Why is it that in older textbooks the DFT or FFT is defined as having scaling of (1/N) for direct FFT whereas in newer ones it doesn't? If we take...

Why is it that in older textbooks the DFT or FFT is defined as having scaling of (1/N) for direct FFT whereas in newer ones it doesn't? If we take the DFT of say 1,1,1,1 the answer is 4 but surely an answer of 1 makes more sense as it is the average value. of 4 ones. I know people say - "Oh we can scale it later", but it doesn't make mathematical sense. The other point is that the

hello, I have a question about image processing and Matlab :). How is it possible to do radial/circular average of 2D FFT. I have an image, I...

hello, I have a question about image processing and Matlab :). How is it possible to do radial/circular average of 2D FFT. I have an image, I did 2D FFT on it, and now I would like to have amplitude over r (r = radius). So, the 2D FFT of my image represents a "spot" now, so I would like to take different values of radius r (to say 10-20, for example), for every radius to calculate the mean v...

Hello everybody, I'm a DSP newbie and have some basic questions. I want to process a signal with a FFT, a filter and then with an IFFT...

Hello everybody, I'm a DSP newbie and have some basic questions. I want to process a signal with a FFT, a filter and then with an IFFT back in a time-domain signal The test system has the following setup. 1.) FFT of the time-domain signal 2.) IFFT of the freq-domain signal Both transformation are with complex values. The ifft is implemented as fft with confugated input values. As t...

I'm developing a code to remove the noise in real time, so I need low latency between input and output. I'd like to work with 128 samples block...

I'm developing a code to remove the noise in real time, so I need low latency between input and output. I'd like to work with 128 samples block size. The FFT size may be 4096 so I have to use the overlapped method. I have copied the overlapped algorithm from a book but I not sure about it. It seems that I can't overlap as I like, but at least it must be > = FFT/2, is it true? In the follow

What is the effect of lowered resolution of intermediate results on an FFT? I am considering a number of implementation choices for a...

What is the effect of lowered resolution of intermediate results on an FFT? I am considering a number of implementation choices for a fixed-point FFT. The time-series data is inherently 16-bit integers (audio data). I want to do a 8192-point FFT on this data. Because of the need to explicitly handle overflows (in the butterfly operations) in a fixed-point implementation, it is conveni...

Hello, I'm rather new to DSP stuff, so I've got some little questions. At the moment, I coded a little audioplayer which transforms the...

Hello, I'm rather new to DSP stuff, so I've got some little questions. At the moment, I coded a little audioplayer which transforms the audio data to spectrum using FFT and then back to sample data before playing it back. So far, so good. And the way I understand, the result of the FFT is an array of amplitudes for every possible sine wave. But how should those numbers be interpreted? Are...

Im' testing a real FFT routine in c++. I've got a sine wave of 512 samples, norm freg = 1/32, with sample 1 at 0 and the last sample at -1 - a...

Im' testing a real FFT routine in c++. I've got a sine wave of 512 samples, norm freg = 1/32, with sample 1 at 0 and the last sample at -1 - a discontinuity. It's going through a real FFT routine of length 9. I'm getting 10.log() spectral components of magntude on the order of 1.27 e37 ? Something isn't right, eh? Thanks in advance. -- Best Regards, Mike

Hello all, Sorry for starting this topic all over again. I had seen some previous discussions on zero padding and when I started reading them...

Hello all, Sorry for starting this topic all over again. I had seen some previous discussions on zero padding and when I started reading them I completely got lost. When I am provided with samples which are not of power of 2 and I need to implement FFT, I zero pad the samples to the next highest power of 2. I do FFT using Cooley Tukey algo and observe that the frequency componets in s...

Hi everybody! I have a question regarding FFT. I'm working with radar data & matlab. I have a block of data of 512 samples and I'm doing its...

Hi everybody! I have a question regarding FFT. I'm working with radar data & matlab. I have a block of data of 512 samples and I'm doing its FFT, but I want to do the same with exactly the same block of data but in blocks of 64 samples each, so I should do 8 FFTs right? What I don't know is how to merge those 8 FFTs afterwards, to be able to compare the two methods, that is, the FFT of 512...

Hi, I am trying to plot my signal(sum of two sines of different frequencies) in the the frequency domain using FFT function of matlab. The...

Hi, I am trying to plot my signal(sum of two sines of different frequencies) in the the frequency domain using FFT function of matlab. The magnitude plot -> y_mag = real(fft(x,N) is giving correct result. But the phase plot -> y_phase = imag(fft(x,N)); is not giving correct result..... Can someone help me..? Thanks & Regards, shakes_ck _____________________________________ Do

I got a little problem when performing a FFT convolution. I try to have the output to have the same amplitude as it would with a...

