Questions tagged [fft]

The fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse.

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Could kernel density map be recovered with known kernel function?

I'm confused whether a KDE map could be recovered with known kernel function. The KDE map (with no noise) generated with fast fourier trasnformation (FFT) could be recovered on very high accuracy (<...
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25 views

What is the meaning of the length of diagonal lines in FFT

I am relatively new to FFT analysis of images and have a question about them. I like to think I understand the basics but many of the properties shown in a FFT image are beyond me. My main question ...
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Methods for aligning FFT bins with an FSK signal

Say I want to demodulate some FSK modulation. My (novice) understanding is a pretty good way to do this is by taking the FFT, with the length chosen such that the bin spacing is equal to the tone ...
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Understanding convolution of Chirp z algorithm

I dont´t understand how works the convolution part of the Chirp z. I understand how the DFT is transformed \begin{align*} x(k) = \sum_{n=0}^{N-1} x(n) W_N^{kn} \end{align*} to this expresion: \...
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25 views

How to find frequency band after folding using single channel ADC

I want to to explore some signal processing techniques that is used to identify frequency band using FFT folding Following sequence is used in implementation Input->ADC->FFT->Frequency detection If ...
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33 views

Why are low frequency peaks not sharp in scipy fft?

I am using numpy/scipy to plot graphs of sine waves. frequencies at 15 Hz or higher give nice, sharp peaks, but at lower frequencies, the peaks are smeared and the actual peak frequency can't be seen ...
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2answers
64 views

Evaluate performance of FFT Windows

lately i've been interested in FFT windowing, i've experimented various windows in Matlab, that made me more curious: There are normalized parameters (CG, Scalloping loss etc...) for every window ...
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1answer
2k views

FFT Algorithm: Split Radix vs Radix-4

I wanted to know the difference between split radix and mixed radix algorithm. I also wanted to know what is the difference between radix 2 ,radix 4 and radix 8 FFT
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1answer
41 views

How to achieve a smoothed frequency phase response with no outliers

I have two sampled signals, which I then perform wavelet analysis on, by synthesising the Filterbank, perform the dft on each kernel, and the dft on the sampled signals, and multiply together. ...
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1answer
50 views

Irregularities in tone generated using FFT data

I am implementing a simple program to generate tone in MATLAB using FFT/iFFT by zeroing all frequency bins except for the one frequency that I'd like to generate a tone in. Sampling frequency is ...
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1answer
43 views

Matlab: Different 1-D FFT results with and without zero-padded

Recently I am implementing FFT with C code. So I use Matlab for algorithm verification. As Radix-2 FFT was chosen, I've learned that zero-padding technique could help to reach 2^N limitation without ...
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2answers
146 views

Estimation of filter response

If I have samples of input say x(1:500) and it passes through FIR filter with 9 taps and some unknown coefficients. The output y(1:508) is also known. The aim is to estimate the filter response in ...
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65 views

Matlab FFT not producing symmetric spectrum

I am plotting a FFT of a sampled RC pulse but my resulting spectrum isn't symmetric - it's offset. ...
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45 views

Why the spectral coherence is unity for all frequencies between single-frequency time series and itself

In the example below, I am plotting the coherence between time series and itself. The time series do has one frequency.The coherence magnitude was one for all frequencies. I wonder why it is not zero ...
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18 views

Is KissFFT library good at decomposing the time domain data into the frequency domain data

Hope everybody is having a good day! I wonder if anybody could help me understand on how to use KissFFT library to get the Magnitude vs Frequency data out of time domain signal, for instance: RPM vs ...
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28 views

What determines peaks in FFT?

I ran FFT on three audio files and found that the results for some have more peaks than the other. Could anyone give me any conceptual explanation as to what determines these peaks? Below are plots of ...
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1answer
24 views

What is the difference between the V-OFDM and OSDM

I am trying to understand the difference(s) between V-OFDM (Vector Orthogonal Frequency Division Multiplexing) and OSDM (Orthogonal Signal Division Multiplexing) which are used as a multicarrier ...
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54 views

Multi Resolution STFT for audio

I am looking at trying to achieve a multi resolution STFT analysis on a log sine sweep audio measurement. I have an impulse, and I would like to perform two different windowed length FFTs on the ...
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3answers
352 views

What is the proper way to implement a real time spectrogram?

I am trying to implement a real time spectrogram and I am not sure that I am implementing it the right way. First I decided to use Matlab, I was taking a short recording of lets say 0.1 seconds and ...
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24 views

Skew measurement with phase deviation

I am calculating the standard deviation of skew (= phase/2*pi*fin) from the 1000 monte carlo runs of the following code. In the y0, there is no input skew., but in y1 there is a skew present. Its ...
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1answer
48 views

FFT processing of IQ data

My time-domain sampling rate of IQ data is Fs. Matlab FFT assumes spectral bandwidth is Fs/2, per the Nyquist criterion. I understand that IQ data has bandwidth of Fs. How do I do FFT of such IQ data ...
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1answer
34 views

Signal processing using numpy python

To process a .wav audio file with numpy (using fast Fourier transform algorithm). I want to process an audio signal at a particular interval with a sampling frequency 44100hz and sampling rate of 20ms ...
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Extraction of brainwave data from eeg

I'm fairly new to signal processing/data analysis and already read several papers & questions on researchgate but it seems that I lack the "foundational knowledge" to 100% understand the ...
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1answer
88 views

PSD subtraction

I am interested seeing the difference between two power spectral densities (PSD) as a noise reduction exercise The blue line is the psd of my signal, and the the orange line is the psd of the ...
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3answers
634 views

Distribution of energy in frequency bands

On my wav-file (music), I do a short-time Fourier transform (STFT). I have spectrum, which spans from $0\textrm{ Hz}$ to $f_s/2$. I took out the range between $1$ and $1000\textrm{ Hz}$, which I ...
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23 views

