Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [fft]

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

0
votes
0answers
8 views

OFDM modulator: Transmission time calculation

I have a problem with a certain task. The frequency of the signal sampling at the OFDM modulator output is 20 MHz. The length of the protection period is 2 microseconds and it is 20% of the ...
0
votes
0answers
20 views

When we compute doppler FFT, how can we find values corresponding to negative frequency?

I have a question. In case of FMCW radar processing, we compute 2stage FFT. The first FFT(range FFT) is used to find a distance between a radar and a target, The second FFT(doppler FFT) is used to ...
1
vote
1answer
26 views

Checking Parseval's Theorm for Gaussian signal by using Scipy

I'm trying to check Parseval's theorm for Gaussian signal. It's well known that fourier transform of $\exp(-t^2)$ is $\sqrt{\pi}\exp(-\pi^2 k^2)$. So I implement it by using quad and simps. I think ...
0
votes
1answer
21 views

GCC-PHAT (Generalized cross correlation) always peak at delay=0 on real audio signal

I have studied the GCC-PHAT algorithm to estimate TDOA on audio signals at 2 mics. Here is my MATLAB implementation: ...
0
votes
0answers
39 views

Method for the Localisation of Impulsive Noise in Speech Signal

I'm sorry if this question has already been answered, but I couldn't find anything. I'm working on a program for noise detection and need to locate the position of impulsive noise. The following image ...
0
votes
0answers
33 views

Equivalence of ML and FFT peak finding for Single-Tone estimation

My understanding is Maximum Likelihood and FFT peak finding for a single tone produce the same results assuming the ML is restricted to the same frequencies as the FFT. I was wondering if there was ...
0
votes
0answers
25 views

retrieving complete 2d autocorrelation function from 2d power spectral density function (numpy.fft.ifft2)

My question is at the boundary between signal processing and python. I have a 2d power spectral density function (PSDF) constructed on Nx/2 + 1 and ...
0
votes
1answer
23 views

Clarification on the application of window pre-FFT

Good morning, I have a simple question about the application of a Hanning window before performing an FFT. My application is pretty textbook, i'm decoding a 4-FSK signal. Question: why does the ...
0
votes
1answer
31 views

DFT of a series of RC exponentials

Context: I'm trying use matlab to apply a single-pole filter to a time-domain ramp waveform that is generated by a sequence of time-shifted "RC steps" that are added together. The time domain voltage ...
0
votes
1answer
35 views

Why is the size of results from FFT half the size of the input, while that is not the case in image processing?

When dealing with real data, Fourier Transform produces symmetric results and FFT algorithms discards half of it. An input with 1024 points will yield only 513 points in the output. However, in image ...
0
votes
0answers
20 views

PSD Periodogram smaller segments compared to larger segment

I am calculating the power spectrum of a heart rate variability via FFT and a Welch window. I have a sample of 500 points as the input signal. The signal was broken up into two 128 point segments. ...
0
votes
1answer
22 views

real time signal analysis of output from an audio device

I'm writing a test program that can detect pops/cracks/noise (unknown frequencies and duration) in the audio output of an audio device. The purpose of this program is to reduce human error and make ...
3
votes
1answer
69 views

Why is this recursive DFT algorithm not equivalent to this iterative method?

Edit 1/30 - Taking @Fat32's edits into account, it seems like there is still an issue with the scale of the frequency axis. While version 2 correctly identifies the response at 1 HZ, version 1 seems ...
0
votes
0answers
21 views

Convolution in the Hartley Domain

The convolution Theorem of the Hartley Transform is given by $$ Y_{Ha}(k) = X_{Ha}(k)H_{Ha}^{e}(k) + X_{Ha}(-k)H_{Ha}^{o}(k) $$ where, $$ H_{Ha}^{e}(k) = \frac{H_{Ha}(k) + H_{Ha}(-k)}{2} $$ $$ H_{...
0
votes
0answers
31 views

Accelerometer signal processing

I'm new signal processing (this is my first pratical application), so I ask sorry if my question is simple. My challenge is to see the displacement of accelerometer when I have vibration too. I do ...
0
votes
1answer
45 views

Does dividing the magnitude spectrum of white noise by sqrt(2) give an RMS magnitude spectrum?

