Physics

Questions tagged [noise]

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39 views

Detection of an optical noise with a photodetector, noise-equivalent power (NEP)

I am trying to find the minimum power that can be detected by a photodetector for which I know its noise-equivalent power (NEP). The standard formulas are: $$\mathrm{SNR} = \frac{\langle i_s^2(t)\...
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1answer
48 views

Do noise-cancelling headphones make a lot of unheard noise?

The way noise cancelling headphones work is by listening to sound, and created the inverted sound to 'cancel it out'. Doesn't this mean that the headphones create double the amount of noise, but our ...
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3answers
87 views

Why is “a very silent room” louder than “leaf noise” / “breathing noise”?

I recently was at night in my bed room and used the Schallmessung Android App (on a Samsung S7). It showed 20 dB while laying on some furniture. I could not hear anything; to me, the room was ...
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27 views

Non-Markovian noise coupled to atomic system

I want to calculate the density matrix element's average over all the realization of Gaussian colored noise when the atomic system is coupled to the said noise. I know how to do it for atomic energy ...
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Question on the correlation function of dichotomous Markov noise

Setup: A two-state switching process $I(t)$ between two values $\Delta_1$ and $\Delta_2$ with rates $\alpha$ and $\beta$ can be represented by the transition probabilities $$ P_{ij}(t) = \frac{1}{\...
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1answer
34 views

Calculate dark noise in CCD given a pixel's counts for two exposures

Suppose I took two pictures with the same CCD camera in totally dark room. The first picture was exposed for 1 microsecond, and the pixel given was 20 scales of grey. The second picture was exposed ...
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16 views

Exponential decay and growth oscillations at beginning and end of Fourier transform of data

I have some data from an photo-detector, which I think should correspond to white noise, but when I plot the Fourier transform of the data, I get a plot with exponential decay at the beginning and ...
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1answer
59 views

Identify reasons for laser intensity fluctuation

I got a Mitsubishi LPC-826 laser diode (single mode) with laser driver iC-HG. There is no cooling device, but data was captured after 30 mins switching on (which should be temporally stable). The beam ...
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2answers
32 views

Shot-Noise in optical detectors

I'm somehow struggling with the definition of the SNR (S/N) of optical detectors when it comes to shot-noise. I found some literature where it is defined as follows $$SNR = N/\sqrt{\bar{N}} = \sqrt{\...
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2answers
104 views

Do planes have to be noisy?

I tend to think of noise as an undesirable waste of energy because the generator was not designed for that purpose. But that doesnt mean this waste can be avoided. So I wonder how much of this noise ...
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36 views

Is thermal (Johnson) noise intrinsically stochastic?

Thermal (Johnson) noise is caused by electron collitions. Since movement of electrons is intrinsically stochastic according to Quantum Mechanics (assuming the Copenaghen interpretation), does this ...
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1answer
65 views

Unexpected wavelength jumps in a laser observed: a fundamental noise source in VCSELs?

I observed an unexpected signal while developing an interferometric sensor using a VCSEL laser. In order to debug this noise I designed the following device that converts minute changes in the laser's ...
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1answer
33 views

Unknown pulses from SiPM without any source or detector?

I have a SiPM set up with its PCB, no amplification at all, reading out to an oscilloscope. If I supply 29.8 V, which is the maximum power (with overvoltage), I get some random peaks on the ...
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22 views

Is there a physical limit to silent quadcopters, and what are the parameters?

Quadcopters can now navigate fairly well indoors. One could imagine many possible uses, including telepresence and security, but which are limited because of the loud noise. Assuming zero 'motor ...
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0answers
77 views

Radiation Pressure Noise in Gravitational Wave Detection

I am trying to work out where equation 9 comes from in Martynov et al. (2016), who discuss the radiation pressure noise in the LIGO detector. $$L(f) = \frac{2}{cM\pi^2 f^2} \left(h \nu G_{-} P_{\rm ...
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38 views

Unit strength Wiener process

I am not much aware of Brownian motion and/or the Wiener process. Recently I have been reading a research paper where they mention a variable $dW$ as a "unit strength Wiener process". My question is ...
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1answer
34 views

About sound of non-existent channels on FM

Well, I have learnt about resonant frequency due to series capacitor and inductor, and how the current at resonant frequency is highest, but i am confused about the sound, which appears even when no ...
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2answers
69 views

Perfect sound-canceling devices

Noise-canceling headphones can reduce a lot of ambient sound, but they are not 100% perfect. (Especially in the human vocal range.) Is there any physical principle preventing the creation of perfect ...
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1answer
43 views

Can one formulate a fluctuation-dissipation theorem in presence of non-Gaussian noise sources?

