I tried to run this experiment in MATLAB: numberOfSamples = 80; sampleBlock = randn(1,numberOfSamples); counter = 1; for numberOfZeros =...

I tried to run this experiment in MATLAB: numberOfSamples = 80; sampleBlock = randn(1,numberOfSamples); counter = 1; for numberOfZeros = numberOfSamples:2000 x = [sampleBlock zeros(1,numberOfZeros-numberOfSamples)] ; y = filter(H,1,x); G1 = abs(fft(y,2*length(x))); G2 = abs(fft(x,2*length(x))).*abs(fft(H,2*length(x))); numberOfZerosVector(counter) = numberOfZeros; varianceOfError(c...

As a DFT/FFT newbie I have a (probably naive) question: I was asked to use an FFT to find the low frequency term in data collected from...

As a DFT/FFT newbie I have a (probably naive) question: I was asked to use an FFT to find the low frequency term in data collected from an accelerometer. I used the routines in FFTW appropriate for 1D real- valued data. Looking at "out" - the array of complex-valued coefficients for F - assuming the zero-th indexed value corresponds to the lowest frequency, which is guaranteed to have a zero...

Hi, I am trying to use interpolation to detect an FFT peak between bins however my interpolation results in the same peak as the FFT. I am...

Hi, I am trying to use interpolation to detect an FFT peak between bins however my interpolation results in the same peak as the FFT. I am inputting a 50Hz sine wave.. Sampling freq is 6500hz and I have 2048 sample points. There fore my bin freq is 3.17hz which multipled out gives me a 50.8hz nearest bin frequency which is what my code is giving me. I am trying to see where my i

Hi, I'm researching ways to interpolate the sampled spectrum of a signal as given by a 512 point FFT. I typically only use the output of...

Hi, I'm researching ways to interpolate the sampled spectrum of a signal as given by a 512 point FFT. I typically only use the output of the FFT as is, but I occasionally need to resample the continuous spectrum in a non-uniform manner. I can't take a longer FFT to interpolate by zero-padding in the time domain, and usually only a few new samples of the spectrum are needed anyway. I fou...

hello. In Matlab I am generating a signal and noise. I am trying to measure both the signal and the noise (separately) to check I...

hello. In Matlab I am generating a signal and noise. I am trying to measure both the signal and the noise (separately) to check I am generating the correct values. I use a 512 point FFT for this. The FFT is complex. My input signal is real only. My sample rate 512MHz. My signal is 100MHz. The reading I use is the maximum of all the outputs after taking the magnitude. If I have a 1 ...

I know I'm missing something basic ;) Having begun with a very long signal ( m samples ) Done a fft on a series of windows n...

I know I'm missing something basic ;) Having begun with a very long signal ( m samples ) Done a fft on a series of windows n samples long ( m > > > n ) optionally performed some operation in the frequency domain done an inverse fft on each of the modified windows How do you "glue" things back together in the time domain? Thank you.

I trying to figure out whats the best method to measure distortion products from a single test tone. Distortion will be relatively low and...

I trying to figure out whats the best method to measure distortion products from a single test tone. Distortion will be relatively low and good S/N ratio. First I tried using FFT, but I run into the trouble of accurately extracting amplitudes and frequency information. The test signal is of arbitrary frequency and so FFT side lobes make it difficult obtaining spectral data. The othe...

Hello Forum, the fft of a rectangular, even, symmetric sequence show a nonzero real part and a zero imaginary part. All good so far. However...

Hello Forum, the fft of a rectangular, even, symmetric sequence show a nonzero real part and a zero imaginary part. All good so far. However the phase spectrum is nonzero: zero at some frequencies, pi at some frequencies , -pi at some others.... The phase spectrum is given by atan(Imag(fft)/real(fft)), so it should give zero.... why not? thanks fisico32

Ive been recently using FFT for Pitch Detection and I notice that, although the notes are correct (e.g. C, D#, etc.), there are a lot of notes...

Ive been recently using FFT for Pitch Detection and I notice that, although the notes are correct (e.g. C, D#, etc.), there are a lot of notes that are in the wrong octave (e.g. E2 is categorized as E3, C3 is categorized as C4, always an octave up). Why is this the case? My algorithm is after calculating the FFT bins, I get the bin with the greatest intensity and calculate which frequency it is...

There are a number of techniques available for estimating the frequency of a off-center sinusoid from the FFT bins around the one with peak...

There are a number of techniques available for estimating the frequency of a off-center sinusoid from the FFT bins around the one with peak magnitude. Can we also estimate the phase of the off-center sinusoid using similar methods? Would a legal approach be to find the frequency using the well-known methods and then interpolate the complex FFT data to get a complex response at the estimated f...

