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17
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2answers
2k views

Maximum delay for effective active noise cancelling?

Active noise cancelling reduces unwanted sound by sending the inverted phase of the original phase: (Source: Wikipedia) Theoretically, this seems logical to me. However, in real life, the anti-...
13
votes
3answers
3k views

Is this thought experiment violating the the Second Law of Thermodynamics?

There is an adiabatic box, with a board in the middle, which is adiabatic too.The board separates the box into two parts and there is a small hole in it, which is close to a coil and the hole has a ...
13
votes
3answers
378 views

What does a blackbody sound like?

Update: According to this wikipedia article, blackbody radiation is just thermal noise (Johnson–Nyquist noise); if that's what I'm looking for, what does it sound like? If a blackbody has a ...
12
votes
2answers
2k views

How can IR cameras see things colder than the camera?

I’ve read that only cold-blooded animals develop IR vision to spot warm prey because a mammal would blind himself with his own heat and not be able to see anything. But I’ve seen a FLIR camera, ...
8
votes
3answers
730 views

Will a damped harmonic oscillator, with no initial amplitude, oscillate if there was background “noise”?

Suppose I have a damped harmonic oscillator which is at rest, sitting comfortably with no initial amplitude, obeying the equation $$\ddot{x} + \frac{1}{Q}\dot{x} + x = 0$$ where x is the vertical ...
7
votes
3answers
953 views

What information is contained in the quantum spectral density?

Consider a harmonic oscillator system with Hamiltonian $$\hat{H} = \frac{1}{2} A \hat{u}^2 + \frac{1}{2} B \hat{v}^2 \qquad [\hat{u}, \hat{v}]=i \gamma $$ where $A$, $B$, and $\gamma$ are all real. ...
7
votes
1answer
273 views

How does LIGO remove the effects of environmental noise?

Since LIGO is dealing with readings at nanometers, events such as vehicles driving nearby, and constant (but extremely minor) tremors of the earth can cause movement with the mirrors at nanometers. ...
7
votes
1answer
267 views

What Causes the Noise Floor of Modern CCDs?

CCDs are getting pretty good these days, but all systems are subject to noise. A typical value for a CCD seems to be 20 electrons RMS per pixel. This article from qsimaging.com says CCD Read ...
7
votes
1answer
9k views

What part of the fan blade actually does the noise generation?

I'm trying to identify the sources of noise in spinning fan blades and what causes them. Is the noise only generated by the lead edge of the blade 'cutting through' air? and different parts of it (...
6
votes
1answer
234 views

Why is Johnson noise a Gaussian process?

Noise processes in engineering and physics are frequently assumed to be Gaussian processes. This allows use of convenient analytical techniques. The question then arises as to why natural processes ...
6
votes
2answers
389 views

Shot noise at high frequencies (can it really be ideal white noise?)

Quantum shot noise (either optical intensity noise or electrical current noise) described by the noise spectral density of $2 e I$ (electrically) or $2 h \nu P$ (optically). So it is white noise. I ...
5
votes
2answers
2k views

Generating Pink Noise

I've generated some white noise in Excel by using the formula $$2*\mathrm{Math.RAND}()-1$$ I would now like to create some pink noise. I believe this is done by applying some sort of filter to the ...
5
votes
2answers
349 views

Modeling stochastic process with frequency-dependent power spectrum

I'm trying to model of Johnson-Nyquist noise propagation in a nonlinear circuit. An ideal (linear) resistor can be modeled very nicely by the Fokker-Planck equation (equivalently, the drift-diffusion ...
5
votes
1answer
171 views

Does the skin effect, eddy current / hysteresis losses contribute to Johnson noise in an inductor?

Based on my very basic understanding of the Johnson noise, it's not just a DC phenomena, but should change with frequency in a system, where there is a frequency dependent, real component to the ...
5
votes
0answers
96 views

How does LIGO reduce noise below what it is detecting? [duplicate]

LIGO is designed to detect changes in length on the order of 10,000ths the scale of a proton. I know they are extremely well isolated from their surroundings, but how could we even approach isolation ...
5
votes
1answer
75 views

Pink noise in low-dimensional systems

Pink noise (1/f) is often cited as a signature of complex or critical systems. Is it possible for a low-dimensional time-independent first-order system to generate pink noise? Intuitively it seems ...
4
votes
1answer
76 views

Do error checking costs of quantum computing shrink BQP?

