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The sampling frequency can only be applied to Sampler s in which each sample is periodically taken. There is no rule that limits a sampler from taking a sample at a non-periodic rate. The common notation for sampling frequency is which stands for frequency (subscript) sampled. SAMPLING THEOREM The Nyquist-Shannon Sampling Theorem states that the sampling frequency has to be greater than twice the Nyquist Frequency or, equivalently, twice the Bandwidth of the signal being sampled. If a signal has a bandwidth of 100 Hz then to avoid Aliasing the sampling frequency must be greater than 200 Hz. In other words, the sampling frequency must be at least twice the maximum frequency component of the signal. Otherwise, the original signal cannot be recovered from the sampled signal. OVERSAMPLING In some cases, it is desirable to have a sampling frequency more than twice the bandwidth so that a Digital Filter can be used in exchange for a weaker analog Anti-aliasing Filter . This process is known as Oversampling . AUDIO In Digital Audio , common sampling rates are:
VIDEO SYSTEMS In Digital Video , the sampling rate is defined the frame/field rate, rather than the notional pixel clock. The image sampling frequency is the repetition rate of the sensor integration period. Since the integration period may be significantly shorter than the time between repetitions, the sampling frequency can be different from the inverse of the sample time. When analogue video is converted to Digital Video , a different sampling process occurs, this time at the pixel frequency. Some common Pixel sampling rates are:
Aliasing of high-frequency Luminance components shows up as a Moiré Pattern . SEE ALSO
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