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

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what is the significance of pilot carriers in ofdm

in an OFDM system having a radix two FFT (Say N=64) . all of these sub-carriers are not utilized. while some of the carriers are nulls to prevent leakage in to adjacent bands, say a four to five ...
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46 views

Overlapping with flat-top window MATLAB

I am applying a flat-top window to signal because I am very interested in its actual amplitude in the time-domain. I have read that overlapping will improve results. I am using MATLAB and the ...
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32 views

Flat-Top Window

I am calculating the velocity of a moving table (Vs) whose motion is sinusoidal by using an encoder connected to a motor shaft. On this moving table I have a lattice tower on which are mounted a ...
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1answer
24 views

What is the significance of the DFT in SC-FDMA systems?

Long term evolution (LTE) systems use single-carrier frequency division multiplex (SC-FDMA) in the uplink. In such a system, there is a DFT block and a sub carrier mapping block before the IFFT block. ...
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124 views

Is there a way to further optimise my FFT?

I've written my own FFT but wanted to know if there was perhaps a way to combine the Cooley and Turkey methods. So far I've got N/2 log N real multiplies for transforming a real signal. My current ...
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50 views

Recursive version of DFT as presented in Cooley-Tukey paper

The seminal paper of Cooley and Tukey provides an iterative method for computing the DFT for a sequence of length $N$. Specifically, they mention a method which utilizes the fact that $N$ can be ...
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1answer
77 views

Compare Overlapping FFTs to a longer FFT

How would you compare the SNR gain from a longer FFT (more samples) to overlapping FFTs? Given the choice, which one would you pick and why? Update: Suppose you have 2048 samples of a signal. ...
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1answer
20 views

Determining effect of powers of DFT matrix conjugate on input without multiplying

Suppose I have a DFT matrix $F$ of dimensions $N \times N$ where $N$ is a power of $2$. I convert it into a unitary matrix $\displaystyle U = \frac{F}{\sqrt{N}}$ and compute $S = U^* U^* $. $S$ ...
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24 views

The error between the theoretical value and the simulation value of imaginary part of the FFT results

As we know, a complex analytic signal can be obtained through Fourier transformation of a real value function, and the imaginary part can be reconstructed by Hilbert transform of real part. But I have ...
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25 views

Error tolerance for MUSIC (Multiple Signal Classification)

I would like to know if there is rule about how much can a matrix X-hat deviate from original matrix X $$\epsilon \le ||X -\hat{X}||_2$$ for MUSIC algorithm to still work. $$\hat{X} = X + Noise$$ I ...
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1answer
81 views

Is it customary to correct for the gain of a window?

Consider how the Hanning window is defined: 0.5 - 0.5 * cos(n*2*Pi/(N-1)) By this definition, it has a gain of 0.5, which is simply the average value of the ...
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49 views

fft magnitude scaling

I use the following code to calculate the fft of 1024 samples of a 200 Hz windowed sinusoid (code taken from aurio touch apple example app): ...
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3answers
91 views

About Discrete Fourier Transform vs. Discrete Fourier Series

I am new to the field of signal processing. I am wondering what is the difference between DFS(Fourier Series) vs. DFT(Fourier Transform). For common applications, usually we get a segment(length ...
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2answers
61 views

Thoretically, what makes multi-pitch detection so difficult?

For multi-pitch detection, I mean for example pressing several piano keys at the same time. For signal pitch detection (pressing one key at a time), after FFT, mostly the frequency with the largest ...
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2answers
70 views

Best method to do piano key pitch detection?

For example, when playing piano, at the same time, print out the key notes by analyzing the signal of piano sound. How to do some pre-processing to remove the noise? When calculate with FFT, noise ...
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0answers
19 views

Analysis and algorithmic complexity of the Constant Q transform

Here I am again (Implementation of the constant Q transform + property questions) :) I was reading this paper on a constant-q transform algorithm, where they managed to turn the following equation ...
2
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1answer
52 views

Memory requirements for FFT

I have a system with limited memory. So basically the question is this: If I have (say) 24KB of data space and 4096 data samples of single precision floats (16KB) can I do an FFT on the data? More ...
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2answers
91 views

Calculation of sampling rate and its effect on an Image?

