A physiological sensor has intensity compensation introduced along an optical path from emission to detection so as to compensate for unequal tissue attenuation as a function of wavelength. The sensor has emitters configured to transmit optical radiation having multiple wavelengths into a tissue site. At least one detector is capable of receiving the optical radiation after tissue attenuation. An equalization is capable of compensating optical radiation intensity so as to account for differences in tissue attenuation across at least a portion of the multiple wavelengths.