Prefactors computing PSD of a signal with numpy.fft VS. scipy.signal.welch

The power spectral density St of a signal u may be computed as the product of the FFT of the signal, ...
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1answer
23 views

LOW SIGNAL NOISE RATIO FFT

I am processing an audio signal with CS4244 codec at 24 bits and 48kHz. Every 2048 samples the FFT is calculated and its amplitude. Without input signal I get FFT values ​​close to 30dB. With maximum ...
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472 views

Curved noise floor and ugly unexplained peaks after FFT

It has been so long since I studied this at University, so I'll better ask here if I'm doing something really wrong here. I'm using a USRP frontend for L1 band surveillance. I want a 20MHz bandwidth, ...
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5 views

Noise evaluation using piezo sensor

I'm not familiar with piezo (contact) sensors for measuring vibrations/noise. Suppose an object produces sound up to 5khz in frequency, then in order to capture this information my piezo sensor would ...
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1answer
57 views

Serial filtering using FFT

lets say I have 3 audio filters for a realtime DSP application. For simplictity each has length 256 (as well as the input signal). The filters should work in series. Starting with filter IR h1(n) and ...
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1answer
61 views

Frequency estimation of circularly shifted single tone signal

I have a discrete signal $y[n] = <e^{j ~ 2 \pi f ~ n}>_J + ~w[n]$ with $n \in [0, N[$ and $w[n]$ AWGN, $<x[n]>_K$ denotes the signal $x[n]$ circularly shifted by $K$ samples. Let's define $...
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2answers
118 views

Higher-order Kronecker product

I am trying to generate a 2D DFT matrix in matlab, which I need for 2D compressed sensing (CS) problems. Lets say $N_1=8$, $N_2=16$, then according to the requirement of CS, to generate a 2D DFT ...
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75 views

How to do FFT fractional time delay (SOLVED)

I am trying to time-shift a signal using the FFT, however I have encountered some strange effects that depend on the size of the time-shift. I need to be able to shift the time by an arbitrary amount -...
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945 views

FFT of ecg signals

Could anybody tell me why should zi made FFT for ecg signals? For me it seems more simple to use time-domain, but I saw some ecgs in frequency domain and I don.t know how to interpret the results. ...
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325 views

Matching LPC frequency response to raw sample data frequency response

Background: The intention is feature/formant extraction from speech input. I have used an FFT on raw samples in the past and have done simple peak picking from a weighted average of frequencies over ...
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1answer
4k views

Finding phase angle via FFT

I am using the FFT to calculate the amplitude and phase of AC cos signal. Regarding amplitude it gives me an accurate result but I get wrong result for a phase: 6 degrees instead of 36 degrees. My ...
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1answer
93 views

Inverse FFT - synch the phase

Is there any way to synchronise phase of output of inverse DFT in each buffer? When I send the output of inverse DFT to the speaker it sounds nasty. Of course I know the „windowing functions” but it ...
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1answer
127 views

Precompute parts of an FFT on streamed data inputs

I've implemented Radix-2 & Radix-4, DIT & DIF variants of the cooley-tukey FFT algorithm and they perform well on test data. Now for a project, my algorithms will be applied to a real-time ...
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2answers
157 views

How to determine the original size of the FFT used in unknown OFDM symbol

Given an unknown OFDM symbol consisting of 9144 samples, interested to know the size of the FFT used in the TX/Number of bins. Down-sampling to 512,256,128,64,32 yields the following. Do not see how ...
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765 views

Verification of all steps needed to extract MFCCs from raw audio data

I need some verification on steps required to extract MFCCs from raw audio as I'm finding that some sources outline them slightly differently. Get raw audio frame Run window function (eg Blackman) on ...
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1answer
349 views

Filtering odd and even frequencies

I consider a signal of length $N = 2^n$ for some $n$. I want to derive two signal from it, one containing only the odd frequencies and one only the even frequencies. Each of these signals have length $...
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61 views

Manually creating a lowpass filter from the frequency domain: what phase?

In an attempt to gain a better understanding of DSP, I want to create a very simple (1D) lowpass, or I think more correctly "stop-band" or "band-reject" filter, to filter out a single frequency, e.g., ...
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1k views

MATLAB : How to filter a data signal

I have a data signal (column vector) with N values taken over at specific sample rate (dx) at a fixed frequency. After taking the Fourrier transform of this signal and representing it in the Fourier ...
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393 views

What is the effect of the natural logarithm in the frequency domain?

I have read that taking the natural logarithm of a signal $x$ in the time domain will introduce a spectral broadening and hence "up-sampling" process before the logarithm is required. I tried to test ...
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153 views

FFT of triangular wave

I am new in dsp.. so please bear with me. I want to plot FFT of a triangular wave. I am using the code below to first generate the triangular wave and then take its FFT ...
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16 views

Detection time of a spur using FFT?

Say I have the following parameters, NFFT=2^14 Fs= 50 MHz main signal @ 22 MHz and its alias at 28 MHz at signal power -40 dbfs and a spur @ 2 MHz and its alias at 48 MHz Leave aside the alias's. ...
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1k views

Extracting peak frequencies using FFT vs. time-domain peak finding

I am trying to compare two processing algorithms that I believe should be producing very similar results. I am processing acceleration signals over the course of the day and we expect to see a ...
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872 views

DFT and multiplication/convolution equivalence

Is there a simple or potentially intuitive explanation for, with the DFT, vector multiplication in one domain being equivalent to circular convolution of the transforms of the vectors in the other ...
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855 views

harmonics of a signal and FFT

Consider that we have a discrete signal of finite length. How can we find the amplitude and phase corresponding to different harmonics of this signal in Matlab? Thanks.