hz) with a sampling rate of 2500/sec. my FFT size is 8192 or 16384. In either case I observe harmonics with multiples of the sine frequency with decreasing amplitude. I assume that the discrete FFT will create such artifacts, but how can I tell how much of these are real (my signal generator in principle may also hav...

## Fixed point FFT

inHi, I have to implement the FFT for a vector long 2048 samples in a DSP which does not support floating point. Do you have any link to already...

Hi, I have to implement the FFT for a vector long 2048 samples in a DSP which does not support floating point. Do you have any link to already written code that computes the FFT with integer computation? Thank you in advance

## Radix -4 FFT -savings over radix -2 FFT?

inHi All, Is there a big saving (computational complexity) of Radix-4FFT over Radix-2FFT. Given: 512 Points FFT. Processor: Lucent...

Hi All, Is there a big saving (computational complexity) of Radix-4FFT over Radix-2FFT. Given: 512 Points FFT. Processor: Lucent 16410(C/speed -> 195MHz). There is a reference FFT assembly library(with Radix 2) which gives an estimate of 13592 cylces. It looks too high for my application. My opinion is that if we can manage to compute one butterfly within 10 cycles - the cycles shou

## questions on FFT

inHi all, I feel confused with some trivial questions and your help is highly appreciated. 1. Suppose Y(k) is the N point FFT of the original...

Hi all, I feel confused with some trivial questions and your help is highly appreciated. 1. Suppose Y(k) is the N point FFT of the original data, for me, the power spectrum is Y.*conj(Y). However, the example in "Matlab help" of fft tells that the power spectrum is Y.*conj(Y)/N. 2. I need to calculate the power of a specific band, for example 10-20Hz. What I do is just to take FFT and su...

## zero-padding and normalization for fft

inhi all, Normally to normalize an fft such that a pure sinusoid with amplitude of 1 in time domain will correspond with spectrum with magnitude...

hi all, Normally to normalize an fft such that a pure sinusoid with amplitude of 1 in time domain will correspond with spectrum with magnitude of 1 in frequency domain, I perform fft then devide the obtained spectrum by N/2 (where N is the length of the signal). Now I want to pad zeros so that the spectrum will look better, do you know how to normalize fft in this way such that a sinusoid ...

## help on abs() within matlab

inHi, I'm new to matlab and I'm developing fft matlab code for hardware prototype. I have passed floating point code and try to verify it...

Hi, I'm new to matlab and I'm developing fft matlab code for hardware prototype. I have passed floating point code and try to verify it with fixed point algorithm. I met problem here. 1). I use fi(x) to define input and then use fft(x) to check matlab original results. I got message: Function 'fft' is not defined for values of class 'embedded.fi'. Why I can't use fft() here? Is there a solu...

## phase of FFT

inHey all, I'm new here. Currently I'm struggling with the phase of FFT. I read that the phase of FFT is relative to the start of the time...

Hey all, I'm new here. Currently I'm struggling with the phase of FFT. I read that the phase of FFT is relative to the start of the time domian signal. In my measurement I recorded a signal which is a sinus sweeping from 100hz to 3000hz. after FFT i obtained a phase spectrum within the specified frequency range. what I dont get is how do we get for each frequency component a phase if the phase...

## Is there a sample Java code for fixedpoint FFT?

inHi, I have now a Java code implementing real FFT. I need actually Java code for implementing integer (fixed-point) FFT. I mean with this that...

Hi, I have now a Java code implementing real FFT. I need actually Java code for implementing integer (fixed-point) FFT. I mean with this that the FFT accepts Java int type as input and produces Java int type as output. If there is no Java fixed-point FFT, how can I convert the existing Java real FFT to a fixed-point FFT? Would please somebody give a code example in Java. PS: I can now perfor...

## Convolution in C# using Exocortex

inHi, I can't get my results in C# to match those in MATLAB. I'm using the following code (assume the matrices in C# are already zero...

Hi, I can't get my results in C# to match those in MATLAB. I'm using the following code (assume the matrices in C# are already zero padded): MATLAB: 1. fft(x); 2. fft(y); 3. z = ifft(x.*y); C# 1. Fourier.FFT(x, FourierDirection.Forward); 2. Fourier.FFT(y, FourierDirection.Forward); 3. for (j = 0; j < x.Rows; j++){ z[j] = x[j] * y[j]; } // results match to here 4. Fourier.FFT(z, Four

## FFT convolution giving different results from convolution

inI read the chapter about FFT convolution (chapter 18) on dspguide.com and from what I understood, to perform a FFT convolution, you perform...

