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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Period of non-harmonic Fourier sum

I am wondering if there is a formula for the period of the sum of $N$ cisoids of the form $e^{j\frac{2\pi}{N} i\, \omega_k}$ where the frequencies $\omega_k \in \left[-N/2,N/2\right]$, $k=0,\ldots,N-1$...
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155 views

How to prevent Signal drifting when changing frequency

When I recreate a signal it seems to look great. But when I try and increase it's frequency (which is done in a for loop and the variable new_freq=2) it starts to drift. See Image below (The top ...
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1answer
582 views

How to understand FFT results of scipy.fftpack?

I calculated FFT for a speech wav-file using scipy.fftpack. How do I read (understand) the return of FFT? I have read that it supposed to be like so: y[0] is 0Hz loudness, y[1] is 1Hz loundess, ... y[...
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1answer
89 views

Phase distortion of frequency warping by using Praat

I am trying to do speaker conversion by frequency warping method. I modify the function Spectrum_shiftFrequencies() in Praat by scaling the FFT spectrum of a voice. When one scaling factor is ...
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1answer
250 views

Getting frequencies out of a FFT

I use this FFT and wrote a short program to test it. ...
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1answer
69 views

How to analyse periodic data obtained from a vibration experiment?

I have data from a vibration experiment on a structure. This data was obtained by attaching an accelerometer to a FFT analyser, which records the data at a high sampling rate (typically in kHz range) ...
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1answer
866 views

Real-time frequency recognition in python

I'm a newcomer to signal processing, so forgive my ignorance. I'm working on a project in Python that will play a .wav file and pick out the dominant frequency as it plays. I've found a few examples ...
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1answer
195 views

How to determine relative distance between 3 in-phase transmitters by analysis of received signal

I would like to determine with high accuracy the relative distances between three RF transmitters a few meters apart by analysis of phase interference in the received wave, the receiver being at an ...
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1answer
532 views

FFTW - Inverse FFT input data

I am trying to use FFTW function for IFFT: fftw_plan_dft_c2r_1d(size, out_cpx, out, FFTW_ESTIMATE). My goal is to input desired frequency response data and ...
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1answer
988 views

Power Spectrum in dBFs

I'm trying to get the spectrum of my signal in dBFS units. I'm not sure what is the refernce that I should devide by. I computed the power spectrum as follows: 1) FFT normalized to the number of ...
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1answer
340 views

Kiss fft does not work after giving it more than 32 samples

I am trying to take data from an accelerometer and apply Kiss FFT to the samples. I'm using a Freescale Kinetis FRDM-K22F board. I want to use 64 samples, but when I run the program I get an error ...
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1answer
2k views

Frequency response of a filter - fft vs. freqz

I have designed my filter using firhalfband(N,Fo,A), which gives me the filter coefficients. Then I try to see the frequency response of it. I use these two ...
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1answer
3k views

comparing 2 audio files in c#

I have 2 audio .wav files recorded by the the same person with the same word. Each audio file has a format of 16bit, 44.1kHz and is a mono channel. I would like to know how to compare these 2 audio ...
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2answers
1k views

MATLAB : How to filter a data signal

I have a data signal (column vector) with N values taken over at specific sample rate (dx) at a fixed frequency. After taking the Fourrier transform of this signal and representing it in the Fourier ...
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12 views

Autocorrelation of vector of images

I have a set of images (think a ball getting bigger and smaller). I want to assess the periodicity in this string of images (each data point in my signal is an image). How can I go about doing this in ...
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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
156 views

Spectral Subtraction python implementation error

I am trying to implement Spectral subtraction in python. I am new to DSP. I used this article as reference and below code is what I can come up with. Of course I did not get the expected output. I ...
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2answers
192 views

Phase difference b/w two sinusoidal signals using FFT

I am trying to understand how to find phase difference b/w two real sinusoidal signals and then align the phases of two sinusoidal signals using this difference. In the first step, however, i have to ...
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1answer
167 views

Finding resonance peaks from sine sweep vibration test

I'm trying to perform FFT analysis on data from an engine "rpm sweep" test to find resonance peaks on the DUT. There are three tri-axis accelerometers along with time, engine speed, engine torque, ...
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2answers
248 views

FFT uncertainity in frequency

Hello What would the uncertainty be in frequency vs amplitude graph for the frequency? the peak amplitude is the dominant frequency, what is the uncertainty of that frequency? Thank you!
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1answer
143 views

Filter length in a Filtered-OFDM system

In a filtered-OFDM system, lets say we have the following parameters: ...
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1answer
737 views

MATLAB's $\tt bandpower$ function - How does it work?

So the function bandpower(x,fx,freqrange) calculates the average power within the selected frequency range. So it basically takes a part of the periodogram, but ...
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1answer
116 views

Making a mesh out of the parameters from a STFT

I do not possess much knowledge about signal processing, so i hope to do a find an answer. I am reading a wav-file and then apply a fft on it. In theory, i think i have a 3 parameters i can use. Time ...
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1answer
295 views

Can't get FFT of Sample & Hold sinusoidal wave in Simulink

Simulating of Sample-and-Hold fails: "Buffer" block generates the error "All sample times must be discrete. No continuous or constant sample times are allowed" Any suggestions ? Thanks in advance. ...
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1answer
486 views

Digital signal and frequency analysis

I am generating a digital signal with software. I have defined the vector $$[0,1,1,1,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0] $$ and my sampling rate is 8 million per second. The frequency spectrum is ...
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1answer
647 views

Explain how to apply Hanning window to Fourier amplitude spectrum

This example code was used to answer a question about applying a window on the Fourier amplitude spectrum. How to apply Hamming Window? I have a question about the section of code related to the ...
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1answer
164 views

what is the preffered data and FFT length for blackman harris window for improving Accuracy due to ENBW Consideration of window?

for Rectangular window if data length is 1K then FFT Length Should be 1K FFT only because ENBW of rectangualr window is 1.0 but for Minimum 4-Sanple BlackmannHarris window is 2.0. so for improving ...
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1answer
365 views

fft2 of interferometric image - how to interpret the result in term of dominant frequency

I have an interferometric image which shows fringes at a certain frequency, basically a dominantly periodic signal overlaying the information that I want to extracthere are the fringes that I want to ...
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1answer
66 views

SNR problem with different sampling rates using innerproduct

I'm trying to measure the amplitude of a sinusoidal component in a noisy signal. Since the signal frequency is known beforehand, I'm calculating scalar product with a sine and cosine base function ...
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1answer
262 views

FFT: Linear to Logarithmic (TM4C, CMSIS & NeoPixels/ws2812)

I'm trying to perform an FFT using the CMSIS libraries. My FFT_Output[] provides 1024 bins of data as expected. The issue is that it's linearly spaced and I want to change it to a logarithmic scale ...
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36 views

Can I find FFT for signals with odd number of element

I am said to divide signal into two parts even and odd numbered {index/value of n} .What if number of elements in x[n] is odd out will I divide into two networks?
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35 views

Retrieve covariance matrix from array of fft

I have 10000 power spectral density vectors of 64 frequency bins each. My input is therefore are 10000x64 matrix of real values. Those are obtain from fft of time series of temporal signal I don't ...