I know that for a given signal, the sampling frequency $F_s$ must be twice or more than maximum frequency of the signal $F_m$. It is easy to understand the concept for a 1D signal. But I don't know ...
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16 views

what's the appropriate signal/noise ratio(SNR) if a mixed-signal(periodic signals plus noise) looks mostly like noise?

I'm new to DSP. My confusion is: if we get a mixed signal, we can use FFT or spectrum analysis to visually know the signal consists of some sin signals on low-frequency and middle-frequency, and ...
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1answer
49 views

FFT on XY data points

Are there any algorithms out there that can do a FFT of 2D or XY data (not sure of the exact terminology here), I don't mean XY data like in a graph I mean XY/2D data points like a circle or a smiley ...
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3answers
63 views

Rendering a spectrogram of audio data - resulting magnitudes are all too close together

I'm working on creating an application which will render a spectrogram of the audio in an MP3 file. I'm having some trouble, though - after running the audio samples through my program, the resulting ...
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2answers
42 views

phase angle of harmonic

I have generated sinsuoids containing fundamental with harmonics using C++. Fundamental frequency is 50 Hz and each of the harmonic has phase offset of 60 degrees. I have applied flattop window before ...
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1answer
61 views

Simple fft to Gaussian pulse with MATLAB

trying simply to create femtosecond pulse in MATLAB exactly like in the attached image, the carrier frequency is around 374THz, and my sampling frequency is 10 times the carrier. The results of ...
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2answers
126 views

Plotting Real Amplitude of Sine Wave in FFT

Consider a sine wave having an amplitude of 9 and a frequency of 0.3 Hz. I wish to perform an fft and plot the frequency on the x-axis and the real amplitude (i.e. 9) on the y-axis. I am using the ...
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1answer
45 views

Matlab FFT keeps plotting mirrored values

My Matlab FFT plot keeps showing the mirrored values of my frequency of interest. In this example I am looking for 250Hz with a 3200Hz sampling freq. The FFT plots my value at 266Hz as well as 1330 ...
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76 views

Get Mirrored FFT Results in Real part

Ok, I'm new to the whole Dsp thing, so sorry if the question is a lame one I'm trying to extract frequencies from a signal provided by a radio Device (Win Radio G31DDC- IFstream). The radio provides ...
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34 views

how to comparing two audio signals?

I know this question has been asked in so many places but I can't still figure out how to solve this. I have two audio signals of breathing. One is a healthy breathing and it is saved inside the ...
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35 views

Comparing vibration frequencies

I have two iron pipes, one bent and cracked, and one whole. On one end Ive attached a vibration motor (200hz) and on the other end Ive attached a vibration sensor. I do a fft and then get out the ...
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1answer
57 views

How to reconstruct the signal which is subjected to FIR filtering - Matlab

I have a signal $x$ which is corrupted by Gaussian noise. The signal $x$ is convolved with a filter with coefficients $h = [1, -2, 1]$, to generate signal $y$. Now the signal is taken to Discrete ...
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1answer
58 views

FFT analysis of binned data of different length

I am conducting experiments to collect wind speed data from wind anemometers placed on a moving platform. Closely, there is a fixed wind mast holding a wind vane. Prior to analysing the wind data from ...
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1answer
77 views

Can I ignore the Nyquist criterion?

If I have a signal with frequencies up to 2000 Hz but I'm only interested in the frequency range up to 500 Hz, is it correct to sample at 1000 Hz $(f_\mathrm s \geq 2 \cdot f_\mathrm{max})$? Or do I ...
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1answer
58 views

FFT of signals with different sampling frequency

I am trying to combine two sets of data together, each of them having different sampling rates. For example if I sampled a 100 Hz sin wave at 1KSPS, and another 150Hz sin wave at 1.5KSPS, would it be ...
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4answers
119 views

Selectively improve the frequency resolution of FFT (DFT)

I have a digitally sampled signal(sampling frequency = 4000 Hz) which contains analog frequencies from 0 to 1000 Hz. I wish to have a frequency resolution of 100 Hz(like 0,100,200,300 Hz .. 1000 Hz) ...
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1answer
62 views

How to calculate bandwidth require for OFDM

I read LTE PHY profile and do not understand the relationship between number of FFT and bandwidth. For example LTE downlink channel bandwidth 1.25MHz and 5MHz have 128 FFTs and 512 FFTs accordingly. ...
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2answers
74 views

Why are window functions used when calculating spectral estimates, really?

