Questions tagged [noise]
The noise tag has no summary.
314 questions
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Why does flowing water produce what sounds like white noise?
Why does flowing water produce what sounds like white noise? Is this due to a certain type of turbulence? Is there a proof that it white (or pink or Brown?) noise?
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Time-domain algorithm to generate noise with Power Spectral Density (PSD) $S(\omega,T) \propto \coth(\omega/T)$ sequentially
I need to numerically generate colored noise with a Power Spectral Density (PSD) $S(\omega,T) \propto \coth(\omega/T)$ (quantum thermal noise). I cannot use standard Spectral Synthesis (Inverse FFT) ...
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Complex systems with noise
A complex system is typically defined as a system composed of many interacting components whose collective behavior cannot be easily inferred from the behavior of the individual parts. The whole ...
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Activity origin in simulations
I am doing a research on active matter and I see there are two main ways to introduce the activity to a particle (or set of particles). The most straightforward is introducing an intrinsic velocity in ...
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Is it okay if your signal and noise have the same statistical distribution?
Please bear with me if this seems like a very basic question. Let's say you want to detect a signal by measuring a variable $x\in[0,\infty)$. Let's say you know the variable $x$ follows a probability ...
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Including laser linewidth in the master equation
Suppose I have a modified Jaynes-Cummings hamiltonian $H_S$ with two cavity modes. I have derived the master equation for this system including decay of both cavity modes: $$\dot{\rho} = -i/\hbar [H_S,...
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Deriving the power density of Johnson's noise (as in Feynman's Lecture I.41)
This is a question related to sections 41.1 41.2 and 41.3 of the Feynman Lectures on Physics (vol I). Below, I will summarize the content of section 41.1 and 41.2 and then report what is unclear to me ...
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Noise, earplugs and bus brakes [closed]
In order to reduce a little the noise from the commute, I've been using musician earplugs. While some of the noise is reduced, the screech when the bus brakes feels more penetrating, more "in my ...
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Total field operator from a laser
I have been a bit confused recently about the total field operator from a laser source (coherent).
What would be a "good" representation of the quantum state of my laser propagating? (let's ...
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What is the laser linewidth?
I want to measure the linewidth of a laser in practice (ideally both before and after locking it to a ultra-stable cavity). I expect linewidths of 10's kHz, before locking, and 100 Hz - 1 kHz after ...
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Noise term in ODE
Imagine that I am in a lab measuring a certain force that is time dependent, e.g. there is a spring subjected to changes in temperature, which results in a time-dependent stiffness,
$$F(t)=k(t)\delta,$...
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Detection of gravitons via excess quantum noise
In the recent paper that won first prize of the 2025 Gravitational Research Foundation essay contest, Probing Quantum Structure in Gravitational Radiation by Manikanden & Wilczek, it is claimed ...
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What noise does heterodyne detection have in quantum optics? How does it depend on integration time?
I think the following is true, please correct me if I'm wrong. For coherent states, such as that come out of a laser, the intensity in a single mode is a Poisson distribution with mean given by the ...
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Confused about noise power spectral density measurement
My question was started from this paper. The topic of the paper is related to linewidth measurements, but my question is even before that, related to the way the noise power spectral density (PSD) ...
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Power spectral density of a laser's frequency noise
I am a bit confused about what power spectral density (PSD) is in the context of a laser. In particular, I came across this paper. In Fig. 1 they show PSD vs frequency. As far as I understand, PSD is ...
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Does the anomalous skin effect lead to increased noise at high frequencies?
I was recently reading about the anomalous skin effect, wherein the models governing the skin effect behaviour break down as the frequency gets high enough for the skin depth to approach or fall below ...
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Characterization of Markovianity, Gaussianity, and color for noise processes
Consider a noise process $\xi(t)$ that has some statistics in time. There are various ways to characterize such a process, 3 being Markovianity (independence from history), Gaussianity (Gaussian ...
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Fluctuating electric field or Johnson noise inside a cavity
I have read that "power is dissipated by the thermal motion of electrons in an imperfect conductor, and these fluctuating currents imply the presence of fluctuating electromagnetic fields in the ...
