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

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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
43 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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0answers
74 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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0answers
28 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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0answers
34 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
55 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
52 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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0answers
41 views

Not obtaining conjugate symmetry

In Matlab, I have set up input cosine signals with different frequencies and also time delayed versions of the signal. The idea is that a time delay would produce a phase shift in the frequency domain ...
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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
57 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
34 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
69 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
100 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
72 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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0answers
25 views

Matching Two sound waves

Am new in IOS.Anybody please help me to comparing two audio signals(files-1.recorded file,2.original file) with step by step proceedure.I heard about Acceleratedframework.Is accelerated framework is ...
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1answer
54 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
110 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 ...
3
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3answers
457 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
41 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 ...
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1answer
77 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
42 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 ...
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3answers
227 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
45 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
66 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
73 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 ...
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2answers
44 views

Amplifying part of a signal

If I want to amplify a certain frequency in a digital signal, can I just take the FFT, increase the real part of the value for the frequency I want (leaving the imaginary part alone), and then take ...
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0answers
38 views

Ads detection using MFCC and DTW

I am doing a project to detect Advertisements from transmission by using clipped segment (slogan) of an advertisement, based on looking at the audio track as follows: Audio Signal $\rightarrow$ ...
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2answers
99 views

Created Matlab echo signal: Is it an actual “echo?” Or am I just manipulating the signal to make it seem like an echo?

This is just an outline of what I did (assume that all my dimensions fit): ...
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0answers
54 views

Noise analysis with periodogram. problem with different resolutions

I don't understand what happened in my simulation. I would like to perform a trade off between 2 ways to estimate power in frequency bands. I want to detect spurious frequencies. First method: I ...
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2answers
62 views

Implementing Short Time Fourier Tranform

I have a 512 sample frame, lets call it X. The frame is further divided into four sub-frames of 128 samples each. Each of these sub-frames have a different ...
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1answer
77 views

Calculating the Power spectral density

I've already asked this question on SO, but didn't get an answer, I tqake a shot here. I am trying to get the PSD of a real data set by making use of fftw3 ...
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1answer
66 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
66 views

Software defined radio panadapter

I am trying to make a panadapter for a software defined radio and I am a little bit stuck and hope someone can help me. I have an I Q signal from my radio. (Actually I am using an IQ wav file from ...
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2answers
61 views

Verifying channel response identity

If $x[n]$ is input signal, $y[m]$ is output signal, $h[m]$ is impulse response of the channel, then the following relation holds $\lvert Y(\omega)\rvert = \lvert H(\omega)\rvert^2 . \lvert ...
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0answers
38 views

Looking for an algorithm that computes weighted average of frequencies intensity from narrow band in spectrograph

I am searching for the algorithm that takes (audio) signal as an input and outputs weighted intensity of the frequencies of some narrow band (axis X) in time (axis Y). Frequency in the middle of that ...
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1answer
64 views

Determine frequency content of variable rate signal

What is the proper way to calculate the frequency content or spectrum of a signal with a variable (but measured) sample rate? I.e. get similar results as you would from an FFT, but for data not ...
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1answer
65 views

2D FFT of image and sharpness

I'm trying to make some simply autofocus algorithm for my device and pretty confused with 2D FFT results. As I know for now - number of high-frequency's components in 2D FFT will say me that image is ...
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2answers
76 views

What is the rate of change of amplitude? Frequency?

I know that frequency is not the same as the rate of change of amplitude, but why? Surely a high frequency is when your amplitude changes rapidly. Does an FFT perform something similar to ...
0
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1answer
80 views

how can I analyze a basic sine wave for its frequency phase and amplitude at a particular point in time in matlab

How can I analyze a basic sine wave for its frequency phase and amplitude at a particular point in time in MATLAB? Are there any tools to do that? I am trying to do additive synthesis of inharmonic ...
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0answers
112 views

filtering out specific waves in scattering pattern

I have the following (experimental) image, with its correponding raw data in .csv format here. The pattern represents the scattering of a laser field off a point defect located in the center. One ...
0
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1answer
55 views

What are some ways to detect the fundamental frequency in a signal using without using FFT?

I am trying to estimate the fundamental frequency in a signal to corroborate the result which I have got by FPGA implementation of an FFT algorithm. Hence, could someone give me some idea how to do ...
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0answers
55 views

DSP Demodulation advice sought - please help

my field of engineering is condition monitoring. I use vibration analysis to determine the current state of health of a machine and then recommend any course of action required to ensure it does not ...
3
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2answers
105 views

At which point in the signal processing chain to use Hann Window?

I have a question about signal processing. Experienced with embedded design and code, but DSP is in new territory. Thus far I am using the CMSIS DSP library functions, which are working well. I am ...
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1answer
52 views

deciphering the frequency response from the input data

Newbie to Signal processing, sorry if the question is basic. I have a data set consisting of 601 values. The values being time Vs voltage . The voltage values have transients in them. My aim is to ...
1
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2answers
100 views

Image Reconstruction:Phase vs. Magnitude

Figure 1.(c) shows the Test image reconstructed from MAGNITUDE spectrum only. We can say that the intensity values of LOW frequency pixels are comparatively more than HIGH frequency pixels. Figure ...
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1answer
67 views

FFT filter to remove cd scratch

I have a .wav file which came off of a cd with a scratch, so there is a periodic "clicking" of about 6 Hz. I was playing around with trying to squash the clicking by taking FFT and filtering the ...