# What is Noise: Definition and 501 Discussions

Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, noise is indistinguishable from desired sound, as both are vibrations through a medium, such as air or water. The difference arises when the brain receives and perceives a sound.Acoustic noise is any sound in the acoustic domain, either deliberate (e.g., music or speech) or unintended. In contrast, noise in electronics may not be audible to the human ear and may require instruments for detection.In audio engineering, noise can refer to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as a hiss. This signal noise is commonly measured using A-weighting or ITU-R 468 weighting.In experimental sciences, noise can refer to any random fluctuations of data that hinders perception of a signal.

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1. ### B Sine wave noise at different frequencies

Supposed your audio bandwidth is set to 20000Hz. And the signal is 10mV and there is spec of 2mV noise at 20000Hz bandwidth. Does it mean if a function generator would produce constant 10mV with different frequencies between 20Hz to 20000Hz. The noises in the sine waves of each would be similar...
2. ### A Poisson noise on ##a_{\ell m}## complex number: real or complex?

1) In a cosmology context, when I add a centered Poisson noise on ##a_{\ell m}## and I take the definition of a ##C_{\ell}## this way : ##C_{\ell}=\dfrac{1}{2\ell+1} \sum_{m=-\ell}^{+\ell} \left(a_{\ell m}+\bar{a}_{\ell m}^{p}\right)\left(a_{\ell m}+\bar{a}_{\ell m}^{p}\right)^* ## Is Poisson...
3. J

### I Noise Proportional to Square Root of Illumination: Need Formula Help

Many people have said that the noise that affects laser light is proportional to the square root of the illumination. But I can't find the formula. Can anyone help?
4. ### A Measurement uncertainty due to thermal noise

I have a charged particle in a Penning trap. The particle motion is non-relativistic and the energy is high enough such that we can assume it is not in the quantum regime. For the purpose of the question I am interested only in the axial motion of the particle, so basically this is a classical...
5. ### A Two level system in a thermal noise electric field

Hello! I have a 2 level system with a dipole moment d. I want to simulate numerically the evolution of the system under an external sinusoidal electric field (far off resonant). This is straightforward using SE. However I also have on top of that another electric field, created by a coupling of...
6. ### B Probability of seeing peak noise in a given time window

Hi! Say I have a electric signal that has an RMS noise value of 10uV, I would calculate peak noise by multiplying by 6.6, so 66uV. I am looking for an equation that describes the probability of seeing a noise voltage that reaches 66uV in a given viewing time window. For example if I look at the...
7. ### A Expression of Shot noise when expanding ##a_{\ell m}## coefficients

I would like to arrive at the following expression for the quantity ##o_{\ell}## ( with "DM" for Dark Matter ): ##o_{\ell}=b_{s p}^2 C_{\ell}^{D M}+B_{s p}## with Poisson noise ##B_{s p}=\frac{1}{\bar{n}}(\bar{n}## being the average number of galaxies observed). the index "sp" is for spectro...
8. ### A Relation between a_{\ell m} noise and Poisson noise with C_{\ell}

We assume two galaxy population, ##\mathrm{A}## and ##\mathrm{B}##; the corresponding maps have the following ##a_{\ell m}## : ## \begin{aligned} &a_{\ell m}^{A}=b_{A} a_{\ell m}^{M}+a_{\ell m}^{p A} \\ &a_{\ell m}^{B}=b_{B} a_{\ell m}^{M}+a_{\ell m}^{p B} \end{aligned} ## Here, ##b_{A}## and...
9. ### I Can ground albedo near a highway refract noise upward?

I live near some highways that are roughly "a couple of miles" away. On some blessed days they are inaudible, and on other days they roar with a low frequency sound that penetrates into every corner of the basement. (If frequency matters, it would be most preferable to refract sound at 20Hz...
10. ### DC-DC conv. Ripple affecting Speech Recognition - Capacitance multiplier

Into a project I am working is use 12Vdc SMPS to power an audio amplifier and some more components. We have no “noise” on that stage. Then I use a step down converter to convert the 12V to 5V and power a mic preamplifier (Respeaker – usb Mic array) and a development board. There is a lot of...
11. ### I Noise Whiteness hypothesis in Kalman filtering

In Kalman filter mathematical treatment I have always read that a foundamental hypothesis is represented by the whiteness of the process noise. I have tried to do again the mathematical steps in the Kalman filter derivation but I can't see where such hypothesis is crucial. Could you help me...
12. ### B White noise frequencies and Audio Speakers

Hi everyone . unfortunately for health reasons I have to give it a try and put a pair of audio speakers in my bedroom to reproduce white noise during sleep. I need to know if the audio speakers I already own are able to reproduce the range of frequencies I need, namely that of rain and sea waves...
13. ### How to make an audio processing device for noise reduction ?