BQP is the set of problems solvable in polynomial time for a given error tolerance, and it is suspected to be larger than P (and BPP, which is probably equal to P). However, inability for the gates to ...
4
votes
1answer
317 views

total noise power of a resistor (all frequencies)

Let's calculate the power generated by Johnson-Nyquist noise (and then immediately dissipated as heat) in a short-circuited resistor. I mean the total power at all frequencies, zero to infinity... $$(...
4
votes
1answer
2k views

Signal-to-noise ratio of the difference between two signals

Something tells me this must be a fairly simple question, but I have somehow been unable to find an answer to it. In short: I need to calculate the difference between two signals, A and B, each one of ...
4
votes
2answers
5k views

Decibel level addition of multiple noise sources

If I have four computer fans of which each is said to run at 46 dB, and they run close to each other, how loud is the whole system? I somehow recall from my physics course that 10 decibel ...
4
votes
1answer
429 views

White Noise Generator Through Low Pass Filter - Autocorrelation of normalized data dropping below 0 (showing negative correlation)

I am doing the following experiment: http://physlab.lums.edu.pk/images/a/ab/Correlation.pdf It is basically a white noise generator running through a low pass filter. Sample voltages are taken and ...
4
votes
4answers
479 views

Friction at zero temperature?

By the fluctuation-dissipation theorem (detailed-balance for Langevin equation), $$\sigma^2 = 2 \gamma k_B T$$ where $\sigma$ is the variance of noise, $\gamma$ is a friction coefficient, $k_B$ is ...
3
votes
2answers
7k views

Why does noise affect FM radio less than AM?

Frequency modulated waves are less susceptible to noise compared to amplitude modulated signal. This is because the information in an FM signal is transmitted through varying the frequency, and not ...
3
votes
1answer
193 views

Hearing background noise from earphone while there isn't any connection

Once my friend told me that he was listening some background noise while his earphones were not plugged in any device. I didn't believe him but 10 minutes ago I experimented the same. I can certainly ...
3
votes
3answers
203 views

What does “an average over noise” mean in Zwanzig's book

This is a very specific question about Robert Zwanzig's book Nonequilibrium Statistical Mechanics. Specifically, what is he talking about in equation 1.25 on page 10 that he calls "an average over ...
3
votes
2answers
599 views

why isn't the variance of Fano noise proportional to the number of photon arrivals?

I've been reading "Photon Transfer" by James Janesick and in Chapter 3 (http://spie.org/samples/PM170.pdf) he describes the various sources of noise in a CCD. Basically, incoming photons interact with ...
3
votes
2answers
267 views

Detailed balance condition for coupled Langevin equation

Suppose $a$ and $m$ are real variables and they satisfy the following two coupled Langevin equations: $$ \dot{a}=F_a(a,m)+\eta_a(t);\quad\dot{m}=F_m(a,m)+\eta_m(t); $$ where $\eta_a$ and $\eta_m$ are ...
3
votes
2answers
198 views

The heat equation in relation to smoothing algorithm

Recently I learned about a technique in image processing, which has its roots in something called the 'heat equation' from physics. The original creators of this technique were inspired by the physics ...
3
votes
1answer
77 views

Why is dark current on CCD devices pixel dependent

I'm reading about sources of noise in cameras while taking images - One of them is the dark current. That is, some electrons in the CCD device of a camera are set free due to thermal noise. Those free ...
3
votes
1answer
50 views

Finding the noise spectral density of a quantity made from different noisy components

I'm looking for the expression of the noise spectral density of the magnetic flux $\Phi$ generated by a noisy voltage signal $V$ applied to a resistor with Johnson-Nyquist noise $R$ which produces a ...
3
votes
1answer
254 views

How to create a barrier for sound waves?

Is there a way to create a barrier so that sound waves cannot pass through? Does laser light have this ability to act as a barrier or bounce sound waves back? This came to my mind when I was ...
3
votes
1answer
232 views

Autocorrelation of noise - negative correlation

I am investigating autocorrelation of electrical noise as part of an undergraduate experiment (as detailed in http://physlab.lums.edu.pk/images/a/ab/Correlation.pdf). I sampled noise voltages using an ...
3
votes
1answer
25 views

Coupling constant for an object in a photon gas

I want to model a photon gas as a bath of harmonic oscillators, and examine the effects of this bath on a system which is also a harmonic oscillator. The trouble I'm having is in relating the ...
3
votes
0answers
118 views

Sound - for purposes of vibration

What is the best way to distribute noise from more than one source (I'm envisioning a system with many), within a dome, with the ground as its primary target, at optimal frequencies and volumes to ...
2
votes
2answers
418 views

Sound source not in a straight line with the sound receiver - does that make a difference?

