Questions tagged [frequency-domain]
The frequency-domain tag has no usage guidance.
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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 ...
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0answers
22 views
Frequency Domain - Meaning [duplicate]
I'm new in digital signal processing and having hard time understanding this. By Fourier Transform I mean Discrete Fourier Transform as it's the only one I'm learning.
As far as I know Fourier ...
0
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1answer
30 views
LP to BP transformation steps
Considering the following problem, What i know to convert from LP signal to BP signal is to:
Draw the FD of the LP equation
From it I can draw the FD for BP
From this graph I can deduce the equation ...
1
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1answer
38 views
How do I warp a 1 dimensional signal in frequency domain?
I want to implement VTLN (Vocal Tract Length Normalization).
It is equivalent to warping the signal in the frequency domain according to the following graph.
I can't wrap my head around how one ...
1
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1answer
46 views
Visualising OFDM subcarriers in the frequency domain
Im struggling to understand why in some images the frequency domain shows clear bars with amplitude and phase and with 0 frequency variation (it is clear that the frequency of the waves does not ...
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2answers
78 views
Sampling with an alternating impulse train
The have the following question:
A signal $m(t)$ with bandwidth 500Hz is first multiplied by a signal
$g(t)$ where $\displaystyle g(t)=\sum_{k=-\infty}^{\infty}(-1)^k \delta(t-0.5*10^{-4}k)$. The ...
0
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2answers
41 views
How to interpret correlation angle from frequency domain
Since the coefficient of one frequency could be seen the length of the signal projects on that frequency basis.
And the length is
$$|a|\cos\theta= \frac{a\cdot b}{|b|} $$
If I divide the ...
1
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2answers
63 views
Is it right to talk about dynamic range on frequency domain?
I'm comparing three frequency response's plots from simulations and experiments and I observed that two of them look like clamped to a DC component, where the max dB value is i.e. 100 and the min is ...
0
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1answer
48 views
Counting blinks of a LED
I'm working on an algorithm that counts blinks of a LED. I have series of non-neagtive integers. They represent brightness of a LED in time. I give you two examples of these integer series below. ...
1
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1answer
50 views
Break a signal into segments, add them together and then perform an FFT on the result
If you break a 4 second signal into 0.5 second segments, add them together and then perform an FFT on the resultant 0.5 second data.
Will the FFT / frequency spectrum be the simlar to an FFT on the ...
0
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2answers
113 views
Why do frequencies of analog signals range from $-\infty$ to $\infty$ while frequencies of digital signals are restricted to $[0,2\pi]$?
In Fourier analysis while dealing with discrete-time signals, frequencies range from $0$ to $2\pi$ why? Intuitively how can i understand it?
0
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1answer
358 views
Computation of the Inverse DCT (IDCT) Using DCT Or IFFT
Is there a way to compute the inverse discrete cosine transform (type-2) by leveraging either a DCT, FFT, or IFFT algorithm? I have seen ways to compute the DCT using FFTs, and I've seen ways to ...
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2answers
731 views
Understanding the frequency domain [duplicate]
I'm trying to understand what frequency domain is. I found general explanations on the Internet, for example:
frequency-domain graph shows how much of the signal lies within each given frequency band ...
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1answer
80 views
Convolution offset and factor in frequency domain
See this link. The following Convolution in Spatial domain code is written in C#.
...
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2answers
265 views
Finite and Infinite support in time and frequency domain
It's known that signals with a finite support in time has an infinite support in frequency (talking about Fourier Transforms).
A common example that is given for the claim is the triangle function ...
0
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1answer
53 views
why transmitting a long pulse its spectrum gets spread?
I'm transmitting an RF signal with a CC1101 at 440 MHz.
This signal is a constant of 1, so the spectrum should be a delta.
Using a SDR dongle, I've checked the spectrum and it's wider than a delta ...
0
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1answer
49 views
Bilateral Laplace transform and existence of Fourier transform
I was reading from Athanosios Papoulis' "The Fourier integral and its applications." and they referenced the bilateral Laplace transform and Fourier Transform as:
$$F(p)=\int_{-\infty}^{\infty}e^{-pt}...