Hello everyone !I am working on noise reduction and I wanted to do some experiments with an arduino. I took an arduino which get music (as an example) in input by jack. It also has a microphone and in a first try the goal is to get as an output the music - the noise around... To act like a kind...
14. ### A Calculating the variance of integrated Poisson noise on a defined quantity

It is in cosmology context but actually, but it is also a mathematics/statistical issue. From spherical harmonics with Legendre deccomposition, I have the following definition of the standard deviation of a ##C_\ell## noised with a Poisson Noise ##N_p## : ## ...
15. ### Engineering Noise Floor/Device Temperature Problem

Hi everyone, I would like to get some help with the following problem. I'm not sure if my answer is feasible. Thanks. My attempt at a solution: I used the noise power equation: Pn= 10*log10(kTB) and converted the -100 dBm to dBW by subtracting 30 dB to get -130 dBW. Then I tried to find the...
16. ### Engineering Practical design of an inverting Schmitt trigger with noise tolerance

This is regarding the positive feedback of an Op-Amp and the inverting Schmitt trigger. This is a typical inverting Schmitt trigger - I need to design the Schmitt trigger such that I have a threshold voltage of around 2V, when my ##+-V_{CC} = 8V##. The slew rate of the Op-Amp allows for a...
17. ### Comp Sci Signal to Noise Ratio Calculation in Decibels: How to Simplify with Decibels

So pretty confident I understand part (a) however for part (b) I'm not sure if I have carried it out correctly if someone could give me a pointer? (b) 5dBmV Input as a voltage: 5=20Log(V/1mV) V=105/10 V=1.77827941mV Then the noise level is 20dbμV so changing to a voltage: 20=20*Log(V/1μV)...
18. ### A Obtaining the noise level of a camera

How can I subtract the camera noise from my real image? Basically, I want to calculate the center of gravity of a diffracted spot without the influence of my camera noise. I will be glad to know how this can be done.
19. ### A Photometric Galaxy Clustering Error and Poisson Noise

The error on photometric galaxy clustering under the form of covariance which is actually a standard deviation expression for a fixed multipole ##\ell## : ## \sigma_{C, i j}^{A B}(\ell)=\Delta C_{i j}^{A B}(\ell)=\sqrt{\frac{2}{(2 \ell+1) f_{\mathrm{sky}} \Delta \ell}}\left[C_{i j}^{A...
20. ### I The power spectrum of Poisson noise

I thought that if we Fourier transformed the counts of the sum of the signal from the source and the Poisson noise, and obtained the power spectrum, we would get the following, ##P_{j}=P_{j, \text { signal }}+P_{j, \text { noise }}+\text { cross terms }## but I found the following description...
21. ### Most stable, lowest noise voltage references?

Summary says it all, I think. If you just want to link me to a bunch of papers, that's fine by me. All I was able to find out on my own is that mouser and digikey have a lot of off-the-shelf voltage references they want to sell me that get about order of ##10^4## SNR at those timescales. SNR...
22. ### A Add factor Δℓ or Δℓ^2 in the variance for integrated Shot noise

I have the following expression for an error on a Cℓ : ##\sigma(C_{\ell,X})=\sqrt{\dfrac{2}{(2 \ell+1)\Delta\ell \,f_{\mathrm{sky}}}}\left[C_{\ell,X}+N_{X}(\ell)\right]## where ##X## corresponds to spectroscopic/photometric shot noise and with ##\Delta\ell## is the bin width between 2 values...
23. ### I Finding bias of the coin from noise corrupted signals

Suppose there are two persons A and B such that both have a personal communication system which can transmit and receive bits. B has a biased coin whose bias is not known. A asks B to toss the coin 2000 times, send a 0 when a tail comes up and a 1 when a head comes up. It is known that whatever...
24. ### I Why does a drip of water into water make a noise?