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The response of a linear quantum amplifier to broadband signals
I have been studying related knowledge of quantum linear amplifier noise limit recently, and the main reference material is Caves' literature. In this paper, the author uses equations (4.5, 4.40a, 4....
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What is the maximum possible noise level on Earth and what would be its consequences? [duplicate]
The theoretical situation described here comes from the SCP-498 page.
SCP-498 is a theoretical device. It is an alarm clock that is triggered every 11 minutes, and creates a noise of 30dB. Until ...
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Can shot noise in a multi-species system always be expressed in terms of a Fano factor?
Consider a simple model of a two-species system of charge carriers $c$ and $d$ (say, both fermionic, with potentially different masses and dispersions but the same charge). Can the shot noise of such ...
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Long time behavior of noise process with flat spectral density and upper cutoff frequency
From this question we find that given a noisy process $x(t)$ with known spectral density $S_x(\omega)$, the mean square displacement is
$$
\langle x(t)^2 \rangle = t^2 \int_0^\infty S_\dot{x}(\omega) \...
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Noise in gravitational wave detections
I'm reading a paper (https://doi.org/10.1103/PhysRevD.49.2658) in order to understand the use of Fisher Matrix in gravitational wave detection. I'm a bit confused with the assumptions they do about ...
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Shot noise limited detection
can somebody please explain the significance of shot noise limit? I am trying to understand why and how shot noise degrades image quality, for e.g., while imaging weakly scattering specimens using an ...
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In hetero- homodyne detection, what does it mean to operate at the Quantum Shot Noise limit?
I am an electrical engineering by trade, working on the analogue part (Transmitter & Receiver) of a quantum optical communication channel. By this, I mean I have not much experience on things ...
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What is the correlation between Brownian noise's low frequency components and the actual movement of particles?
I do have some crude training in mathematics, but I'm not a physicist or engineer. So I'd appreciate a simple not too technical explanation.
I conceptually understand how hitting a piece of wood will ...
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Using the functional derivative and delta function for proving The Fokker-Planck Equation
I am reading "Lectures on Phase Transitions" by Nigel Goldenfeld, specifically Chapter 8, where the Fokker-Planck equation is derived. I found the following part of the proof, but there are ...
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Method of inserting random numbers in the numerical calculation of mean-squared displacement for brownian particle
I am trying to plot Mean-Squared-Displacement for a passive Brownian particle. For that I'm using the discretized over-damped version of the Langevin equation as: $$x(i+1)=x(i)+\sqrt{\frac{2.k_BT.\...
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How can I determine an error on total noise?
I am analyzing the data for an experiment, where we measured the total noise in a system. The total noise is defined as the variance of the signal (and is equal tot the integral over the noise ...
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Feynman claimed "The ear is not very sensitive to the relative phases of the harmonics." Is that true?
In The Feynman Lectures on Physics, Dr. Richard Feynman claimed that the ear (I assume he meant the human ear) is not sensitive to the relative phases of harmonics.
However, I was asked to test ...
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Can absolute silence exist and how are thermal and quantum noise a limit? [closed]
For my exam, I must answer the question: can absolute silence exist? While doing research, I obviously heard about noises internal to our body and noises external to our environment but I also heard ...
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Does a rubber mat reduce the impact to the floor below?
My lack of physics knowledge is preventing me from solving an everyday life problem. Please bear with me!
Say I have a second-floor apartment and I want to do deadlifts. I am afraid of the floor ...
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Are all types of noise a result of lack of complete knowledge about the given system? What does this say about the physicality about information?
I am currently studying the basics of quantum information theory. When we study a system (classical or quantum), any undesirable influence out of our control is usually referred to as noise, and this ...
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Fokker-Planck equation for colored noise Langevin equation
I was wondering if there is a way to derive the Fokker-Planck equation for Langevin equation with a general colored noise:
$$m \ddot{x} = -\frac{\partial V(x)}{\partial x} - \gamma \dot{x} + F(t)$$
...
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Why and how white noise cancels other background noises?
