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Questions tagged [fft]

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

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68 views

Frequency resolution - resolution BW relation for different window functions

I am working on FFT based spectrum analyser and I am not sure how to proceed calculating the RBW. According to the document (page 20) in the link, RBW described as $k \frac{f_s}N$ where $f_s$ ...
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2answers
103 views

Comparing FFT for increasing time intervals in a signal

Assume a dataset where the rows represent signals: each signal $s$ is sampled at a sampling rate $f_s$ and available as an array of common length $T$. For an increasing sequence of integer times $t_i &...
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48 views

Solving the PDE of a signal in an optical fiber

Disclaimer Please let me know if this is not the right place to ask this question. Disclaimer Part 2 I have no background in signals. My focus is in mathematics. In my programming class, we are ...
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2answers
76 views

How to efficiently control an FIR's magnitude response by altering its phase spectrum

Question: Extensively searching the space of all possible vectors of length $n$ to satisfy a (non-overdetermined) requirement is possible in principle. Hence, there is a way to calculate a complex ...
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0answers
50 views

FIR Audio Equalizer Crackling Noise

I've implemented a few FIR filters into a song equalizer, but there seems to be a crackling that I'm unsure how to fix. Heres a video for reference: https://www.youtube.com/watch?v=IlzWRYpv0rk. Noise ...
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1answer
685 views

differences between DIT & DIF algorithms

What are the differences between decimation in time and decimation in frequency algorithms of FFT, especially as their names suggest? How can I see/understand that decimation in time domain is taking ...
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1answer
66 views

complex multiplier in divide and combine FFT

I am studying radix 2 algorith from Proakis' book. But I'm a bit confusied why 1st DFT $G_1$ is not multiplied by complex entity while 2nd DFT $G_2$ is being multiplied by complex entity $W$ as shown ...
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1answer
28 views

value of complex multiplier in DFT/FFT

I am studying proakis book digital signal processing using matlab 3rd ed but i am bit confused about calculation of value complex multiplier W fig is attached. i am not able to understand how the ...
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0answers
30 views

Determine 3 most dominant frequencies in a signal, PSD or just the absolute value of a Fourier transform?

I have a noisy ECG signal recorded for 5 minutes. My goal is to determine heart rate every 2 seconds. To find out 3 most dominant heart rates (Beats per minute) in a 2s-signal should I calculate its ...
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2answers
328 views

What would be the effect of repeating samples in time domain on frequency domain?

Consider the operation of up-sampling a signal n times by repeating each sample n times in the time domain. What would the frequency domain response of the resultant signal be like given the frequency ...
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3answers
634 views

How large FFTs can pull signals out of the noise floor?

I am trying to detect unknown RF tones around -140 dBm and my scan BW is 5 MHz, going through the Noise power calculations the signal is below the thermal noise based on the scan BW. I read that using ...
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1answer
39 views

DFT of Transient vs. Analytical Solution

I'm trying to compute the Fourier Transform of a lightning impulse waveform. The python code I'm using is below. The problem that I am running into is that the magnitude of the DFT and the magnitude ...
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1answer
88 views

Limitation on the shift theorem of DFT due to frequency resolution?

The shift theorem states that shifting a sine wave in time domain by t is equivalent to multiplying the corresponding DFT coefficient of the signal by a complex exponential e^(-jwt). Described by the ...
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0answers
44 views

How to sample a transfer function (angular spectrum) in the frequency domain?

I am having this problem in Fourier optics, where I am using the Angular spectrum method (a lti filter) to calculate the electric field at the required plane given ...
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1answer
88 views

Power spectrum RMS or peak

I’m a newbie and wondering if I calculate the power spectrum from the peak amplitude or from the amplitude rms ? This is my matlab script so far: ...
0
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1answer
33 views

Practical insightful time domain functions [closed]

This question might be a little bit different, but i am having hard time to find some sort of a list/book/website/advice, with very practical time domain functions that provides useful insgihts for a ...
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1answer
39 views

How to differentiate an empty aerosol from a full one using only sound measurements?

