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Reference.org
Downsampling (signal processing)
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<p>In <a href="/facts/Digital_signal_processing/PEG7azr8">digital signal processing</a>, downsampling, compression, and decimation are terms associated with the process of <a href="/facts/Sample_rate_conversion/N2G0ezBM"><i>resampling</i></a> in a <a href="/facts/Multi-rate_digital_signal_processing/N2G0ezBM">multi-rate digital signal processing</a> system. Both <i>downsampling</i> and <i>decimation</i> can be synonymous with <i>compression</i>, or they can describe an entire process of bandwidth reduction (<a href="/facts/Lowpass_filter/QFsUjw7h">filtering</a>) and sample-rate reduction. When the process is performed on a sequence of samples of a <i>signal</i> or a continuous function, it produces an approximation of the sequence that would have been obtained by sampling the signal at a lower rate (or <a href="/facts/Dots_per_inch/V1jh6x0l">density</a>, as in the case of a photograph). </p><p><i>Decimation</i> is a term that historically means the <i><a href="/facts/Decimation_(punishment)/4pEHmnoX">removal of every tenth one</a></i>. But in signal processing, <i>decimation by a factor of 10</i> actually means <i>keeping</i> only every tenth sample. This factor multiplies the sampling interval or, equivalently, divides the sampling rate. For example, if <a href="/facts/Compact_disc/g51GRloc">compact disc</a> audio at 44,100 samples/second is <i>decimated</i> by a factor of 5/4, the resulting sample rate is 35,280. A system component that performs decimation is called a <i>decimator</i>. Decimation by an integer factor is also called <i>compression</i>. </p>