In the classical wave theory, the formula of Doppler effect is f ' = f (1+V/u) where u is the light speed. In vacuum, f ' = f (1+V/c) (i). In media, f ' = f (1+V/(c/n)) (ii). In special relativity, the general expression of Doppler effect is given by the Lorentz transformation and reduced to (i) if V is much less than c. Since the Lorentz transformation is universal, the resultant frequency is always the same no matter in vacuum or media. It cannot be reduced to (ii) in any case. Is it reasonable? How to get general expression of Doppler effect in media and then simplified to (ii) ?