A spurious tidal frequency appearing in an analysis when there is an occurrence of a sea level variation with a periodicity smaller than the sampling period Usually presenting itself only when the observations are taken at intervals greater than one hour or when there is a seiche at the observation site
Where the sampling rate is less than twice the input signal's highest frequency content
Distortion caused by a low sampling rate, as Moire effect or stair-stepped edges
Visibly jagged steps along angled or object edges, due to sharp tonal contrasts between pixels
Unwanted visual effects caused by insufficient sampling resolution or inadequate filtering to completely define an object; most commonly seen as a jagged or stepped edge along object boundaries or along lines
- A phenomenon, which can occur whenever a signal is not sampled at greater than twice the maximum bandwidth of the signal Causes high frequency signals to appear at low frequencies Filtering the signal to a bandwidth less than ½ the sample rate minimizes Aliasing When the signal starts at 0 Hz (baseband signals), bandwidth can be exchanged to maximum frequency in the definition above
Aliasing is what happens when a signal is sampled (converted to digital form) too slowly Specifically, if a signal contains frequencies above half the sampling rate, the sampled version of the signal will have frequencies (aliases) that aren't in the original signal This limit of half the sampling rate is known as the Nyquist limit For example, the CDP samples at 12288 Hz, so if the input signal contains frequencies higher than 6144 Hz the digital signal will not accurately represent the actual signal That is a rather incomplete description of aliasing If you'd like to learn more, the University of California at Santa Cruz has a general discussion of converting a signal to digital form
A phenomenon caused by sampling analogue data at too-low a frequency It results in a digital reconstruction of the original signal at a false, lower frequency This causes higher frequency signals to appear in a spectrum at lower frequencies (Aliasing terms) When analogue signals are digitised, the analogue input must be sampled at a rate at least twice the bandwidth of the signal to avoid loss of data (Nyquist Theorem)
(1) (n ) The jagged artifact in a line or in the silhouette of a curve that results from drawing on a raster grid It is especially noticeable in low-resolution monitors Also called jaggies See also antialiasing (2) (n ) See command aliasing
{i} (Computers) process through which curved lines appear to have a jagged edge due to low-end graphics capabilities; creation of a false frequency when sampling audio data (caused by a low sampling rate)
A set of problematic effects resulting from the usual method of displaying *scalable images on low-resolution screens When converting these images to *bitmaps for display, samples are taken from the theoretical mathematical image, usually at the pixel centres The influence of what is happening at these more or less arbitrary points is thereby greatly exaggerated, causing jagged edges, "pimples" and other undesirable effects (We should really be considering what is happening over the complete area covered by each pixel ) The approach to the problem that takes the generic term, *anti-aliasing, normally denotes careful shading of border pixels Another approach (distinct but complementary) is *hinting, a set of techniques that can in principle regularize features of any graphic, but in practice is confined to font technology
The erroneous interpretation of high-frequency signals as lower-frequency signals Such misinterpretations are an expected result of making discrete measurements with sampling devices such as analog-to-digital (A/D) converters See also anti-aliasing filters
In graphic design, aliasing occurs when a computer monitor, printer, or graphics file does not have a high enough resolution to represent a graphic image or text An aliased image is often said to have the "jaggies "
In audio sampling, a distortion-producing reflection caused by the fact that all frequency components higher than half the sampling frequency are reflected in the lower range Aliasing creates artifacts It can be avoided by processing the waveform to be sampled with a low-pass filter at half the sample rate before digitizing
The jagged edges (or staircasing) that result from drawing an image on a raster device such as a computer screen Compare antialiasing
1 In spectral analysis, error which is due to undersampling One may wish to sample a signal that is known to be band-limited, but whose bandwidth is not known a priori The Fourier transform of Shannon's series is periodic; aliasing is of the form of an overlapping, or superposition of these "replicated" spectra See also Nyquist sampling rate and aliased response 2 In computer graphics, the jagged artifact in a line or curve that results from drawing on a raster grid 3 In computer programming languages, giving access to a region of memory through more than one language entity (e g , pointers in C or C++) Aliasing makes it harder for compilers to optimize code, as they may not understand all the ways in which a given memory location might be modified
Visibly jagged steps along angled lines, or object edges due to sharp tonal contrast between pixels
Defects or distortion in a television picture or audio Defects are typically seen as jagged edges on diagonal lines and twinkling or brightening In digital video, aliasing is caused by insufficient sampling or poor filtering of the digital video
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