Signal Processing Stack Exchange
Signal Processing Stack Exchange

Questions tagged [aliasing]

In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled.

It also refers to the distortion or artifact that results when the signal reconstructed from samples is different from the original continuous signal. When a digital image is viewed, a reconstruction—also known as an interpolation—is performed by a display or printer device, and by the eyes and the brain. If the resolution is too low, the reconstructed image will differ from the original image, and an alias is seen.

Source: Wikipedia.

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Increasing Image Resolution

I know of some oscilloscopes (DSA8300) that repeatedly sample at a few hundred kS/s to reconstruct a few GHz signal. I was wondering if this could be extended to 2D signals (photographs). Can I take a series (say 4) of still pictures using a…
Lord Loh.
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Why does this Moiré pattern look like this?

I was making some gifs of Mobius transformations in Matlab, and some strange patterns began to appear. I'm not sure if a deeper knowledge of the filetype/algorithm is needed to understand this phenomenon, but I thought that there could perhaps be a…
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Is there such a thing as band-limited non-linear distortion?

So if you generate a square wave by just switching a signal between two values, at sample boundaries, it produces an infinite series of harmonics, which alias and produce tones below your fundamental, which is very audible. The solution is…
endolith
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What is the antialiasing algorithm employed by video cards?

What is the algorithm employed by video cards when one talks about for example 8xAA? I thought the algorithm was about looking at neighboring pixels for correction. Yet, I hear that the implementation is just upsampling followed by downsampling.
m33lky
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Alias frequency Formula

I'm taking a multimedia systems class in my MSc Computer Science, and I'm having some trouble understanding the formula for the alias frequency - this could stem from my misunderstanding of the alias signal. My understanding of an alias signal is…
user1058210
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What is the effect of aliasing on the magnitude of the autocorrelation?

I've a question about the effect of aliasing on the magnitude of autocorrelations. From a simulation in MATLAB, I don't see any effect of aliasing or any need to anti-alias filter when I take the magnitude of the autocorrelation. Which means I can…
Hossein
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Can addition of two band limited signals create aliasing?

Can mixing/adding two band-limited signals create any frequencies above Nyquist?
user17127
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Why is aliasing inherently non-linear?

E.g. when having 2 signals $x(t)$ and $y(t)$ and transforming each one with adding their spectra, the operation is linear, as the result would be the same as the transformation of $(x + y)(t)$. Even when looking at the sampling series, each of the…
Starhowl
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Sampling of band-limited white noise

The context is communication where we have a front-end that samples a signal and a noise (but here we focus only on the noise). My goal is to determine the noise power that I should use to simulate (in Matlab) the discrete noise after the ADC. This…
Jérôme
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Demonstrating the effect of aliasing

How does the signal look when we don't use the Nyquist rate to remove aliasing from a signal during sampling? Let's suppose the signal is sinusoidal, with a frequency of 500 Hz and an amplitude of 2. signal = 2*cos(2*pi*500*t) If I sample it,…
Sufiyan Ghori
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Nyquist frequency isn't working

The situation is that I have a signal with linearly increasing frequency, $$\text{sin}(2\pi\omega(t)t),$$ where $\omega(t)=a+bt$ for some $a$ and $b$, and we constantly sample at one point per second i.e. $t=0,1,2,...,T$. An image of this signal is…
CoolMathsGuy
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What's the impact of aliasing in the time domain?

I've been studying digital audio and come across something I can't understand. There appears to be something like a consensus (among those capable of understanding such things) that the impact of aliasing on reconstructed time-domain signals is to…
Jim Austin
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Does sampling in the frequency domain cause time-domain aliasing?

Let's say I have an impulse response $h[n]$. I analyze the power spectrum of that impulse response similar to fourier transformed $h[n]$ corresponding to roughly $H[f]$. Now I compare $H[f]$ with some target $H_{0}[f]$ by subtracting…
panthyon
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Digital to analog aliasing or mirror query... DAC can output negative frequency?

Using a clock Fs = 1 MHz. The Digital to Analog (DAC) can make frequencies upto 500 KHz. 500 kHz to 1 MHz is an alias? Or is it called a mirror?? Is aliasing a concept only on the ADC and sampling process. Does -500 to 0 exist as an alias or mirror…
Natalie Johnson
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Determine maximum frequency of input signal to make system LTI

This is question 4.26 from the third edition of Alan Oppenheim's textbook "Discrete-time Signal Processing". It is stated as follows: Firstly, the answer is the input signal should be bandlimited to 12 kHz. I'm having trouble seeing why it is the…
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