Questions tagged [frequency-spectrum]

The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain.

Filter by
Sorted by
Tagged with
0 votes
0 answers
30 views

Comparing custom Welch periodogram with Julia's Welch periodogram

I wrote my own PSD struct in Julia for practice purposes. It involves two type of constructors: a "direct" PSD and a <...
lafinur's user avatar
  • 135
2 votes
1 answer
120 views

Effects of Hanning window on power

I have written this function in R to compute the power spectrum density (PSD) of a signal: ...
lafinur's user avatar
  • 135
2 votes
1 answer
106 views

How signal generation affect its spectrum

Im trying to get dft of hanning window. Im trying different methods of generating the same signal, yet im resulting with such different graph of signal spectrum. ...
user8464651's user avatar
1 vote
1 answer
54 views

Trying to replicate results from tfestimate function in Matlab

I have been trying to replicate the results from the tfestimate function in Matlab by performing, from my understanding, the corresponding signal processing steps in a separate Matlab script file. The ...
wolfiesax's user avatar
0 votes
1 answer
29 views

Looking for an online course

I work for a company with expertise in electromagnetics physics, specifically dealing with time domain-based simulation software. We routinely need to transform our results into frequency domain, ...
DrEarlGray's user avatar
0 votes
1 answer
69 views

What function can be used to describe periodicity of the signal

im working on a program in matlab for calculation of sampled signal spectrum, and I have a sinusoidal signal with frequency f=100 Hz, sampling frequency fs=250 Hz, every sample is repeated 4 times (fr=...
Wiktuur's user avatar
0 votes
1 answer
60 views

computing the averge power spectral density with python

In order to compute the power spectral density of a signal, we can use np.fft.ftt in python in the following formula: ...
Apinorr's user avatar
  • 25
-1 votes
1 answer
50 views

Result of complex exponential fourier series approximation and trignometric fourier series approximation are not exactly same in MATLAB?

I have a signal and i am trying to observe its approximations using complex exponential fourier series and trignometric fourier series but i am not getting exactly same result(graph of trignometirc ...
Engr's user avatar
  • 3
1 vote
0 answers
57 views

How can it be possible that I hear people voice from my computer speaker?

I searched on web and apparently can be due to truck drivers communicating at CB band which is around 20MHz. And apparently this communication may interference with the frequencies used by computer's ...
allexj's user avatar
  • 13
1 vote
2 answers
83 views

DFT Matrix Oversampled In Frequency?

Edit 2: I am trying to replicate results from this paper Compressed Sensing with Coherent and Redundant Dictionaries. On page 3 the "oversampled DFT" is mentioned as an example of an "...
coult099's user avatar
0 votes
1 answer
38 views

Since harmonics only generate at multiples of the center freq, is it for this reason that the left part of a FT (like sinc) has no physical meaning?

If we have a rectangular pulse function, we know that after a Fourier transform we obtain a sinc: We know that the left part (negative frequencies) has no physical meaning and it's just specular. It'...
allexj's user avatar
  • 13
1 vote
2 answers
54 views

In the frequency domain of a phase modulated signal, why there are are prominent frequency components which are multiples of sampling frequency?

In the frequency domain representation of a digital phase modulated signal, why there are prominent other frequency components which are multiples of the sampling frequency, other than the main ...
Kiran Gunathilaka's user avatar
1 vote
0 answers
44 views

Is there something wrong with MATLAB's pwelch function?

The normalized factor for windowing, is it $(\sum w[n])^2$ or $\sum w^2[n]$? I try to reproduce the pwelch function, if I set the normalized factor to $(\sum w[n])^2$, I get the same result as MATLAB ...
Devin's user avatar
  • 11
2 votes
2 answers
143 views

Bandwidth of a complex pole

Text from "Fundamentals of Speech Recognition (Rabiner)". A complex pole of the LPC model spectrum can be expressed as $Z_i = > r_i \cdot e^{j \omega_i} $, where $r_i$ and $\omega_i$ are ...
Anantha Krishnan's user avatar
1 vote
1 answer
235 views

Why is there a phasor in the transfer function of an ideal LPF?

I'm learning about Low Pass Filters. My professor said the following is the transfer function of an ideal LPF: $$H_{LPF}(f) = G\Pi\left(\frac{f}{2B_{pass}}\right) e^{-j2\pi ft_0}$$ However, i don't ...
Riccardo's user avatar
-1 votes
0 answers
56 views

Relation between harmonics and quantization [closed]

I'd like to make digital samples that construct sine waves. It's nothing but direct digital synthesis (DDS) before the digital-to-analog converter and filter. I want to make a sinewave sample that ...
chicken's user avatar
  • 19
0 votes
3 answers
79 views

Output spectrum of the direct digital synthesis (DDS)

I have a question about the output spectrum of DDS, which consists of a phase accumulator and look-up table. Since the look-up table stores accurate information about sinusoidal waveform, I think ...
chicken's user avatar
  • 19
0 votes
0 answers
24 views

