Questions tagged [power-spectral-density]

The Power Spectral Density (PSD) is the distribution of signal power over frequencies.

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How to process multiple coherent samples in time for a frequency response function

I have $K$ time measurements each of both an input and an output process. Each measurement consists of $N$ points. The measurements include a wanted velocity signal $x(n)$ and additive white gaussian ...
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Is it interesting to look at two conditions and compare their power spectral density at frequencies?

so I am doing my thesis in Neuroscience and trying to prove the alpha blockade, i.e. the reduction in power of the alpha frequency band when the eyes are open compared to when they are closed. I used ...
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26 views

BW of a modulated signal

I come across different types of bandwidth. In digital modulation should it be null to null always? when do we use 3 db bandwidth?
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41 views

Produce PSD from a FFT output

I am using an FFT function in PHP language (https://gist.github.com/mbijon/1332348) which works very well, but cant produce PSD from its output: ...
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65 views

noise floor of attenuator

NF of attenuator is same as the attenuation value as the noise floor remains same but signal level gets attenuated? But NF of amplifier depends on the device as it increases both signal and noise?
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“How is the noise floor of RF section is mapped to ADC noise floor for a 10MHz BW?”

My interpretation is if a gain of 40 is used before AGC -40 dBm become 0 dBm and -121dBm (noise level) becomes -81dBm SNR remain same (assuming NF =0 for theretical purposes). Noise floor of ADC is (6....
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Why is mean-square summation of the area under the curve?

Would someone please kindly help me to nail this "simple" issue? My input is a matrix of power PSD and frequency. I need to get RMS and I read this http://vibrationresearch.com/wp-content/...
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149 views

Autocorrelation and Spectrum Density

Wiener–Khinchin theorem states that autocorrelation function and power spectral density are a Fourier-transform pair - see Wikipidia (and lots of other resources). That means autocorrelation should be ...
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Permutation test on two simultaneously recorded EEG signals

I have two EEG signals that are simultaneously recorded (and has been further synced) using two EEG devices, namely device 1 (ground truth) and device 2 (investigational device). Imagine one device ...
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Find signal power in a band by integrating the PSD in a frequency band (and zeroing the out-of-band DFT bins)

I know that directly zero DFT bins outside a frequency band has the side effect of introducing ringing, as this post says Why is it a bad idea to filter by zeroing out FFT bins?. But what about ...
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Comparing similarity of two simultaneously recorded EEGs in freq domain

I have two EEG signals that are simultaneously recorded during the night (sleep). Imagine one device recorded from channel F4 and the other from Fp2. Now I would like to check the similarity of these ...
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31 views

Power Spectrum analysis arbitrary length signals

I have signals belonging to diseased and healthy samples recorded from multiple electrodes. These signals are taken monthly and are of arbitrary length (say 4-5 mins). I am planning to do a power ...
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Power Spectral Density from Probability Density Function

The samples of a signal $x[n]$ are i.i.d. and follow a triangular pdf with $a = 0,\ b = 2,\ c = 1$: The DC-power of the signal is $$\mu_x^2 = \big(\mathbb{E}(X)\big)^2 = \left(\int_{-\infty}^{\infty} ...
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Power in a frequency band: Spectral estimation versus time domain

I wish to find total power in a given frequency band within different time windows of a signal. I see two methods of doing so, first in the frequency domain. One could estimate the power spectral ...
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Changing Coherence function from float to fixed point

I want to calculate the coherence between two audio signals. After referring a few websites, I found that the coherence is calculated by using the equation $(1)$ which is as follows $$\rm Coherence = \...
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Filter a negative SNR signal whose frequency spectrum lies inside the noise frequency spectrum

I am a newbie in Signal Processing and need your suggestion in the following problem. My signal amplitude is 10 times weaker than the noise. Furthermore, the frequency spectrum of the noise and the ...
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32 views

Why coherence function calculation needs averaging of different segments of the signal?

