Editing Preemphasis improvement

{{Short description|Signal enhancement}}

In FM broadcasting, '''preemphasis improvement''' is the improvement in the [[signal-to-noise ratio]] of the high-[[frequency]] portion of the [[baseband]], ''i.e.,'' modulating signal, which improvement results from passing the modulating signal through a [[preemphasis network]] before transmission.

The reason that preemphasis is needed is that the process of detecting a [[Frequency modulation|frequency-modulated]] signal in  a receiver produces a [[noise]] [[spectrum]] that rises in frequency (a so-called ''triangular'' spectrum).<ref>
{{cite book
  | title     = National Association of Broadcasters Engineering Handbook
  | chapter   = FM and Digital Radio Broadcast Transmitters
  | publisher = Academic Press
  | date      = 2007
}}
</ref> Without preemphasis, the received audio would sound unacceptably noisy at high frequencies, especially under conditions of low [[carrier-to-noise ratio]], i.e., during [[fringe reception]] conditions. Preemphasis increases the magnitude of the higher signal frequencies, thereby improving the signal-to-noise ratio. At the output of the [[discriminator]] in the FM receiver, a [[deemphasis]] network restores the original signal [[Power (physics)|power]] distribution.

''FM improvement factor'' is the quotient obtained by dividing the [[signal-to-noise ratio]] (SNR) at the output of an FM receiver by the carrier-to-noise ratio (CNR) at the input of the receiver. When the FM improvement factor is greater than unity, the improvement in the SNR is always obtained at the expense of an increased [[Bandwidth (signal processing)|bandwidth]] in the receiver and the [[transmission (telecommunications)|transmission]] path.

''FM improvement threshold'' is the point in an FM ([[frequency modulation]]) receiver at which the peaks in the [[RF signal]] equal the peaks of the [[thermal noise]] generated in the receiver.  A [[baseband]] [[signal-to-noise ratio]] of about 30 [[decibel|dB]] is typical at the improvement threshold, and this ratio improves 1&nbsp;dB for each decibel of increase in the signal above the threshold.

==References==
{{Reflist}}

==Sources==
*{{FS1037C}}

[[Category:Radio]]


{{radio-comm-stub}}