Issue with cudafft library and fftshift on odd image dimensions

I'm facing with a code I'm implementing for an exam using the GPU. Specifically, the code I'm writing is in C++, and I'm using the CUFFT library to perform the Fast Fourier Transform (FFT). The ...
overflow''s user avatar
0 votes
0 answers
31 views

NUFFT of non-uniform sampling spectrometer

I am looking to apply Matlab's nufft.m function to a signal non-uniformly sampled with a spectrometer, hence measuring values at discrete frequencies. In this case I believe my sample points t will be ...
liamando's user avatar
0 votes
1 answer
27 views

Understanding frequency band specification in wireless networks

I am trying to clear my understanding of frequency bands. When a particular wireless network standard like WiFi 6 claims operation in the $2.4$ GHz or $5$ GHz band, what do these values refer to? I am ...
MaxFrost's user avatar
  • 383
2 votes
0 answers
39 views

What is the cleanest, most transparent way to rapidly excite a resonant bandpass to a given amplitude (for musical synthesis)?

Background Music audio synthesis can be performed using underdamped resonant bandpasses as harmonic oscillators (set to harmonic frequencies of a given note). These can then be excited when input ...
mike's user avatar
  • 523
0 votes
1 answer
75 views

What are the spikes here in the spectral analyser?

I'm learning to use the spectral analyser in Simulink, and tested it with a 500kHz square wave (sampled at 1MHz). When I set the Resolution Bandwidth (RBW) to 700Hz, the plot was beautiful and shows ...
George guo's user avatar
0 votes
1 answer
58 views

Remove noise from lung sound wav

I am working in this dataset data.mendeley.com/datasets/jwyy9np4gv/3? aiming to develop a machine learning model for classifying various diseases based on lung sounds during both expiration and ...
Zayo's user avatar
  • 1
-2 votes
2 answers
135 views

What is the event that repeats itself in sinusoidal signals

I am studying medical imaging and it has been stated that it is sufficient for Nyquist Theorem to hold for the signal to be Bandlimited. I am trying to understand what is the wave in a signal. What is ...
George Ntoulos's user avatar
-3 votes
1 answer
175 views

Assumptions of Nyquist sampling theorem [closed]

Hoping I can save the question and it doesn't get migrated to philosophy stackexchange as Hilmar said in any case I don't think it is a different question the question was always meant to be ...
George Ntoulos's user avatar
2 votes
2 answers
994 views

Why is energy zero at zero bandwidth?

From the video lecture on noise analysis by Razavi here. Can anyone explain in more detail what Razavi said here? Why is the energy at a single frequency (zero bandwidth) zero? Lets look at the ...
hana's user avatar
  • 163
0 votes
1 answer
66 views

Strange spectra of different volume sines

I am simulating mic input with a sine of 100 values that would, in q4_28 look like this (full period): ...
Øyvind Teig's user avatar
1 vote
1 answer
35 views

Correction Factor for np.fft.rfft

I tested the function np.fft.rfft using the following code and determined the magnitude of a $50 \, \textrm{Hz}$ sine wave. ...
Tom's user avatar
  • 121
1 vote
1 answer
74 views

Is a bandpass filter superfluous when the frequency band of interest after applying the FFT is below the Nyquist frequency?

I have time-series data with a sampling rate of 1 Hz, hence the Nyquist frequency is 0.5 Hz. I am interested in the frequency band 0.01-0.1 Hz and I would like to apply a Periodogram to transform the ...
Philipp's user avatar
  • 125
0 votes
1 answer
50 views

Derive PSD of an MA(1) process

Suppose there is a moving average process of order 1 that also includes a zeroth term thus: \begin{equation} Y_t=\theta\left(B\right)X_t = \left(\theta_0+\theta_1B\right)X_t \end{equation} where $X_t$ ...
hydrologist's user avatar
1 vote
0 answers
38 views

Discontinuities in the frequency domain

I'm trying to implement a waveform such the frequency will look like this - $f(t)=f_0+\left(f_1-f_0\right) e^{\frac{\left(t \pm \delta_t / 2\right)^2}{2 \sigma^2}}$ To do so, I calculate it like this -...
Yarden Sharabi's user avatar
0 votes
1 answer
81 views

Decomposing a signal so that the magnitude spectrum of the decomposed signals lie in some specific amplitude range

Suppose I have the following signal: I can compute its power magnitude spectrum: PSD = np.abs(np.fft.rfft(signal)) Now I would like to pick a specific amplitude ...
user572780's user avatar
3 votes
1 answer
149 views

Removing multiplicative noise (signal) in FFT

I've read up a little here on how to deal with multiplicative noise vs additive noise, with the most simple approach to take the logarithm of the signal to remove the noise. I'm wondering how this ...
user70478's user avatar
0 votes
2 answers
29 views

What does the frequency domain of bipolar Alternate Mark Inversion (AMI) look like?

Someone said to me that Bipolar AMI is not low-pass; it does not include the 0Hz in its frequency domain. I doubt that that is the case. However, at present I am unable to do Fourier transformations. ...
tryingtobeastoic's user avatar
0 votes
1 answer
56 views

Does upsampling require a low-pass filter?