What is the 'gloop' noise; what actually makes the energy noise (from gravitational/kinetic into ... what transformation?), how is that transformed energy then coupled into a propagating wave in air? Further, whatever 'that' is, is it the same for an ocean wave, just godzilions of little drops...
25. ### How to calculate airplane noise as a function of distance?

I live close to the (landing) flight path to a major airport. The city has been working with the airport and the FAA to deal with complaints about the noise the jets make as they come in for a landing. I recently attended a meeting where various solutions were discussed, such as changing the...
26. ### Tuning a PID with extraneous noise on the error signal

Hi all! Forgive the sloppiness of this post, I'm on the road. Suppose you have a servo loop to stabilize parameter X. The issue is, when you measure X, you introduce some measurement error (let's say its white noise for the sake of argument). The noise causes a potential problem: since the...
27. J

### Noise cancellation technique can be used to neutralize laser weapons?

I had an argument with someone about laser weapons and he/she said "haven’t you listened about noise cancelation technology ? the light is electromagnetic wave as the sound is mechanical wave . The laser rays can be canceled the same way and even using the beam’s own energy ". there is any...
28. ### Am I overthinking this? (Noise cancelling headphones for airplane noise)

Can I just shift the wave over by 2Pi to get the opposite wave?
29. ### Block diagram showing how to turn white noise into rain

So I have been looking and trying different thing to synthesize rain noise like this: https://mynoise.net/NoiseMachines/campingRainNoiseGenerator.php but I cannot get it. and the graph that this sound makes did not help at all: can some make a block diagram of how to do this?
30. ### A Expression of the mean and variance of spectroscopic Shot Noise

Hello, I would like to know the right expression for the expression of variance of Shot noise in spectroscopic probe. Sometimes, I saw ##\sigma_{SN,sp}^{2} = 1/n_{sp}## with ##n_{sp}## the average density of galaxies, whereas my tutor tells me that ##\sigma_{SN,sp}^{2} = 1/n_{sp}^{2}## , so I...
31. ### Adding noise and solving stochastic ODEs in Python

The Coupled ODE Model Below are my coupled differential equations, where the only variable I try to meddle with is the ITMblood. The motivation here is if I try to increase ITMblood (in the next section I will show how I do it), at some concentration of ITMblood (most likely a very huge one) ...
32. ### I Amount of Noise extinction in Acrylic glass per thickness in mm

Hey guys, I need your help with the following topic on which I couldn't find sufficient information on the internet to solve. In the need to further insulate my velux roof swing window against against airborne motor and tire sound from the nearby street, I came across the idea to install an...
33. ### What causes the peak in the thermal noise spectrum of an RLC circuit?

Hello! Below is a figure of the thermal noise spectrum of an RLC circuit from a certain experiment. I am not sure I understand the shape. The spectrum is peaked around the resonant frequency. However, in thermal equilibrium, I would expect that the electrons to have random motions, so for a...
34. ### Engineering Linear Filters for Removing Impulsive noise

Hi, I was working on the following homework problem and just wanted to check whether my thoughts were along the right lines: "Explain briefly why a linear filter would not be appropriate for removing impulsive noise in a signal, and suggest an alternative filter." Attempt: When we use a linear...
35. ### I How can one see the noise in the Fourier Domain (Nyquist Frequency)?

Say we have a transform of a line profile that extends out to the Nyquist frequency such that you cannot see the noise level, what could you change in your spectrograph arrangement that would allow you to see the noise level in the Fourier domain? My thought is that we can apply a filter, P(s)...
36. ### Calculating Signal to Noise due to thermal noise

The total noise from other sources and thermal is ##N = N_{other} + N_{thermal}## ##N_{175}/ N_{275} = (N_{other} + \sqrt{2k(175)R\Delta f})/( N_{other} + \sqrt{2k(275)R\Delta f})## I'm not sure how to simplify the expression as ##N_{other} ## is unknown. If I assume ##N_{total} =...
37. ### A Calculating noise of a transducer from molecular vibration

I'd like approximate the noise floor of an ultrasonic air transducer starting from molecular vibrations. Simply put, if I treat atmospheric air as an ideal gas and I confine each air molecule to exist in a volumetric cube with a square face ##A_\mathrm{face}##, then I approximate the number of...

