http://faculty.washington.edu/wilkes...erference..pdf
"Sound waves have speed c, and f and L are related by c=Lf. For an observer moving relative to medium with speed u, apparent propagation speed c' will be different: c'=c±u. Wavelength cannot change - it's a constant length in the medium, and same length in moving coordinate system (motion does not change lengths). Observed frequency has to change, to match apparent speed and fixed wavelength: f'=c'/L."
This is equally valid for light waves - the motion of the observer cannot change their wavelength either. That is, for an observer moving towards the light source with speed v, the speed of the waves will be c'=c+v, in violation of special relativity. The shift in frequency is in fact caused by the shift in the speed of light. Various aspects of the problem are discussed in an essay I wrote for an FQXi contest:
http://fqxi.org/data/essay-contest-f...equency_Im.pdf
"Shift in Frequency Implies Shift in Speed of Light"
Pentcho Valev