I understand that the RMS Amplitude of a sinusoidal signal is around 0.707 ($\frac1{\sqrt2}$) times the Peak Value, but this is not true for noise. However, an FFT of a noise signal indicates ...
0
votes
1answer
50 views

Detrend data with no clear secular trend prior to Fourier analysis?

I am completing Fourier analysis on many different time series of sediment particle flux exiting an experimental flume. Data is collected at a resolution of 1 Hz for durations ranging from ~5,000 to ...
1
vote
1answer
53 views

Why do DFT frequency buckets need to be divided by sample period?

edit: This is my first post in this community. I'm sure that my downvoter had a good reason to do so, but could someone please comment and tell me how I can better format my question? -- I have a ...
0
votes
0answers
48 views

Is discrete cosine transform differentiable?

Is DCT differentiable? I.e. is d(DCT(x))/dx defined? I've seen a few implementations in automatic differentiation software packages, so I suppose the answer is positive, but I'm still missing a ...
0
votes
0answers
50 views

Sampling Frequency, Fast Fourier Transform and some strange results in python

So, I have 2 types of signals - Dirac: $\left[ 1,0,0,0,0..NumberOfSamples \right]$ and Gauss (it's sinus * window_gausian). I need to do some operation in ...
1
vote
1answer
23 views

Quantized error in scatter plots for a hamming windowed LTE signal

I have a time domain signal based on LTE standards. Carrier spacing = 15KHz, Symbols per slot = 6, extended Cyclic Prefix = 512 samples FFT size = 2048, No. of sub carriers = 1200, channel BW = 20MHz, ...
0
votes
1answer
32 views

Failed to Get Silence in Audio Streaming

I want to detect silence in audio streaming. I've been following lot of answers from any website and i feel like know how to do that. but i doubt i'm on the right path coz the result doesn't seems ...
1
vote
0answers
24 views

Resources for learning Sound Processing [closed]

Does anyone know of any resources that explain simply, these are the data objects and variable definitions involved when doing sound processing? I took a class on image processing where we learned ...
0
votes
1answer
48 views

number of samples and Amplitude accuracy,what's the solution to this problem

I'm colleceting data samples from a device (temporal signal) in order to analyze it with FFT function in MATLAB R2015b,first i get N=4063 data points with (delta_t=0.000015s) so my frequency ...
2
votes
1answer
69 views

Comparing multiple signals for similarity

I have multiple (between 2 and 100) signals and need to determine when a significant number diverge from the rest. We're exploring machine learning techniques, but we also want tackle this as a signal ...
0
votes
1answer
63 views

Autocorrelation: numpy versus FFT

I have a series a of values (0 and 1) coming from a Brownian process with drift for which I am studying the autocorrelation. I used two methods: 1) numpy autocorrelation: ...
0
votes
0answers
26 views

FMCW radar 3D FFT for DOA estimation

I'm dealing with transformation of coordinates after I do the 3d FFT doa estimation. Data below is a car in front of the radar board, and the angle of arrival is "0", 50m. Left image is the row has ...
0
votes
1answer
24 views

How to custom optimize cuFFT for a mini batch of multi-channel images?

I am reading a paper, which has the following paragraph. Current GPU implementations of the FFT such as cuFFT are designed to parallelize over individual transforms. This can be useful for ...
0
votes
0answers
18 views

Is it customary to use the period as coefficient when sampling the impulse response?

I have an analog, continuous impulse response $$h_a(t)=u(t)\cdot\sum_{n=1}^4A_ne^{s_nt}$$, and by sampling it with the usual method I get $$h[n]=\Delta th_a(n\Delta t).$$ Now, that $\Delta t$ is a bit ...
0
votes
1answer
51 views

Threshold for peak detection of noisy signal in frequency domain

I have a noisy signal (Gaussian Noise) with a known SNR and known Noise variance. This signal contains a number of Frequency components. My ultimate objective is to detect the components of the signal....
-2
votes
1answer
16 views

performing FFT on Voltage measurments to get Z(f)

I have a csv file containing measurments a system's step response when the step is current and the output is the voltage. output looks something like this and the it's evenly sampled provided I know ...
2
votes
1answer
39 views

Performing DFT twice on an image. Why am I getting an inverted image? [duplicate]

I was asked to perform DFT on an image twice as a part of my school assignment. Why am I getting a blurry inverted image when I perform DFT on an image twice? Sorry, I'm new to image processing and ...
0
votes
1answer
40 views

Autocorrelation sequence in terms of Fourier transform of the underlying signal

Let $x(n)$ be a sequence of length $N$, which is zero outside the interval $(0,N-1)$. Let $X(k), k=0,1,\cdots,N-1$ be the FFT coefficients of $x(n)$, that is, $X(k)=\sum_{n=0}^{N-1}x(n) \exp\left( -\...
0
votes
2answers
69 views

why is my FFT magnitude of real time recording so volatile?

