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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2answers
916 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.
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1answer
194 views
FFT Heart Rate Monitor on Arduino
Part of my project is to build heart rate monitor from Nano and a PulseSensor. I am having trouble working with the Fast Fourier Transform part of the code.
This code here is from a library (...
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0answers
400 views
Python tool for time-frequency analysis
I am trying to perform time-frequency analyses using the PyWavelets (pywt) toolkit for python. My ultimate goal is to perform time-frequency analyses for EEG signals but I am starting with something ...
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1answer
336 views
Image zooming with Fourier transform
I want to go from this image
into this one:
So basically I need to scale the white square. The authors of the paper claim that this can be done in four steps:
zero-padding in real space (image is ...
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1answer
2k views
Comparing Welch and FFT power spectrum density
Based on previous answers from the forum, I implemented a function to compute the Power Spectrum of a 1D time series.
...
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1answer
80 views
Break a signal into segments, add them together and then perform an FFT on the result
If you break a 4 second signal into 0.5 second segments, add them together and then perform an FFT on the resultant 0.5 second data.
Will the FFT / frequency spectrum be the simlar to an FFT on the ...
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2answers
82 views
Matlab and R functions for fft(): N-point FFT and dimension issue [closed]
In MATLAB, Y = fft(X,n,dim) returns the Fourier transform along the dimension dim. For example, if ...
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1answer
1k views
Realize Simulink block “Ideal ADC Quantizer” in Matlab
Yesterday I posted following topic: "FFT alternates '0' for a quantized SIN wave".
During post editing I was perturbed by some affair, I didn't formulate correctly the problem. So, my post was blocked ...
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1answer
192 views
Pitch detection algorithms “give up” after very little
I'm sorry if pitch detection has become a stale topic here, but I'm really interested if anyone has any advice on this topic. I'm looking for the best pitch detection algorithm for stringed ...
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2answers
1k views
How to “rotate the phase”?
I have problem, not sure how to call it but I think it's something called "phase rotating", but not sure.
I make fast Fourier transform on simply square wave, and then I make inverse fast Fourier ...
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6answers
5k views
Is there any practical application for performing a double Fourier transform? …or an inverse Fourier transform on a time-domain input?
In mathematics you can take the double derivative, or double integral of a function. There are many cases where performing a double derivative models a practical real-world situation, like finding the ...
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1answer
53 views
Meaning of a formula about transient frequency bins
I'm trying to understand the following formula in this paper:
Sadly, the paper does not define most of the symbols it is using, so my guesses so far are:
$T_{tr}$ refers to the sampling interval
i....
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1answer
142 views
Could you please confirm my method or correct me on computing the phases of my signals?
I did some measurements, and I have two received signals in two different distances.
By doing the fft on the signals, I have the spectrum, then by using the angle() function in MATLAB on my fft, I ...
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2answers
150 views
Explain Auto-Tune in a simple way
I have to do a presentation about Auto-Tune and its relation to the Fourier transform. What is a good explanation on how does Auto-Tune work?
3
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2answers
3k views
Correlation Using FFT / IFFT (Convolution in Frequency Domain) in Java
I try to find about the delay between two audio files using Cross Correlation in Java. I've already done this algorithm so far that i get a idea about how many samples is the delay.
FFT x1 -> Zero ...
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1answer
808 views
Cross Correlation in Java (Android) Using FFT (Frequency Domain Convolution / Correlation)
I want to implement cross-correlation with the start-symbol and the signal using FFT.
I zero-pad both signals to length N = x.len + y.len -1
Using the convolution theorem:
...
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1answer
252 views
Power spectrum RMS or peak
I’m a newbie and wondering if I calculate the power spectrum from the peak amplitude or from the amplitude rms ?
This is my matlab script so far:
...
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1answer
23 views
Matlab applying an FIR filter to a signal, generated in Matlab
I want to create an FIR in Matlab and apply it to a signal (also generated in Matlab). You will find the code below. I will put my questions in order from here.
1) The filter coefficients vector "b" ...