0
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1answer
39 views
Complex FFT reversing
I've succeeded to compute complex FFT of a data array of interleaved values using the arm_cfft_f32() API of the CMSIS DSP library for Cortex-M4, and got in the same array the FFT results as frequency ...
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0answers
12 views
Is there a criterion that says at what point you can distinguish 2 partially overlapping Lorentzian peaks?
If you have 2 Lorentzian peaks that partially overlap and you have some frequency resolution df (your points in frequency space are separated by df) and both Lorentzian peaks have FWHM $\Gamma$ is ...
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4answers
480 views
Why does the frequency in the DFT have to be an integer?
I don't know why the result of DFT and FFT in MATLAB like below images..
fs=128;
t=0:1/fs:1-1/fs;
x=cos(2*pi*3.5*t);
X=fft(x);
N=length(x);
n=0:N-1;
f=fs*n/N;
plot(f,abs(X)/N);
If I set the ...
0
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0answers
40 views
How to properly filter an image in the frequency domain using matlab
my problem is the next:
I´m starting to understand the world of image processing and I´ve been kind of bugged with the idea of filtering images in frequency domain. I have made a test programm in ...
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0answers
55 views
Plot Background Noise
I am a total newbie in signal processing.
I have been trying to plot on simulink a time/frequency domain noise in PLC (Powerline Communication) that matches a real-world research "...
2
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1answer
185 views
How to calculate a delay between two signals in frequency domain?
Calculation of a delay between two signals is generally done by finding the maximum in the cross-correlation of the two signals (in time domain):
$$
\tau_{delay} = \arg\max_\limits{t}(f(t) \star g(t))
...
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0answers
15 views
What is the best spline to interpolate freq analiser graph
the question is as it is in the topic: What is the best spline to interpolate freq analiser graph?
I am looking something simply and fast to implement. I read about catmull-rom it looks it could be ...
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2answers
80 views
Why are LTI filters not able to output frequencies not present at the input?
I know this a very basic question but I'm just having troubles understanding why.
Thanks in advance!
1
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1answer
57 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 ...
0
votes
1answer
158 views
characterization of DC component
Consider the following two statements:
In time axis:
A signal without a DC component is a signal which doesn't have the zero frequency (the DC frequency)
A signal without a DC component is averaged ...
4
votes
2answers
693 views
Discontinuities in the FFT
So I am taking the Fast Fourier Transform of the following function:
$$ x[n] = \displaystyle\sum\limits_{i=0}^{5} A_{i} \cos\left(\frac{\omega_{i}}{\omega_{s}} n + \phi_{i}\right) $$
Where the ...
0
votes
1answer
283 views
When listening in to an AM signals of various frequencies, how do we exactly tune in?
Alright, so I read on AM and Double Sideband AM, but I don't the more fundamental idea - the frequencies.
Frequency is just: $ \frac{1}{T} $, where T is period
So difference between 5 Hz and 30 Hz ...
1
vote
1answer
1k views
Simulation of FMCW radar in frequency domain
I would like to simulate a FMCW radar in the frequency domain. I used the code (Matlab) I attached below. Specially I am interested in the phase spectrum of the beat signal. In a further research I ...
1
vote
2answers
185 views
Convolution and Modulation Theorem with Octave Example
As far as I know, convolution theorem stated that
$$
x[n] * y[n] = X(e^{j \omega}) Y(e^{j \omega})
$$
$$
X(e^{j \omega}) * Y(e^{j \omega}) = x[n] y[n]
$$
I tried a simple experiment using GNU Octave ...
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1answer
143 views
Convolution of BPSK signal in frequency domain implementation
Here is the simplified version of code which implement convolution of BPSK-signal in frequency domain:
...
2
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1answer
254 views
Meaning and unit of frequency in Laplace (Fourier) transform
Imagine transfer function obtained by Laplace transform, for example:
$G(s) = \dfrac{1}{s+1}$
Now, I would like to do some frequency analysis, so I replace the $s$ with $\omega i$ (let's consider ...
0
votes
1answer
32 views
Does each pixel of the original image has a corresponding coefficient for every scale and every direction calculated by the DWT?
