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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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40 views

About the power spectrum and confidence upper limit of a time-series data

For now, I have a coupled system with 5 variables and use the Runge-Kutta method to integrate. ...
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1answer
36 views

Will noise cancellation with playstation eye improve my spectral analysis?

Im doing some beginners spectral analysis for a homemade reactive RGB LED project and was thinking of ways to improve the accuracy of the audio analysis. Im using a Playstation eye with a Raspberry Pi ...
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1answer
41 views

Number of discrete samples required for the longest wavelength

I am trying to understand the effect of the critical Nyquist frequency when applying the Goertzel algorithm for estimating the power spectrum of a discrete signal. (Goertzel doesn't really matter, ...
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74 views

Applying DFT to OFDM signals above Nyquist rate

Consider an OFDM signal which has $N=8$ subcarriers and is band-limited to $[-B/2,B/2]$, $\sum_k x_k e^{j2\pi kf_0t}$ where $f_0=\frac{B}{N}$. For this case the Nyquist rate is $2\times B/2=B$, i.e., ...
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2answers
271 views

How to increase resolution of FFT?

I have an input signal in the ( 0 - 20 kHz ) frequency range . When i sample this signal maximum sampling frequency is around 40 kHz . When i calculate the FFT using 1024 points i got resolution of ...
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0answers
167 views

Mirrored Spectrogram Mp3

First of all sorry if this is a stupid question, but I am an absolute beginner in this field and have been trying for days now. I'm working on a java program that uses fft to analyze audio files. To ...
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1answer
46 views

I have the scatter plots for a Hamm and Tukey(0.25) windowed data. The complex data plotted from Hamm windowed forms a pattern, why?

The Hamm windowed complex data forms some sort of a quantized pattern whereas in the same code if tukeywin(0.25) is applied normal noise is observed. Any idea why ?
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1answer
76 views

Are there frequency detection methods that are subject to less latency than the Goertzel algorithm?

I am trying to detect oscillations in a small range around 1.5Hz as early as possible. I am currently using the Goertzel algorithm with bins 1.0Hz, 1.2Hz,..., 1.8Hz, and 2.0Hz; with block size N = 500 ...
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1answer
36 views

How to window a time domain signal for 6 symbols with cyclic prefix length of 512 samples?

Based on LTE stds. I am running a simulation for 6 symbols (each having 1200 central subcarriers) each in a 2048 FFT/IFFT bin. To these symbols are appended 512 samples as cyclic prefixes. I have to ...
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1answer
32 views

Same PSD from different FFTs

Is it possible to obtain same PSD from different FFTs? Can anyone explain it mathematically?
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1answer
50 views

Irregularities in tone generated using FFT data

I am implementing a simple program to generate tone in MATLAB using FFT/iFFT by zeroing all frequency bins except for the one frequency that I'd like to generate a tone in. Sampling frequency is ...
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1answer
636 views

How to make DFT in matlab without FFT [duplicate]

Does anyone have a algorithm for DFT without FFT function in matlab? and second question is how can I make zero padding in this algorithm?
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1answer
268 views

Scale Image by using FFT

Can we change the scale of image by using FFT? I mean, how should i do process on frequency domain of image to upscale or downscale the orginal image? The other question of mine is that how can ...
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2answers
551 views

Using Fast Fourier Transform to determine musical notes

Hi guys i am doing a course in Digital Filters and Spectral analysis. We are given a coursework/homework, and I have absolutely no idea what to do with it. I come from Maths background, never done any ...
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1answer
31 views

What is the z-domain transfer function of variable delay?

Is it possible to obtain the transfer function of a signal that has a variable delay? For instance, I have a signal consisting of 10 samples: 0,1,1,1,1,0,0,0,0,1 If I would apply a unit delay to ...
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0answers
96 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
177 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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0answers
57 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
82 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
62 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
2k 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
87 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
46 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
33 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
593 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
1k 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
49 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
187 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
99 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
212 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: ...
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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
43 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
190 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
211 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 ...
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1answer
254 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
159 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
483 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
277 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
71 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
447 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
290 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
48 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
762 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
88 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
152 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
235 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
98 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
49 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
149 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. ...