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Questions tagged [noise]

In signal processing noise can be considered random unwanted data without meaning.

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64 votes
4 answers
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Why is TV static noise always black and white?

Most modern day Cathode Ray Tube (CRT) televisions manufactured after the 1960s (after the introduction of NTSC and PAL standards) supported the circuit-based decoding of colored signals. It is well ...
nabulator's user avatar
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31 votes
3 answers
88k views

Variance of White Gaussian Noise

It could seem an easy question and without any doubts it is but I'm trying to calculate the variance of white Gaussian noise without any result. The power spectral density (PSD) of additive white ...
Mazzy's user avatar
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25 votes
4 answers
6k views

Bag of Tricks for Denoising Signals While Maintaining Sharp Transitions

I know this is signal dependent, but when facing a new noisy signal what is your bag of tricks for trying to denoise a signal while maintaining sharp transitions (e.g. so any sort of simple averaging, ...
John Robertson's user avatar
24 votes
3 answers
9k views

Pink ($1/f$) pseudo-random noise generation

What are some algorithms for generating a good pseudo-random approximation to $1/f$ (pink) noise, yet suitable for implementation with low computational cost on an integer DSP?
hotpaw2's user avatar
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23 votes
4 answers
7k views

How to distinguish voice from snoring?

Background: I'm working on an iPhone application (alluded to in several other posts) that "listens to" snoring/breathing while one is asleep and determines if there are signs of sleep apnea (as a pre-...
Daniel R Hicks's user avatar
20 votes
3 answers
22k views

human speech noise filter

Does anyone know of a filter to attenuate non-speech? I am writing speech recognition software and would like to filter out everything but human speech. This would include background noise, noise ...
rurouniwallace's user avatar
19 votes
6 answers
31k views

How to Generate Band Limited Gaussian White Noise in MATLAB?

In some papers, I read that the additive noise is band limited Gaussian white. How can I simulate this type of noise use MATLAB?
Bo LI's user avatar
  • 333
18 votes
1 answer
29k views

What is the phase and magnitude response of white noise?

I would like to create white noise in the frequency domain, and then transform it to the time domain using python. To understand the problem, I simply generated white noise in the time domain, and ...
Uffe's user avatar
  • 355
18 votes
3 answers
8k views

How do I add AWGN to an I and Q representation of a signal?

I have a wireless communication system that I am simulating in Matlab. I am performing some watermarking through slightly adjusting the phase of the transmitted signal. My simulation takes the ...
Kellenjb's user avatar
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18 votes
3 answers
8k views

Determining the "whiteness" of noise

How does one quantify how "white" some noise is? Are there any statistical measures, or any other measures (FFTs for example) that can quantify how close to white noise a particular sample is?
Kitchi's user avatar
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18 votes
1 answer
3k views

What mathematical tools exist for understanding modulated noise?

Suppose we have a signal $n$ that consists of Gaussian white noise. If we modulate this signal by multiplying it by $\sin 2\omega t$, the resulting signal still has a white power spectrum, but ...
nibot's user avatar
  • 3,803
17 votes
2 answers
18k views

Wiener Filter for Image Noise Reduction (Image Denoising)

I'm trying to get my head round the operation of the Wiener filter for the purpose of image noise reduction. In my case I'll have used another noise reduction filter first and will then use the result ...
trican's user avatar
  • 509
17 votes
3 answers
8k views

How to Remove Gaussian Noise from an Image without Destroying the Edges?

What is the best filter for removing Gaussian noise without destroying the edges? I am using the standard Lena images with additive Gaussian noise and I want to denoise before applying anisotropic ...
Aviral Kumar's user avatar
17 votes
1 answer
327 views

How do I determine whether I have pattern-free noise?

For microscopy, we're frequently testing cameras. Since my applications involve very low signal-to-noise ratio, it becomes important that the noise is free of correlations and patterns, because local ...
Jonas's user avatar
  • 3,091
16 votes
2 answers
5k views

Relationship between entropy and SNR

In general any form of enropy is defined as uncertainty or randomness. In a noisy environment, with increase in noise, I believe that entropy increases since we are more uncertain about the ...
Ria George's user avatar
14 votes
1 answer
44k views

Kalman filter - understanding the noise covariance matrix

What is the significance of the noise covariance matrices in the Kalman Filter framework? I am referring to: process noise covariance matrix Q, and measurement noise covariance matrix R at any ...
Raaj's user avatar
  • 295
14 votes
1 answer
1k views

What are the various definitions for $\rm SNR$, and their associated methods for measuring it?

The definition of $\rm SNR$ seems to be somewhat of a tower of babel in industry. What definitions of $\rm SNR$ are there (feel free to site application), and how exactly can it be measured for that ...
Spacey's user avatar
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13 votes
9 answers
3k views

Estimate Sine Frequency under White Noise — simple and effective method

Given a sinusoidal signal in white noise, how can one efficiently determine its frequency?
RyanRonald's user avatar
13 votes
2 answers
18k views

What are the statistics of the discrete Fourier transform of white Gaussian noise?

