The fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse.

learn more… | top users | synonyms

1
vote
0answers
23 views

Conversion into the Q31 Format

I have a Setup, where I receive 24bit ADC samples in the two's complement in 8 bit chunks. Usually I just "converted" them into a signed 32bit integer like this: ...
2
votes
1answer
27 views

Difference between a digital lock-in amplifier and a FFT when extracting phase of a signal?

I am trying to measure the relative phase of a sine wave fixed at a particular frequency in a noisy environment. My initial approach is to simply collect $N$ samples, take an FFT, and then just ...
0
votes
0answers
19 views

FFT in different coordinate systems

Is there a transformation that will enable one to calculate the FFT in an arbitrary coordinate system? What I am interested is the following two cases: The space is Euclidean and infinitely ...
0
votes
2answers
23 views

FFT over a fixed and equal numbers

I've got a vector of $100 000$ numbers. All numbers are equal ($7000$ for example). If I perform FFT over this vector, what will I get? From my understanding, I should receive a fixed DC line. Is ...
1
vote
1answer
39 views

Current harmonics via FFT — do peaks matter?

Typically, one would perform an FFT on a current waveform and measure it's magnitude at multiples of the line frequency (e.g. 50Hz, 60Hz) to get the harmonics, and subsequently the Total Harmonic ...
3
votes
2answers
69 views

Minimum bit-width for fixed point FFT outputs

I was wondering if there is a formula to determine what the best case (minimum) bit-width should be for the imaginary and real outputs of an fixed-point FFT, assuming an input bit width of $M$ ($M$ ...
0
votes
1answer
86 views

Positive and negative frequencies: how to prove they are independent?

This seems to be quite a basic question but is there some detailed proof why interference power (i.e., power spectral density) coming from the positive and negative frequencies are independent? I am ...
0
votes
1answer
29 views

Filtering/Analyzing Complex Data stream

I receive complex I and Q data from an USRP. I want to do a Hamming window LP filter on the data. However, I don't get the grasp of how I use the complex data. It is unusual because most of the time ...
0
votes
0answers
20 views

Frequency autocorrelation function - Communication channel

If we have two discrete stochastic spectra and each spectra has $N$ points. We want to calculate the autocorrelation of these spectra, what should be the number of points in the resulting ...
0
votes
1answer
24 views

Sub Band DFT response

With a DFT lets say I had a signal occupying 0Hz to 2048Hz and i am using 2048 bins. Can a DFT by design (say FFTW) only calculate the responses in a Sub Band like 768Hz to 1280Hz or -64Hz to -256Hz ...
1
vote
2answers
59 views

Extract parameters of a single harmonic

Context I need to extract the parameters of a single harmonic in a signal. For instance if $$ x(t) = A \sin (\omega_0t + d_0) + B \sin (\omega_2t + d_2) $$ then $f(x, \omega_0) = (A, d_0)$. This ...
-1
votes
1answer
59 views

Complex Conjugate

If I have a complex spectrum and I add it to its complex conjugate will I get a zero phase version of the original? Will this also reduce noise? It seems like this is simply phase cancellation. ...
0
votes
0answers
17 views

How to calculate Fourier's coefficients of a $T$-periodic function with Scilab?

I have a vector of a size $N>1$ (it represents the values of a $T$-periodic function on a interval). I want to calculate its Fourier's coefficients with the fft, ...
1
vote
1answer
17 views

Can Sparse Fourier transform be used for sparse signal in other domain

I've read that sparse fast Fourier transform can be used to compute the Fourier transform of a signal that is sparse in frequency domain much faster compared to FFT. My question is that can SFFT be ...
1
vote
1answer
23 views

Matching LPC frequency response to raw sample data frequency response

Background: The intention is feature/formant extraction from speech input. I have used an FFT on raw samples in the past and have done simple peak picking from a weighted average of frequencies over ...
13
votes
2answers
639 views

Why real part of FFT converts image into rotation + original?