0
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1answer
73 views
Improvement of SNR by sampling different number of cycles using FFT of a fixed length singal
My question relates to Fourier transform of signals with different lengths in time but the same fixed length of the digitized signal with different sampling rates.
Specifically, how does the number ...
0
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1answer
80 views
How to get the MLSEEqualizer work with IFFT and FFT blocks in the communication system?
Matlab MLSEE equalizer works fine with the QPSK modulated signal when the signal is propagated
over the multipath channel. However, if there are IFFT and FFT blocks used at TX and RX sides, ...
0
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1answer
4k views
Fourier Transform of a Pulse Train (Frequency Comb Simulation)
I am trying to take a Fourier transform of a femtosecond pulse train and plot the frequency spectrum.
I followed this question and am able to create a pulse train and plot both the time and frequency ...
0
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1answer
28 views
Aliasing correspondance with respect to DFT
Given a sampling frequency Fs lets say we plot the magnitude of the fft of a temporal signal $x$, for different frequencies above the Nyquist frequency, to show the effect of aliasing:
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1answer
69 views
Harmonics in Quantal Histogram
I'm studying what I believe to be a system that produces a (noisy) quantal response (i.e. there should be a minimum increment of response). To do this, I've plotted a histogram of some ~6000 amplitude ...
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2answers
746 views
why Sampling with higher than nyquist frequency is causing aliasing?
fm=20000 and I am sampling following signal at 65000 Hz:
...
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0answers
8 views
Obtain points in signals which cause correlation
I've got two large .wav files (tens or hundreds of minutes each). I know that at some points these files contain very similar areas - actually, these areas are the ...
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2answers
40 views
Why there is error between My DFT and built in Matlab FFT?
I'm trying to implement DFT/IDFT and FFT/IFFT in Matlab and C.
I got wrong values while I implement IDFT/IFFT. So I'm trying to find a mistake.
Just for DFT, I used this algorithm to implement it in ...
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4answers
218 views
How to see the amplitude of each frequency?
do you know software that exports spectrograms to images of 500x22000 pixels?
all the spectrograms that I know show diffused frequencies and it does not look very good
I just want to see the amplitude ...
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0answers
37 views
FFT Amplitude Resolution
What's the relationship between sample rate, sample length, ADC quantization, and FFT output amplitude resolution?
Suppose I have N samples, sampled at Fs such that I can use a radix-2 FFT. My ADC ...
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0answers
16 views
What is wrong with band passing by inverse Fourier transforming a section of a signal's frequency spectrum? [duplicate]
If the question is unclear, here is what I mean in Python using scipy.fftpack:
ifft(fft(arr)[x:y], len(arr))
What is wrong with this method of band passing?
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3answers
702 views
How do I calculate peak amplitude of the signal components after zero padding and FFT?
I am learning about DFT and trying to apply it to some audio processing. I am new to DSP but experienced in programming and have some background in math and physics. The FFT algorithm I use (lomontFFT)...
4
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3answers
22k views
Calculating values of frequency bins in Python
I have to use FFT to determine the period of waves inside a signal. After applying FFT on a window of 10000 point from a signal, I get something like this:
What I don't understand is that FFT is ...
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2answers
55 views
How to select the sampling frequency when the input signal frequency is not known
I am trying to observe the noise produced by UPS present in our lab, under no load (a normal running condition when its power is on). As I don't know its frequency range, I have randomly chosen 4 ...
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1answer
210 views
What Are the Suggested Resources for Extensive Knowledge About the Fourier Transform (DFT, FFT, etc…)? [closed]
I would like to improve my knowledge about Fourier Transform related subjects.
What are the recommended resources in order to self study about it?
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3answers
4k views
Interpreting the FFT results of a structural vibration problem
System: Cantilever beam type models, with an accelerometer on the end. The beam base is excited at various frequencies in harmonic fashion on a shake table. This results in vibration in the beam. The ...
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2answers
91 views
Multiple different length Windows for high resolution realtime FFT
I am looking at trying to achieve a 'realtime' (as quick as possible to acquire, process and present data) FFT application to analyse audio.