Hope the graphics will help me explaining my question better. Let's say the box would be a room in the fourth floor, and the sound source would come from cars in the street. It is clear that in case ...
2
votes
1answer
96 views

Is there $\frac{1}{f^{0.5}}$ noise?

I've heard of $\frac{1}{f^0}$ noise (white noise), $\frac{1}{f}$ (pink, or sometimes tan noise), and $\frac{1}{f^2}$ (brown noise). But why no $\frac{1}{f^{0.5}}$ or $\frac{1}{f^{\pi-2}}$ noise. Do ...
2
votes
2answers
52 views

Are white noises always Markovian?

Are white noises always Markovian? I am a bit confused about it. As white noise always has a constant power spectrum, its auto correlation function must contain a delta function of time. Thus the ...
2
votes
0answers
58 views

Rationale for definition of input/output operators in quantum langevin equations

I am going through Gardiner & Zoller's 'Quantum Noise', and following the derivation of the Langevin equations in terms of input/output operators. Let the bath Hamiltonian be: $$H_B=\hbar\int_{-\...
2
votes
0answers
175 views

The origin of contact noise?

I was trying to measure the noise of a device with metal probes. I was not sure whether I should trust the results because I was told contact noise might contribute to some degree. I am a little ...
2
votes
0answers
263 views

Schottky and shot noise

I am looking for a little history on shot noise: when was it first predicted and first measured? In particular, what was the role of Schottky? His 1918 paper "Über spontane Stromschwankungen in ...
1
vote
2answers
194 views

What is the fundamental reason for noise?

I have read that noise is a result of there being "no such thing as a perfect one-way valve". That energy transfer is never perfectly one-way; there will always (at some level) a finite flow of energy ...
1
vote
1answer
2k views

What does 'zero-mean random noise with standard deviation equal to 1' mean?

Can anyone tell me what the meaning is of the phrase: "zero-mean random noise with standard deviation equal to 1"? Also, I want to know why not except zero-mean random noise and standard deviation ...
1
vote
1answer
22 views

How to convert noise (Lwa db) for a particular distance?

If default noise level is given, how can I calculate the noise level at a particular distance? For example, if a generator says it's noise level is Lwa $99 ~\mathrm{db}$; how much noise level in $~\...
1
vote
1answer
474 views

Determine fan sound (dB) based on its rotational speed (RPM)

I am trying to find the sound amplitude or level produced by a fan, knowing its RPM. Is there a simple formula for it? What other parameters does it depend on? Assume I have all the fan properties, ...
1
vote
1answer
95 views

What is meant by shot noise?

Question In the context of quantum mechanics and more specifically photon counting, what is meant by shot noise? Additional information Here is what I already know. The number of photons hitting ...
1
vote
1answer
221 views

Johnson-Nyquist noise for resistive element with temperature gradient

In Nyquist's 1928 paper, Thermal agitation of electric charge in conductors, the voltage noise for a resistor is derived assuming a circuit in thermal equilibrium and one temperature. How does the ...
1
vote
2answers
85 views

Any noise slowly starting to take effects?

I am studying a system subject to random noise, or a system driven by some noise, for example, heat flow or wave propagation perturbed by noise. I would like to know if there is a real system where ...
1
vote
2answers
1k views

Noise amplitude increases as sample rate increase

I am testing the material properties of some very low stiffness materials. I'm using a force probe connected to software, sensing at about a hundredth of a gram of force. Now, what's interesting is ...
1
vote
0answers
23 views

Dependence of Noise Tolerance of waves

Electromagnetic waves are used for transmission of any message. And different kinds of waves have different noise-tolerance. If my guess is right then the noise tolerance is a property of wave which ...
1
vote
0answers
24 views

Noise created due to change in Air Pressure

Background : My blower in one of the experiments is generating noise due the a short airflow path to atmosphere. The reason is due to a sudden change in pressure (high to low) the high noise is ...