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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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 ...
166 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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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 ?
75 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 ...
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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Same PSD from different FFTs

Is it possible to obtain same PSD from different FFTs? Can anyone explain it mathematically?
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 ...
609 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?
264 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 ...
530 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 ...
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 ...
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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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 ...
149 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 ...
232 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: ...
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 ...
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 ...
148 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. ...
136 views

Question based on scaling the FFT for obtaining PSD

Following is the code given in MATLAB's site to estimate PSD using FFT. ...
114 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 ...