I am trying to understand coherence function calculation. I am working with a non-linear system without any noise. Coherence function is defined as: I understand that coherence is 1 for N=1, but I ...
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Practical implementation of Expected Value?

If i compute the average power of my input signal random variable $X(t)$ as $$R = E[X^2(t)]$$ i.e. as the expected value of a random process, is this really just an estimate of average power? More ...
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RMS of signal vs average amplitude

I am trying to estimate the average amplitude of some signal with frequency 6 Hz, sampled at ~300 Hz. See figures for a part of the signal and its dft calculated using matlab. I estimate the average ...
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64 views

Definition of “Power” in “Power Spectrum” (for translator)

I'm a technical translator who recently undertook translation of documents related to signal processing. Being a novice in the field, I'm searching the web for terminology and concepts. It appears ...
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56 views

Why use PSD to analyze a signal instead of its Fourier Transform?

Let's imagine I have a perfectly known signal $s(t)$ and I want to analyze its frequency components. I noticed that mostly everyone would use the PSD of $s(t)$ to do that, instead of simply use the ...
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16 views

Normalised APSD

How you compute the Normalised APSD of a signal using python's scipy.signal libary. Do you compute only the APSD of the signal and divide it by (PSD * df) or there is something else?
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Perceptual Based Adversarial Audio Attacks

I am reading this paper Perceptual Based Adversarial Audio Attacks I have a doubt what is meant by weighting in the frequency domain and what does Section 3.4-equation-4 wants to convey .Please refer ...
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How to perform a permutation analysis of PSD?

I am new to Python & MNE Python. I want to perform a permutation analysis between the PSD of two conditions (1 & 2), across all subjects. I've written the following code for data that I have ...
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27 views

Fourier Transform of a PSD and response of a PSD input

Does a Fourier Transform of a white noise exist? If so, what is its general form? It is possible to compute the fourier transform of a Power Spectral Density? My problem in detail. I have to compute ...
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How to determine SNR required for adding AWGN noise to clean IQ samples?

I'm doing an experiment w.r.t PSD output. I have generated some 11a IQ samples and checking its PSD output in MATLAB using pwelch and comparing with the PSD output obtained using hardware. Here are ...
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24 views

Oversample or undersample correlated noise?

I wish to measure nontrivial (non-Gaussian) broadband current noise for its distribution and power spectral density. The noise is amplified (with transimpedance amplifier) with some characteristic ...
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PSD Accelerometer and Gyroscope

I used Xsens IMU and collected 1 Hour static data for accelerometer and gyroscope. I used the pwelch analysis in matlab to calculate the onsided PSD. The plots looks the following: How do I ...
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How to extract the Freezing Index from Accelerometer data?

I'm working on a project to detect Freezing of Gait episodes for Parkinson's Disease patients, and according to this paper and other ones, extracting the freezing index which is "The power in the “...
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Welch’s Algorithm of Averaging Modified Periodograms

I am second year Undergrad student in computer engineering . I have a homework problem where I needed to compute Power Spectral Density . I'm using MATLAB as I noticed that it has good documentation ...
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80 views

Wiener Khinchin theorem : struggle in the derivation

I am reading Introduction to quantum noise, measurement and amplification, and I need to understand the Wiener Khinchin theorem: how to derive it. I also need to understand some context around this ...
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Sinusoid amplitude loss in power spectrum estimation using Pwelch method

I am trying to estimate the amplitude or power spectrum of a sinusoidal signal using Pwelch method. The following is the matlab code I use. ...
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50 views

Evaluating discrete spectral density at only a few frequencies

I'm trying to obtain the spectral density at three particular frequencies for a computational chemistry problem that I'm working on (if you are curious, it has to do with the estimation of Nuclear ...
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43 views

Smoothing PSD plot

I am currently working with a signal, and I am interested in plotting its spectra. I have used python, I have computed the signal values, and I have an array that has the time-series values of the ...
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How to determine number of observations based on measurement frequency?

