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

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Mathematical justification for zero padding?

This question asks what's the point of zero padding. The accepted answer is certainly very insightful, but I don't understand a big chunk of it: Zero padding allows one to use a longer FFT, which ...
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18 views

Calculating Phase Response for 2 microphones given the input

I want to measure and compare the phase response of two identical microphones. To do this, I have a pressure chamber, which allows to apply the same pressure to both microphones. I apply a sweeped ...
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0answers
15 views

Fourier transform of moving image sensor

Consider an image sensor that is moving with some velocity $\mathbf{v}(t) \in \mathbb{R^3}$, and an orientation $\mathbf{R}(t) \in SO(3)$. Treat those vectors as fixed. At a specific time $t$ the ...
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16 views

Which Frequency output is correct?

I have taken and modified the following code from this CodeProject article: https://dotnetfiddle.net/mVfT77 The following GUI test produces good results: https://dotnetfiddle.net/gV9akg Now, I ...
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1answer
28 views

Why can FFT only operate on images with specific properties?

Can FFT only operate on Grayscale images? If Yes, why? Can FFT only operate on images with dimensions of power of two? If Yes, why?
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1answer
32 views

MATLAB center frequency shift

I am wondering how to shift the center frequency of the below complex data from 0, to say 20 MHz (10 MHz to 30 MHz- 20 MHz bandwidth). I tried to change the indexing of the bins but I could not get ...
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1answer
42 views

The frequency response function (FRF) fails to detect the antiresonance of a system

I am trying to identify a vibrational systems by computing the frequency response function (FRF) of the system when a chirp signal is applied to its input. After comparing the FRF computed and the ...
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1answer
42 views

Butterworth filtering behaving unexpectedly -MATLAB

I'm new to signal processing but I'm trying to understand how the Butterworth filter works. To do so, I did the following: I assumed a sampling frequency of 100Hz and wanted to attentuate everything ...
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54 views

remove static noise from audio

I have a recording with a static noise added throughout the audio. the longest silence period I could extract was this: audio_file however, it contains some moments of new sounds of flipping pages. ...
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31 views

Is my approach for Splitting a magnitude across multiple bins correct?

I'm trying to synthesise a sine wave whose frequency is between bin centre frequencies per this post: Splitting a magnitude across multiple bins in an IFFT I'm trying to split my sine's magnitude ...
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1answer
38 views

What factors go into choosing DCT type 1 over type 2 or type 3 etc?

I'm a newcomer to the DCT, DFT etc. I understand that they're intrinsically related, I understand that the DCT tends to "compress" the information in a signal towards the first few bins, leaving the ...
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1answer
88 views

Splitting a magnitude across multiple bins in an IFFT

By Georg-Johann own work, CC BY-SA 3.0. I’m trying to synthesise a sine wave using an IFFT at a frequency between bin centre frequencies. Here are the details ...
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1answer
34 views

Finding the maximum and minimum frequency of a 2D image

Suppose I transform the image into frequency domain and obtain a 2D array of complex numbers. How can I determine the minimum and maximum frequency from that array? By finding magnitude of each ...
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1answer
36 views

PSD looks to clean/continuous

I generated an signal with a base frequency of $50\textrm{ Hz}$ and its harmonics and quantization noise in it (as an array in MATLAB). It's sampled fast enough to make sure there is no aliasing etc. ...
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0answers
17 views

When doing Fourier extrapolation how can I adjust the projection to give correct results?

In the answer to http://stackoverflow.com/questions/4479463/using-fourier-analysis-for-time-series-prediction there is a snippet of code for doing Fourier extrapolation. However, it only works ...
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2answers
60 views

How can I implement convolution in frequency domain?

Suppose, we have a bitmap image represented as a 2D integer array, int [,] image2D; whose FFT is Complex[,] fftImage2D; ...
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0answers
19 views

Quantifying patterns in the time-domain of a signal

I have a rather general question. Supposing I have 2 audio signals as seen in images 1 & 2 below, and when analyzing the power spectrum density of both signals, they are equal (i.e. the rms power ...
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0answers
35 views

Efficient computation of Chirp Z Transform

Chirp Z Transform (1, 2, 3) is more powerful than zooming techniques (I use it to actually trace non-stationary chirp signals) and very usable in signal processing, but it's flexibility comes at price ...
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0answers
10 views

Windowing the sequence to compute Correlation

I want to compute the Correlation Functions of the input and output time-domain sequence, ...
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0answers
16 views

amplitude of FFT analysis rotor encoder

I have 2 motors turning at the same speed (rotor encoder). I want to analyze their movement (rotation) in fft . If their axis of rotation was exactly at the center the FFT result should have been a ...
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0answers
16 views

generate 1D periodogram from noise spectrum

I have computed the noise power spectrum $S$ from an input image. Basically, I get spatial frequencies i.e. F (lower range = 0 , high range = some high value) and the corresponding noise values for ...
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0answers
46 views

Epilepsy seizure detection in EEG

I want to develop a method to detect the occurrence of epilepsy seizure in an EEG signal. I am using a large data set for number of patients so the algorithm has to detect the seizure in any of the ...
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2answers
34 views

Remove background noise from recording

I have a sample speech recording with background noise. I managed to extract part of the noise signal, and put the noise and the contaminated signal in the same plot. I have done fft-analysis on ...
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1answer
41 views

FFT spectrogram in log frequency space. How?

