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

learn more… | top users | synonyms

0
votes
0answers
16 views

What's the use case and explanation of frequency-domain subsampling?

In my solution to a certain problem I use subsampling in the frequency domain. Amazingly, it produces good results. Is it really that awkward to see subsampling in frequency domain? What the ...
2
votes
1answer
46 views

How to analyse Phase spectrum of 2D signals?

I am beginner in image processing. When I applied Fourier transform on two images say Lena and Cameraman etc., I obtained magnitude and phase spectrum for each one. I want to concentrate on phase ...
1
vote
2answers
48 views

DFT vs FFT: does odd number works for DFT only?

I am always confused between FFT and DFT. In both algorithm, it has been assumed that the signal is periodic (so my understanding is that, if you have a 20 sample point signal, and you do DFT or FFT, ...
2
votes
1answer
52 views

Is image reconstruction possible using its magnitude only?

Let us take any image like Lena or cameraman. I know that when Fourier transform is applied on image,spatially global features like amplitude and phase are obtained locally. My question is whether it ...
0
votes
1answer
31 views

Phase is not linear in frequency domain after delay in time domain

When impulse response is symmetric around sample zero phase entirely zero. in = 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 0 , 0 , 0 -> This gives zero phase result As I know if I apply a delay in time ...
0
votes
2answers
49 views

Phase response of FFT in practice

As I know if the impulse response is symmetric around sample zero phase response should be entirely zero. The code below just set a rectangular window for vector "in" ...
0
votes
1answer
38 views

Beginner - use FFT to display spectrum/equalizer

At first, I want to say that I'm totally beginner in DSP and I don't have enough math education to understand Fast-Fourier transformation. I'm a programmer and I want to archieve something like ...
1
vote
1answer
71 views

Basic question about chirp signal

Suppose I generate chirp signal with the following python code: ...
2
votes
1answer
50 views

Efficient calculation of correlation function every N_th point

I would like to calculate a long correlation function of length say, 1e6 points. I have a prior knowledge that the correlation peak will be in point k*1000. Is there an efficient way to apply this ...
0
votes
1answer
48 views

Extracting amplitudes of components from FFT

I have a 4096-point FFT of a continuous pipe organ sound (no windowing). I wish to extract the relative amplitudes of the various harmonically-related sinusoidal components for voicing analysis. I ...
0
votes
0answers
25 views

Does FFT magnitude spectrum graph consist of spectral lines or points

Hi I am using zedgraph to plot an FFT of a signal using c#.The FFT spectrum gives coefficients vs the frequency bins.I am confused whether the plot should consist of spectral lines(ie verticle lines) ...
0
votes
1answer
30 views

Microphone Array null steering unexpected results after IFFT

I am writing an open source microphone array simulation program:SharpEar. When I give uniform weight to microphone array elements, the result in the angle is a sinc function as expected. There are 41 ...
0
votes
1answer
25 views

Window function for signal with 3-5 sine waves inside

Should I apply some window before FFT if i want to find 5 frequencies in signal? Signal is pure 5 sinusoids + some noise generated during trecording on analog cable.
0
votes
1answer
19 views

Frequency Domain Filtering with big kernel size

I use FFT to do filtering in frequency domain, but when I use big kernel I got shift on border, I think it's due to nature of cyclical convolution and I need to do more zero padding. But how to ...
0
votes
0answers
30 views

Signal FFT conversion problem

I got the time domain signal from experimental work as per below. The blue is x-direction,green is z-direction and red is y-direction. When i convert the signal into FFT using MATLAB, I got as per ...
0
votes
0answers
33 views

How to plot Full spectrum with negative frequencies

I'm trying to do frequency analysis on signal of a rotating shaft. The signal is generated in two measurement planes i,e X-position and Y-Position. I was able to use fft and transform into frequency ...
1
vote
1answer
44 views