I am currently wondering about the frequency spectrum when performing upsampling using linear interpolation. As far as I know, linear interpolation corresponds to a $\text{sinc}^2$ function. If I ...
hajo's user avatar
  • 101
0 votes
0 answers
25 views

Spectrogram of sound pressure data

I have sound pressure data in the form of Pascal,Pascal A-weighted, dB, and dBA. I want to compute a spectrogram in MATLAB.And I want to show color values as sound pressure level (dBA).But when I am ...
Shivam's user avatar
  • 1
0 votes
0 answers
46 views

I need help deciphering an audio file .mp3 file to get an answer. From a game

I was given a .mp3 audio file needed to be deciphered however I don't know how. I found the spectrogram which outlines the words "youtube", so I suspect the final answer might have a youtube ...
max's user avatar
  • 1
0 votes
1 answer
73 views

Finding the impulse response between two microphones

I have made recordings of a single source (musical instrument) with multiple microphones and in the interest of limiting the size of the final project, I would like to find a way to get the impulse ...
arno sica's user avatar
1 vote
1 answer
69 views

Power Spectral Density and Total Power Calculation for Signal

I am currently working on analyzing a signal with the autocorrelation function given by: $$R(\tau) = 100 \cos( 10000\pi\tau) (Λ(2000\tau))^2$$ I need assistance in plotting the power spectral density ...
Javad Ibrahimli's user avatar
1 vote
0 answers
55 views

Spectrum and Fourier transform of a sine wave

Take for example: $x(t)=A\sin(2\pi f_0t)$. The Fourier transform of this signal is $\hat{s(f)}=\frac{A}{2i}(\delta(f-f_0)-\delta(f+f_0))$. If we want to represent the spectrum of the signal we would ...
fi-xgamex do's user avatar
0 votes
0 answers
20 views

Allan variance plot does not match with the true plot

I am trying to simulate an Inertial Measurement Unit (IMU) by generating sample noisy gyroscope and accelerometer data. Currently I am analyzing the simulated gyroscope( gyro) data. Using the noise ...
user146290's user avatar
1 vote
1 answer
96 views

Fourier transform magnitude of the sum of two signals

Let $$\mathscr{F}\Big\{x_1(t)+x_2(t)\Big\}=X_1(f)+X_2(f)$$ I think that in general $$\big|X_1(f)+X_2(f)\big|^2\leq\big|X_1(f)\big|^2+\big|X_2(f)\big|^2$$ but I was wondering if $$X_1(f)X_2(f)=0,\qquad\...
giannisl9's user avatar
1 vote
0 answers
36 views

Calculating k-space coverage from antenna positions

I work with radar and I want to understand which spatial frequencies I can measure, i.e. the k-space coverage, given a set of coordinates of transmitter-receiver combinations. The ideal coverage for a ...
DominikR's user avatar
0 votes
1 answer
201 views

Magnitude and phase spectrum of a periodic signal

Let the following T-periodic signal : I found that $$ x(t) = \frac{A \cdot t}{T} \qquad 0 \le t < T $$ and its Fourier series is : $$ x(t) = \frac{A}{2} - \frac{A}{\pi} \sum_{n=1}^\infty \frac{\...
MOHAMED SALHI's user avatar
4 votes
1 answer
181 views

Applying Lowpass filter on a signal in time domain gives ringing artifacts - how to get rid of them

EDITED AND UPDATED: My signal is an impulse response. In the following figure: The frequency spectrum of the impulse response (original signal) is shown by blue line. The original signal is ...
Tanmayee Pathre's user avatar
0 votes
1 answer
59 views

jumps in spectrogram of frequency ramping

I create spectrogram of a sine wave that changes its frequency from 60 MHz to 70 MHz over a period of 1 millisecond. can someone help me understand why I see those jumps? how can I make it smoother? <...
Yar Sha's user avatar
  • 25
1 vote
1 answer
68 views

Why is the FFT of an even real valued vector not real?

I am trying to find the PSD of a signal by taking the DFT of its auto-covariance sequence. My code is as follows ...
Asmodeus's user avatar
1 vote
1 answer
51 views

Up-sampling images and the Periodicity of the copies

In the three figures below, $H(e^{j\omega})$, $H(e^{2j\omega})$, and $H(e^{4j\omega})$ are shown. I understand that up-sampling shrinks the spectrum. However, I need a few clarifications: Why does up-...
mmcmp's user avatar
  • 13
0 votes
0 answers
36 views

Cross-quantilogram method

What is this method in general? What is the main difference between the quantile cross-spectrum (QS) approach developed by Baruník and Kley (2019) and the cross-correlation function (QS) developed by ...
gurbuz's user avatar
  • 1
1 vote
0 answers
26 views

Noise color in multidimensional frequency space - is there an angular effect or dependence?

I understand that if there is a non-constant level of noise in one-dimensional frequency space, e.g. noise variance increasing linearly with frequency gives "blue noise" in the iFFT space. ...
Samalama's user avatar
  • 111

1
2 3 4 5
27