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4
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1answer
64 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 ...
6
votes
1answer
116 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 ...
5
votes
1answer
64 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 ...
1
vote
1answer
56 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 ...
2
votes
2answers
280 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 ...
1
vote
1answer
107 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
0answers
19 views

why can noise induce multistability, particularly in (bio)chemical systems

There are several instances that people claim that a system is monostable in a deterministic model, but when they consider stochastic models, from either master equations or Fokker-Planck equations, ...
8
votes
3answers
629 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 ...
1
vote
0answers
78 views

Transition rate of two level system subjected to noise

(this question is simpler than its length implies. I did this on purpose to provide a nice complete development for future readers) The setup Suppose we have a two-level quantum system with ...
0
votes
0answers
28 views

Why do thermal noise exist in the $\mu V$ range?

I am not familiar with thermal physics. I am conducting an experiment where I have to use muscle signal to control a car. I have noticed that in the literature a lot of thermal effects such as ...
8
votes
3answers
424 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. ...
3
votes
2answers
158 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 ...
2
votes
0answers
29 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: ...
0
votes
1answer
39 views

Power spectral density of noise: what is $\mathcal{N_0}$ in $S_X(f)=\mathcal{N_0}/2$?

My question is regarding power spectral density of white gaussian noise. It is known that the power spectral density of white gaussian noise is $$S_X(f)= \frac{\mathcal{N_0}}{2}$$ My question is does ...
3
votes
1answer
135 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 ...
0
votes
0answers
14 views

How does time relate to frequency in terms of averaging to reduce noise?

It seems for the longer time we average, the more frequencies we can incorporate in calculating the V(rms) of the noise. Why is this?
1
vote
1answer
109 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
0answers
46 views

Noise of a fiber optic gyro

I have not much experience with noise handling or calculations, furthermore in my researches couldn't find a similar problem, so here is my attempt: Having a fiber optic gyro that is rated with a ...
1
vote
0answers
22 views

Help to find nature of noise gotten from digital oscilloscope [closed]

I've got strange noise while using digital oscilloscope (Auris B-424). Spectrogram of this signal presented on this image: (X time in seconds, Y frequency in Hertz, in this image case from 0 to 50 ...
0
votes
1answer
501 views

Frequency spectrum and histogram of white noise

I haven't been able to find any images with, so here goes: In the frequency/Fourier spectrum, how does white noise look like ? Is that just random dots all over the place, making it very hard to ...
2
votes
1answer
94 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 ...
0
votes
0answers
79 views

On the relationship between entropy and chaotic noise

I have few conceptual questions related to application of chaos in communications. Kolmogorov-Sinai Entropy1 , Kolmogorov-Sinai Entropy2 and Kolmogorov-Sinai Entropy3 KS is an entropy metric for ...
3
votes
1answer
132 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 ...
0
votes
0answers
177 views

Thermal noise from capacitor; circuit analysis

I'm trying to model the thermal noise from a capacitor. The capacitor is connected directly into an amplifier with resistance $R_{A}$ and capacitance $C_{A}$. A noisy capacitor is modelled as a ...
7
votes
1answer
227 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 ...
5
votes
2answers
217 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 ...
0
votes
2answers
160 views

Derivation of the Thermal Noise Spectrum

The thermal noise spectrum is given by: $$\mathcal{S}(f) = \frac{\hbar f}{2(e^{\frac{\hbar f}{kT}} - 1)}$$ This equation seems really similar to the Dirac-Fermi distribution but where does it come ...
3
votes
0answers
100 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 ...
1
vote
0answers
26 views

Vibrational noise for scientific apparatus on a satellite

Say we're running an experiment on a satellite in some earth orbit. For example, maybe we're imaging something with transmission electron microscope or we're catching atoms in ion traps --- really ...
2
votes
2answers
3k 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 ...
0
votes
2answers
128 views

Noise cancellation solution for pool filter motor [closed]

I live in a condo, there is pool filtering equipment located outside my bedroom. Can anyone suggest a noise cancellation solution for the hummmm of the motor?. The equipment is in a 12ft x 12ft x 3ft ...
2
votes
0answers
103 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 ...
0
votes
1answer
156 views

Making pink noise (1/f) using list of frequencies [closed]

I would like to see what type of noise I would get if I used just the frequencies in my voice. I created a matlab array using fft to get a ...
7
votes
1answer
3k 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 ...
3
votes
2answers
161 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 ...
-1
votes
1answer
266 views

High frequency sound transmission through plastic. I can't hear enough treble! [closed]

I have a large cylinder made of a rigid thick plastic with a speaker inside of it. I want to be able to hear high pitched / high frequency noise from the outside but I'm primarily hearing bass. The ...
12
votes
2answers
1k 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 ...
0
votes
1answer
79 views

Numb3rs TV series - Antenna

Most of you might have watched the TV series 'Numb3rs'. http://en.wikipedia.org/wiki/Numb3rs In one of those episodes they were discussing about how to capture the contents on the screen of a ...
4
votes
1answer
74 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 ...
1
vote
2answers
178 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 ...
0
votes
1answer
70 views

Noise is a form of dissipation?

(Mechanical) noise is a form of dissipation? For example, when the computer fan turns it produces noise. This noise is a form of dissipation in addition to heat produced by the machine (computer)? If ...
3
votes
1answer
263 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
4answers
416 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 ...
0
votes
4answers
247 views

Isotropy and Noise

If you have a field which value is just Gaussian noise plus a constant do you call it isotropic? there is no preferred direction however it is not "the same" in all directions if "the same" means ...
5
votes
2answers
327 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 ...
1
vote
2answers
84 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
1answer
284 views

noise level (units confusion)

i had a question in one of my classes regarding SNR in underwater acoustic channels. There are a couple of terms with the unit dB re uPa. I know it stands for dB ...
1
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2answers
990 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 ...
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
3k 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 ...