Emphasis (telecommunications)

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In signal processing, pre-emphasis is a technique to protect against anticipated noise and loss. The idea is to boost the frequency range that is most susceptible to noise and loss beforehand, so that after a noisy and lossy process (transmission over cable, tape recording...) more information can be recovered from that frequency range. Removal of the frequency boost caused by pre-emphasis is called de-emphasis, reducing the boosted frequency range back to its original amplitude. Emphasis is commonly used in many places ranging from FM broadcasting (preemphasis improvement) and vinyl (e.g. LP) records to PCI Express. For example, high-frequency signal components may be emphasized to produce a more equal modulation index for a transmitted frequency spectrum, and therefore a better signal-to-noise ratio for the entire frequency range.