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.

View More On Wikipedia.org
Recent contents Top users
  1. N

    Photocurrent shot noise correlation function

    Hi I have stumpled upon the following expression for the correlation function of the photocurrent shot noise for a photodiode <\delta i(t)\delta i(t+\tau)> = \frac{e^2\eta}{h\nu}P\delta(\tau) where η is the quantum efficiency and P the power in the signal. δ(τ) denotes the Dirac delta, which...
  2. X

    Noise term η(t) in Langevin equation

    Langevin equation describes the brown motion. But I don't understand the nose term η(t) in the equation. What's the relationship between η(t) and the force proportional to the velocity due to stoke's law? I mean they both belong to the force between the collisions with the molecules of the...
  3. L

    Occasional beeping noise coming from computer.

    I'd say about every 15 minutes or so, a faint beeping noise is coming from my computer. It's really hard to tell where it's coming from, but I'm pretty sure it's my computer. I shut down my computer last night and I believe I heard it in the middle of the night. So I'm thinking it's my power...
  4. A

    Generating A Noise Signal from a Digital Processor

    Hey guys, If I wanted to go about generating just a plain noise signal (don't care what the signal consist of), at a certain frequency (say 10 MHz) what is the best way to go about doing that? If possible I would really like to use a microprocessor or ARM processor (due to the higher...
  5. P

    Variance of White Noise: How Can It Have Infinite Power?

    Hi, I have a pretty simple question which I thought I do not need to make a topic about, but Google is actually not helping, which is surprising. So here it goes: How can white noise have infinite power if its variance is finite? As far as I am aware, the following is always valid for a...
  6. K

    How to measure noise from a current source

    I'm asked to get the noise signal from the constant current source I built with a 741 Op-Amp. I know I have to read it from the scope, but how do I go about the connections to the scope, and what other procedures must I follow to read the noise contribution? Pls refer to the figure provided in...
  7. P

    Fixing noise spikes caused by AC switching

    I have a situation where I see spikes (with ringing) on the output of DC power supplies whenever something AC powered is switched in the room. The spikes change in magnitude; they can be as bad as 3 volts peak-to-peak; I suspect they change "randomly" because they are related to when the device...
  8. U

    Measuring Current Noise Density

    I have a power source that is supposed to be low noise, and i want to verify that the data the company sent me is indeed accurate. In order to do this, i want to reproduce their graph showing current noise density (nA/root(Hz)) on the Y axis, and Hz on the X axis. I am an undergraduate physics...
  9. S

    Trying to use LMS adaptive filtering to remove noise with a reference signal

    I have a device (fNIRS, though knowledge of fNIRS probably isn't necessary to help) which produces very noisy signals and a noise reference. The noisy signal consists of a combination of a desired signal, and a noise signal, which is a scalar and phase shift of the noise reference. However, I'm...
  10. P

    Is there any circuit for generating Gaussian Noise with

    Is there any circuit for generating Gaussian Noise with a mean and variance. we should have control to change mean as well as variance accordingly. thanks.
  11. N

    Laser Frequency Fluctuations: Noise Spectrum Explained

    Hi I have read the following online (http://tf.nist.gov/general/pdf/1819.pdf): "Regardless of the application, the basic goal of locking the frequency of a laser to a cavity is to reduce the frequency fluctuations between the laser and cavity. The noise spectrum of the laser’s frequency...
  12. J

    Self Noise in Dynamic Microphones

    The diaphragm in a dynamic microphone moves a wire coil in the presence of a magnet to induce a current related to the movement. Other types of microphones, like electret and condenser microphones have self noise - noise not attributable to the amplifier. I wonder if all of the "self noise"...
  13. I

    Johnson noise and a magnetic field

    Would the frequency spectrum of Johnson noise change at all when a magnetic field is applied? My guess is not much, since the field changes only the direction of motion of the electrons, not their speed.
  14. B

    Signal to Noise ratio in CCD

    Homework Statement The 2-D image of a faint galaxy observed by a CCD covers 50 pixels. For an exposure of 5 seconds a total of 10^4 photo-electrons are recorded by the CCD from these pixels. An adjacent section of the CCD, covering 2500 pixels, records the background sky count. During the...
  15. Z

    XRF, the Auger effect, scattering and noise.

    Hello everyone, I have a few questions regarding the principles behind XRF spec, as most of the sources I've consulted either don't go into enough detail and miss bits out (undergrad textbooks), or are simply beyond my current level of understanding (QM papers etc). When, for example, a...
  16. L

    Engineering Reducing noise in strain gauge using an RC circuit

    Vibrations of a motor (40Hz) cause noise on the signal of a strain gauge that monitors load on a cantilever that measures periodic load changes at the rate of 1/minute. Design a filter that reduces the signal caused by the vibrations by 90%. I thought about a low pass filter that has a cut...
  17. S

    Active Noise Control for Waterjet | Hi Everyone Forum

    Hi Everyone I am new to this forum. I currently work for a company that uses a flow waterjet. It is an awesome machine but of course it can be super loud. I am in the process of researching a way of reducing or even canceling out the noise that it produces. I believe that Active Noise Control...
  18. S