If I have a test instrument that only outputs the real part of the FFT, is it possible to fabricate the complex FFT from the real part to...

If I have a test instrument that only outputs the real part of the FFT, is it possible to fabricate the complex FFT from the real part to enable calculation of the transfer function? This instrument has more than one channel.

Hi All, I am simulating Rayleigh fading channel, but when I estimate the channel by estimate = fft(channel,N), where N is the number of...

Hi All, I am simulating Rayleigh fading channel, but when I estimate the channel by estimate = fft(channel,N), where N is the number of subcarriers, I get this message (Function 'fft' is not defined for values of class 'channel.rayleigh'), so what does that means, Any help for this will be appreciated, Hassan

Hi all, Thanks for reading and please feel free to comment. I am having problems with matlab fft on autocorrelation data. When performing...

Hi all, Thanks for reading and please feel free to comment. I am having problems with matlab fft on autocorrelation data. When performing a fft on my normalised autocorrelation data i got a imagnary part that is not equal to zero around x=0 and also at the near end of the x-axis, but, in between all points are equal to zero. Imagnary plot that i got looked like below, ...

Hi, I am a student working with the Xilinx C model of the FFT. Following are my settings: Pipelined arch. (this restricts the scaling to be...

Hi, I am a student working with the Xilinx C model of the FFT. Following are my settings: Pipelined arch. (this restricts the scaling to be applied only after every pair of radix-2 butterflies) Precision of 8 bits. Twiddle precision 8 bits. FFT size 1024. If I use a conservative scaling schedule of [2, 2, 2, 2, 2] (i.e. divide by 4 for every pair of Radix2 BFs) ... most of the out...

In practice, I have an approximate frequency of 125kHz that I need to measure accurately. Since I am already grabbing 2048 sample chunks at 500uS...

In practice, I have an approximate frequency of 125kHz that I need to measure accurately. Since I am already grabbing 2048 sample chunks at 500uS intervals and doing FFTs the question is: how accurately can an FFT determine the frequency? M More generally, what is the relationship between sample rate, accuracy and the FFT method? Of course, there are other methods such as counting and timing...

Hello, I am trying to detect mutiple peaks in a FFT. 90% of the time the primary peak (Highest magnitude) is the only return i am interested...

Hello, I am trying to detect mutiple peaks in a FFT. 90% of the time the primary peak (Highest magnitude) is the only return i am interested in. But sometimes i have multi peaks and i need a way to detect these peaks. It gets tricky especially with the noise in the fft resembles mini-peaks. I get multi peaks when i have reflections in a signal, and i want to determine these reflection points when ...

Let's say I have an FFT of the given size N, and I want to get an estimate of a frequency of a noisy tone (input SNR ~ 1/N). Increasing FFT...

Let's say I have an FFT of the given size N, and I want to get an estimate of a frequency of a noisy tone (input SNR ~ 1/N). Increasing FFT size is not an option. I can do the following processing: 1) Average the magnitudes for every bin through several FFTs, then do a curve fit through max_bin, max_bin-1, max_bin+1 to find the peak. 2) Do the FFT, then estimate the frequency by on...

I'm experimenting with analyzing speech. I'm also more comfortable thinking in terms of a "spectrum analyzer display" than the "spectrograms"...

I'm experimenting with analyzing speech. I'm also more comfortable thinking in terms of a "spectrum analyzer display" than the "spectrograms" that I see on most speech recognition pages. The question is "How does the spectrum of a speech sample vary with time?" My first approach was: 1. calculate fft of a window 2. plot it 3. calculate fft of a window offset from first window ...

Hi, I need help in order to convert a 512 sample FFT to dB values. Here is the flow process of what I do. 1) Get 512 sample of data 2)...

Hi, I need help in order to convert a 512 sample FFT to dB values. Here is the flow process of what I do. 1) Get 512 sample of data 2) Apply A window function (Hanning | Backman_Harris) 3) Do FFT 4) Calculate power by re*re+img*img, note I'am not taking square root as I have to convert it to DB anyway 5) I then use 10Log(power) to get the db. The problem is I'am not getting th...

So, there are algorithms out there to perform an FFT on real data, that save (I think) roughly 2x the calculations of FFTs for complex...

So, there are algorithms out there to perform an FFT on real data, that save (I think) roughly 2x the calculations of FFTs for complex data. I did a quick search, but didn't find any that are made specifically for FPGAs. Was my search too quick, or are there no IP sources to do this? It would seem like a slam-dunk for Xilinx and Intel/Altera to include these algorithms in their FFT li...