Questions tagged [noise]

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Commutator of an operator with its Hermitian adjoint in linear quantum systems

I have a commutator of a single-mode photon field operator $\alpha$ with its Hermitian adjoint $\alpha^{\dagger}$. [$\alpha$, $\alpha^{\dagger}$] When this commutator gives a negative value, $\alpha$ ...
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2answers
54 views

Under what assumptions does $\langle\eta(t_1)\eta(t_2)\rangle=\int d\eta_1d\eta_2\eta_1\eta_2p(\eta_2,t_2;\eta_1,t_1)$ become $\delta(t_1-t_2)$?

In the Langevin model, if we make the assumption that the random force $\eta(t)$ acting on the Brownian particle is a stationary, Markovian, and gaussian process, does it automatically ensure that the ...
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Compute the variance of spectroscopic Shot Noise in cosmology context

I would like to know the right expression for the expression of variance of Shot noise in spectroscopic probe. Sometimes, I saw $$\sigma_{SN,sp}^{2} = 1/n_{sp}$$ with $n_{sp}$ the average density of ...
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47 views

Pink noise and averaging

Disclaimer: I am aware this is somehow at the boundary between physics and statistics, but I have the impression that it is more likely that somebody doing/studying physics, rather than statistics, ...
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1answer
43 views

Is this intuitive understanding of “averaging over all realizations of a noise” correct?

Consider a continuous random variable $\eta(t)$ such that $$\langle \eta(t)\rangle=0, \forall t$$ where the average $\langle ...\rangle$ is taken over all possible realizations of the noise at any ...
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54 views

Why do I hear static when I plug in my earphones incorrectly?

I use simple earphones which are wired with my laptop. Most of the times I unconsciously plug them in without looking and at times instead of going in the port they touch the laptop body near the port ...
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3answers
67 views

Deterministic and stochastic chaos

I have a question about chaos, but first a foreword of what I understood. Noise refers to the random variation of values. Usually unwanted, noise causes a measurement to fluctuate over time. Chaos ...
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1answer
24 views

Relationship between intensity and sound level

So I know that for every tenfold increase in intensity, the sound level increases by 10 dB. So if the intensity is increased by a factor of 100000, the sound level increases by 50 dB. I also know that ...
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1answer
47 views

Noise Cancellation - Destructive Interference

We know that active noise cancelling headphones work by playing a signal in your ear which is 180º out of phase with the ambient noise. If we compare the two waves, the peak in one wave is completely ...
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20 views

Relationship between noise spectral density and quantum absorption/emission: I don't understand the derivation

In this paper, on page 57 he performs a calculation that I don't understand. Maybe there is an implicit physical assumption behind so this is why I am asking it here. The context (not necessary to ...
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9 views

Expression for covariance matrix as a function of distance

I am studying a tracking problem in which the measurement noise, assumed to be Gaussian, increases as a function of the distance to the target. I am seeking an expression for the covariance of this ...
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2answers
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Can unjammable radio communication be achieved by transmitting an error-correcting code of high-energy pulses in a secret, unpredictable pattern?

Signal jamming seems like an annoyingly simple way to sabotage a lot of interesting ideas. It has historically been used to block reception of propaganda broadcasts, and also to ruin military ...
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Data augmentation in $k$-Space

I am working on denoising data in $k$-space for MRI (magnetic reasonance imaging) using Convolutional neural networks, and I am wondering what would be some suitable data augmentation techniques ...
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Normalization of Phase Noise / RF Power Spectrum to 1 Hz RBW

I used a Rohde & Schwarz Phase Noise Analyzer to take some phase noise and RF spectrum measurements. All in all, I'm trying to compute the linewidth of a laser from a measurement. I cannot detail ...
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Does laser coherence length impact phase noise?

I am trying to simulate laser phase noise numerically by creating a random phase $\phi(t) = \sqrt{2\pi\Delta\nu_L} \int_{0}^{t} dW(t)$, where $\Delta\nu_L$ is the laser linewidth in Hz and $\int_{0}^{...
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1answer
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Does phase of a signal (very low frequency, 0-100Hz) change due to pink noise?