The fluctuation dissipation theorem relates the linear response of a system to Gaussian fluctuations. The natural question that comes to my mind is the possible derivation of an analogous FDT in ...
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3answers
99 views

Shot noise and single photon detection

I am looking into the noise considerations of a single photon detector, specifically an avalanche detector. I am wondering if it makes sense to think about shot noise when considering a single photon. ...
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89 views

Shot noise derivation

In the lecture notes I use to study on shot noise I found the following derivation for the Fourier transform of $$\phi_{shot} (t) = \langle (I(t+t_0)-\langle I\rangle)(I(t_0)-\langle I\rangle)\rangle =...
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2answers
337 views

How do silent kettles work? [closed]

I just had to buy a new (electric jug) kettle, and as I was bugged by the loud noise the old one made I was please to see that one can now buy silent ones. At first the new one made just the same ...
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72 views

Transition rate in systems without thermal noise

I've been lately reading about Transition State Theory (TST) and different methods to estimate the transition rates between metastable states in the context of chemical reactions using the review ...
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2answers
69 views

Estimate of the period of noisy “event counting” data

I have a set of experimental data, which come from a periodical event. More specifically, these are detections from a single photon detector, so there is no intensity, I only have the timestamps of ...
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1answer
29 views

Noise level x amount of meters away from an outdoor singer: sphere or semi-sphere?

When computing the noise level x amount of meters away from a singer who is singing outdoors, should one rely on the standard formula $I=\frac{P}{4πr^2}$ (and then convert 'I' into decibels) or ...
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0answers
34 views

What is all the known information contained in thermal noise?

I've read up a little bit on thermal noise, which is an unavoidable noise in materials when $T>0K$. Thanks to this noise, by measuring the voltage across a material, it is possible to extract the ...
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1answer
76 views

Noise covariance matrix

I've been trying to understand this paper. The paper seems to be about analyzing noise properties of a superconducting coplanar waveguide microwave resonator. They use an IQ mixer to perform ...
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1answer
36 views

Noise reduction approaches in optical spectral measurement

I am using an optical spectrometer to measure some surfaces in the visible, and since the signal is quite noisy I wondering what would be the best way to reduce the noise. In particular, are there ...
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1answer
3k views

Noise cancellation device for entire rooms [closed]

I recently met a group who were exploring active noise cancellation devices for entire rooms. Their approach essentially revolved around detecting incident noise on the room and blasting inverse ...
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0answers
18 views

Why a CRT TV shows B/W noise when not tuned [closed]

When an old color tube TV with no relevant digital bits in it is not tuned to any TV station, the noise is black & white. Why is the noise not all RGB?
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29 views

What is a zero dimensional stochastic system?

I happened to read a statement about Zero-dimensional stochastic systems in the context of Noise-induced phase Transitions (https://doi.org/10.1140/epjb/e2018-80624-9). I am not sure what does a zero-...
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1answer
81 views

Why are the active noise cancellation headphones subjectively better in reducing “periodic” noise?

According to experience of mine and of my friends using active noise cancellation headphones, the technology is much more efficient in reducing "periodic" noise, such as humming of jet engine, fridge ...
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27 views

Balancing noise energy contributions with friction term

I'm looking for a result that would say something about the way in which to pick a proper constant $\sigma$ in generic models of the form: $$ \ddot{x} = - \gamma \dot{x} - \nabla V(x) + \sigma \xi(t) $...
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1answer
76 views

Sudden change in noise levels [closed]

This is real life issue I am having currently and I am puzzled as to why it happened. I posted the question in the engineering section but it was put on hold as too broad. I have no other way to ...
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2answers
101 views

Converting from free field to reverberant field (Noise break out to outside)

If you have a noisy room (reverberant field) and you want to know how loud it sounds to a guy standing in the park outside how do you calculate that. I have a formula in a book about noise break-out ...
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0answers
78 views

Is there a simple uncertainty-principle explanation for the quantum noise limit of an amplifier?

