In telecommunication, deeemphasis is a system process designed to decrease, within a band of frequencies, the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation differences or saturation of recording media in subsequent parts of the system.
It is the complement of pre-emphasis, and the whole system is called emphasis. The frequency curve (response) is decided by special time constants, from which one can calculate the cutoff frequency.

Pre-emphasis is commonly used in audio digital recording, record cutting and FM radio transmission.

In serial data transmission, de-emphasis has a different meaning, which is to reduce the level of all bits except the first one after a transition. That causes the high frequency content due to the transition to be emphasized compared to the low frequency content which is de-emphasized. This is a form of transmitter equalization; it compensates for losses over the channel which are larger at higher frequencies. Well known serial data standards such as PCI Express, SATA and SAS require transmitted signals to use de-emphasis.

[edit] See also

• Pre-emphasis

[edit] External links

• Deemphasis - Frequency response and equalization EQ - Conversion: time constant to cut-off frequency and vice versa