I got a little problem when performing a FFT convolution. I try to have the output to have the same amplitude as it would with a time-domain convolution. To do so, I set the sum of the values of the samples of my kernel to 1.0, and after I FFT the kernel and the signal to convolve, I divide the values of both signals by the square root of the number of samples (which is the same since they...

Hi all, I am working on a fixed-point FFT based application. The Input to FFT is a real signal while the FFT Core is Complex (a.k.a it can...

Hi all, I am working on a fixed-point FFT based application. The Input to FFT is a real signal while the FFT Core is Complex (a.k.a it can take real and imaginary inputs). Normally, one would tie the real signal to real input of the core and the imaginary input to zero. In order to optimize the resources, I want to use the complex input of the FFT Core efficiently. According to articles I f...

Hi there! I'm working on Pulse compression for radar signal using FFT, the echo is N points, and the length of match filter is also N points, then...

Hi there! I'm working on Pulse compression for radar signal using FFT, the echo is N points, and the length of match filter is also N points, then I use N points FFT to calculate the pulse compression result, it seems that I can indeed get the right result. I just get a little confused, since two N-points signals for linear convolution needs L(L> =2N-1) points FFT to get the right thing. Is there

Hello All! I want to built fast routine of FFT in C/C++, eg. void fft(double *xr, double *xi, double *yr, double *yi, int n ) n =...

Hello All! I want to built fast routine of FFT in C/C++, eg. void fft(double *xr, double *xi, double *yr, double *yi, int n ) n = 2^m; however I don't have a lot of experience in this. Should I use FFTW (Fastest Fourier Transform in the West)? Can it be really the fastest in double precision floating point? And Why? Any comments are apprecialted. Thanks, Andrzej

Which integer FFT implementation would be best for the Nintendo DS? I'm writing a tuner for the DS and I've decided to use FFT to analyze the...

Which integer FFT implementation would be best for the Nintendo DS? I'm writing a tuner for the DS and I've decided to use FFT to analyze the microphone data to find the input frequency. DS Stats: ARM946E-S @ 67 MHz primary CPU ARM7TDMI @ 33 MHz secondary CPU 4 MB primary RAM 32 MB secondary RAM No VFP only FPU + DSP extensions Which integer FFT implementation would work best (must be...

Suppose i have a symbol of 64ms of duration (512 samples). Then i can run a FFT(512) to get metric. But, i want to probe something...

Suppose i have a symbol of 64ms of duration (512 samples). Then i can run a FFT(512) to get metric. But, i want to probe something different. You imagine i divide the symbol received in 4 chips (like a Fast Frecuency Hopping of 4 chips by symbol), then i run 4 FFT's, one for each chip and i would like add the 4 FFT's of any manner without loss energy. Example: I take 1/4 of symbol (128 sa...

Hello Shawn Steenhagen, yes I have this document, can you tell me, if I think right? so, I take my output, a then I should build a...

Hello Shawn Steenhagen, yes I have this document, can you tell me, if I think right? so, I take my output, a then I should build a magnitude of FFT of output. abs(x) (I think, I need it that's why, because I take only positive magnitude) I found on mathworks.de one text, it stand there, that I should "scale the fft so that it is not a function of the length of output." also X=X/siz...

Well, first post- a newbie question: What is the best place to find basic free code for FFT analysis that is compatible with Visual Basic...

Well, first post- a newbie question: What is the best place to find basic free code for FFT analysis that is compatible with Visual Basic .NET? I am starting with FFT analysis and want to move on to image processing, but want to start with something basic I can test.

hi i need to compute a floating pt. radix 4 1024 pt fft on a floating point DSP (TMSC6701). Does anybody has any efficient code or links...

hi i need to compute a floating pt. radix 4 1024 pt fft on a floating point DSP (TMSC6701). Does anybody has any efficient code or links to help me with. i tried using the DSP library fft function provided by TI but found the output to be incorrect. Can anybody help me with this problem?? Regards Vivek

Hi All, i was going through DSP book by proakis, there i came across the following realted to for which sampling frequency what is the...

Hi All, i was going through DSP book by proakis, there i came across the following realted to for which sampling frequency what is the fft lenght to be used like, Sampling Freq FFT Length 8KHz 256 22KHz 512 32KHz 1024 44.1/48KHz 2048 My query is on what...