Does wavelenght change in Doppler effect?

Wavelength or frequency.....

The speed of transmission.

velocity

I believe it is more than just sound, it applies to light as well. It is actual, not apparent. It is the shortening of the wavelengths as it approaches and the lengthening of them as they get further...

Whenever the frequency of a sound wave changes, regardless of what caused itto change, the change is perceived as a change in the pitch of the sound.