Having just read the rather long article on Wikipedia about window functions, I still do not see the mathematical point in using window functions when calculating spectral estimates (using e.g. ...
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1answer
106 views

Is the periodogram squared-magnitude DFT or squared-average DFT?

How is the periodogram defined? I have been searching the internet a lot, and I find two different definitions: periodogram is the squared magnitude of the DFT periodogram is the squared average of ...
2
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1answer
75 views

How does the number of frequency-domain sampling points influence the outcome of an inverse FFT?

Given some frequency-domain representation of an impulse response. How does the number of frequency-domain sampling points influence the outcome of an inverse FFT, if I keep the sampling frequency ...
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1answer
56 views

Crash course on turning engineering formulae into computer code?

I'm trying to teach myself about the basics of feature extraction from digital signals. Specifically, I want to try monophonic then polyphonic pitch recognition. I don't have any university level math ...
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0answers
124 views

How to estimate PSD, and time delay of a random signal?

I'm trying to estimate the power spectrum and time delay for random signals. the signals were taken from two sensors, 10 cm apart. My aim is to estimate the PSD first then estimate the time delay in ...
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3answers
470 views

disadvantages of FFT, it can not extract enough frequencies without enough samples

Let's say sampling rate is $Fs = 44\mathtt{kHz}$, now I have $N = 2048$ samples, then I can get $N/2 + 1 = 1025$ frequencies. I'm confused by Matlab's FFT documentation that says the frequencies are ...
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0answers
45 views

Using Fourier Transform on Gyroscope

The original idea is to calculate distance from accelerometer input. However, accelerometer reading also contains the gravitational values, thus to remove gravity, I tried using Gyroscope. The idea ...
0
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1answer
87 views

Frequency response of a filter - fft vs. freqz

I have designed my filter using firhalfband(N,Fo,A), which gives me the filter coefficients. Then I try to see the frequency response of it. I use these two ...
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2answers
30 views

Color artifacts in Fourier transformed image

I am working with images and Fourier transforms. I am trying to understand what might be causing some artifacts in my output image. I am starting with a 512x512, RGB image of Lenna. I FFT the ...
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2answers
56 views

Doppler Frequency Resolution for Radar

Doppler frequency is calculated by the formula $f_{d} = 2*v_{r}/\lambda$, where $v_{r}$ is the radial velocity and $\lambda$ is the radar wavelength. Normally FFT is used to detect the doppler ...
2
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3answers
243 views

Number of FFT points required for a specific frequency resolution for an oversampled signal

I have a bandpass signal centered at 2 MHz and bandwidth of 50 kHz (the signal frequency varies from 2 MHz - 25 kHz to 2 MHz + 25 kHz). This signal is being sampled at 10 MHz. I want a frequency ...
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1answer
72 views

Writing a Discrete Fourier Transform program

I would like to write a DFT program using FFT. This is actually used for very large matrix-vector multiplication (10^8 * 10^8), which is simplified to a vector-to-vector convolution, and further ...
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1answer
46 views

What Information does the phase of a cross power spectra give me?

I obtain the cross power spectra by the following steps: compute the FFT of signal A and B Multiply A with the conjugate of B store it in C (cross power spectra) Now looking at the Phase of this ...
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2answers
86 views

Running an FFT filter on a large data set

I have a non realtime application where I need to run a bandpass FFT filter on a data array of between 5k and 10k data points. Do I break it up into (say) 256 point chunks, run the FFT on that and ...
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1answer
77 views

FFT Matlab - Meaning of Frequency Vector

I'm following a tutorial about the FFT. It's well explained but I don't understand the meaning of the frequency vector: ...
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1answer
83 views

How to remove background noise from sound file for analysis

I'm working on a project at my university and it involves background noise recognition/classification. I'm very new to this so I'm unsure what to really search/google or where to really begin any ...