So I'm working on a problem where I'm measuring a signal with two different instruments -- one is a low frequency measurement system (1 Hz), and the other is a high frequency measurement system (200 ...
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How to take the inverse FFT of Welch's power spectral density in Python?

I have calculated the power spectral density of a weakly-stationary signal using Welch's method (as implemented by scipy.signal.welch in Python), and am looking to take the inverse Fourier transform ...
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RMS from calculation from PSD using Welch's method [duplicate]

I've used Welche's method on a vibration signal to get the averaged FFT which I want to used to calculate the PSD from which I can calculate the RMS. Within the Welche method i've use Hann window ...
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52 views

Blackman-Tukey Autopower equation

I am looking over Blackman-Tukey method for Autopower. It uses the DFT after a window is applied on a autocorrelation. $$ Power Spectrum = \frac1{2\pi} \ \sum_{(k=-(N-1))}^{N-1} w[k] R[k] e^{-i\...
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Power Spectral Density units

I am trying to compare power spectral density values (obtained from dsp.SpectrumAnalyzer) with PSD values obtained from hardware which has a VSA. MATLAB's documentation says that " The power spectral ...
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151 views

Cross correlation and cross power spectrum for signal + noise

Quick question about my understanding of cross correlations and cross spectral densities. Let $C_{ab}$ be the cross correlation between the signals $a$ and $b$, i.e., $C_{ab}(\tau) = \langle a(t)b(t+\...
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obtain envelope of spectrum

To extract a 2001-sampled envelope of magnitude of the spectrum of a signal, I have divided the frequency axis into 2001 intervals. In each interval, I find the 3 largest spectrum magnitude values ...
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38 views

Understanding white Gaussian noise variance

Referring to the bellow figure, assume the WGN has a constant PSD equal to N0. When filtered at $B_1 = 100 Hz$, the variance of the time domain noise is $σ_1^2$, and when filtered at $B_2 = 5 Hz$, the ...
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58 views

Calculate autocorrelation of a sinus

I am a beginer in signal processing. I am currently studying a signal $s(t) = \cos(h(t))$, and I have to calculate its autocorellation. Since $h(t)$ is periodic of period $T_s$, I calculated the value ...
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38 views

How is the RMS value greater than its mean square value?

Currently learning about PSD curves to which I have a query regarding the attached curve. Why is the RMS value greater than its mean square value. I understand the RMS to be the the square root of ...
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92 views

Contradictory results from power spectral densities and autocorrelation in shot noise

I have a white noise generator circuit which involves a Zener diode meant to undergo breakdown across a resistor $R1$, and am trying to compare power spectral densities and autocorrelation of the ...
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41 views

Calculating PSD, Cross PSD by using FFT outputs

I am having the FFT results of two distinct voice signals. Let's say the FFT results of these two signals are of the form (a+ib) and (c+id). Now, I want to calculate the PSD of each signal and also ...
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33 views

Calculating Cross Power Spectral density between two complex signals

I have a small misunderstanding of cross power spectral density between two complex signals. I know that it is the Fourier transform of cross correlation between two signals. Let's say the complex ...
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Running the BM3D Denoising Algorithm in Python with unknown noise type, what PSD value should be used?

I am looking to apply the BM3D denoising filter to an image. There is a past post where a user applies the bm3d pypi package to achieve this here. This user applies the bm3d filter as follows: <...
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67 views

Leakage in power spectral density estimation

What does it mean for a power spectral density exhibiting leakes from one frequency bin to other. I am reading a book which states the following: "Often the time series we use as input for our ...
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Noise floor flatness in IQ FFT window

I am doing a simple $P_{in}$ - $P_{out}$ linearity test for my RF generator/receiver system. The generator provides an IQ modulated CW single tone with $P = - 80dBm$ at 1 GHz. If we look at the RF ...

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