Processing 47-53 MHz signal sampled at 96000 Hz

I am fairly new to the topic of DSP and FFT and I have hit a mental block. For a project, I am trying to pick out frequency's with amplitude peaks in a 47-53 MHz signal. This signal is being put ...
0
votes
2answers
55 views

Negative values of the FFT

I try to describe a simple signal in the frequency domain with the use of FFT function: ...
0
votes
2answers
67 views

Simple FFT convolution with impulse response wav file doesn't give the right results

I have been trying to find a solution to my FFT convolution problem but everything that I have found while searching hasn't been helping me. I have a working forward and backward FFT function, that I ...
0
votes
0answers
23 views

How to scale FFT Output for Count Data

I have page count views sampled once per day for 7 years, and I'm FFt-ing this data to look for periodic trends. I'm accustomed to performing FFT's on voltage outputs from bench equipment and ...
0
votes
0answers
21 views

Stationarity tests of time series in the frequency domain for signal analysis in FFT or multitaper

Strict stationarity is the strongest form of stationarity. It means that the joint statistical distribution of any collection of the time series variates never depends on time. So, the mean, variance ...
0
votes
0answers
24 views

Measuring typical seperation between patches using 2D Fourier Transform

I need to extract information about the typical distance between the black patches in an image like the one I attached here. Typical distance would be the the most frequent separation between two ...
1
vote
1answer
55 views

Real-time block processing setup on ARM

newbie question here. im working on a system thats running 32khz sampling rate, audio, 16 bit dac. currently our system had a very hard latency requirement of 1 sample. so no problem, we read 1 ...
0
votes
2answers
50 views

Transforming FFT to Detect Baud Rate

I've seen in practice taking an FFT of a signal, then transforming it by the 2nd, 4th, etc. power (depending on signal type) to determine the baud rate. I'm trying to implement this in my code, but am ...
0
votes
0answers
27 views

Square signal: from a period histogram to a frequency analysis

I have a dataset of square waves (with periods slightly varying from the nominal one) and I read the times between edges with a PIC microcontroler, so I can obtain a histogram of periods. The data ...
0
votes
0answers
44 views

Combine multiple FFT

I have been acquiring data through ADC and into memory, the input signal are square waves that step down in frequency as time goes by. Due to memory, I have a fixed maximum number of samples per FFT. ...
0
votes
0answers
42 views

How I can optimize the DFT become the FFT?

As title, I am trying to understand fast Fourier transform, but I have a little trouble, that is: The DFT said that we must multiply the matrix 2n x 2n with ...
0
votes
2answers
103 views

time domain data into FFT using Matlab

I do like to generate the FFT from time domain history data (experimental lab) using MATLAB. I am not so sure if my coding is right? Can someone verify the coding. My code is as follow: ...
0
votes
1answer
34 views

Apply FIR filters to Extract Stego from WAV data

I appreciate anyone that takes a moment to help me with this problem. I've been banging my head against the keyboard for a while, searching forums and DSP tutorials and I can't figure this problem ...
0
votes
1answer
47 views

What is the correct inverse function of the Matlab function fft? [closed]

I used the Matlab function fft but I am not sure which function is the correct inverse to go back to the time domain.
1
vote
2answers
48 views

Fixing my FFT Plot

I'm trying to plot my FFT of File. This i my result. I made my FFT application: I want to obtain something very similar to plot of WaveSpectra, please tell me my mistakes.. My FFT The result from ...
0
votes
0answers
30 views

Matlab coding for bandwidth interval

I have time domain history data. Then, I convert it into FFT to get the frequency domain history data. The problem is, how to determine the bandwidth of the FFT data? Is it automatically synchronize ...
1
vote
0answers
25 views

Noise Removal from an image

What type of filters can be used to remove Poisson noise in an image? I tried applying Gaussian filter to few points in the spectrum.
3
votes
2answers
125 views

OFDM transmitter bandwidth

Theory Suppose an OFDM transmitter with four subcarriers is implemented using the structure shown below. If the serial data input rate is 40 bps, each parallel stream will run at 10 bps. ...
0
votes
1answer
57 views

Real valued FFT in Matlab

I'm trying to compute FFT of size (N/2) for sequence of real values of length N. I'm using this recipe. Here is my code in matlab: ...
1
vote
0answers
28 views

Relationship between FRF, FFT, AutoPower, & CrossPower

Given A is an input signal & B is an output signal: I know that the frequency response function (FRF) is defined as the CrossPower of AxB divided by the AutoPower AxA. Logic tells me I should be ...
0
votes
0answers
31 views

Applying a custom filter to FFT results?