I have read this image: taken its FFT (2D) and then Inverse FFT to get exactly the image back. Code is provided for reference: ...
0
votes
0answers
16 views

Motor Current Signal Analysis on a PWM Motor

My goal is to do a Motor Current signature analysis(MCSA) to detect any within a DC-motor.The Motor I am experimenting with, is driven and controlled using a PWM signal with supply PWM "frequency" ...
3
votes
1answer
81 views

unexplainable aliases in spectrogram

My scope has 200 MHz bandwidth and can sample at 4GS/s I'm sampling a 138 MHz RF signal at 500 M Sa/s storing 14 M points. When I plot the spectogram in matlab I get the following ...
1
vote
1answer
46 views

Computation of Only Even or Odd Frequency Bins of DFT

I have an algorithm where I am computing the FFT of a large signal. However, I desire only the even or odd terms of the DFT of the signal, but not both. Currently, I discard these undesired terms. Is ...
1
vote
1answer
64 views

Determining the fundamental frequency/pitch of a note

What I am trying to achieve is getting the fundamental frequency of a note played by an instrument. What I have already done is performing an FFT on a samples of audio file, and here's what I get: ...
0
votes
3answers
61 views

Output signal length after fft

I am trying to understand the functionality of fft.m in matlab . For example: if I input a signal of length $7$, and use the FFT function, the output is of the ...
0
votes
1answer
25 views

Division of complex signal by frequency response

I have a measured signal (time domain) which i take the fft of. I have a measured frequency dependent sensitivity (magnitude and phase (radians) as a function of frequency) which I need to apply to ...
0
votes
1answer
37 views

How do I measure frequency of an audio file into an array?

So I know how to plot fft the audio file within Matlab and a window pops up. My question is, what next? I want to know how to go about measuring the frequency(s). I have two similar audio files, of ...
1
vote
1answer
30 views

sinus generation and it's fft in radians

I'm trying to generate sine signal and display it's fft in radians, byt I meet several issues that I can't understand. Please find my script below: ...
0
votes
0answers
27 views

How to calibrate two microphones to same frequency range

I am recording stereo with two same microphones but they are physically insulated from eachother and have some additions on sound input side. Not to complicate story, I have a human head simulation ...
0
votes
2answers
31 views

Measuring amplitude of a spectral component

I'm trying to measure the amplitude of a spectral component in a signal. The component's frequency is always known beforehand. I take a given number of samples, apply the flattop window to reduce ...
-2
votes
1answer
23 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 ...
0
votes
2answers
33 views

Sampling rate vs sampling time of FFT

I am having some trouble understanding the sampling time and frequency used in the computing of the FFT, and I was wondering if someone could make it clear for me : The Sampling time: the time in ...
0
votes
1answer
71 views

Obtaining the FFT of a data set collected through an accelerometer

I'm using MATLAB to analyse a very large sample of acceleration data collected using the MPU9150 IC. My aim is to plot the FFT for this large sample of data. The daya is of three axes; $x,y,z$ and I ...
1
vote
1answer
44 views

Difference between fft(signal, nfft) and fft(signal)

I want to know the difference between these following commands (matlab) and why I get two different outputs? fft(signal); fft(signal, nfft); I found that ...
1
vote
1answer
52 views

DC component in accelerometer data - filter before or after XYZ Euclidean sum

I'm working on filtering accelerometer XYZ data. The aim is gait-pattern recognition via finding characteristic frequency points and feeding these to a artificial neural network. The trouble is, and ...
2
votes
2answers
126 views

Features of a non-periodic signal for comparison

I am looking for comparing a signal (256 / 512 point discrete | non-periodic ) (obtained after extracting some features from the captured image) with a database of around 5000 signals (256 /512 point ...
0
votes
1answer
26 views

Do I need the sampling frequency in order to gain periods out of FFT?

