"De-emphasis is the use of an amplitude-frequency characteristic complimentary to the one used for pre-emphasis prior to transmission and recording.
Pre-emphasis is the process of increasing the strength of some frequency components of a signal to assist in the system; mainly to ensure good high-frequency reproduction in FM broadcasting.
It works by phase modulation. A network that increases the modulation index of the higher modulation frequencies relative to the lower ones is inserted at the transmitter. i.e. it exagerates the frequencies most likely to distort, thus giving a lower noise/signal ratio. The de-emphasis bit just squashes the signal back down to its original amplitude (relative to the LF)... A bit like Dolby Noise reduction, but for RF."
Disclaimer: All the info given here is incomplete, there's always something missing. This is basically to cover our own backs, but for someone with a bit of sense it shouldn't be too hard to fill in the blanks. The authors of this page and the carriers do not take any responsibility whatsoever for any action you may carry out as a result of you reading or using this information. Any documentation provided is given for research purposes only.