# 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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### Band energy and Parseval theorem

In Python, I consider a dummy signal as follows: fs = 512 sig = np.random.standard_normal((fs,)) sig corresponds to 1s of ...
216 views

### Wavelet transform and FFT using to extract feature power bands with EEG signals

I am using 5 channels [ fz , cz , c3 , c4 , pz] to detect drowsiness of driver My First Question is, what is the right input to get feature power band ( Theta , alpha , gamma , beta ) to wavelet ...
284 views

### Windowing a signal for FFT

I am actually working on a project involving the cross-correlation of two signals. My cross-correlation code is working fine, but I suspect that I should apply a window to my data set in order to ...
45 views

### How to Calculate the number of DFTs taken in a STFT

Given variables of window size (W), overlap (O), and length of the Signal (S) (in my case, length of a song) and I am trying to determine an equation that gives me the number of DFTs that would be ...
188 views

### Phase Modulation and Intermodulation Anomaly ? (Spectrum plots inside - **Updated**)

I have a MATLAB script for modelling a two tone signal (a sum of two sinusoids) going through a non linear transfer function (such as an amplifier). The amplitude of a signal is amplified non linearly,...
69 views

### psd of an ac voltage signal

In an lab class experiment who's subject of interest was Johnson's noise I measured the ac voltage of a battery. Now I wish to find the psd of the measurement and show that it is constant. 1.Is such ...
202 views

### Arbitrary Phase FIR design using FFT

I want to design a digital FIR filter to cancel the phase of an analog Butterworth filter (i.e. the phase is smooth) i.e. the filter has unity gain with just an inverted phase component. The ...
174 views

### Adding phase to a signal that has multiple frequencies

An amplifier changes the phase at different amplitudes of asignal. I am using amplifier data in a MATLAB model. I have constructed a signal that is a sum of sinusoids of different frequencies with ...
412 views

### pdf of the sum of gaussian distributions using fft Ask [closed]

I am trying to derive the pdf of the sum of independent random variables. At first i would like to do this for a simple case: sum of gaussian random variables. I was surprised to see that i don't get ...
218 views

304 views

### FFT - mixed radix - bit reversal

I wonder what is bit reversal for mixed radix FFT. Is there any algorithm that compute the bit reversal for various mixed radix FFT? Here should be mention why I want that. For example if I have ...
99 views

### FFT phase spectrum to suppress noise?

All that I heard so far about phase spectrum - that it is very hard to process. Are there any methods to do that, and is it possible to extract information about the noise from phase spectrum?
121 views

### How make FFT when buffer size is not 2^L

I still try to understand FFT :) I know I can do something like that: float bufferSize = 500.0f; int correction = log2(bufferSize); bufferSize= pow(2, correction); ...
40 views

### DSP Hardware recommendation or is it even needed?

I'm new in embedded programming. Trying to choose a dsp, they seem very feature rich for my planned usage. I want to analyze 18 signals (simultaneously or near simultaneously) real time. I want to do ...
508 views

### different solutions in matlab / octave using dft and fft

i am new here in dsp.stackexchange and I am trying to do my first basic steps with fourier-transformation. Some years ago I learned the basic theory in university and also developed a fft ...
2k views

### Understanding FFT: FFT size and bins

I'm trying to implement an FFT to understand how it works. I'm using a random sound file (so i can't control the size of the signal), with a sampling frequency of 44,1Khz. I'm using this library ...
207 views

### How to see the amplitude of each frequency?

do you know software that exports spectrograms to images of 500x22000 pixels? all the spectrograms that I know show diffused frequencies and it does not look very good I just want to see the amplitude ...
1k views

### Real and imaginary part of signal after fft

I will take two sine waves i) 0.1 AMPLITUDE with no phase shift ii)0.4 amplitude with some phase shift 20 degree (Considering Both same frequency). In time domain - If i divide signal 1 by signal 2 ...
75 views

### FFT radix-2 in audio - resolution issues - logarithmic scale - sample rate VS buffer size

I would like to ask how to deal with audio DSP. Is FFT good at all to deal with audio? I am working on an app, that generates a single impulse, rout it to an EQ plugin, and the output of the plugin is ...
1k views

### Why is the size of the output of the FFT of a signal is same as the size of the input signal?

I am kind of new to the DSP domain. I was trying to get the frequencies associated with a signal by performing FFT over it. I used numpy.fft.fft for this. ...
413 views

### FFT implementation with decimation in frequency vs decimation in time?

When using FFT implementations which would be the advantages of using decimation in time (DIT) vs decimation in frequency(DIF) and vise-versa? I have read here that in practice there is not much ...
240 views

### FFT - radix 2 - decimation in time -frequency range

​ Hello, I would like to ask how to decrease (make it narrow) frequency range for calculations in FFT radix 2 - decimation in time - algorithm? Let me explain what I exactly mean: When you compute ...