    Estimate of noise statistics within some error

    This question concerns estimating the PDF of noise, based upon observations of a data stream consisting of noise embedded with transient signals. I would like to know if my Proposed Solution is a correct approach. Suppose I have "long" stream of seismic data, consisting of noise, and with...
  19. M

    Noise in Engines: Investigating Chain & Sprocket Design

    hi.. can someone help me out with noise in engines.. i am specifically interested in noise due to running of chain on sprockets.. it is a sort of whistling noise... which are those parameters in design of sprocket and chain which contribute in noise.. we can also talk in terms of different...
  20. N

    MATLAB Creating Noise / Filtering With Matlab FFT for Tap Sound Masking

    I am trying to create noise that has similar spectral properties of a recorded tapping sound (so that I can mask the tapping sound). I was thinking that if I generate noise, and then multiply the fft of the noise by the fft of the tap sound, it would sort of "filter" the noise to the desired...
  21. iVenky

    1/f noise at zero frequency or dc

    I read about 1/f noise. It says it is inversely proportional to frequency. What would happen at zero frequency or dc? Will it go to infinity? But when we measure some dc value we don't find any infinite voltage which clearly disproves this equation. What is the reason behind this? Thanks in...
  22. H

    Kalman, White Noise, Sensor Specification, Discretization?

    Hi. I have a few questions about sensor specifications and its implementation in a Kalman Filter and simulation of gyroscope/accelerometer output. Abbreviation used: d - discrete c - continuous Q1: From book: Aided Navigation - Farrell (you don't need the book to understand the...
  23. J

    Active Noise Cancellation / Soundproofing

    I would be very interested and grateful for guidance on how viable it would be to contain a noise in a relatively small area. If the aim was to contain a noise through passive and active noise cancellation and the noise source could be contained within a small area, could the technology used in...
  24. T

    Thermocouple Accuracy and Noise?

    I'm looking to use the MAX31855 thermocouple-to-digital converter, to measure temperatures in the range of 0-350C. According to the manufacturer, the ADC inside the chip is identical for every different type of thermocouple, just a different sensitivity is programmed in depending on the type of...
  25. B

    Guitar effect introduces noise if I'm not touching it's metal case. Why?

    As the title says, a guitar effect I built introduces a lot of white noise, which goes away when I touch it's case. I removed the circuit from the case and found the noise also goes away when I hold the input sockets. How do I fix this? Thanks for any help!
  26. M

    Rate of Noise in Three Sensors

    Homework Statement Suppose you have two sensors with rates of noise R_{A}^{noise} and R_{B}^{noise}. Suppose an erroneous signal occurs if the two sensors have a noise trigger within time \tau of each other. Show that the rate of false signals is R_{AB}^{noise}=2R_{A}^{noise}R_{B}^{noise}\tau...
  27. S

    Noise Calculations for OP27 Op-Amp

    I want to make sure I understand what I am reading in various spec sheets when they quote their noise measurements and I hope that you-all can confirm that I am on the right track. Take the OP27 Op-Amp as an example, which is described as a low-noise precision operational amplifier...
  28. A

    Why No Noise is Added to Sound Travel Through a Wall?

    We know that when sound travels through solids like a wall, the air molecules interact with solid molecules in porous medium to transmit the information hidden in sound wave.The question is that why no noise is added to someone's voice when we hear it from other side of a concrete wall ?
  29. S

    Why don't shooting stars make a noise?

    Pretty self explainable. Why do they not create a sonic boom when they enter Earths atmosphere
  30. G

    Signal to Noise Ratio Between Spacecraft Transmitter and Receiver Antenna

    Homework Statement Determine the SNR for the spacecraft that uses a transmitter power of 16 W at a frequency of 2.4 GHz. The transmitter and receiver antenna gain are 28 dBi and 60 dBi, respectively. The distance from the space- craft to ground is 2 ϫ 1010 m, the effective noise temperature...
  31. J

    Measuring the White Noise Produced by a Resistor

    Hi all, I want to measure the white noise produced by a resistor in my circuit. In order to do this I did the following: 1. Ground the excitation voltage of the circuit and measure the white noise voltage produced by connecting the output of the circuit to a 8.5DVM 2. Subtract the Avg DC...
  32. V

    Function Smoothing/ Noise Reduction

    Hi, my problem involves a laser sensor as a bin level sensor. what i want to do is get rid of the noise from the signal obtained. the spikes in the picture below are because the location of the laser sensor has to be where it is and when large rocks move down into the chute they pass infront...
  33. J

    Is the Frequency of Current Noise Voltage Dependent?

    Hello I have been doing a set of experiments in order to try and measure the current noise of a thick film resistor. I basically attach a low noise, power supply, to a thick film resistor and slowly increasing the power supplies voltage to that resistor. I am noticing a strange phenomena...
  34. S

    Quantum and classical noise for random number generation

    The gold standard for generating random numbers is the quantum effect of nuclear decay -- particles and photons being emitted from the atomic nucleus -- and unless you are one of those Hidden Variables types this is really random. The silver standard is thermal noise. There is a nice article in...
  35. DaveC426913

    Medical Experiencing a Clicking Noise in My Right Ear - Any Advice?