I was reading a paper and the authors say that they extract FFT spectrograms and log-scale in frequency domain. I understand how the general spectrogram is computed, but how to make it log-scale in ...
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2answers
66 views

Conversion into the Q31 Format

I have a Setup, where I receive 24-bit ADC samples in the two's complement in 8-bit chunks. Usually I just "converted" them into a signed 32-bit integer like this: ...
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1answer
69 views

Difference between a digital lock-in amplifier and a FFT when extracting phase of a signal?

I am trying to measure the relative phase of a sine wave fixed at a particular frequency in a noisy environment. My initial approach is to simply collect $N$ samples, take an FFT, and then just ...
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0answers
27 views

FFT in different coordinate systems

Is there a transformation that will enable one to calculate the FFT in an arbitrary coordinate system? What I am interested is the following two cases: The space is Euclidean and infinitely ...
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2answers
55 views

FFT over a fixed and equal numbers

I've got a vector of $100 000$ numbers. All numbers are equal ($7000$ for example). If I perform FFT over this vector, what will I get? From my understanding, I should receive a fixed DC line. Is ...
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1answer
67 views

Current harmonics via FFT — do peaks matter?

Typically, one would perform an FFT on a current waveform and measure it's magnitude at multiples of the line frequency (e.g. 50Hz, 60Hz) to get the harmonics, and subsequently the Total Harmonic ...
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2answers
88 views

Minimum bit-width for fixed point FFT outputs

I was wondering if there is a formula to determine what the best case (minimum) bit-width should be for the imaginary and real outputs of an fixed-point FFT, assuming an input bit width of $M$ ($M$ ...
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1answer
90 views

Positive and negative frequencies: how to prove they are independent?

This seems to be quite a basic question but is there some detailed proof why interference power (i.e., power spectral density) coming from the positive and negative frequencies are independent? I am ...
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1answer
34 views

Filtering/Analyzing Complex Data stream

I receive complex I and Q data from an USRP. I want to do a Hamming window LP filter on the data. However, I don't get the grasp of how I use the complex data. It is unusual because most of the time ...
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0answers
22 views

Frequency autocorrelation function - Communication channel

If we have two discrete stochastic spectra and each spectra has $N$ points. We want to calculate the autocorrelation of these spectra, what should be the number of points in the resulting ...
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1answer
30 views

Sub Band DFT response

With a DFT lets say I had a signal occupying 0Hz to 2048Hz and i am using 2048 bins. Can a DFT by design (say FFTW) only calculate the responses in a Sub Band like 768Hz to 1280Hz or -64Hz to -256Hz ...
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64 views

Extract parameters of a single harmonic

Context I need to extract the parameters of a single harmonic in a signal. For instance if $$ x(t) = A \sin (\omega_0t + d_0) + B \sin (\omega_2t + d_2) $$ then $f(x, \omega_0) = (A, d_0)$. This ...
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1answer
61 views

Complex Conjugate

If I have a complex spectrum and I add it to its complex conjugate will I get a zero phase version of the original? Will this also reduce noise? It seems like this is simply phase cancellation.
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17 views

How to calculate Fourier's coefficients of a $T$-periodic function with Scilab?

I have a vector of a size $N>1$ (it represents the values of a $T$-periodic function on a interval). I want to calculate its Fourier's coefficients with the fft, ...
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1answer
18 views

Can Sparse Fourier transform be used for sparse signal in other domain

I've read that sparse fast Fourier transform can be used to compute the Fourier transform of a signal that is sparse in frequency domain much faster compared to FFT. My question is that can SFFT be ...
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1answer
30 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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2answers
669 views

Why real part of FFT converts image into rotation + original?

I have read this image: taken its FFT (2D) and then Inverse FFT to get exactly the image back. Code is provided for reference: ...
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0answers
21 views

Motor Current Signal Analysis on a PWM Motor

My goal is to do a Motor Current signature analysis(MCSA) to detect any within a DC-motor.The Motor I am experimenting with, is driven and controlled using a PWM signal with supply PWM "frequency" is ...
3
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1answer
87 views

unexplainable aliases in spectrogram

My scope has 200 MHz bandwidth and can sample at 4GS/s I'm sampling a 138 MHz RF signal at 500 M Sa/s storing 14 M points. When I plot the spectogram in matlab I get the following spectrogram(Data,...
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1answer
52 views

Computation of Only Even or Odd Frequency Bins of DFT

I have an algorithm where I am computing the FFT of a large signal. However, I desire only the even or odd terms of the DFT of the signal, but not both. Currently, I discard these undesired terms. Is ...
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1answer
87 views

Determining the fundamental frequency/pitch of a note

What I am trying to achieve is getting the fundamental frequency of a note played by an instrument. What I have already done is performing an FFT on a samples of audio file, and here's what I get: ...
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3answers
62 views

Output signal length after fft

I am trying to understand the functionality of fft.m in matlab . For example: if I input a signal of length $7$, and use the FFT function, the output is of the ...
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1answer
42 views

Division of complex signal by frequency response

I have a measured signal (time domain) which i take the fft of. I have a measured frequency dependent sensitivity (magnitude and phase (radians) as a function of frequency) which I need to apply to ...
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1answer
44 views

How do I measure frequency of an audio file into an array?

So I know how to plot fft the audio file within Matlab and a window pops up. My question is, what next? I want to know how to go about measuring the frequency(s). I have two similar audio files, of ...
1
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1answer
30 views

sinus generation and it's fft in radians

I'm trying to generate sine signal and display it's fft in radians, byt I meet several issues that I can't understand. Please find my script below: ...
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0answers
29 views

How to calibrate two microphones to same frequency range

I am recording stereo with two same microphones but they are physically insulated from eachother and have some additions on sound input side. Not to complicate story, I have a human head simulation ...