Questions tagged [noise]

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Convert noise measurements that used 3-dB exchange rate (ER) to 5-dB

NIOSH uses 3-dB as the exchange rate (ER) for sound measurement, while OSHA uses 5-dB as the ER. Is there any way to convert the measurements using these two approaches? If yes, how can we do that? I'...
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What causes this strange noise in a pair of walkie-talkies?

Let us suppose that Bob and Alice both have walkie-talkies. They are both 3m apart from one another. Alice pushes her walkie-talkie to speak but instead of speaking, she starts walking toward Bob. ...
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What does photon-limited imaging mean?

The following link is about Photon-Limited Imaging, https://engineering.purdue.edu/ChanGroup/project_QIS.html. Is there any definition of Photon-Limited Imaging. From the paper Photon-Limited Object ...
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Is it possible to obtain noise level in electrons using only one camera?

In the link, https://www.photonstophotos.net/GeneralTopics/Sensors_&_Raw/Sensor_Analysis_Primer/Photon_Transfer_Curve.htm there is one figured called Standard Photon Transfer Curve – Multiple ISOs ...
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-1 votes
2 answers
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Does sound travel through FINGERS?

as we know that sound's speed is fastest in solid (and slowest in air). QUESTION - what is the reason when we close our ears and don't really hear loud noises though sound travels faster in solids?
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Consistency of Lindblad-type operator evolution equations

One frequently comes across Lindblad-type operator evolution equations in the Heisenberg picture of the form $$ \frac{\mathrm{d}}{\mathrm{d}t} A =\mathcal{L}^{\dagger}(A), $$ where the adjoint ...
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1 answer
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Frequency dependence of noise at advLIGO

Here's a picture showing how different sources of noise affect the sensitivity of LIGO I'm trying to understand the frequency dependence of each curve. I'll specifically focus on seismic noise, ...
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1 answer
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Removing $1/f$ noise with lock-in-amplifiers

On the Wikipedia page for 1/f noise (at the bottom of the page) it suggests the noise can be reduced if the signal of interest is at DC. DC signals suffer from significant 1/f noise, so one method of ...
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Higher-order Langevin noise correlation

Supposing Langevin noises are white noise, we know that the noises F are Gaussian and higher-order noise correlations, $\langle F_{t1}F_{t2}...F_{tn}\rangle$ can be decomposed by the second-order ...
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Legendre spherical harmonics - Does it make sense to have multipole interval lower than 1?

I introduce in the context of a physical noise $B$ a factor $\Delta\ell$ multipole appearing in the expression of the variance $\operatorname{Var}\left(B\right)$ of $B$. The formula is the following : ...
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57 votes
3 answers
7k views

Why doesn't oil produce sound when poured?

I've noticed that unlike other liquids, when pouring olive oil for example, I don't hear any sound at all from it. Usually you can hear an audible sound as a cup gets filled with water, as the sound ...
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Can there be multiple shot noise sources? For example: laser & camera

Suppose you have a system consisting of a laser, a filter (with transmission $T$), and a camera. To my understanding, both the laser and the detector produce shot noise. Is that correct? For a camera ...
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4 answers
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Can a metal sheet roof be vibrated at audio frequencies?

So I'm renting a cheap place for now due to certain circumstances. Problem is outside noise is excessive because there is no ceiling and the roof is only a metal sheet... Lately I play white noise to ...
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How to experimentally verify, if the intensity of light from an External Cavity Diode Laser (ECDL) is shot noise limited?

I have an ECDL and i want to experimentally verify if it is shot noise limited or not. Any reference will be helpful.
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1 answer
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Difficulty bounds in a white noise model

Suppose we make a measurement in a real/virtual experiment for which the noise is given by a white noise (Gaussian) model. Suppose also that we have a very good filter or machine learning (ML) model ...
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4 votes
2 answers
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Why does shot noise rise with frequency in LIGO sensitivity?

In plots of the sensitivity of the LIGO interferometer, photon shot noise is the dominant noise source at the high frequency end, e.g. this graphic: It appears to rise roughly in linear proportion ...
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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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3 answers
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Are stationarity, Markovianity and Gaussianity sufficient conditions to ensure that the random force on a Brownian particle is delta correlated?

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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4 votes
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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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1 answer
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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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3 votes
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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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4 answers
206 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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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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1 answer
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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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2 answers
152 views

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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1 vote
0 answers
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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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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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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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1 vote
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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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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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2 votes
1 answer
35 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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0 votes
1 answer
257 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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2 votes
1 answer
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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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1 vote
1 answer
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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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1 vote
1 answer
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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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-1 votes
1 answer
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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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1 vote
2 answers
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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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0 votes
1 answer
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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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2 votes
1 answer
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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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2 votes
2 answers
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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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1 vote
2 answers
277 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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2 votes
1 answer
46 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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1 answer
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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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1 answer
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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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1 vote
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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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6 votes
2 answers
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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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2 votes
1 answer
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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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2 votes
1 answer
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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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