The challenge I have is to detect an empty spray container using sound measurements only, since I can't place any sensor directly into the container because of the mechanism that tightens it. My main ...
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1answer
52 views

Quite confused with Fourier Analysis results

So I'm meant to show how the DFT can find the frequencies, and respective amplitudes, associated to some data. And I have this data set from the curve $$ f(t) = 1 + 2\cos(2\pi t) + 4\cos(4\pi t) $$ ...
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1answer
89 views

Overlap/add time-domain audio frames: How does normalization/scaling work with overlap greater than 50%?

I am attempting to overlap-add time-domain audio frames in a real-time context (with a continuous stream of data coming-in). Each frames consist of 1024 samples and have been previously "Hann" ...
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2answers
74 views

How to understand the discrete and continuous convolution in matlab?

For example,I want to calculate the convolution of two continuous signal in matlab as the image shows. Indeed, I chose to discrete the signal to compute in matlab. Obiviously, the 1st and 3rd are ...
0
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1answer
178 views

Note detection in an audio file.

I am trying to find the given note in an audio file. It has been specifically told that each file contains only one note. So i directly took fft and found the corresponding frequency and then mapped ...
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1answer
103 views

What Is the Point of Doing the Zero Padding? [duplicate]

What are the advantages and disadvantages of doing Zero-padding, in particular the case of speech signals?
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1answer
207 views

What determines the accuracy of the phase result in a DFT bin?

What are the factors that affect the accuracy and precision for the phase that is given by the DFT? Just thinking medium-hard about this, it occurs to me that it must have something to do with the ...
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1answer
112 views

Calculating SFDR from FFT of ADC output

A few months ago, as part of my summer internship, I had performed interfacing of an ADC with FPGA (Zynq-7000). The goal was to take an analog signal from a signal generator, feed it to the ADC and ...
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2answers
57 views

Accurate description of the spectrum of sinusoid waveform added with WGN?

The transmitting signal is $$ s(t) = \sin(20\pi t)+\sin(40\pi t)+\sin(60\pi t) $$ The received signal after AWGN channel is $$ r(t) = s(t)+n(t) $$ where the variance of noise $n(t)$ is $\sigma^2$. ...
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1answer
221 views

problem finding 16 point DFT using two 8 point FFT (Divide and combine algorithm) MATLAB [closed]

Write MATLAB code that determines and plot the N-point Discrete Fourier Transform of x[n] defined by the following equations: x[n]=0.5*pi*n n=0:16 Compute and plot 16-point DFT using two 8-...
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2answers
172 views

How to plot and normalize a spectrum in matlab

I am given the coefficients of an FIR filter. I have created its impulse response through a convolution with a unit pulse. Now I want to plot the frequency spectrum. I perform zero-padding and ...
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0answers
40 views

Frequency bins too powerful at the start and at the end of each sample computed DFT data

I've taken the following link http://coding-geek.com/how-shazam-works/#comments as a project to start practising and learning signal processing and python programming for me to get started in speech ...
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2answers
359 views

Choosing sampling frequency and base interval to eliminate leakage

I'm studying for an exam and have some trouble with an exercise. So I have a continuous-time signal that is $$s(t)=\sin(2\pi f_{s1} t) + \sin(2\pi f_{s2}t)$$ with $f_{s1} = 1.4\text{ kHz}$ and $f_{s2}...
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1answer
61 views

Perform non-power-of-two FFT using ARM CMSIS library

I have 1280 points which I would like to perform an FFT using a M7 cortex with hard floating point engine. As the title suggest I would like to use the ARM CMSIS library to perform a non-power-of-two ...
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1answer
74 views

How can I get the power of a specific frequency band after FFT?

I need help with my matlab code. I have recorded EEG data and now I want to analyse it in matlab. I want to find the mean power of specific frequency ranges (theta: 4-8 Hz,alpha: 8-12Hz etc.). For ...
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1answer
100 views

Spectrogram Interpretation

I collected vibration data (amplitude and time) on a component that was attached to an engine. Using MATLAB I plotted a spectrogram to see what frequencies it vibrated at. The code: ...
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1answer
80 views

OFDM Simulation process

I'm trying to understand OFDM by making a simulation. Are these steps correct? generate M random complex QAM symbols. example: (1+j,1-j,-1-j,1-j....) Split my M samples into a N 2048 sized arrays ...
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1answer
39 views

Why delete high frequence in fft return the area of the most changes?