The quantum noise limit of a microwave amplifier's effective noise temperature, $T_N$, is found by setting $k_B T_N=hf/2$, where $f$ is the frequency of the detected radiation. This may be off by a ...
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2answers
102 views

$1/f$ noise: is it limited?

Basically my question is: I have this doubt because in contrast to the limit $f \to \infty$ (which is an idealization because all system behaves as a low pass for enough $f$), we can perfectly build ...
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1answer
140 views

How to calculate Johnson Noise Voltage?

I used a Johnson Noise calculator to find the voltage of in a steel conductor, but it disagreed with the following calculation where $R = \frac{\rho \ L}{A} = \frac{7 \cdot 10^{-7} \ \Omega \ m \ \ 0....
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1answer
142 views

Normal Distribution vs Poisson Distribution

I am not sure that I understand when to use Normal Distribution and when to use Poisson distribution! For example, in RF communication the channel noise is mainly modeled as Normal Gaussian ...
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1answer
91 views

Typo in Nyquist's 1928 paper?

In Nyquist's famous 1928 paper Thermal Agitation of Electric Charge in Conductors, equation (8) goes as follows : $$ E_\nu^2 d\nu = \frac{4R_\nu h d\nu}{e^{h\nu/k_B T}-1} $$ with $\nu$ the frequency ...
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3answers
2k views

What is the difference between photoconductive and photovoltaic detectors?

What is the main difference between photoconductive (PC) and photovoltaic (PV) detectors? I notice that PC detectors are typically AC coupled (requiring modulation of the light source to generate a ...
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2answers
275 views

What is Johnson noise?

I'm trying to understand Johnson noise and I already read Nyquists paper and did some other reading, but I'm pretty stuck. As I guess there is this missing piece that relates everything, I'll just ...
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3answers
2k views

What is the reason for this pattern of noise in electric kettles?

It always seemed to me that the noise from electric kettles follows a pattern: It starts low, then increases, and decreases again before the water starts to boil. To verify this, I performed a little ...
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1answer
59 views

What is the main noise in a helicopter flying by?

If you were to stop the tail rotor blades in forward flight, and presuming the vertical fin could maintain sufficient yaw control, would the noise footprint of the entire helicopter, as heard from the ...
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1answer
125 views

Effect of Lock-in Amplifier Phase Noise

Suppose that an oscillator with phase noise is used to drive a modulating process and that the same oscillator is used (with an appropriate phase shift) is used to synchronously demodulate the signal ...
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1answer
296 views

Acoustic power spectrum of a natural turbulent flow

For a long time I've been curious about predicting the acoustic power spectrum of river sound from hydrodynamic measurements. What got me started thinking about this topic was repeatedly observing ...
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0answers
38 views

Why does shot noise becomes 'non-shot' beyond a certain threshold?

My understanding of shot noise is that if a process is Poissonian, the noise observed is 'shot noise' and its total variance will go hand in hand with the mean value of the noise. But, judging from ...
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1answer
30 views

Noise produced by foam illuminated by a pwm led

I have a led headlight which seems to use pwm modulation to ajust brightness (led lenser xeo 19R). With an intermediate light power (i.e. not 0% or 100%), the light produce a really small noise, which ...
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1answer
177 views

Noise add to the Lindblad equation or Liouville-Von Neumann equation

I am working on an open system and I would like to use the Lindblad master equation but also I would like to add noise to it. If is possible. All the books and papers I did read about tells me that ...
3
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1answer
187 views

Number of photons required for communication

On one hand, the amount of information I can transmit is proportional to the bandwidth. The higher the frequency, the more information I can transmit. On the other hand, the number of photons is ...

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