Consider a white Gaussian noise signal $ x \left( t \right) $. If we sample this signal and compute the discrete Fourier transform, what are the statistics of the resulting Fourier amplitudes?
DanielSank's user avatar
  • 1,056
13 votes
2 answers
2k views

Detecting drum bpm in a noisy .wav file

I am looking for algorithm(s) to solve the following problem: Given a noisy .wav sound capture (some wind + friction noise on the microphone), how to detect the BPM of a soft drum beat? I have ...
Alex K's user avatar
  • 275
13 votes
3 answers
7k views

ADC performance simulation: How to calculate SINAD from FFT?

While working on this problem, I started to have doubts that my initial definition of $$SINAD = 10 \log_{10} \left( \frac{p_f} {\sum_i{(p_i)} - p_0 - p_f} \right)dB$$ is correct. In this equation, $...
FriendFX's user avatar
  • 338
12 votes
5 answers
10k views

Why is random noise assumed to be normally distributed? [duplicate]

From residual in the linear regression to noise in signal processing are assumed to be normally distributed? By considering them as normally distributed we are kind of telling the pattern in the noise ...
zeal's user avatar
  • 221
12 votes
4 answers
10k views

Why do I see ringing in the output of a digital filter with a narrow transition band?

I am doing some 'extreme' eq for spectral mangling type effects with audio. Im using brick wall filters, and very narrow band pass and reject filters (vst plugins), and I'd like to know if there's ...
Dale Newton's user avatar
12 votes
4 answers
3k views

How does the quantization error generate noise?

I'm learning about sampling and DSP on my own. I have a hard time to understand how the quantization error results in noise. I think I miss a fundamental understanding but can't tell what it is. So ...
Jan Deinhard's user avatar
12 votes
2 answers
495 views

What is the difference between 'de-noising' and what we commonly know as filtering methods to remove noise?

Pretty simple question - I am trying to figure out what exactly is different between 'de-noising' a signal, and simply filtering it (as we commonly know) to remove noise. Is this a case of lexical ...
Spacey's user avatar
  • 9,847
12 votes
2 answers
2k views

Parametrically degrade the speech to remove emotional content

I am happy to accept suggestions either in R or Matlab, but the code I present below is R-only. The audio file attached below is a short piece of conversation between two people. My goal is to distort ...
Geek On Acid's user avatar
12 votes
1 answer
3k views

Approximating the frequency response of a median filter

A median filter is a non-linear and lossy process, so it doesn't have a closed form frequency response as would a FIR filter (say a box filter of the same length) in an LTI system. But how closely ...
hotpaw2's user avatar
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11 votes
4 answers
66k views

Peak Signal to Noise Ratio (PSNR) in Python for an Image

How do I calculate the maximum signal to noise ratio (PSNR) in Python? Is there any library that can calculate PSNR for Image?
Sudip Das's user avatar
  • 211
11 votes
2 answers
7k views

Effect of windowing on noise

I understand that truncating a signal in time 'smears' the frequency response depending on the window chosen. In general, the shorter the signal duration, the more 'flattened' the frequency response, ...
abc's user avatar
  • 269
11 votes
2 answers
3k views

Where can we find noises like Gaussian, Rayleigh, Gamma, exponential noises in real world images?

I know that while taking pictures from a camera, noise may appear in the image. It is often described as Gaussian, but what about the other noises, when do they occur in real world? Please help!
Animesh Pandey's user avatar
11 votes
1 answer
3k views

Smoothing signal / detecting bumps in a data stream

(EDIT: This question follows from Extracting Binary Magnetic-Strip Card Data from raw WAV) Here is my signal (top line) and a basic IIR filter applied (bottom line) (EDIT: my task is to break the ...
P i's user avatar
  • 1,329
11 votes
2 answers
805 views

How can you tell whether there's a signal (when your signal looks a lot like noise)?

This is my snoring detector again. I've gotten pretty good at detecting a signal when there's anything there -- can track from a wall-peeling snore down to breathing you can't even hear in the ...
Daniel R Hicks's user avatar
11 votes
1 answer
879 views

Removing noise from F2F signal

(This question relates to Extracting Binary Magnetic-Strip Card Data from raw WAV) I am extracting the binary sequence from the magnetic strip on a credit card. As you can see, the signal is ...
P i's user avatar
  • 1,329
11 votes
1 answer
355 views

Recover curves from noisy collection of points

Background: I'm trying to make a system that tracks a number of bubbles in a video I'm implementing the bubble detection in the single image case using the Circular Hough Transform. Due to occlusion, ...
Alex's user avatar
  • 113
10 votes
4 answers
15k views

