How to design emphasis circuit to ruduce distortion?

Hi all,
In a FM system,how to design emhasis circuit to get a perfect distortion and S/N?
Thanks,

For FM radio, there is a standard time constant for emphasis and de-emphasis. It is 50μs or 75μs. The stereo decoder is normally designed to have both options.

Thank you for your reply, cookey.And why is it 50us or 75us?any advantage to reduce distortion that other time constant?

The time constant is a tradeoff of several things. Most program material has lower signal levels above the corner frequency. If the frequency was moved down, strong spectral lines would be made higher in amplitude and the modulation index would have to be reduced to meet the maximum peak deviation.

Noise output of a FM demodulator with weak signals is square law with baseband frequency.