This idea of white noise cancelling other background noises is quite popular these days and I always wonder how it works?
https://www.youtube.com/watch?v=nMfPqeZjc2c
This is a sample of white noise. ...
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What duration of a white noise burst is required for it to be "white" at a given frequency or frequency range?
I am running white noise bursts (with very short ramps on/off to prevent discontinuities) through underdamped resonant bandpasses which are tuned to any given $f_0$ and an underdamped $Q$.
Continuous ...
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How to standardize the energy of a Dirac delta function relative to sample rate (width) and amplitude?
Background
I was instructed that a Dirac delta function (impulse from $0$ to $A$ then back to $0$ at short duration) has a white noise audio frequency type excitation distribution here
ie. It should ...
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Is it possible to, like white noise, excite all audio frequencies equally, but with a more immediate & less random burst? Like a signal discontinuity?
I am trying to generate an audio signal that, like white noise, has "equal intensity at different frequencies, giving it a constant power spectral density", but unlike white noise, can be ...
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Does it make sense to whiten the data in order to apply a matched filtering algorithm if my dataset consist of a sinusoid + random Gaussian noise?
With a Python program I generated a sinusoid signal and I added to it Gaussian noise.
Now I want to compute the optimal SNR by applying a matched filtering algorithm.
Since the noise is white (at ...
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Should the Power Spectral Density be complex?
I need help!
I'm trying to calculate the Power Spectral Density of a quantum operator ($\delta \hat{n}(t)$) given by:
$$ \delta \hat{n}(t) = A(t)\delta\hat{a}(t)+A^{*}(t)\delta\hat{a}^{\dagger}(t) $$
...
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Mathematical description of random noise
I am trying to mathematically model the noise affecting a certain physical quantity, say $X(t)$. Then, the noisy quantity would be $X'(t)$ which differs by some small value $\delta$ from the ideal ...
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Allan deviation power expansion
In the 'Hand Book of Frequency Analysis' S3.2, by W.J Riley the frequency stability of an oscillator is expressed as a combination of power-law noises of the form $S(f)\propto f^\alpha$, where $f$ is ...
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Avoiding radar detection using active noise control instead of a stealth fuselage
was reading about different stealth technologies used by modern aircrafts to avoid radar detection.
Wouldn't it be easier to have a receiver on the airplane listening on the radar frequencies and then ...
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Is this a valid alternative definition of the delta function?
The delta function can be defined as:
$$
\delta(x) = \int_{-\infty}^{\infty} e^{-2\pi i k x} \, dk
$$
Loosely speaking, I can understand this because unless $x=0$, the complex exponential oscillates ...
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Measurement paradox
When building electronics to measure usually it is asked what the bandwidth of the signal is and what is the frequency range usually done to limit noise bandwidth and thus have more SNR. To me it ...
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How do I compute the bounds of random walk for a given ellapsed time?
I am trying to model random walk of a gyro, given some manufacturer specifications of maximum random walk in units of degrees per root-hour.
My first step was to generate white noise with a standard ...
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Novikov's theorem for time-independent functional
$\textbf{Introduction}$
Given a Gaussian-colored noise
\begin{equation}
\begin{split}
&\langle z(t)\rangle=0,\\
&\langle z(t)z(t')\rangle=C(t-t').\\
\end{split}
\end{equation}
A given ...
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Why doesn't the sunlight make noises on home satellite dishes?
One of my friends asked me a question to which I could not find a clear answer. We know that the sunlight spectrum includes the entire wave frequencies including those (of the order of 1 GHz) that our ...
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Energy spectral density vs power spectral density vs power spectral density per unit time
I recently started research to measure the voltage noise spectrum of materials to study their phase transitions. Before understanding physics, I am now confused by the three terms used in literature:
...
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Noise spectral density for GW detector
I am reading the book Gravitational waves by Maggiore. On page 337 in Eq. (7.6) he defines the noise spectral density as
$$<\tilde{n}^*(f)\tilde{n}(f')>=\delta(f-f')\frac{1}{2}S_n(f)$$.
I want ...
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