Emphasis (telecommunications)

The pre-emphasis ( accent ) and de-emphasis ( deaccenting ), Eng. preemphasis and deemphasis, used to boost the high frequencies and cut of the low frequencies during recording or transmitting ( linear pre-equalization ), which is subsequently reversed when playing or when received, so that overall a faithful transmission occurs. This approach reduces the noise that occurs at high frequencies amplified.

The emphasis method is applied to radio transmission in which the transfer tape, the record cutting, with many early CDs of the 1980s and occasionally in digital transmission. It must be for this and return equalization respective standards with corresponding time constants. The corresponding transition or cut-off frequencies can be calculated therefrom.

Used emphasis parameter in FM radio

The time constant used in the European FM broadcasting is 50 microseconds, resulting in a cutoff frequency of 3.185 kHz. Equalization causes an improvement in the signal -to-noise ratio by about 12 dB.

In North America a different time constant of 75 microseconds with a cutoff frequency of 2.12 kHz, however, is common in FM radio. It follows that FM radios that were produced for the European region, in an operation in North America have a somewhat poorer signal -to-noise ratio and play higher notes too loud, because the pre-emphasis in the transmitter does not match the equalization in the receiver. Conversely, American FM radio equipment in Europe a slightly muffled sound on, with a likewise poorer signal-to - noise ratio.

These differences in emphasis parameters affect significantly only for high-quality receivers. With cheap FM radios portable radios as these differences are practically alone already for bad speaker systems hardly noticeable.