My goal is to do spectrum analysis of a gear motor. I used Python with the Pyaudio package and made a crude spectrum analyzer that displays the FFT as the sound is being recorded. I recorded 10 ...
1
vote
1answer
28 views

Best way to resample an OFDM signal without interpolating + filtering?

I am working on a custom transceiver with a sampling rate of 3.84 MHz (256 OFDM subcarriers at 15 kHz, although 56 subcarriers are null). I would like to resample the signal to 5 MHz, in order to use ...
0
votes
0answers
24 views

Decoding data hidden using “echo hiding” technique

I'm working on a little project, which centers around steganography. As part of it, I want to implement the audio echo hiding method, but the problem is, I've never done anything related to digital ...
0
votes
1answer
36 views

Linear Chirp parameters from a segment of the signal

Edit:" please see the attached figure. The blue part is all I have. Also, you can neglect the noise term. Assume the signal is deterministic. Typical values of the unknown parameters $\alpha$ and $\...
0
votes
0answers
26 views

How to make function in time domain after fft fit with the corresponding function in frequency domain?

For example, I want to use fft to transform the simple function exp(-x.^2) defined in time domain. And the corresponding funciton in frequency domain is sqrt(pi).*exp(-k.^2/4). And I use the upper ...
0
votes
2answers
50 views

Zero-padding, energy conservation

When calculating the FT of a signal, and the FT of that same signal but after having applied zero-padding to it, should't the amplitudes of the FT of the zero-padded signal decrease with respect to ...
0
votes
0answers
15 views

Use 2D FFT to replace 2D Discrete Fourier Transform (MATLAB)

I met a problem. I ran a code to implement the 2D discrete Fourier Transform, here is the code: ...
0
votes
0answers
41 views

Why convolution in time and frequency domain are not equal?

I was writing this Jupyter Notebook. Then, I unexpectedly faced two visually similar output, but their numerical results were very different. This is the code I used for convolution in the time ...
0
votes
1answer
30 views

Audacity Spectogram view: how to see exact frequency and intensity under the cursor?

In the Spectogram view, simply clicking anywhere with the selection tool gives a vertical line to the top ruler, and shows at the bottom the exact sample, H:MM:SS, or other time coordinate you'd want. ...
1
vote
1answer
76 views

RF demodulation for dummies

Given a signal that's been FM encoded on a carrier wave, what are the individual steps I need to take to demodulate it, and recover the original signal? I don't have a background in signal processing,...
0
votes
0answers
27 views

About the power spectrum and confidence upper limit of a time-series data

For now, I have a coupled system with 5 variables and use the Runge-Kutta method to integrate. ...
0
votes
1answer
35 views

Will noise cancellation with playstation eye improve my spectral analysis?

Im doing some beginners spectral analysis for a homemade reactive RGB LED project and was thinking of ways to improve the accuracy of the audio analysis. Im using a Playstation eye with a Raspberry Pi ...
0
votes
1answer
33 views

Number of discrete samples required for the longest wavelength

I am trying to understand the effect of the critical Nyquist frequency when applying the Goertzel algorithm for estimating the power spectrum of a discrete signal. (Goertzel doesn't really matter, ...
1
vote
0answers
63 views

Applying DFT to OFDM signals above Nyquist rate

Consider an OFDM signal which has $N=8$ subcarriers and is band-limited to $[-B/2,B/2]$, $\sum_k x_k e^{j2\pi kf_0t}$ where $f_0=\frac{B}{N}$. For this case the Nyquist rate is $2\times B/2=B$, i.e., ...
0
votes
2answers
83 views

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 ...
0
votes
0answers
55 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 ...
0
votes
1answer
34 views

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 ?