Currently I am using the transformInPlace() method from here. for a project at university. First of all I thought FFT would be the perfect solution for my ...
0
votes
0answers
19 views

How to get real fft from complex fft calculation using butterfly Decimation in Time approach? [duplicate]

I have written a code to calculate fft using a butterfly structure algorithm. The input to the fft are sampled values of single frequency sinusoidal wave. I need to find real fft, using complex fft ...
0
votes
1answer
45 views

How many DFT bins must I use to get best precision when analyzing melody scale

I need to analyze some signals containing chords. How big DFT spectrum is needed to identify each possible musical note in such a signal sampled at 44100 Hz? I can see that 8192 bins gives some ...
0
votes
1answer
30 views

Where does $\frac{N}{2}$ came from in approximating an N-point DFT?

I've came across the author saying that ... for a real cosine input having k cycles in the N-point input time sequence, the amplitude response of an N-point DFT bin in terms of the bin index m is ...
0
votes
0answers
17 views

How to generate values for frequency axis (y-axis is fft of a signal)? [duplicate]

Suppose I have a signal as a function of time: x(t). If I call fft(x(t)), I will get the spectrum of ...
1
vote
1answer
55 views

How to shift a signal to the center of the frequency domain?

Let's assume I have a 1024 x 1024 matrix that represents the spatial domain. After I perform a FFT and center the frequencies, I get the a signal that looks like the following in the frequency ...
-1
votes
1answer
42 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 ...
1
vote
2answers
83 views

Two-Sided Frequency Spectrum

I am trying to make FFT simulation in Matlab by generating noise added two sinus waves in 60Hz and 100Hz. After adding the noise into these signals then I have applied the FFT as I put my Matlab code ...
0
votes
0answers
19 views

Is adding zeros part of the Hermitian Symmetry process?

I have been reading about DMT/OFDM and every source I find defines their system differently. I simply want to know if zero insertion is part of the Hermitian symmetry process that produces real OFDM ...
3
votes
1answer
68 views

FFT of a $N$-length real sequence via FFT of a $N/2$-length complex sequence

I am doing FFT. The one way I did is to put real part in one array and the imaginary part as zeros and then calculated the FFT. But this take up lots of resources. Now I want to calculate FFT by ...
0
votes
2answers
51 views

Is this graph of Wigner-Ville distribution OK?

I am studying some code for smoothed Wigner-Ville distribution. update 3- solution, graph was over amplified in a 2d overdrive/oversaturation effect. if i divide by 20 only a line is visible. Update ...
0
votes
2answers
32 views

Combining channels into single FFT left/right vs mid/side

I am creating a spectrum analyser to visualize some stereo audio data in real time. I want to display a single spectrum for the input and a single spectrum for the output. The stereo data is the usual ...
0
votes
2answers
49 views

How to do the highest resolution FFT?

I wish to do the FFT of streaming audio data coming into a computer. I am just interested in frequencies from 80 Hz up to 1000 Hz but with a frequency resolution of 3 to 4 Hz and no more. Basically ...
0
votes
0answers
49 views

How to separate opposite direction travelling waves without artefacts?

In shear-waves ultrasound imaging, waves are created which travel in opposite directions. there is need to extract left going and right going shear waves. I have used wavenumber-frequency domain to ...
0
votes
1answer
44 views

Why is this FFT code not working to extract frequencies from a wav audio?

I'm quite new to audio processing and i'm trying to extract frequencies from a wav file. As research papers stated i put the wav audio into a byte array and segmented and trying to apply FFT to get ...
0
votes
1answer
44 views

FFT plot in GNU Radio

i got similar question as in FFT scaling in GNU Radio and quite not clear about the answer given so far. I understood that the FFT plot is a relative value in which we have to use measurement ...
1
vote
3answers
64 views

Performing DFT of streaming audio problem. Is there a limit?

I am trying to write software that will perform the discrete fourier transform of real time data coming from the microphone into the sound card on a computer. I am using Java with the javax.sound ...
0
votes
1answer
40 views

Possible to shift image pixel-wise with FFT?

I know we can shift an image entirely with FFT as http://stackoverflow.com/questions/25827916/matlab-shifting-an-image-using-fft However, is it possible to shift the image pixel-wise? I just found a ...