Zero Crossing of a Noisy Sine Wave

I'm trying to find the zero crossings of a sine wave to transform the sine wave into a square wave. The only problem is that the sine wave is noisy, so I'm getting lots of jitter and false zero ...
Kevin Nasto's user avatar
10 votes
2 answers
4k views

Estimate Taylor series coefficients from samples of a function

Say I have measurements of a function $y = y(x)$, sampled at $x_i$ with some noise, that could be approximated by a Taylor series expansion. Is there an accepted way of estimating the coefficients for ...
Matt's user avatar
  • 913
10 votes
4 answers
10k views

Gaussian White Noise - Relation Between Distribution and Correlation

Im a beginner in signal processing so my question may be obvious. A white noise has the property to have its autocorrelation function that is equal to $$\mathbb{E}[f(t+\tau)f(t)]=\sigma^2 \delta(\...
StarBucK's user avatar
  • 289
10 votes
1 answer
4k views

What is the connection between analog signal to noise ratio and signal to noise ratio in the IQ plane in a quadrature demodulation system?

We would like to compute the quantitative relation between analog noise near the LO frequency and the statistics of points found in the IQ plane after IQ demodulation. In order to completely ...
DanielSank's user avatar
  • 1,056
10 votes
1 answer
2k views

peak limiting/audio compression formula needed

I'm looking for a formula to effectively compress an audio waveform to limit peaks. This isn't an "automatic volume control" application where one would control amplifier gain to maintain a volume ...
Daniel R Hicks's user avatar
10 votes
2 answers
3k views

Is the Kalman Filter a Best Linear Unbiased Estimator (BLUE) for Heteroscedastic Noise?

According to the Gauss-Markov Theorem, a ordinary least squares estimator is BLUE if the noise entering a system is uncorrelated with zero mean and is homoscedastic (has a constant finite variance). I ...
sid's user avatar
  • 233
10 votes
3 answers
443 views

Deconvolution with noisy measurement of impulse response function

I observe a noisy complex-valued signal that has passed through some linear time-invariant filter: $$y(t) = (h * x)(t) + n(t)$$ where $h(t)$ is a causal and finite impulse response, and $n(t)$ is ...
XYZT's user avatar
  • 351
10 votes
1 answer
2k views

How does noise reduction for speech recognition differ from noise reduction that is supposed to make speech more "intelligible" for humans?

this is a question that has interested me for some time now, mainly because I'm working on noise reduction for an existing speech recognition system myself. Most papers on noise reduction techniques ...
marlonfl's user avatar
  • 103
10 votes
2 answers
955 views

What is obtained from the cross correlation plot?

Let’s assume that we have two audio signals, x(t) and y(t) affected by the noise as shown below. And we would like to cross-correlate these two signals and the cross-correlation plot is shown as ...
tuner's user avatar
  • 635
9 votes
4 answers
862 views

Solving Convex Optimization Problem Used for High Quality Denoising

The highest voted answer to this question suggests that to denoise a signal while preserving sharp transitions one should minimize the objective function: $$ |x-y|^2 + b|f(y)| $$ where $...
John Robertson's user avatar
9 votes
2 answers
4k views

Why is Gaussian noise called so?

Can you please explain: why is a specific type of noise called "Gaussian noise"? Why is it relevant to call it Gaussian? Please, explain in layman's terms.
user avatar
9 votes
3 answers
4k views

Using Total Variation Denoising to Clean Accelerometer Data

I know this is maybe a very basic question but I am doing this as a hobby and I can't find a solution to this problem. Basically I am trying to remove some noise from data I am reading from an ...
Andres's user avatar
  • 193
9 votes
1 answer
1k views

limit to possible noise shaping?

I want to do noise shaping in a 100kHz, 16 bit application, so as to shift all quantization noise to the 25khz-50kHz band, with minimal noise in the DC-25kHz band. I set up mathematica to create a 31-...
tobalt's user avatar
  • 468
9 votes
5 answers
2k views

Improving Digitization by Adding White Noise Before Oversampling

I was reading a physics book and it said that when digitizing a signal white noise was added to improve the process. I don't understand how this works. Therefore my question is: When digitizing an ...
SiberianSloth's user avatar
9 votes
1 answer
3k views

How to estimate the signal-to-noise ratio of a waveform?

I have a signal: $f_i(t_i=i\Delta t)$, where $i = 0\ldots n-1$. The signal seems to vary quickly around a slower varying "trend". I am assuming that the quickly varying part is noise and the slowly ...
Andy's user avatar
  • 1,783
9 votes
2 answers
2k views

How to detect continuous noise in audio call?

We want to detect bad audio quality in audio call. Should we extract this information from amplitude or frequency spectrum ? Is there any technique/transform/filter available for this ? Example: I ...
user31281's user avatar

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