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

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Determination of cut-off frequency using power spectral density

I am new to DSP and my question is a very simple one. It is about determining the right cut-off frequency. I calculate the power spectral density using FFT by Welch's algorithm. However I am confused ...
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1answer
48 views

Can I take piecewise FFT of a larger input sample?

I have a N point sequence x. Let X be the fft(x). (Assume x is arbitrary) where, x=[x1 x2 x3 x4 x5 x6 x7 x8] fft(x)=[X1 X2 X3 X4 X5 X6 X7 X8] How do I get the ...
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1answer
31 views

Sub pixel shift causes weird results

I am trying to shift an image on a subpixel level, with the method described here: ...
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21 views

Choosing the frequency for a comb filter

I have an audio sample. From doing FFT on it it looks as if I need to use a comb filter to remove resonant frequencies. This is what I generate: I honestly have no clue where to start ...
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1answer
86 views

Why does FFT generate a jaggedy signal

I have an application that fills a buffer from my computer's microphone and does an FFT. My objective is to figure out what frequencies are in the sample. I've tested the application by whistling as ...
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1answer
33 views

The Nyquist-Theorm behind the fft

I saw a code in Python in the scipy.org (http://docs.scipy.org/doc/scipy-dev/reference/tutorial/fftpack.html) and found this: First question: Is it right that T = 1/800 <==> fs = 800 Hz fulfill ...
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25 views

How to simulate two OFDM Users with low complexity FFT/IFFT?

have two User one of them sending over freq (0-B] and the other transmit over (B-2B]. Both of them are using OFDM and each one has Nc subcarriers. I wanted to simulate the received signal using ...
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18 views

Subscripted assignment dimension mismatch error while doing FFT processing Overlap Save Method

I don't know why this happens The code works fine for L = 5 only however I need to be able to vary L without issues here is my code ...
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3answers
101 views

What is the difference between general microprocessors, DSP and FFT chips?

I know that a general purpose microprocessor requires 18 operations to perform each butterfly of the FFT, but I do not understand how does using using a DSP or FFT chip improve FFT processing? Any ...
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34 views

How would you select the top n frequency of a sample from a noisy audio file?

I am trying to select the top n frequency spectrum from a wav file for my feature vector ...
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40 views

to find transfer function for experimental data and check its correctness

http://www.sciencedirect.com/science/article/pii/0167610587900225 http://www.sciencedirect.com/science/article/pii/0167610579900266 paper which i refered for calibration of pressure sensors i want to ...
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1answer
34 views

What is the distance metric in dynamic time warping?

I am reading the lecture slides from this site http://luthuli.cs.uiuc.edu/~daf/courses/CS-498-DAF-P/Lecture%2018%20-%20Time%20series,%20DTW.pdf In slide 24, the lecture suggest using metric of the ...
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1answer
31 views

Why do we need to normalize a WAV file before calculating the FFT?

I am trying to calculate the FFT of a signal stored in a WAV file using SciPy. I found a solution here, but it seems like we need to perform this step before the FFT: ...
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3answers
82 views

Why does an 8 point DFT behave differently from a 16 point?

I have a 50 Hz sine wave sampled at 1600 Samples/second.I'm computing the 16 point DFT.So my fundamental frequency is 100 Hz. I then decimated the 1600 samples to 400 samples.I then computed the 8 ...
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29 views

Windowed FFT vs Morlet

I wonder if there is a difference between taking a Wavelet Transform on a signal s using a Morlet Wavelet w (i.e. correlation between s and w) and taking the Fourier Transform on subsequent parts of s ...
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0answers
23 views

Filtering of accelerometers data for double integration

This question in strictly related to this one http://scicomp.stackexchange.com/questions/16057/numerical-integration-and-filtering-of-acceleration-experimental-data but in this case I would like to ...
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2answers
44 views

Singal processing for undersampled signal

I have got a set of pressure data from a boiler which has been sampled at 45Hz and I need to extract a frequency component of 250Hz from the signal. Using a standard FFT method doesn't display ...
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19 views

FFT scaling in GNU Radio

In GNU Radio Companion, I have created a very simple flow graph where I generate a 1 kHz, 2.0 volts peak-to-peak sine wave, and feed it into an FFT sink and a time domain sink. The reference dB in ...
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33 views

How to, efficiently, identify telephone number from the key pressed data audio file?

A very common homework question. You are given an audio file(.wav) which has the recording of the keys pressed during a telephone call. You have to identify the telephone number from this audio file ...
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28 views

Mind helping me understand what this matlab code is doing? is this a PSD? or FFT?

I'm trying to learn how to get a useful frequency response of a single plucked string on a guitar. I have some old code that I'm working off of... It works in that i get a spectral response, but i ...
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56 views

Detect Frequency of Incoming Audio on Raspberry Pi

I've been lurking around these forums for a while and they've been a great help to me in the past. However, I've been researching this problem for the past 2 days or so and can't seem to find a ...
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33 views

Reducing latency due to FFT windowing for a real-time signal

I need to compute the amplitude of a certain frequency band as the input to a PID algorithm. My system looks like this: ...
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0answers
21 views

Best way to reduce data to its symmetric and antisymmetric components

I have some noisy data that looks like this: I want to find the components that are symmetric and antisymmetric with respect to magnetic field. The first thing I tried was just using: Symmetric ...
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4answers
88 views

Find Short Clip of Audio Within Longer Clip Of Audio

I need help figuring out a way to automatically synchronize two audio files that are both different recordings of the same source. More info below. This example is from a concert, where there is ...
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1answer
29 views

FFT widow to dsp processor. ff meaning fft

I am applying 8 samples and triangular window to my fft engine. I am getting the results but not accurate (approximately equal with some tolerance). I am calculating MATLAB reference as below : ...
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2answers
62 views

How to design a filter with custom group delay — why is it an IIR?