I want to take a pixel and find its coefficients calculated by the discrete wavelet transform for every scale and every direction. But as the DWT subsamples images, I don't see how to do that. Do I ...
2
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2answers
587 views
Is it possible to apply a frequency filter a time domain signal?
Is it possible to frequency filter a time domain signal, without converting the signal to a frequency domain..
My question comes in regards how MFCC according to wiki and other pages describe the ...
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votes
0answers
79 views
How can I determine the similarity of frequency spectra?
I want to determine a measure of similarity between two time series of different length. More specifically, I want to compare single channel EEG data of some specific phase during seizure activity of ...
0
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2answers
121 views
Fourier transform
Fourier transform of a DC signal is an impulse at the origin.
Now if the spectrum of a signal is the plot of the amplitudes of the respective frequencies of each harmonic, then the Fourier transform ...
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vote
2answers
439 views
Closest two frequencies that can be resolved
Forgive me if I misuse the terminology.
I wish to transmit two slowly changing analogue signals by amplitude modulating two higher frequency sinusoidal carrier waves. I will superimpose the two AM ...
0
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1answer
78 views
Convert fixed frequency bandwidth samples to time domain
I'm trying to convert signal (bandwidth 1400 MHz, start freq 9300 MHz, stop freq 10700 MHz, step 3.5 MHz) from frequency domain to time domain. Signal data in frequency domain, as well as signal data ...
-1
votes
1answer
218 views
Stationary signal: time-domain vs frequency domain
If I understand correctly, a signal is stationary if:
time domain: it's generated from the same distribution at each instant time.
frequency domain: its frequency content does not change in time.
...
0
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2answers
557 views
Implementing a Band-Pass Filter from Scratch
I am trying to implement a band-pass filter from scratch. Here is an article which I thought explained the nuts and bolts of how to build one; the author combines a low-pass with a high-pass filter (...
0
votes
1answer
531 views
frequency domain zero padding in OFDM
I have a matlab code for OFDM system, in this code the auther added a zero padded subcarriers before the IFFT stage, in the middle of the raws, and added zero padded guard interval after IFFT, my ...
0
votes
1answer
371 views
Derivation of downsampling in the frequency domain
I'm having some trouble with this derivation
$$s_d = \begin{cases}1&\text{for}\quad m\quad\text{multiples of}\quad D\\ 0 &\text{otherwise}
\end{cases}$$
then $s_d$ is somehow rewritten to:
$...
0
votes
1answer
410 views
Corresponding frequency domain filter of spatial domain filter in image processing?
My question is:
Suppose that we have low pass spatial domain filter that averages 4-connected neighbors of that pixel and it doesn't consider its pixel in averaging. Find its corresponding filter in ...
0
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0answers
961 views
Operations applied to functions in time domain and frequency domain
I am trying to make a succinct summary of how algebraic operations in the time domain translate in the frequency domain (via the use of Fourrier/Laplace transforms). Here is what I have derived so far:...
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2answers
241 views
Smallest FFT buffer size given zero-padding
I am currently working on a project that involves processing an audio signal by dividing it into chunks of size B. The buffer is then zero padded to have a size of 44100 points, after which FFT is ...
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2answers
2k views
Why Frequency Domain conversion is Important in Digital Image Processing?
Any Image enhancement technique can be easily applied to the normal images. Still, most of the folks say that frequency domain conversion of the images can lead to better enhancement. Why do we need ...
3
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2answers
97 views
How to discard coefficients in the frequency domain without losing too much quality?
I was reading a text that shows that one can throw away 66% of the coefficients and gets an image that is still acceptable.
I tried to replicate it using python (last example) and selectively ...
0
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4answers
93 views
Why does changing the frequency of a single component change total sum of amplitudes in my FFT?
I have the following code which generates a single simple sine wave with amplitude $1$ and then calculates the Fourier transform, normalises it, and finally takes the sum of all the components.
...
0
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2answers
364 views
What proportion of a padded FFT should be actual values
For a given signal, I've been told that you can pad the vector with $0$s at the end to get a larger DFT, and as a result get more precision in frequency bins.
What are the limits to this approach?
...