I have setup my app to acquire a set of samples, apply a ...
0
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1answer
615 views
frequency domain zero padding in OFDM
I have a matlab code for OFDM system, in this code the auther added a zero padded subcarriers before the IFFT stage, in the middle of the raws, and added zero padded guard interval after IFFT, my ...
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vote
3answers
1k views
How do I perform Spectral Analysis (FFT, Windowing, Detrending) on Sonic Anemometer Data?
I am having trouble with all of the forums that I have looked at thus far.
I have one day's worth of Sonic Anemometer data. I want to see the spectral analysis of this data. When the anemometer data ...
0
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1answer
356 views
FFT and Power Spectrum Normalization
On many websites, including MathWorks, it was suggested to normalize the fft spectrum (MATLAB or numpy) by dividing it by the total number of samples ($N$). For a sinusoidal signal, for example:
$$x(...
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1answer
235 views
Applying a filter kernel defined by a continuous equation in the frequency domain
I have a filter kernel $K(\omega)$ completely defined in the frequency domain as a continuous function of angular frequency $\omega$. I know $K(\omega)$ defined as a continuous mathematical equation.
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2answers
128 views
Shifting signal smaller than discrete step
I have a image that I need to shift with less than a pixel.
My plan was to do a Fourier transform and multiply the signal with $e^{-aiu-biv}$ where $a, b$ are the shifts in x and y direction. This ...
4
votes
2answers
2k views
What is the right way to extract particular frequency phase information from FFT?
Signals acquisition:
Two proximity sensors are positioned Orthogonal to each other. These would be measuring the vibrations of a rotating shaft.
Problem:
Each of these 2 signals has two dominant ...
5
votes
2answers
3k views
Filter size vs. FFT size and Overlap add
First of all I would like to say that :
I'm new to DSP and in a "learning curve" hence the "basicness" of my questions.
I've read as many posts/articles as possible on the internet but still need "...
1
vote
3answers
116 views
Reverse engineering a digital filter
I have 2 simultaneous signals that both are designed to measure eye movements.
They are sampled at 250 Hz.
We have 12 subject recordings.
For 3 stable periods in each subject, we choose 256 points and ...
0
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0answers
22 views
improving performance of KNN classifier on FFT
I need to classify whether a product is passing or failing based on a noise check. I have 100 labeled "good" product and 100 "bad" product. For each, I recorded the sound for 3 seconds and each chunk ...
1
vote
3answers
369 views
Why is pitch detection necessary in pitch correction?
I am trying to understand the process of changing the pitch of a signal. After performing the FFT on a windowed signal, we have the frequency information for the signal. Why can we not simply change ...
3
votes
2answers
1k views
Problems Using FFT to Compute Impedance in a Model Neuron
I'm a neuroscientist currently investigating the resonance properties of a single neuron model that a colleague and I have constructed. The language we code in is Julia, which I hope is similar enough ...
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2answers
290 views
Calculate the harmonics in the power supply of $50\textrm{ Hz}$ using FFT
I need to calculate the harmonics in the power supply of $50\textrm{ Hz}$.
If suppose I need to calculate up to 20 harmonics.
Then my sampling frequency by Nyquist criteria should be :
$$f_s \ge 2 ...
0
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1answer
376 views
How to smooth (or interpolate) phase of FFT and reduce data points
I am writing some code for audio analysis, and have currently got two signals with FFT performed on them.
I get the phase of my complex array by using:
...
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2answers
66 views
Is spectral leakage normal for FFT?
I record a sample of 2000 data points, with a sampling rate of 40khz, so freq. resolution is 20hz. I multiplied the chunk of data with a Hanning window prior to doing the FFT.
I recorded a 1khz test ...
0
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2answers
97 views
Intermittent Harmonics, Is there a physical explanation?
I am doing some frequency analysis of a vibration signal from a spinning rotor,
I am expecting to see peaks corresponding to the rotational frequency of the rotor. So the fundamental frequency ...