Say I have an FIR filter with desired magnitude characteristics. I could imagine using an allpass IIR in series with the FIR to alter the group delay characteristic to provide both a 'magnitude ...
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2answers
168 views

Conceptual question on FFT and chirp signal

If I take the FFT of a sinusoid I will get a plot whit all the energy of the signal concentrated at the sinusoid frequency. But what happens if I have a signal in which the frequency keeps ...
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1answer
67 views

Help on implementing an IIR filter

I am new to signal processing and and having difficulty understanding how to implement an IIR filter. The reference is athttp://www.dxatlas.com/rocky/Advanced.asp in the Band scope section. It ...
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1answer
75 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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39 views

Processing IQ signals

Signal Characteristics: The IF (I/Q) signal consists of a DC component and an AC component. DC Component: 2.52V; AC Component: 1.72 – 2.04 V (V P-P); BW: 20Hz - 500kHz; Power: 20dB Requirement: Now ...
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1answer
141 views

How to take the FFT in a limited range of frequencies?

When using the fft function in Matlab to take the Fourier transform, one can specify the number of FFT points, nfft, and the ...
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1answer
39 views

Calculate Damping using FFT

Given the following signal I would like to calculate the rate of damping. I presume that I need to find out where the peaks are using some kind of smoothing on the sample data. After performing an ...
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43 views

FFT signatures of QR codes

QR codes have three finder patterns at the edges (See image here) These patterns are inserted to enhance the detection of location of the code on a comparatively larger image. They produce some ...
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1answer
44 views

Efficient algorithm for computing area under convolution?

Consider $N$ discrete signals $x_1(n), x_2(n), \ldots,x_N(n)$ each a bounded support of size $M$. To convolve them, we can zero-pad each of them, multiply their FFTs, and take the result's inverse ...
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18 views

Dynamic time warping with correlation as the cost function

I want to compare two signals using dynamic time warping, to find a time-mapping between two signals but I am not quite getting the expected result. Question 1 Can you set the dynamic time warping ...
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0answers
15 views

how to caculate the 95% level of significance based on the lag-1 autocorrelation of power spectra?

I am wondering how to calculate the $90$ or $95$ % significance level of power spectra based on AR(1) Auto regressive. Thanks in advacne
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2answers
106 views

Merits of “Zero-Phase” Zero Padding

I understand the reasons for zero-padding a finite signal before FFT. However, I was reading this book (http://www.dsprelated.com/dspbooks/sasp/Zero_Phase_Zero_Padding.html) where the topic is Zero ...
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1answer
69 views

FFT on Hamming Window Function [duplicate]

I want to apply Hamming window function the Audio sample then find out its fft.. ...
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1answer
44 views

downsampling an fft signal

I am currently working with a set of wavelet transforms that I came across in a paper. The paper suggests that I first apply the FFT on the source image and then perform the downsampling. So it says ...
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1answer
43 views

Merging pattern for FFT solutions

I have the generic problem of analysing a discretly sampled signal, lets say at 100Hz, and would like to compute features (ML application) of this signal at different scales: An instantiation of this ...
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30 views

calculating frequency spectrum using fft for video

How to process video with DFT/FFT - getting the frequency using PCO camera in c#,and how to interlink video frames with frequency transform.
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1answer
107 views

Find similarity of sound signal

So I was working on a program to comparing the similarity between the pronunciation of a word, First I got the audio file, and I use FFT on it to get the amplitude over frequency array, then I just ...
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1answer
68 views

Removing frequency using FFT

So if I were to have an $n$ length sample of a given sample rate and were to run it through an FFT, resulting in $n$ complex elements. How would I obtain the frequency bins, such that if I know the ...
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1answer
97 views

How to improve an FFT AM demodulator for NOAA APT satellite imagery?

My question involves proper FFT Technique for AM demodulation, in the special case where the modulation rate exceeds the carrier frequency. This question has a specific hobbyist application, the ...
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0answers
37 views

2D FFT vs 2 Pass 1D FTT

We know that the 2D FFT can be performed by taking the FT along the rows and then taking the FT along the columns. I'm wondering how theoretical performance compares to the direct 2D FT case, which ...
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1answer
80 views

Find a sinusoidal fit from data with fft

I have a vector with raw data (120 samples). From the frequency spectrum I can tell there is one dominant frequency component. Now I am supposed to use the fft data (magnitude and phase) to find a ...
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1answer
85 views

Plotting DFT in dB

I'm having a little trouble plotting the DFT of a signal in dB. I can get the picture up nicely when using the magnitude but when I try converting the magnitude to decibels it all goes south. I've ...
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0answers
31 views

Size obtained by applying Linear convolution

We know that applying a filter on an image is called correlation or convolution depending on the filter angle. In Gonzalez I have read that we can apply linear convolution on an image. Here I have a ...
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19 views

generation of frequency with magnitude 1

hi i need to generate F=[F0,F1,........Fn-1] wer n=16 such that lFnl=1..... so i understand i need 16 freq samples whose magnitude sums upto 1..... now i need to generate it in matlab...... can anyone ...
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1answer
90 views

Reconstructing time domain signal with Hanning window

I am currently working on a frequency domain real-time application on a digital signal processor. Currently for one time frame of my algorithm I read in time domain data into a buffer, perform a ...