Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [fft]

FFT is an acronym for Fast Fourier Transform. Use this tag for FFT-related questions. Try to also select a specific chip or software tag when possible.

Some articles about the fft for learning more:

http://en.wikipedia.org/wiki/Fft

http://en.wikipedia.org/wiki/Discrete_Fourier_transform

http://www.dspguide.com/ch12.htm

http://www.complextoreal.com/chapters/fft1.pdf

http://www.complextoreal.com/chapters/fft2.pdf

http://www.complextoreal.com/fft3.htm

215 questions
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Why should I use digital filters rather than simply manipulate signals in the frequency domain and then recover them into the time domain?

I'm quite a novice in signal processing and I know this question may be too broad. But I would still like to hear hints from experts. I was taught to use butter (to design Butterworth filter aka the maximally flat magnitude filter) and filtfilt…
Kouichi C. Nakamura
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Why use the fast Fourier transform for noise reduction instead of a classical electronic filter?

I'd like to know how to remove environmental noise from a speech recording. I've made some research and I've noticed that most of the methods proposed use the fast Fourier transform. But why can't you use a classical electronic filter to remove the…
Jazis
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What's the junk at the end of my FFT in LTSPICE?

Why do FFTs have junk on the high frequency end? Suppose I go to simulate this circuit in LTSPICE: simulate this circuit – Schematic created using CircuitLab Where the LTSPICE sine and simulation parameters are: SINE(0 1 1K 0 0 0 1000) .tran 1…
watkipet
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2 answers

How to select frequency resolution and window size in FFT?

I am doing spectrum analysis of a time varying signal with frequency changing from 200Hz to 10kHz. I am using the FFT for analyzing the frequency component in the signal. My questions are: How to decide on the frequency resolution and window width…
nitin
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9
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2 answers

Strange extra frequency in crystal oscillator

I have inherited a circuit from another designer using a 12.288 MHz crystal as the source for an audio clock. We recently had supply chain issues and I was asked to approve an alternate part with identical specifications. As part of this I compared…
stefandz
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3 answers

How to achieve coherent sampling in practice

In the context of measuring a sinusoidal source with an ADC, coherent sampling (i.e. capturing an integer number of periods) allows the use of a rectangular window without spectral leakage. How does one actually do this in practice? I am testing a…
DavidG25
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4 answers

Performing FFT at low frequencies but high resolution?

To put this in context, I'm looking to achieve both high speed and high accuracy for measuring biosignals through the FFT. I'll describe a quick example to see if I understand this properly as well as to illustrate my question. So, if I have this…
Scorch
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7
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6 answers

Audio spectrum analysis: PC Software vs Hardware Spectrum Analyzer

I need to do some audio spectrum analysis (basically, listening to a machine and tell if it is properly calibrated). I will record the sound it makes with a microphone (it sounds differently if it is calibrated correctly than if it is not), and then…
Nicholas
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2 answers

Using FFT for spectral analysis: How to convert from power to dBm?

I have the output of my FFT, an array of complex numbers, and each one has been computed to the magnitude squared. To my understanding, the magnitude squared is equivalent to the power, so in order to map to dBm, I would take 10 * log(x) of each of…
upswimsdn
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Fast Fourier Transformation of incomplete signals

I would like to perform a FFT on a signal with equally sampled values of which some are missing. (Actually, they are not even missing, but simply erroneous, so I can't use them, but I can detect when I have a wrong samplepoint.) Is there a way to…
DonQuiKong
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2 answers

Uniform Linear Array (ULA) beamwidth and angular resolution using FFT

I have a four element uniform linear array receiver and I want to know what will be the angular resolution if I perform perform Fast Fourier Transform (FFT) over antenna elements. As I think that it will be same as the beam width of the array. The…
Zeeshan
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What is the efficient way to perform FFT for large set of Samples?

I'm trying to perform FFT for large set of samples, Sampling Rate : 1 MHZ No. of Samples Captured : 1 Million (1 sec duration) currently what I'm doing is, I've added zero padding so that it matches to 2^n, and now the total number of samples are…
SanVEE
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6
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2 answers

FFT is not showing noise

I have current values and respective time. There is noise in the signal. But when I am calculating FFT, it is not showing I have recorded the values at every 5ms. below is my code: time = data['Time'].values current = data['Current'].values # 2.…
Teena
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6
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2 answers

Getting different FFT results in LTspice comparing to MATLAB and Python

I have a 10 seconds of sampled data. Sampling rate is 1kHz. I uploaded the text file which is a two column time vs voltage data; it can be downloaded here. I performed FFT in MATLAB, Python and LTspice. MATLAB and Python agrees when I plot but I…
cm64
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Meaning of phase in Fourier Transform of audio signal

I'm looking at the Fourier Transform (really, at a sliding DFT) to analyze (visually and intuitively) the frequency components of a sound over time. But the DFT produces complex numbers, and I'm not sure how or whether to visualize them. Should I…
Grumdrig
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