Tagged Questions

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

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26 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
43 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 ...
2
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2answers
126 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
47 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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0answers
16 views

Spectral analysys using fft

i have a set of values with 10000 samples.i have performed overlapped fft using 256 points .how can i find out frequency for my overlapped fft output.i know that we can find out frequency from i*fs/L ...
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1answer
67 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
34 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
90 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
36 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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0answers
35 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 ...
0
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1answer
42 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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0answers
16 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
12 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
91 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
53 views

FFT on Hamming Window Function [duplicate]

I want to apply Hamming window function the Audio sample then find out its fft.. ...
0
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1answer
40 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
42 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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0answers
20 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
95 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
65 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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0answers
24 views

Inverse fourier transform normalization - Filtering in frequency domain

After the multiplication of two signals in frequency domain, I have applied inverse FFT to get filtered signal. What could be the multiplication factor to be used after applying inverse FFT to get ...
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1answer
75 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
27 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 ...
1
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1answer
71 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
64 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
29 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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0answers
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
60 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 ...
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1answer
66 views

2D deconvolution of recorded electron beam data

I'm currently working on a project that involves using an electron gun and it would be really nice to know the spot shape of the electrons coming out of the gun (the frequency of electrons at some x,y ...
0
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1answer
90 views

Inverse fourier transform by using a random phase and an original magnitude (matlab)

I want a image. Firstly I want to do fourier transform and get the magnitude and phase information. And then make a new random phase, finally use the changed random phase and original magnitude to ...
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0answers
14 views

Estimation of dominating frequencies of pseudorandom signal

I have generated a gaussian distributed pseudorandom signal using command randn(). Then I plotted its frequency response with FFT. Now how I will come to know what ...
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1answer
45 views

Cross correlation vs FFT for finding phase between 2 signals

I have been struggling with this issue for months now, trying to understand which one to pick: FFT or cross correlation. I am given a sine wave (with phase, amplitude, frequency and time vector ...
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1answer
123 views

Cooley-Tukey Implementation of FFT in Matlab

For my course I need to implement a 30 point Cooley-Tukey DFT by transforming it into a 5x6 matrix. I have tried to implement using the following Matlab code: ...
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2answers
60 views

Purpose of Phase Information

I am learning Fourier Transform from many days but till now I am not able to understand what does phase angle image show us or tell us? They say that MAGNITUDE tells "how much" of a certain frequency ...
2
votes
2answers
105 views

FIR implemented via FFT — low-pass works good, high-pass gives distorted results. What's wrong?

I'm implementing (in software) FIR filters. I have done two implementation: convolutional one and based on multiplication in frequency domain with FFT/IFFT. I'm using standard FFT implementation (not ...
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1answer
106 views

Dividing Audio signals into Barks Bands

I want to apply the following steps in matlab 1) Read the audio data 2) Apply window function on that data 3) Apply fft on the result of window function 4) Make power spectrum of fft 5) divide ...
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1answer
31 views

Frequency of the wave in frequency domain

If we have a 1-dimensional wave in time domain, it can be represented in frequency domain with x axis indicating the frequency of the wave and y axis indicating amplitude/magnitude of the wave. But ...
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1answer
43 views

Frequency Spectrum of an image

I have been studying about Frequency Domain from many days but still i am not able to clear one of the confusion. We say that in frequency domain an image is represented as waves. What I am able to ...
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1answer
50 views

FFT window corrupts signal

this is a newbie question. My goal is to create audio filter that cleans human speech from noise. I started with learning all about fft filters. At first I've created simple fft filter with ...
0
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1answer
62 views

How to find phase difference between 2 signals, one has an unknown function

I have a system that is forced by a sinusoidal function with specific amplitude, phase and frequency ( all these are known ahead of time). I get a deformation of sinusoidal form as well (think of a ...
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0answers
28 views

Phase difference betwen 2 signals, 1 signal with unknown function

I understand this question may have been addressed however I have a major difference. I started out with a sinusoid of form A*sin(2 pi freq t + phase) and I know ...
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2answers
43 views

Relationship between Fs (the Nyquist frequency), and the frequency used with a sine wave

Say you are given a vector t =[...] for the time to be used to generate a sine wave of a certain frequency say FHz. I have all the data for t so I can conclude what dt is (my dt = 1d-5). Now I am to ...
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2answers
46 views

How to transform large set of audio samples using FFT?

Well, I am new to DSP so I apologize for the basic question. I am trying to transform audio 16bit PCM (which I store in normalized 0.0-1.0 range) samples into frequency domain using fft. I ...
2
votes
1answer
54 views

Avoiding edge repeats in a FFT convolution

I am trying to use FFT as a fast way to convolve a image, however one of the downsides of this is that the "kernel" image will repeat when reaching the edges of the sample. Is there a way to avoid ...
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2answers
72 views

direct Frequency domain FIR filtering vs Overlap-add method

I'm trying to do bandpass filtering of a EEG signal samples at 250Hz and benchmarking the following 4 methods of FIR filtering for different filter orders. The length of the signal is 15000 samples. ...
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votes
1answer
60 views

fft of a complex signal

I am new to dsp and just have a vague understanding of fft process. i know fft is used to convert time to freq domain.... i need to generate a sequence of frequencies such that F=[F1,F2,.....Fn-1] ...
0
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1answer
55 views

Explain Shift property of DFT

Please check the link What effect does a delay in the time domain have in the frequency domain? Here it is said that if you delay your input signal by D samples, then each complex value in ...
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2answers
95 views

What do you get applying FFT to Music?

I am trying to take a section of a song (approx 1.5 seconds) 44100 sample rate equals sample size of 65536 which is 2**16. I want to find the frequency of the piano note that is played in the window ...
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0answers
26 views

Welch's Overlapped Method

I am measuring wind speed using a number of different anemometers. These anemometers are placed on a structure which exhibits sinusoidal motion. Thus, the signal of the anemometers contains both the ...
0
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1answer
25 views

what is the significance of pilot carriers in ofdm [duplicate]

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 ...