I read the chapter about FFT convolution (chapter 18) on dspguide.com and from what I understood, to perform a FFT convolution, you perform a FFT on your filter kernel and on your signal (after you have changed their size and zero padded), you multiply each real and imaginary part of the two signals, and then you perform an IFFT, and with that you're supposed to get the same result as with a ...

## FFT sanity check.

inDebugging an FFT... If an FFT time-domain input comprises say, 1.5 cycles of sine starting positive going followed by another 1.5 cycles of...

Debugging an FFT... If an FFT time-domain input comprises say, 1.5 cycles of sine starting positive going followed by another 1.5 cycles of sine starting positive going - in other words has 3 cycles with an inversion half way along, then the real and imaginary FFT outputs at the 3-cycle frequency should be zero. That's right, isn't it? Cheers -- Syd

## How do I deal with final scaling factor in 8K FFT?

inIn the implement of dynamic scaling FFT(8k for DVB-T), a scaling factor is incremented at the end of each stage if the maximum value of the stage...

In the implement of dynamic scaling FFT(8k for DVB-T), a scaling factor is incremented at the end of each stage if the maximum value of the stage is large enough to cause overflow in next stage and the data in the memory is scaled down. In the end of the FFT, I will have a final scaling factor SF. That is to say, y0 = fft(x); // SF = 2; y1 = fft(x/2); // SF = 1; y0 and y1 w...

## plotting FFT in matlab

insuppose f(x)=exp(-x^2) then it's fourier transform is also exponential. I'm trying to perform FFT and plot it. I'm using this but it is not...

suppose f(x)=exp(-x^2) then it's fourier transform is also exponential. I'm trying to perform FFT and plot it. I'm using this but it is not showing exponential behavior. please help me with plotting the FFT x=-10:0.01:10; y=exp(-x.^2); N=5000; z=fft(y,N); F=[-N/2:N/2-1]/N; plot(F,z,'b');

## FFT Rounding error?

inI computed this forward FFT using MS VC++ 6.0 and FFTW: http://www.holmea.demon.co.uk/Misc/FFT.gif I don't think the "tail" should flick up...

I computed this forward FFT using MS VC++ 6.0 and FFTW: http://www.holmea.demon.co.uk/Misc/FFT.gif I don't think the "tail" should flick up like that at the low-frequency end. Is this caused by a lack of floating-point precision? TIA

## calling FFT function from dsplib tms320vc5510

hi, this is my first time using tms320vc5510 dsp board by TI. i need to process my signal using FFT. thus, i had generated a 12 cycle sine...

hi, this is my first time using tms320vc5510 dsp board by TI. i need to process my signal using FFT. thus, i had generated a 12 cycle sine waveform to test the FFT. i had referred to TMS320C55x DSP Library Programmer?s Reference (SPRU422i) on how to call the FFT function from dsplib but some how the output was not really as desired. i suspect there was something wrong with my source code. m...

## Real-Only FFT

inHi DSP people, Is there a way to do complex FFT (with imaginary components) with a real only FFT alogarithm ? Thanks !

Hi DSP people, Is there a way to do complex FFT (with imaginary components) with a real only FFT alogarithm ? Thanks !

## 2D FFT window function

inI have some questions about length of windowing functions applied to 1D and 2D FFT. For a N point 1D FFT, it is very straightforward, I can...

I have some questions about length of windowing functions applied to 1D and 2D FFT. For a N point 1D FFT, it is very straightforward, I can generate a N point window function, and multiply it with the signal before doing FFT. But for N*N point 2D FFT, what length of window function should I use? Should I generate a N*N point window same to the one used in 1D FFT, or a N point window and repeat the...

## Rectified FFT

inHi Everybody, I have a question that may or may not make sense: is it possible to take the FFT of a fully recitified sine wave (the positive...

Hi Everybody, I have a question that may or may not make sense: is it possible to take the FFT of a fully recitified sine wave (the positive half cycles are inverted) and still produce the same results as would be calculated with the same waveform non-rectified? Is this possible? Do I need to do anything special before or after the FFT calculations? Thanks much, Ben

## FFT processor architecture

inhello, i'm designing a fft processor.Can any body please give me details of various architectures of fft processors.And topics on which i...

hello, i'm designing a fft processor.Can any body please give me details of various architectures of fft processors.And topics on which i should concentrate more. with best regards, truely pavan This message was sent using the Comp.DSP web interface on www.DSPRelated.com