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Questions tagged [noise]

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2answers
34 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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0answers
20 views

What is the physical origin of salt and pepper noise on a camera?

I've been noticing that a particular high end camera sensor (IMX250MZR) seems to have salt and pepper noise when the exposure time is particularly long (1000 ms vs 10 ms). Also the sensor is uncooled, ...
3
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1answer
27 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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0answers
10 views

How many equivalent continuous sound pressure levels (LAeq) can you fit in a given period?

Anyone familiar with environmental noise will understand the concept of integrating sound level meters -> obtaining a single value sound pressure level with the equivalent energy of the measure time ...
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2answers
33 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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0answers
50 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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0answers
28 views

Auto-covariance of Poisson process

I am studying Poisson processes, in particular the case of a source emitting particles which are then counted by a detector (they could be photons in a weak laser beam for example). The counting as ...
2
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2answers
74 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 ...
2
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0answers
70 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 ...
0
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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
29 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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0answers
65 views

Using lock-in to measure $ f $ instead of $ f' $

What I know about lock-in measurement is the following: you have a device you want to test and instead of giving it a DC input, you would modulate your DC input with some sinusoidal modulation and ...
1
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1answer
70 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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0answers
13 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
699 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
17 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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0answers
25 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-...
2
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1answer
66 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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0answers
26 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) $...
1
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1answer
64 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 ...
0
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2answers
47 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
54 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 ...
2
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2answers
86 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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0answers
11 views

How are sensor noise variances combined?

I am trying to implement an extended Kalman filter for attitude estimation on a cubesat. The satellite takes two vector measurements each with their associated measurement noise, modelled as a zero-...
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1answer
86 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....
3
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1answer
105 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 ...
1
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1answer
88 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
1k 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 ...
4
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2answers
208 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 ...
32
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3answers
2k views

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

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 ...
1
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1answer
55 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 ...
0
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1answer
88 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
241 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
37 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 ...
2
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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 ...
1
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1answer
116 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
167 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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0answers
19 views

Bottlenecks on information transfer through a system?

Can anyone recommend some good sources of reading material about how information is 'squeezed' through a system, meaning that rather than pass maximal information to the next processing stage, at some ...
0
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0answers
47 views

Magnetic noise due to Johnson noise

For a circuit consisting of a solenoid and a resistor, does the Johnson noise of the resistor induce white magnetic field noise in the solenoid? For that matter, does the intrinsic thermal noise due ...
1
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1answer
44 views

Why is the ratio thermal noise/temperature constant?

I understand that more temperature means more molecules hitting each other and therefore more noise. But why is the ratio between the two roughly constant? If the temperature doubles, why would its ...
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0answers
35 views

Why does chaotic noise take the form of fractals?

I've heard that Mandelbrot discovered the Mandelbrot fractal after studying patterns in chaotic noise in data communication. But why does noise take this form in the first place?
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0answers
50 views

Why do I hear noise out of my headphones when rubbing its male connector to a metal container's wall filled with water?

When I rub the male jack of my heaphone cable to the inner walls of any metal container filled with water, I can hear crackling noises. I don't know how could this little bit of rubbing generate such ...
1
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1answer
79 views

The Langevin equation - nature of the forces

The Langevin equation is given by: $$m\ddot x=-\gamma \dot x+f(t)$$ where $f(t)$ is some stochastic force. I know that the first term on the RHS is to do with viscous drag and the second term is to ...
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2answers
244 views

How much can bottles of mineral water reduce the noise in a typical room?

The main point can be understood just be reading the question. But there's more to it. I want to buy around 300 liters of water to stack them up against the wall through which I get (and produce) ...
0
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0answers
38 views

Meaning of signal-to-noise ratio for a CCD camera

What is the meaning of signal-to-noise ratio for a CCD camera and what information is inferred from that? Is noise playing the role of error in measurement? If so, then an S/N equal to 10, for example,...
1
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1answer
74 views

What causes hum in a coil with an air core?

I am designing a controller to cut down heat production in electrically actuated solenoids (12VDC, 10A). This is not for proportional control. I am using a 50% duty cycle and have been experimenting ...
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1answer
85 views

Interpreting FFT background noice

There is some construction down my street and I think the drills are putting off a high pitch noise so I downloaded a spectrum analyzer. they have an FFT plot here: The "57-dB-A" I guess is the ...
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0answers
55 views

Distribution functional of colored noise

We know that for white noise the probability distribution functional (PDF) is $$P[\eta]=e^{-\int\frac{\eta(t)^{2}}{4D}dt} \, .$$ What is the PDF for colored noise?
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287 views

What is the link between path integral source terms and the propagator?

Consider a diffusion process defined by $$\frac{\partial \phi}{\partial t} = D \frac{\partial ^2 \phi}{\partial x^2}$$ where $\phi$ is the probability density of a particle's position and $D$ is the ...