    There's just no way to ask this without imagining the smirks and jibes I'm going to get, so make em good. There's a noise inside my head. I am not looking for a diagnosis, this is just curious conversation, and I will most definitely to go my doctor for any advice. Every once on a while...
  36. V

    Calculating Noise Power, SNR, and Bit Error Probability

    I have values of time, and volts of a noise signal. I am trying to determine the noise power, signal to power ratio and bit error probability. How would I go about doing this? Thanks.
  37. T

    Level of johnson-Nyquist noise in analog voltmeter

    Hello, I was wondering if anybody could answer a quick question: What is the typical level of Johnson-Nyquist noise in an analog voltmeter in equilibrium (short circuited)? Is it millivolts? What is the level for an AC current of order mA at 50Hz?
  38. mnb96

    Fourier transform of noise

    Fourier transform of "noise" Hello, when we want to get the magnitude of the Fourier frequency spectrum of a function f we typically calculate F(\omega)=\int_{\mathbb{R}}f(x)e^{-i\omega x}dx and then consider |F(\omega)|. We can do this as long the signal (=function) is deterministic, that...
  39. A

    Estimation of X in Gaussian Noise

    Given {X}=[x_1 x_2 ... x_n]^T where {x_i} \in \{ 0, a_1, a_2, a_3 \}^n, a_i \in \mathbb{C} and Z = \{z_1 z_2,...,z_n \} where z_i ~ N(0,\sigma^2) is a Complex Gaussian RV with mean 0 and variance sigma^2. Suppose we observe Y Y = HX+Z where H is known and its elements are independent...
  40. Y

    Help in noise calculation of BJT.

    All the models I see is mostly common emitter, I have a circuit with AC equivalent shown in Fig a. Where v_s \; is the signal voltage and the source resistance R_s. I want to calculate the equivalent input noise voltage. Here is what I attempt to do it: 147190[/ATTACH]"] I show the equivalent...
  41. U

    MATLAB In these images,how can I remove the backgrnd noise in matlab?

    I have to isolate the cell(seen as a bright blob) in the attached images from the background the zig-zag. The problem is essentially that the intensity/brightness of the cell is almost equal to its backgraound, so I can't just subtract frames!
  42. Y

    Household noise from AC line, lights etc.

    What is the main frequency components of noise from AC line, florescent lights, appliances and other common household stuff? I know there are 60Hz and 120Hz from rectifying. Do I have to worry about 180, 240, 300, 360 ( 60X1, X2, X3, X4, X5...) etc.? Which one are the strong ones?
  43. 5

    What are the Common Causes of Power Line Noise?

    Hello, So I have a question about electric power lines. Today I was under some large power lines and I noticed some ticking noises. I had never noticed this noise before and was curious I thought maybe the current flowing through the lines was too great, and the lines were arcing to...
  44. B

    Modeling shot noise on Mathematica

    I've been having some trouble modeling shot noise for a photomultiplier tube on Mathematica - I know that I have to use a random number generator and the Poisson distribution to do it, but I'm having trouble synthesizing everything. (There are many things I'm going to leave just as parameters...
  45. R

    Signal to Noise ratio dB levels

    Hello, I have some 10 signals in noisy and nonoise(noisy+good) situations. I just calculated the power of each signal in two cases and then used SNR formula for dB(10log noisy/nonoise). Now, I got noise levels in dB's. Here, i confused that these dB levels are referred to...
  46. wukunlin

    How does fm actually suppress noise

    So I have been taught about FM having noise supressing characteristics, but in that particular course the lecturer told us not to worry about it as it is out of the course syllabus. So I tried to look up on the details on the internet but all I keep seeing is that FM supresses noise but I...
  47. R

    Reducing Noise in Waveform - Tips & Techniques

    Hello, I have a waveform that have noise when my pump stroke hit some mechanical part. i have converted the waveform into frequency domain to see the noise frequencies. I don't know the actual original frequency of the pump but i just decresed noise by stroke not touching the...
  48. V

    Filter White Noise: Designing FIR Moving Average Filter

    I want to generate a Gaussian white noise as an input to a vibration exciter. Since, it does not follow the high frequencies I need to low pass filter the signal. I need to implement a filter which makes minimum distortion to my signal in terms of temporal correlation of the filtered signal and...
  49. A

    Noise generated from turbulent shear flow

    Hi guys, its been awhile since i have been back. Right now, i am involved in some research on aeroacoustics and i have been trying to get some of the basic fundamentals on aerodynamic generation of sounds. Unfortunately most of the online literature do not give much details on the physics of...
  50. A

    Polar bear family's noise seal feast

    This unique 6-minute video shows a she-bear and her two cubs devouring a seal, while mummy bear is growling for miles around to be heard, to warn off others from getting too close. http://www.dagbladet.no/2011/09/07/nyheter/innenriks/isbjorn/dyrenes_nyheter/17989869/
Back
Top