One might experience pink noise when dealing with low frequency signals (0-100Hz). Curious to know whether pink noise has an effect on phase of the signal specially in lowest frequencies 0-10Hz.
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1answer
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Diffusion in porous media - interface flow

i have been working on a problem lately where i think i m missing some basic understanding: I consider the diffusion of a macromolecule in porous media, which i see as Brownian motion through the ...
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0answers
35 views

Decoupling noises

This is an experimental physics problem: Say I have 3 random variables $P_1, P_2, P_3 $ such as : $\Delta P_i=\Delta_Q P_i +\Delta_0P_i \ \ \forall i$, where $\Delta$ is the variance, this equations ...
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1answer
35 views

Does noise-cancelling cancel out the impact of a loud noise on your hearing?

So what I am trying to ask here is whether noise-cancelling headphones are actually working because the listener hears both, the noise-cancellation acoustic wave as well as the original acoustic wave, ...
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13 views

Dicke switching for radars

A question about Dicke switching for e.g. radio antennas. Some background so that we're all on the same page: fluctuations in the gain of the detector can dominate the low power signal. Dicke ...
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0answers
14 views

Derivation for resistor noise using transmission lines

Typically, in the derivation used for resistor noise, I see a hypothetical voltage source (the equivalent noise source) with a source resistance of R, connected to a transmission line of ...
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1answer
129 views

Solving linear Lindblad equations in the Heisenberg picture?

I'm interested in solving the explicit time dependence of operators in a simple open system described by a Lindblad equation. The concrete example I'm interested in is a harmonic oscillator with the ...
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1answer
35 views

Frequency analysis

What's the difference between Constant Bandwidth Filter and Constant percentage bandwidth filter? I mean not just the basic difference but a little detailed one, couldn't find much on the internet!
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37 views

Probabilty Density for $x$

Suppose that I have the function $$x(t)=e^{-b(W(t))^2} \ \ \ \ \ \ \ \ (1)$$ where $W(t)$ is just a Wiener process (i.e. a Gaussian in general). I want to know what the probability density for $x$, $P(...
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1answer
37 views

Nyquist noise and thermal equilibration

Let there be given two identical lumped element resistors $R_1=R_2$ whose heat capacities are also equal and given $C_1=C_2$. We assume the resistors are attached to thermostats, one at temperature $...
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1answer
136 views

Spectral density of fluctuations (white noise/delta-correlated process)

Let I be the current flowing across some junction as a result of N charge carriers of charge q. And let $\langle I (t) \rangle$ be its average. Assume a particle number distribution such that its ...
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31 views

Octave analysis Versus FFT analysis?

Why is the one-octave method more significant or of great value compared to FFT analysis? Is it because of the sensitivity of the human ears to perceive sound in octaves? is there any other reason?
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1answer
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What frequency ranges are best for speakers? [closed]

I have two speakers, one is a 6-inch speaker and another one is Peavy PR 10 (Large speaker). What frequency ranges are best suited for each of the speakers and why?
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2answers
48 views

How to show connection between measured data (sound in $\rm dB$) and the size of speakers? [closed]

How can we relate the measured data of speakers with its SIZE (speaker)? I have the data on white noise and pink noise (FFT and 1/3 octave), I'm a bit confused about how to show the relationship (...
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1answer
38 views

When is white noise appropriate in physical systems?

Almost every textbook and a journal article that deals with thermal noise in the context of optical fields (such as signal processing, micro-ring resonators, laser sources, etc.) assumes that the ...
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1answer
65 views

Modelling sky noise using a 2D array with plane waves

I have a question about modeling sky noise which should be filtered by a spatial filter 4f system. My approach for this task is to use a 2D array with random amplitude values and another 2D array that ...
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13 views

Large signal for short time vs. small signal over longer time

I am trying to understand if using a lock-in amplifier for noise reduction will help at all in the following scenario: I have a signal that I generate which is being detected by some detector that has ...
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Intuition behind Johnson-Nyquist noise?

I've been doing a lot of reading on Johnson-Nyquist (thermal) noise lately, and sadly much of the material I've come across either looks at things from a very engineering prospective (that is, little ...
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2answers
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Is it possible that a tall bush could actually severely block nearby sounds/noises?

I live (against my will) on the bottom floor of an apartment building, with a car road nearby. I made this text illustration to help you see the situation: ...
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1answer
88 views

How can I tell if a photodetector is thermal noise limited or shot noise limited?