I think I am missing something here and I do not quite understand why. Background: I am collecting quadrature signals from a software defined radio. There are two signals, the I, and the Q which is ...
0
votes
1answer
80 views

Phase difference between two sinuisoidal signal

Currently, I have two signals, the main components of both signals are 60Hz, but both also have weaker response at 180Hz + small amount of noise. As shown in the photo below, I want to find the phase ...
1
vote
1answer
34 views

Energy and SpectralFlatnessMeasure taken for PCM audio VoiceActitivyDetection

I'm trying to implement the VAD algorithm in this paper: http://ms12.voip.edu.tw/~paul/Papper/Steganography/iLBC/(VAD)Real-Time_VAD_Algorithm.pdf I'm polling a microphone on an Android phone, and ...
0
votes
1answer
51 views

Formulas to plot Frequency Impulse Response Coefficients

I made this question newbie:Plotting FFT and Impulse Response Coefficients, using Java I have the IRC: Impulse Response Coefficients: $h(k), k = 0, 1,.., N-1$ Low Pass: ...
0
votes
1answer
35 views

Has anyone used Siglib? Answer a question on the FFTr function?

I'm hoping someone - anyone can answer a question on the Siglib library call to perform an FFT on data. There's no examples anywhere I can find that provide a real application using data from an ADC, ...
0
votes
2answers
57 views

Spectrogram of a chirp and its FFT

This question follows from an answer to this other question: Conceptual question on FFT and chirp signal I wrote a code starting from the spectrogram to compare it with the FFT result. ...
0
votes
1answer
35 views

How to narrow the frequency band of a wavelet

I have a ricker wavelet with a dominant frequency of 15 Hz. The fourier transform shows its frequency band is almost to 50 Hz. How can I narrow the frequency band of this 15 Hz ricker wavelet? I ...
1
vote
3answers
93 views

How to determine SNR from FFT of measured data?

I am doing impedance measurements, where I do a frequency sweep of a test current, and I measure the resulting voltage. Offline, I compute the FFTs of the voltage and current, and I want to make sure ...
1
vote
2answers
82 views

FFT: Removed padded zeroes?

I have an application where I do this: DFT->Filter->IDFT on a range For computational performance I'm zero-padding my FFT to a power of two, but when I ...
0
votes
3answers
69 views

detect impact from digital audio

I've started a hobby project which is to detect and count the number of impacts (for example someone clapping, bouncing a ball or hitting a boxing bag). I've been reading and playing around (in java) ...
1
vote
2answers
77 views

FFT Overlap in Matlab

I am getting incorrect amplitude of my signal post FFT (90% error) and it does not improve after applying any of the window functions prior to FFT. After reading a number of articles, I believe FFT ...
0
votes
1answer
75 views

Conceptual question on FFT/IFFT (IFFT existence)

I was reading "Discrete and continuous Fourier transforms: analysis, applications and fast algorithms" written by E.Chu and, at some point, I found something that I could not completly understand. ...
1
vote
2answers
74 views

Using only positive frequencies in fourier domain, How will it affect the ifft?

I am going to do some kind of transformation and transform a data to another domain, and again back to the first domain. For this, I take a fourier transform of the data and separate the positive part ...
2
votes
2answers
114 views

system response: time vs frequency. Why do I get different magnitudes?

I am simulating a linear system described by the following equation $m \ddot{x} + c \dot{x} + k x = A \sin(\omega t)$ ...