I am designing the pattern of a quilt my wife is making. The quilt is made of 15x20 squares of exactly six shades of blue - dark at one end to light at the other end. The gradient will be "noisy". I want to experiment with that noise. I am exploring Photoshop to do this visually, but it...
39. ### How do pull up and pull down resistors remove electrical noise?

I’m doing a project with my Arduino, and I’ve seen some tutorials on YouTube explaining how to use pull up or pull down resistors to make the input values on the board reliable, basically either a 0 or a 1 without any random changes from other em sources. The only thing is I still don’t...
40. ### A Average of the power spectrum of Poisson noise

I am learning about noise that follows a Poisson distribution. When I do a Fourier transform of the data with only Poisson noise to get the power spectrum, what is the average value of the power spectrum?
41. ### Optimizing Exposure Time for Different Magnitude Stars

Summary:: An image was taken with a ##60## second exposure time of a 6th magnitude star and the signal to noise ratio was detected to be ##S/N = 20##. a. What should the exposure time be if you wanted a ##S/N = 100##? b. Now calculate the ##S/N## if it were a 2nd magnitude star for a ##10##...
42. ### A Why the Poisson noise level is set to 2 after applying Leahy norm

I am studying about power spectrum analysis in high energy astrophysics. I cannot understand why the Poisson noise level is set to 2 after applying Leahy normalization. $$P_{j}=2 /_{N \mathrm{ph}}\left|a_{j}\right|^{2}$$ The above is the equation for leahy norm, Can I expand the equation from...
43. ### Which type of capacitor has lower 1/f noise: MLCC or film?

I am working on a low noise capacitive feedback TIA where I need to achieve a pretty low voltage/current input referred noise and so I started researching components. For the resistors and transistor I know about 1/f noise, etc. and I'm confident in my choice but it dawned on me, what about the...
44. ### A Non-entangling environmental noise in QM/QFT

Does non-entangling environmental noise actually exist? The existence of such a thing seems to be fundamentally inconsistent with the properties of quantum entanglement. It seems to me that if non-entangling environmental noise does exist, then standard QM - or QFT for that matter -...
45. ### I CCD Readout Noise vs Temperature

Hey all. I tested my astro camera a while back and found what looks like a temperature dependent readout noise value. Which is odd, as everything I've ever read has told me that readout noise is independent of sensor temperature. I took 50 bias frames at 5°c intervals, from -15°c to +20°c and...
46. ### Lawn/Garden Improving noise reduction for ear muffs

The lining on my ear muffs which contact the ears, developed cracks and eventually split apart. I decided to try and repair the muffs, so they would have noise reducing qualties than those were better than any typical store bought muffs. Unfortunately, the finished product, reduced the outside...
47. ### Building RF Noise Generator Circuit w/ LM324D SMD Op Amp

I haven't been building electrical circuits for quite a while, but I'm now trying to create a circuit that produces RF random noise. I found this webpage with some information about it. http://www.n5ese.com/noise.htm There is this diagram there: I have an LM324D SMD op amp with pins...
48. ### Creating noise images with Python and OpenGL

Hi I am learning how to do a line integral convolution with OpenGL given a vector field. So, as a first step, I need to learn how to create an nxn noise image. Are there any good tutorials/books I can use to learn how to do this?
49. M

### Would a portable railgun make a lot of noise?

I'm using a portable rail gun in my novel - details in the paragraph below - but I wondered whether it would be as quiet as I'm suggesting. The slugs are coming out at Mach 5, which is a touch under 6,200 kmh. Obviously, they're breaking the sound barrier in the barrel, so would a tiny (or big)...
50. ### How can I effectively suppress Poisson noise in my data?

Hi all I would like to know how to suppress the spectrum of Poisson noise. At first, I tried "binning". I made the data of Poisson noise which sums up 4Hz sin wave.(the data number##N=10000##,and the data time is 1s) and I average out the data every 100bins. After this, I derived the power...