I'm new to ||image-processing|| and || fft filters || I have a relative smooth $\mathtt{2D}$ (circle) gaussian surface (height $10$) with several "holes" in it, and the surrounding area [has] some ...
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1answer
84 views

Fast Fourier Transform using numpy

I am a computer science student and didn't really have signal processing as a subject. Maybe I should be clear on the concepts of sampling rate and frequency of the signal but I am a little confused. ...
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1answer
86 views

Question based on scaling the FFT for obtaining PSD

Following is the code given in MATLAB's site to estimate PSD using FFT. ...
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2answers
76 views

Shifting signal smaller than discrete step

I have a image that I need to shift with less than a pixel. My plan was to do a Fourier transform and multiply the signal with $e^{-aiu-biv}$ where $a, b$ are the shifts in x and y direction. This ...
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0answers
41 views

dsPIC33E ADC to FFT help

I am sampling an audio range signal with a bandwidth of 3100Hz and then applying a FFT using the DSP library example from Microchip to determine the most dominant frequency of the signal. On the last ...
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2answers
119 views

Why is my DFT/FFT always 90° out of phase?

I'm doing an FFT using Python and Numpy on one machine, and C# on another. I'm using some dummy data that mimics how I'll eventually be gathering data from sensors in the C#/UWP application. The two ...
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1answer
95 views

Damped sinusoidal form FFT of signal

I'm doing an assignment for the course Signal analysis where I have to analyse a signal. I've tried quite some things now but it's still bothering me that the FFT is looking weird, and not looks like ...
3
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1answer
73 views

FFT of a $N$-length real sequence via FFT of a N/2-length complex sequence

I would like to optimise FFT algorithm by only using a FFT of size $N/2$ to transform a real sequence of length $N$. There are already many questions and many excellent answers on the matter (here for ...
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1answer
53 views

Attenuate frequency bin in FFT array resulting in artifacts

Am trying to remove noise for certain frequency bands by attenuating freqeuncy bins in the FFT array. However this results in artifacts to be formed, where there are clicking sounds in between each ...
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2answers
103 views

How to determine the original size of the FFT used in unknown OFDM symbol

Given an unknown OFDM symbol consisting of 9144 samples, interested to know the size of the FFT used in the TX/Number of bins. Down-sampling to 512,256,128,64,32 yields the following. Do not see how ...
0
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1answer
124 views

If my sampling rate is not high enough to capture all frequencies, can I accurately capture low frequencies?

Let us say that my sampling rate is 1000 Hz. This enables me to accurately capture every frequency in the 0-500 Hz range according to the Sampling Theorem using a DFT. However, there are higher ...
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1answer
202 views

Two voice pronunciation comparison similarity MFCC + DTW

Calculate each MFCC to compare wave file A and wave file B, and then use FastDTW to measure the distance after two sets of MFCCs. We compared the four wave files and obtained the Euclidean distance ...
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1answer
211 views

What is the proper way to implement a real time spectrogram?

I am trying to implement a real time spectrogram and I am not sure that I am implementing it the right way. First I decided to use Matlab, I was taking a short recording of lets say 0.1 seconds and ...
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1answer
52 views

Break a signal into segments, add them together and then perform an FFT on the result

If you break a 4 second signal into 0.5 second segments, add them together and then perform an FFT on the resultant 0.5 second data. Will the FFT / frequency spectrum be the simlar to an FFT on the ...
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1answer
50 views

frequencies in sound: multiple possibilities?

First, I am by no mean a sound engineer (as you will guess later). I was just wondering something while looking at the waveform of a .wav for a given shape of waveform on a duration of 2 sec for ...
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1answer
77 views

Is sparse signal in time domain is sparse in Frequency domain

In OFDM system, if we have a multi-path environment, we supposed to have a sparse received signal in time domain, then $FFT$ is performed to convert it into frequency domain. My question, does the ...
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1answer
62 views

Defining frequency axis for periodogram

I am trying to simulate example 8.2.2 from Hayes, Statistical Digital Signal Processing and Modelling, on MATLAB. Let $x(n)$ be a WSS process consisting of random phase sinusoid in unit variance. $$ ...