Most datasheets for photodetectors only specify the noise equivalent power, making no distinction between thermal noise (Johnson noise) and shot noise. For modelling purposes, how do I know whether ...
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26 views

LISA acceleration noise formula

In the Laser Interferometer Space Antenna (LISA) mission proposal document, section 4.2 (page 17) there is a formula for the test mass acceleration noise level: \begin{equation} S_a^{1/2}\leq 3\cdot ...
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Do lightwaves that have been superimposed on by other waves accumulate noise?

My understanding of why light seems to "slow down" when travelling through different mediums is that the photon interacts with the electrons within a given material and this excites the ...
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1answer
55 views

How does one sound drown out another?

If I'm laying in bed at night with the fan on, I cannot hear nearby traffic. If the fan is off, I can hear the traffic. What is/are the principle(s) involved in this phenomenon?
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1answer
41 views

Is it possible to use destructive interference to eliminate sound coming from a road? [closed]

I've been thinking about the problem of how to block or mitigate road noise. Rather than using a physical structure, is it possible to generate directional sound (by any means) that could/would ...
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0answers
49 views

Noise power spectral density and $|X(\omega)|^2$. Why are those quantities associated usually ? Their definitions are different

I consider a generic signal $X(t)$. We could imagine to fix ideas $X(t)=\sqrt{R}I(t)$ ($R$ being a resistor and $I$ current flowing through it) The energy of this signal is defined as $E=\int_{-\infty}...
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1answer
93 views

How does the Brownian motion of air molecules compare to the threshold of human hearing as a function of frequency?

This fantastic question essentially asks what is the noise floor of air? Both the answer given on that thread and the value stated by Microsoft are around -23 or -24 dBSPL. However, overall loudness ...
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29 views

Difference in mathematical formula between signal to noise ratio (SNR) and signal to noise and distortion ratio (SINAD)

I am trying to get a grip on mathematical meaning of signal to noise ratio (SNR) and signal to noise and distortion ratio (SINAD). What I found out is that in terms of power: $$SNR=\frac{P_{signal}}{...
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1answer
72 views

Force from Johnson Noise

A capacitor in parallel with a resistor will have a random noise $\mathrm{voltage^2}$ across it of average value $V^2 = k_{B}T/C$. If this is a parallel plate capacitor, you can show that the average ...
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1answer
84 views

Meaning of $\frac{1}{\sqrt{dt}}$ in stochastic forcing

I am running a 2D fluids simulation with a stochastic forcing $f$ in a doubly-periodic box, i.e. solving $$ \frac{\partial \nabla^2 \psi}{\partial t} = J(\psi,\nabla^2 \psi) +f,$$ where $J$ is a ...
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1answer
36 views

What is a real model of thermal electrical noise?

A common model for electrical noise is to assume a flat frequency distribution, i.e. white noise. However, this results in theoretically infinite energy. So my question is: What has to be accounted ...
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60 views

Johnson Nyquist noise with voltage driving

In his 1928 paper, Nyquist derives the famous Johnson-Nyquist noise relation which is, to be very precise according to his paper: It gives the variance of the voltage at the boundary of a resistor ...
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2answers
37 views

How to express the “size” of measurement noise in a dynamical system

I have a discrete [non-linear] dynamical system $x_{n+1} = f(x_{n})$. There is measurement error, so my observables are a time series $\left\{ \hat{x}_{n}\right\} _{n=1}^{N}$ where $\hat{x}_{n}=x_{n}+\...
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1answer
253 views

Clean and simple derivation of Johnson Nyquist noise

I am not sure to get the derivation of Johnson Nyquist noise. I would like to understand it under black-body radiation approach. Consider this reference: http://www.pas.rochester.edu/~dmw/ast203/...
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What part of static noise in FM radio and analog TV is due to CMB?

When you switch analog FM radio or analog TV channel to non-existing station (in-between channels),- then you hear/watch just plain static noise. Question what I am interested is- what part exactly of ...
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Is there a graphical summary of which modulation technique to use in communication systems using Visible Light Communication techniques?

I am currently looking at various papers written (some listed at the bottom) that discuss how laser pulses can be modulated to send encoded messages to a receiver for communication systems. The more I ...

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